Reproduction and resistance to stress: when and how

When urban exploiters cannot cope with urban stressors anymore: Lessons from an experimental manipulation of developmental corticosterone levels in the house sparrow (Passer domesticus)

Urbanization is known to be associated with deep and rapid environmental changes that may be a threat to biodiversity. In that context, urban exploiter species are relevant to study because they usually thrive in cities and their population trends can help us assess the impact of recent urban environmental changes on urban wildlife. Recently, the house sparrow (Passer domesticus), a typical urban exploiter, has shown drastic population declines in numerous cities, and previous studies have shown that young urban sparrows bear elevated corticosterone levels. We conducted a long-term experimental study to test if such early-life exposure to corticosterone could be involved in the decline of urban house sparrow populations. We experimentally manipulated developmental exposure to corticosterone of house sparrow chicks and examined the short- and long-term impacts of this manipulation on several organismal systems (endocrine axes, metabolism, behaviors) and performance metrics. Early-life exposure to corticosterone had detrimental impacts on multiple physiological and behavioral traits of this urban exploiter (growth, competitive and anti-predator behaviors, survival). Interestingly, it was also associated with long-lasting endocrine (HPA and HPG axes) and metabolic changes that may allow sparrows to cope to a certain extent with urban constraints, notably by adjusting individual stress-coping strategy, reproductive investment and metabolism to an urban way of life. Altogether, this integrative study supports the hypothesis that the detrimental impact of urbanization on house sparrow populations could be mediated by developmental exposure to corticosterone. It highlights that endocrine mechanisms may help us better understand how wild vertebrates are impacted by urbanization and environmental changes.

Resilience and robustness: from sub-organismal responses to communities

Coping with challenges is essential to life on earth. Determining the processes that generate resilience and robustness to disturbance across levels of biological organization is increasingly important as the pace of global change accelerates; however, to date, multiscale models have primarily focused on population to ecosystem scales. In this opinion article we combine conceptual models from different fields to develop a unified a framework of resilience and robustness that explicitly links sub-organismal responses with higher-level outcomes. This framework predicts that interactions among sub-organismal response components - including their temporal dynamics and the plasticity of homeostatic regulatory networks - are key drivers of current and future resilience.

Differences in fur cortisol levels of three migratory bats

Understanding how organisms respond to their environments is challenging, especially due to the complex processes related to metabolism, energetics, and reproduction. Glucocorticoids (GCs) are metabolic hormones that provide insight into internal process and may trigger a variety of behaviors. To understand how changes to the environment influence wildlife, we must ideally measure levels of GCs in wildlife populations that are relatively undisturbed by anthropogenic change or natural disaster. In free-ranging mammals, cortisol is a primary GC hormone and can be measured in fur. Bats are the only mammalian order to have evolved true flight and, in North America, most species of bats are in the family Vespertilionidae. By measuring cortisol levels during energetically expensive periods of an animal's life history, we can document 'baseline levels' related to different life stages, sexes, and ages. We collected fur from hoary (Lasiurus cinereus), silver-haired (Lasionycteris noctivagans), and little-brown Myotis (Myotis lucifugus) bats from southern Alberta and Saskatchewan. Herein we report their baseline levels of fur cortisol, noting interspecific differences between species. We found that bats known to migrate longer distances had higher levels compared to bats that migrate shorter distances, and then hibernate. Interestingly, we found no differences in levels between the reproductive stages for any species. Finally, both silver-haired and hoary bats show a strong difference in fur cortisol levels between adults and juveniles. We suggest that the elevated levels are likely associated with events for mothers during lactation which are then incorporated into the pups' fur while nursing.

Recovery through resistance? nesting urban female song sparrows (Melospiza melodia) have a lower glucocorticoid response to disturbance and return to parental care as quickly as rural females

Urbanization represents a dramatic and relatively rapid change in the environment that has profound impacts on wild animals. Shifts in behavior and endocrine mechanisms of stress response could allow animals to successfully survive and reproduce in urban habitats. Numerous studies have examined the behavioral and physiological responses of territory-holding male songbirds to urbanization. However, breeding females likely experience anthropogenic noise, light at night, and human disturbance more frequently, and their behavioral coping responses to these disturbances are limited during incubation. Moreover, breeding females face higher energetic demands (allostatic load). Understanding how some species cope with novel urban habitats requires studying individuals facing the greatest challenges, such as breeding females. Therefore, we compared the glucocorticoid stress response and behavioral recovery from a disturbance between urban and rural female song sparrows (Melospiza melodia) during incubation. If facultative adjustments to the glucocorticoid stress response allow birds to cope with urban habitats, we predicted that urban females would return to parental care behaviors after a standardized stressor as soon or sooner than rural females, and that urban females would have a lower glucocorticoid response to the stressor. We captured female song sparrows at the end of the incubation period and measured their glucocorticoid (corticosterone) levels at baseline and after 30 min of standardized restraint. Concurrently, we installed radio frequency identification (RFID) systems at the nest to capture the time to return to parental care behaviors. We found that incubating urban females had significantly lower corticosterone levels when controlling for sampling timepoint (baseline and restraint-induced) compared to rural. Nest return times did not differ across habitats, and latency to return was not significantly correlated with corticosterone levels. Our findings are consistent with prior work in breeding male song sparrows at our study sites; urban males provide higher parental care and have lower restraint-induced corticosterone levels. The absence of a relationship between glucocorticoids and behavior makes it unlikely that these hormones directly regulate parental care, but lower corticosterone levels in urban birds could reflect stress resistance, which has been hypothesized to permit animals to breed in challenging or novel conditions such as urban habitats.

Adrenal response to competitive singing: glucocorticoid metabolites in male Saltator similis (Aves, Thraupidae)

Song competitions involving passerines, such as the Green-winged Saltator (Saltator similis), are legally permitted in Brazil and attract widespread participation. This study aimed to assess the adrenal response in male S. similis by comparing glucocorticoid metabolite (GCM) levels in uro-faecal extract samples collected during three competitions with those from a rest day (3 days before the competition, D-3), a day before the competition (D-1), the day of the competition (D0) and a day after the competition (D1). Simultaneously, we examined the potential variation in GCM levels among other males not engaged in song competitions but subjected to ex situ conditions much like those of participating males. GCM levels were measured using a direct enzyme immunoassay (EIA, CJM006), which was physiologically (ACTH challenge) and analytically validated (parallelism, accuracy and precision tests) for the species under study. The results indicated that the average GCM concentration was lower in the competition group (33.43 ± 22.09 ng/g) as compared to the control group (70.09 ± 29.45 ng/g; P = 0.01). However, concentrations spiked significantly on competition day (D0: 38.29 ± 26.12 ng/g) as compared to the rest day (D-3: 28.64 ± 17.86  ng/g; P = 0.02), suggesting acute stress response. Given the elevated GCM levels observed during competitions, further research is necessary to confirm the welfare of these birds under competition conditions and to explore the long-term effects of such stressors.

Dominance and aggressiveness are associated with vasotocin neuron numbers in a cooperatively breeding cichlid fish

Within dominance hierarchies, individuals must interact in a rank-appropriate manner, thus behavior and its underlying neural mechanisms must change with social status. One such potential neural mechanism is arginine vasotocin (AVT), a nonapeptide which has been implicated in the regulation of dominance and aggression across vertebrate taxa. We investigated the relationship between social status, dominance-related behaviors, and vasotocin neuron counts in daffodil cichlids (Neolamprologus pulcher). Daffodil cichlids live in stable, mixed-sex, cooperatively breeding social groups that are organised into linear dominance hierarchies. Group members of both sexes exhibit complex behavioral repertoires which differ depending on their current social status. We recorded agonistic behaviors within groups of daffodil cichlids and correlated these with the number of AVT cells within the three distinct neuronal populations in the preoptic area of the brain, comparing across social status and sex. We found that parvocellular AVT neurons were more abundant in dominant individuals than subordinates. We also found that numbers of both parvocellular and magnocellular AVT neurons were positively associated with aggression in dominant individuals. AVT neuron counts were unrelated to submissive behavior in subordinate fish. Our data emphasise the role of AVT in modulating status and aggression in social vertebrates.

Biological agency: a concept without a research program

This paper evaluates recent work purporting to show that the "agency" of organisms is an important phenomenon for evolutionary biology to study. Biological agency is understood as the capacity for goal-directed, self-determining activity-a capacity that is present in all organisms irrespective of their complexity and whether or not they have a nervous system. Proponents of the "agency perspective" on biological systems have claimed that agency is not explainable by physiological or developmental mechanisms, or by adaptation via natural selection. We show that this idea is theoretically unsound and unsupported by current biology. There is no empirical evidence that the agency perspective has the potential to advance experimental research in the life sciences. Instead, the phenomena that the agency perspective purports to make sense of are better explained using the well-established idea that complex multiscale feedback mechanisms evolve through natural selection.

Variation in faecal testosterone levels in male gray whales on a foraging ground relative to maturity and timing

Understanding wildlife reproductive seasonality is crucial for effective management and long-term monitoring of species. This study investigates the seasonal variability of testosterone in male Pacific Coast Feeding Group (PCFG) gray whales, using an eight-year dataset (2016-2023) of individual sightings, drone-based photogrammetry and endocrine analysis of faecal samples. We analyzed the relationship between faecal testosterone levels and total body length (TL), body condition (body area index, BAI), sexual maturity and day of the year using generalized additive mixed models. Our findings reveal a significant increase in faecal testosterone levels in mature males (MM) towards the end of the foraging season. This increase was not observed in JM, highlighting age-dependent development of sexual characteristics. No significant relationship was found between testosterone levels and TL. Additionally, BAI was not significantly associated with testosterone levels. Our results suggest that the increasing testosterone levels in MM gray whales may indicate preparation for mating before the southbound migration. These findings provide valuable insights into the reproductive biology of PCFG gray whales and underscore the importance of non-invasive faecal sampling for studying reproductive seasonality in large whales. Our approach not only provides further insights into the seasonality of male reproduction for the PCFG gray whales but also offers tools to enhance the understanding of male reproduction in baleen whales broadly with non-invasive approaches.

Diet-induced plasticity modifies relationships between larval growth rate and post-metamorphic behavior and physiology in spadefoot toads

It has frequently been hypothesized that among-individual variation in behavior and physiology will correlate with life history traits, yet the nature of these correlations can vary. Such variability may arise from plasticity in trait development, which can amplify or attenuate trait correlations across different environments. Using the Mexican spadefoot toad (Spea multiplicata), we tested whether relationships between larval growth rate and post-metamorphic behavior or physiology are influenced by a key mediator of developmental plasticity: larval diet type. Spea multiplicata larvae develop on two alternative diets, with slower growing omnivores feeding on detritus and faster growing carnivores consuming live fairy shrimp. We found that correlations between larval growth rate and post-metamorphic behavior and physiology differed by diet type. Among detritus feeders, faster growing larvae developed into juvenile frogs that were not only bolder but also had higher hypothalamic-pituitary-interrenal axis reactivity (an indicator of stress responsiveness) and longer telomeres, suggesting greater somatic maintenance. In contrast, among shrimp feeders - which exhibited faster growth overall - larval growth rate was less strongly correlated with juvenile behavior and physiology, indicating that a shift from omnivory to carnivory can attenuate trait correlations among individuals. Overall, our study suggests that developmental plasticity induced by different diet types can modify relationships between life history traits and individual behavior or physiology.

Transcriptomic Insights into Post-Spawning Death and Muscle Atrophy in Ayu (Plecoglossus altivelis)

In semelparous species like the ayu (Plecoglossus altivelis), spawning is followed by rapid physiological decline and death; yet, the underlying molecular mechanisms remain largely unexplored. This study examines transcriptomic changes in ayu skeletal muscle before and after spawning, with a focus on key genes and pathways contributing to muscle atrophy and metabolic dysfunction. Through RNA sequencing and DEG analysis, we identified over 3000 DEGs, and GSEA and KEGG pathway analysis revealed significant downregulation of energy metabolism and protein degradation. In post-spawning ayu, a rapid decrease in body weight was observed, accompanied by a decline in the expression of myosin heavy chain genes, which are major muscle protein genes, and gene expression changes indicative of muscle atrophy. Decreased expression of AP-1 transcription factors associated with muscle development and aging was also evident. PPI network analysis identified carbohydrate catabolism protein gapdh may be the key factor that led to muscle atrophy and accelerated aging in ayu. Our study revealed that after spawning, the ayu muscle tissue undergoes strong metabolic disorders and cellular stress responses, providing special insights into the mechanisms through the post-spawning death of ayu.

Hypothalamic-pituitary-adrenal axis plasticity across life-history stages of a free-living subtropical finch, Amandava amandava amandava

The alterations of phenotypic traits (morphology, endocrine physiology, and behavior) in response to predictable environmental cues across life-history stages in seasonally breeding birds enable successful culmination of reproduction. The present study elucidated the plasticity of the hypothalamic-pituitary-adrenal (HPA) axis in a subtropical free-living finch, Amandava amandava amandava, and suggests the crucial role of the baseline corticosterone (CORT) to coordinate energetic readiness across life-history stages. Birds were captured monthly from an area (25.1337° N 82.5644° E) in Uttar Pradesh, India, from June 2014 to May 2015. Only male birds were included in this study corresponding to different life-history stages (6/life-history stage; 2/month): pre-breeding (June-August), breeding (September-November), post-breeding (December-February), and quiescent phases (March-May). The pituitary expression of adrenocorticotropic hormone (ACTH), adrenal interrenal cell morphometry, and plasma level of the CORT showed varied patterns across life-history stages. The density and immunointensity of the ACTH-immunoreactive corticotropes and the interrenal cell number increased along with the significant plasma CORT elevation during the breeding cycle (both pre-breeding and breeding phases). CORT might facilitate the energy demand for the display of sexual behavior (nest-building, courtship), testicular recrudescence, and foraging of food for offspring during the breeding cycle. On the contrary, plasma CORT decrease in the post-breeding and quiescent phases might enable the bird to molt avoiding the protein catabolic effect of the hormone. Given the complexity involved in the study of baseline CORT in free-living birds, more studies are needed to better understand the crucial role of the HPA axis in the modulation of life-history stages in this and other subtropical avian species.

Does Migration Constrain Glucocorticoid Phenotypes? Testing Corticosterone Levels during Breeding in Migratory Versus Resident Birds

Corticosterone, the main glucocorticoid in birds, is a major mediator of the incredible physiological feat of migration. Corticosterone plays important roles in migration, from preparation to in-flight energy mobilization to refueling, and corticosterone levels often show distinct elevations or depressions during certain stages of the migratory process. Here, we ask whether corticosterone's role in migration shapes its modulation during other life-history stages, as is the case with some other phenotypically flexible traits involved in migration. Specifically, we use a global dataset of corticosterone measures to test whether birds' migratory status (migrant versus resident) predicts corticosterone levels during breeding. Our results indicate that migratory status predicts neither baseline nor stress-induced corticosterone levels in breeding birds; despite corticosterone's role in migration, we find no evidence that migratory corticosterone phenotypes carry over to breeding. We encourage future studies to continue to explore corticosterone in migrants versus residents across the annual cycle. Additionally, future efforts should aim to disentangle the possible effects of environmental conditions and migratory status on corticosterone phenotypes; potentially fruitful avenues include focusing on regions where migrants and residents overlap during breeding. Overall, insights from work in this area could demonstrate whether migration shapes traits during other important life stages, identify tradeoffs or limitations associated with the migratory lifestyle, and ultimately shed light on the evolution of flexible traits and migration.

From eggs to adulthood: sustained effects of early developmental temperature and corticosterone exposure on physiology and body size in an Australian lizard

Developing animals are increasingly exposed to elevated temperatures as global temperatures rise as a result of climate change. Vertebrates can be affected by elevated temperatures during development directly, and indirectly through maternal effects (e.g. exposure to prenatal glucocorticoid hormones). Past studies have examined how elevated temperatures and glucocorticoid exposure during development independently affect vertebrates. However, exposure to elevated temperatures and prenatal corticosterone could have interactive effects on developing animals that affect physiology and life-history traits across life. We tested interactions between incubation temperature and prenatal corticosterone exposure in the delicate skink (Lampropholis delicata). We treated eggs with high or low doses of corticosterone and incubated eggs at 23°C (cool) or 28°C (warm). We measured the effects of these treatments on development time, body size and survival from hatching to adulthood and on adult hormone levels and mitochondrial respiration. We found no evidence for interactive effects of incubation temperature and prenatal corticosterone exposure on phenotype. However, incubation temperature and corticosterone treatment each independently decreased body size at hatching and these effects were sustained into the juvenile period and adulthood. Lizards exposed to low doses of corticosterone during development had elevated levels of baseline corticosterone as adults. Additionally, lizards incubated at cool temperatures had higher levels of baseline corticosterone and more efficient mitochondria as adults compared with lizards incubated at warm temperatures. Our results show that developmental conditions can have sustained effects on morphological and physiological traits in oviparous lizards but suggest that incubation temperature and prenatal corticosterone do not have interactive effects.

Climate Change Impacts Pair-Bond Dynamics in a Long-Lived Monogamous Species

Climate change can influence populations of monogamous species by affecting pair-bond dynamics. This study examined the impact of climate on widowhood and divorce, and the subsequent effects on individual vital rates and life-history outcomes over 54 years in a snow petrel (Pagodroma nivea) population. We found that environmental conditions can affect pair-bond dynamics both directly and indirectly. Divorce was adaptive, occurring more frequently after breeding failure and leading to improved breeding success. Divorce probabilities also increased under severe climatic conditions, regardless of prior breeding success, supporting the 'Habitat-mediated' mechanisms. Overall, pair-bond disruptions reduced subsequent vital rates and lifetime outcomes. Climate forecasts from an Atmosphere-Ocean General Circulation Model projected increased male widowhood rates due to decreased sea ice negatively affecting female survival, despite considerable uncertainty. These findings highlight the importance of environmentally induced changes in demographic and pair-bond disruption rates as crucial factors shaping demographic responses to climate change.

Testosterone variation in a semi-captive population of Asian elephants in Myanmar

Hormones are known to be involved in life-history trade-offs as systemic signals that establish functional links among traits and regulate key behavioural and physiological transitions between states in organisms. Although major functions of many steroid hormones such as testosterone are conserved among vertebrates, circulating concentrations vary widely both within and across species, and the degree to which observed hormone concentrations mediate life-history responses to environmental variation is less understood. In this study, we investigated how faecal testosterone metabolite (FTM) concentrations varied with extrinsic and intrinsic factors. To do so, we took advantage of a 6-year period of longitudinal sampling of FTM, indicators of stress and oxidative status in a semi-captive population of Asian elephants (n = 3163 samples from 173 individuals) in Myanmar. We determined how the variation in FTM is associated with age, sex, origin (captive-born or wild-caught), seasonality of the environment, individual stress level [measured by faecal glucocorticoid metabolite (FGM) and heterophil to lymphocyte ratio (H/L)] and oxidative status (reactive oxygen metabolite concentrations and superoxide dismutase activity). We reported that FTM increased with age from juvenile to adulthood for both sexes, with higher FTM concentrations in males than females. Moreover, elephants showed significantly higher FTM concentrations during the hot season and monsoon than in the cold season. However, for the physiological indicators, we found contrasting results. While FTM concentrations were strongly positively correlated with FGM concentrations, FTM concentrations were not related to H/L ratios. Finally, we found no relationship between FTM and the oxidative status of individuals. Our study provides new insights on the factors associated with variation in testosterone concentrations-a key hormone for reproduction and fitness of individuals-in Asian elephants living in their natural environment, which has relevance for effective conservation measures of this endangered species.

Breeding zebra finches prioritize reproductive bout over self-maintenance under food restriction

Reproduction requires high amounts of energy, and challenging environments during breeding can force parents to prioritize their current reproductive bout over self-maintenance or vice versa. However, little is known about how common stressors, such as food restriction, can influence these trade-offs during breeding, and the physiological mechanisms for these trade-off decisions. In this study, adult zebra finches (Taeniopygia castanotis) were subjected to a control diet (ad libitum) or a 40% food restriction while raising nestlings and fledglings, and we measured body mass, furculum fat, plasma corticosterone (CORT) and blood glucose levels of the parents at the time of pairing, when their offspring fledged, and when their offspring reached nutritional independence. We also measured body mass and growth rate in the offspring from hatching until the end of the treatment period. Food-restricted parents had lower body mass when their offspring fledged and reached nutritional independence and higher baseline CORT when their offspring fledged compared to controls. Offspring did not differ in body mass or growth rate between treatment groups. However, there was no effect of food restriction on parents' furculum fat, baseline glucose, the adrenocortical response, or the glucose response. Furthermore, path analysis results suggest that alterations in baseline glucose is the primary driver of changes in body mass in parents and offspring brood mass. Taken together, these results suggest that food restriction during chick rearing in a short-lived passerine drives parents to prioritize their current reproductive bout over self-maintenance, and glucose could potentially be a mechanism for diverting energy toward parental effort.

Revisiting the specific and potentially independent role of the gonad in hormone regulation and reproductive behavior

Gonadal sex steroid hormones are well-studied modulators of reproductive physiology and behavior. Recent behavioral endocrinology research has focused on how the brain dynamically responds to - and may even produce - sex steroids, but the gonadal tissues that primarily release these hormones receive much less attention as a potential mediator of behavioral variation. This Commentary revisits mechanisms by which the reproductive hypothalamic-pituitary-gonadal (HPG) axis can be modulated specifically at the gonadal level. These mechanisms include those that may allow the gonad to be regulated independently of the HPG axis, such as receptors for non-HPG hormones, neural inputs and local production of conventional 'neuropeptides'. Here, I highlight studies that examine variation in these gonadal mechanisms in diverse taxa, with an emphasis on recent transcriptomic work. I then outline how future work can establish functional roles of gonadal mechanisms in reproductive behavior and evaluate gonad responsiveness to environmental cues. When integrated with neural mechanisms, further investigation of gonadal hormone regulation can yield new insight into the control and evolution of steroid-mediated traits, including behavior.

Stress in the social environment: behavioural and social consequences of stress transmission in bird flocks

The stress response helps individuals cope with challenges, yet how individual stress levels shape group-level processes and the behaviour of other group members has rarely been explored. In social groups, stress responses can be buffered by others or transmitted to members that have not even experienced the stressor first-hand. Stress transmission, in particular, can have profound consequences for the dynamics of social groups and the fitness of individuals therein. We experimentally induced chronic stress within replicated colonies of zebra finches and used fine-scale tracking to observe the consequences of stress-exposed colony members for the behaviour and reproduction of non-manipulated colony members. Non-manipulated individuals in colonies containing stress-exposed individuals exhibited reduced activity, and fewer-but more differentiated-social bonds. These effects were stronger in colonies with a greater proportion of stress-treated individuals, demonstrating that the impact of stressors can reach beyond directly exposed individuals by also affecting their group mates. We found no evidence that socially transmitted stress affected reproduction or long-term physiological measurement in unmanipulated birds, even though the stress-exposed demonstrators laid slightly fewer eggs and showed stressor-dependent changes in feather corticosterone. Social transmission of these effects, if occurring at all, might be more subtle.

Multiple stressors disrupt sex hormones and fitness outcomes: effects of hypoxia and turbidity on an African cichlid fish

Freshwater organisms face a complex array of environmental stressors that can negatively affect endocrine function and subsequent fitness outcomes. Hypoxia and turbidity are two environmental stressors that are increasing due to human activities that could lead to endocrine disruption and reduced reproductive output. Our research addresses how hypoxia and elevated turbidity affect traits related to reproductive success, specifically sex hormone concentrations, investment in reproductive tissues and body size. We used wild fish from two populations (a river and a swamp) of an African cichlid, Pseudocrenilabrus multicolor, to produce offspring that were reared in a full factorial split brood rearing experiment (hypoxic/normoxic × clear/turbid). River and swamp populations represent divergent habitat types with respect to the stressors of interest, being well-oxygenated but turbid or hypoxic and clear, respectively. Overall, we found evidence for plastic responses to both stressors. Specifically, we found that there was an interactive effect of oxygen and turbidity on testosterone in males from both populations. Additionally, males of both populations reared under hypoxic conditions were significantly smaller in both mass and standard length than those raised under normoxic conditions and invested less in reproductive tissues (quantified as gonadosomatic index). Hypoxia and turbidity are experienced naturally by this species, and these environmental stressors did not affect the number of eggs laid by females when experienced in the absence of another stressor (i.e. normoxic/turbid or hypoxic/clear). However, there was an interactive effect of hypoxia and turbidity, as females reared and maintained under this treatment combination laid fewer eggs. This research underscores the importance of considering the possibility of stressor interactions when determining how anthropogenic stressors affect fitness outcomes.

Androgen and glucocorticoid profiles throughout extended uniparental paternal care in the eastern hellbender salamander (Cryptobranchus a. alleganiensis)

The behavioral endocrinology associated with reproduction and uniparental male care has been studied in teleosts, but little is known about hormonal correlates of uniparental male care in other ectotherms. To address this gap, we are the first to document the seasonal steroid endocrinology of uniparental male hellbender salamanders during the transition from pre-breeding to nest initiation, and through the subsequent eight months of paternal care. In doing so, we investigated the correlates of nest fate and clutch size, exploring hellbenders' alignment with several endocrinological patterns observed in uniparental male fish. Understanding the endocrinology of hellbender paternal care is also vital from a conservation perspective because high rates of nest failure were recently identified as a factor causing population declines in this imperiled species. We corroborated previous findings demonstrating testosterone and dihydrotestosterone (DHT) to be the primary androgens in hellbender reproduction, and that cortisol circulates as the most abundant glucocorticoid. However, we were unable to identify a prolactin or a "prolactin-like" peptide in circulation prior to or during parental care. We observed ∼ 80 % declines in both primary androgens during the transition from pre-breeding to nest initiation, and again as paternal care progressed past its first month. In the days immediately following nest initiation, testosterone and DHT trended higher in successful individuals, but did not differ with males' clutch size. We did not observe meaningful seasonality in baseline glucocorticoids associated with breeding or nesting. In contrast, stress-induced glucocorticoids were highest at pre-breeding and through the first two months of care, before declining during the latter-most periods of care as larvae approach emergence from the nest. Neither baseline nor stress-induced glucocorticoids varied significantly with either nest fate or clutch size. Both stress-induced cortisol and corticosterone were positively correlated with total length, a proxy for age in adult hellbenders. This is consistent with age-related patterns in some vertebrates, but the first such pattern observed in a wild amphibian population. Generally, we found that nesting hellbenders adhere to some but not all of the endocrinological patterns observed in uniparental male teleosts prior to and during parental care.

Sex, season, age and status influence urinary steroid hormone profiles in an extremely polygynous neotropical bat

Several polygynous mammals exhibit reproductive skew in which only a few males reproduce. Successful males need strength, stamina and fighting ability to exclude competitors. Consequently, during the mating season their androgens and glucocorticoids are expected to increase to support spermatogenesis and aggressive behavior. But, during the nonmating season these hormones should decline to minimize deleterious effects, such as reduced immune function. Bats that exhibit harem polygyny in which males aggressively defend large groups of females year-round are ideal for assessing hormonal and other consequences of extreme polygyny. Here we use DNA methylation to estimate age and gas chromatography, tandem mass spectrometry to profile steroid metabolites in urine of wild greater spear-nosed bats, Phyllostomus hastatus, across seasons. We find that condition, measured by relative weight, is lower during the mating season for both sexes, although it remains high in harem males during the mating season. Average age of females is greater than males, and females exhibit substantial seasonal differences in androgens, estrogens and glucocorticoids with higher levels of all hormones during the mating season. Males, however, show little seasonal differences but substantial age-associated increases in most steroid metabolites. Harem males have larger, persistently scrotal testes and are older than bachelor males. While cortisone generally declines with age, harem males maintain higher amounts of biologically active cortisol than bachelor males all year and cortisol levels increase more quickly in response to restraint in males than in females. Taken together, these results suggest that attaining reproductive dominance requires hormone levels that reduce lifespan.

Down-regulating the stress axis: Living in the present while preparing for the future

The measurement of glucocorticoid (GC) hormones provides us with a window into the stress physiology of vertebrates and the adaptative responses they use to cope with predictable and unpredictable changes in the environment. Baseline GCs inform us about the metabolic demands they are subject to at that point in their yearly life-history stage, whereas GC changes (often increases) in response to acute challenges inform us on their capacity to cope with more immediate environmental challenges. However, baseline GC levels and the kinetics of GC responses to acute stressors can vary substantially among and within species, depending on individual characteristics (age, sex, condition, life-history stage). In addition, a thorough understanding of the stress status of an animal requires moving beyond the measurement of GCs alone by focusing on downstream measures of metabolic activation, such as oxidative stress. Here, we evaluated the changes in blood cortisol and oxidative stress markers in wild adult Columbian ground squirrels (Urocitellus columbianus), following a 30-min capture-handling stress performed in mid-late June. Measurements were taken when males were post-reproductive and preparing for hibernation and adult females were weaning litters. We found three key results. First, the time-course of GC increase was markedly slower (by an order of magnitude) than what is currently reported in the literature for most species of mammals, birds and reptiles. Second, there were marked differences in the male and female response, linked to differences in life-history stage: females close to weaning had abolished GC responses, whereas post-reproductive males did not. Third, there were mild to moderate increases in oxidative damage and decreases in oxidative defenses in response to our short-term challenge, consistent with the idea that short-term acute metabolic activation may carry physiological costs. However, these changes were not correlated to the changes in GCs, a novel result suggesting a disconnect between the hormonal stress response and oxidative damage.

Baseline and stress-induced steroid plasma levels and immune function vary annually and are associated with vocal activity in male toads (Rhinella icterica)

Theoretical models predict that elevated androgen and glucocorticoid levels in males during the reproductive season promote immunosuppression. However, some studies report decreased stress response during this season. This study investigated annual variation in plasma corticosterone and testosterone levels, plasma bacterial killing ability (BKA), and neutrophil to lymphocyte ratio (NLR) in free-living male toads (Rhinella icterica). Toads were sampled in the field (baseline) and 1 h-post restraint over five months, and we considered the occurrence of vocal activity. Baseline corticosterone, testosterone, and BKA showed higher values during the reproductive period, specifically in calling male toads. The NLR was similar throughout the year, but higher values were observed in calling toads. Moreover, baseline NLR and BKA were positively correlated with both testosterone and corticosterone, suggesting higher steroid levels during reproduction are associated with enhanced cellular and humoral immunity. Despite fluctuation of baseline values, post-restraint corticosterone levels remained uniform over the year, indicating that toads reached similar maximum values throughout the year. Testosterone levels decreased following restraint before one specific reproductive period but increased in response to restraint during and after this period. Meanwhile, BKA decreased due to restraint only after the reproductive period, indicating immune protection and resilience to immunosuppression by stressors associated with steroid hormones during reproduction. Our results show that baseline and stress-induced hormonal and immune regulation varies throughout the year and are associated with vocal activity in R. icterica males, indicating a possible compromise between steroids and immune function in anuran males.

Manipulation of a social signal affects DNA methylation of a stress-related gene in a free-living bird

Social status directly affects the health of humans and other animals. Low status individuals receive more antagonistic encounters, have fewer supportive relationships and have worse health outcomes. However, the physiological and cellular processes that mediate the relationship between the social environment and health are incompletely known. Epigenetic regulation of the hypothalamic-pituitary-adrenal (HPA) axis, the neuroendocrine pathway that activates in response to stressors, may be one process that is sensitive to the social environment. Here, we experimentally manipulated plumage, a key social signal in female tree swallows (Tachycineta bicolor) and quantified methylation of four genes in the HPA axis before and after treatment. We found that dulling the white breast plumage affected methylation in one gene, CRHR1; however, the effect depended on the original brightness of the bird. Methylation in this gene was correlated with baseline corticosterone levels, suggesting that DNA methylation of CRHR1 helps regulate glucocorticoid production in this species. Methylation in two other genes, FKBP5 and GR, changed over the course of the experiment, independent of treatment. These results show that methylation of these genes is labile into adulthood and suggest that epigenetic regulation of the HPA axis could help birds respond to current environmental conditions.

Effects of blood extraction and ecophysiological experiments on stress in adult males of Liolaemus attenboroughi

Stress during laboratory experiments can affect the outcomes of ecophysiological studies. The serum corticosterone concentration (CORT), the leukocyte profile, heterophil/lymphocyte ratio (H/L), and the presence of blood endoparasites were analyzed as a proxy of stress and immunological state in adult males of the lizard Liolaemus attenboroughi, endemic to Patagonia, Argentina. The results of the ecophysiological variables (preferred temperature, running speed, locomotor endurance, and body condition index, BCI) were analyzed in relation to stress indicators obtained from blood samples taken at three different times: at capture, and on the third and seventh days in the laboratory. Males at capture showed a high percentage of lymphocytes and heterophils and a low of basophils, monocytes, and eosinophils. Haemogregorina-type endoparasites have been recorded in the genus Liolaemus for the first time. The proportion of infected males remained stable during captivity; however, these males showed higher CORT levels, increased percentages of basophils, and decreased percentages of lymphocytes. There was a significant increment in CORT and H/L, and a decrease in BCI during laboratory experiments, compared with baseline values at capture. The performance was not related to the CORT or the repeated blood sampling. The BCI decreased, possibly due to energy reserve mobilization caused by acute stress. This study shows that blood extraction and ecophysiological experiments over 7 days have a minor effect on the stress indicators used.

Prolactin is associated with proximity to incubating partner rather than parental care in black-headed gulls

The peptide hormone prolactin plays an important role in the expression of parental care behaviours across bird and mammal taxa. While a great deal is known about how plasma prolactin concentrations vary across the reproductive cycle, the few studies that investigate how prolactin relates to individual-level variation in parental care have reported mixed results. We argue that, since parental care is also affected by social interactions and environmental constraints, prolactin may better reflect behaviours that are indirectly related to parenting than the absolute level of care that is eventually expressed. In this study, we tested for associations between plasma prolactin and the expression of both parental care and proximity to the partner in incubating black-headed gulls, Chroicocephalus ridibundus. Baseline prolactin levels increased with calendar date but were unrelated to incubation behaviours. However, parents who showed a weaker decrease in prolactin to an acute stressor spent more time in close proximity to their incubating partner while not on the nest themselves, suggesting that individual variation in stress-induced prolactin changes reflect differences in parents' tendency to be closely associated with their partner and the joint nesting attempt. Baseline and stress-induced levels of the stress hormone corticosterone were unrelated to both prolactin levels and parental behaviours, suggesting that this hormone is not a strong moderator of parental care in black-headed gulls. One potential explanation for the link between prolactin dynamics and partner proximity is that prolactin reflects parental motivation to provide parental care or retain contact with the breeding partner, but further work is needed to directly test this hypothesis.

Dietary inclusion of a Saccharomyces cerevisiae metabolite improved reproductive performance but did not affect intestinal permeability in two chicken meat breeder lines

Gastrointestinal dysbiosis is a disturbance in mucosal homeostasis, producing low-grade chronic intestinal inflammation and impaired intestinal barrier function. It is induced by several factors, including nutrition and stress, which are both significant factors when considering current broiler breeder practices. A great grandparent (GGP) chicken meat line was identified displaying clinical signs characteristic of potential dysbiosis, including wet droppings and litter, in addition to reduced reproductive performance when compared to a consistently high performing line. This study aimed to determine whether the reduced reproductive performance observed in these hens was a result of dysbiosis and whether dietary supplementation with a Saccharomyces cerevisiae (SC) fermentation product would alleviate clinical signs. Dietary inclusion of SC did not influence intestinal permeability, WBC differentials, or corticosterone concentration in either the wet litter (WL) or high-performing (HP) breeder lines. Compared to hens from the HP line, WL line hens had a significant increase in intestinal permeability at 26 wk (onset of lay). WL hen heterophil counts were increased markedly at week 26 before declining. At weeks 26, 32, and 37 there were also significant increases in monocytes. Higher plasma corticosterone was also observed in WL hens at 37 wk. No significant differences in heterophil to lymphocyte (H:L) ratios or feather corticosterone were observed between lines. Dietary inclusion of SC supplementation to breeder diets had some benefit in regards to reducing hen mortality, improving egg production and hatchability but only in the WL line. Results from this study did not indicate that hens from the wet litter line were experiencing gut dysbiosis. Chronic intestinal inflammation may be a possible reason for the increase in intestinal permeability. These results do indicate that both breeder lines may be exhibiting physiological stress. Future investigation into the physiology and behavior around point of lay is required to find novel strategies to alleviate this stress and in turn, potentially improve welfare and production outcomes.

Behave yourself: effects of exogenous-glucocorticoid exposure on larval amphibian anti-parasite behaviour and physiology

Parasites represent a ubiquitous threat for most organisms, requiring potential hosts to invest in a range of strategies to defend against infection-these include both behavioural and physiological mechanisms. Avoidance is an essential first line of defence, but this behaviour may show a trade-off with host investment in physiological immunity. Importantly, while environmental stressors can lead to elevated hormones in vertebrates, such as glucocorticoids, that can reduce physiological immunity in certain contexts, behavioural defences may also be compromised. Here, we investigate anti-parasite behaviour and immune responses against a trematode (flatworm) parasite by larval amphibians (tadpoles) exposed or not to a simulated general stressor in the form of exogenous corticosterone. Tadpoles that were highly active in the presence of the trematode infectious stage (cercariae) had lower infection loads, and parasite loads from tadpoles treated only with dechlorinated water were significantly lower than those exposed to corticosterone or the solvent control. However, treatment did not affect immunity as measured through white blood-cell profiles, and there was no relationship between the latter and anti-parasite behaviour. Our results suggest that a broad range of stressors could increase host susceptibility to infection through altered anti-parasite behaviours if they elevate endogenous glucocorticoids, irrespective of physiological immunity effects. How hosts defend themselves against parasitism in the context of multiple challenges represents an important topic for future research, particularly as the risk posed by infectious diseases is predicted to increase in response to ongoing environmental change.

Biological validation of faecal corticosterone metabolites as a non-invasive stress assessment in translocated California valley quail (Callipepla californica)

US quail species are vulnerable to population declines as a result of climate change, habitat loss and habitat fragmentation, all of which can result in physiological stress. Additionally, population restoration techniques (PRTs), like translocations, also induce stress. Traditional assessments of avian stress hormone levels include capturing and handling birds to extract blood, methods that are inherently stressful and can compound stress analyses. However, the stress hormone corticosterone (CORT) is metabolized from the blood and excreted in faeces as faecal corticosterone metabolites (FCMs). FCMs have been used as a non-invasive measurement of stress hormone levels in a variety of species, but must be validated for each species. The objective of this study was to biologically validate the use of FCMs as a non-invasive measurement of CORT levels in California valley quail (Callipepla californica). Reference and treatment quail were acclimated for 3 weeks in an outdoor aviary. Subsequently, treatment quail were subjected to a simulated 48-h translocation, a common and stress hormone-inducing PRT. Faecal samples were collected every 4 h and processed using an enzyme immunoassay. Mean FCM concentrations of treatment quail (41.50 ± 16.13 ng/g) were higher than reference FCM concentrations (24.07 ± 10.4 ng/g). These results biologically validate the use of FCMs as a non-invasive method to assess CORT levels in California valley quail, demonstrate diurnal variation in quail CORT levels, and confirm that quail translocations are a stress-inducing PRT. Ultimately, this research validates a new non-invasive tool for stress response measurement to advance quail research, management and conservation.

Child abuse and pubertal timing: what is the role of child sex and identity of the perpetrator?

BACKGROUND

This study investigated the association between child abuse [child neglect (CN), emotional (CEA) and physical abuse (CPA)] and early puberty with special regard to sex-specific effects concerning child and parental perpetrator.

METHODS

Data assessment took place within the framework of the LIFE Child Depression study, a longitudinal study on the development of depressive symptoms and disorders between child- and adulthood in Leipzig, Germany. A sample of 709 children (8-14 years) was recruited from the general population and via psychiatric hospitals. Data on pubertal status were assessed using an instrument for self-assessment of tanner stages (scales of physical pubertal development). Information on menarche was provided by parents. The Parent-Child Conflict Tactics Scales (CTS-PC) served for data on child abuse.

RESULTS

Regarding physical puberty markers, significant correlations were found, especially with child neglect (CN) and child emotional abuse (CEA). Regression analyses, controlling for Body-Mass-Index (BMI) and Socioeconomic Status (SES), revealed that children affected by child neglect perpetrated by mother (CNm) and child emotional abuse (CEA) parent-non-specifically enter puberty significantly earlier. Sex-specific analyses identified child neglect perpetrated by mother (CNm) to be associated with early puberty in girls and child emotional abuse perpetrated by father (CEAf) with early puberty in boys. Concerning the onset of menstruation, there was a significant positive correlation between early menarche and parent-specific and non-specific child neglect (CN), as well as between early menarche and child emotional abuse perpetrated by the mother (CEAm). In regression models that controlled for Body-Mass-Index (BMI) and Socioeconomic Status (SES) no significant associations were maintained. Child physical abuse (CPA) was not associated with early puberty.

CONCLUSION

Results outlined child neglect (CN) and child emotional abuse (CEA) to be sex- and perpetrator-specific risk factors for early pubertal development. Knowledge of sex- and perpetrator-specific effects could help clinicians to specify their diagnostic process and to define differential prevention and treatment goals for children with experiences of CN and CEA. Further research on the sex-specific impact of parental CN and CEA on girls' and boys' puberty is needed.

Bioinformatics analysis of a disease-specific lncRNA-miRNA-mRNA regulatory network in recurrent spontaneous abortion (RSA)

BACKGROUND

This study investigated the molecular mechanisms of long non-coding RNAs (lncRNAs) in RSA using the lncRNA-miRNA-mRNA regulatory network.

METHODS

The present study obtained expression datasets of long non-coding RNAs (lncRNAs), messenger RNAs (mRNAs), and microRNAs (miRNAs) from blood samples of individuals with unexplained recurrent spontaneous abortion (RSA) and healthy controls. Differentially expressed lncRNAs (DELs), mRNAs (DEMs), and miRNAs (DEmiRs) were identified. A regulatory network comprising lncRNA, miRNA, and mRNA was constructed, and Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were conducted to analyze the biological functions of DEM. Also, a protein-protein interaction (PPI) network was made and key genes were identified.

RESULTS

A total of 57 DELs, 212 DEmiRs, and 301 DEMs regarding RSA were identified. Later analysis revealed a lncRNA-miRNA-mRNA network comprising nine lncRNAs, 14 miRNAs, and 65 mRNAs. Then, the ceRNA network genes were subjected to functional enrichment and pathway analysis, which showed their association with various processes, such as cortisol and thyroid hormone synthesis and secretion, human cytomegalovirus infection, and parathyroid hormone synthesis. In addition, ten hub genes (ITGB3, GNAI2, GNAS, SRC, PLEC, CDC42, RHOA, RAC1, CTNND1, and FN1) were identified based on the PPI network results.

CONCLUSION

In summary, the outcomes of our study provided some data regarding the alteration genes involved in RSA pathogenic mechanism via the lncRNA-miRNA-mRNA network and reveal the possibility of identifying new lncRNAs and miRNAs as promising molecular biomarkers.

Endocrine flexibility can facilitate or constrain the ability to cope with global change

Global climate change has increased average environmental temperatures world-wide, simultaneously intensifying temperature variability and extremes. Growing numbers of studies have documented phenological, behavioural and morphological responses to climate change in wild populations. As systemic signals, hormones can contribute to orchestrating many of these phenotypic changes. Yet little is known about whether mechanisms like hormonal flexibility (reversible changes in hormone concentrations) facilitate or limit the ability of individuals, populations and species to cope with a changing climate. In this perspective, we discuss different mechanisms by which hormonal flexibility, primarily in glucocorticoids, could promote versus hinder evolutionary adaptation to changing temperature regimes. We focus on temperature because it is a key gradient influenced by climate change, it is easy to quantify, and its links to hormones are well established. We argue that reaction norm studies that connect individual responses to population-level and species-wide patterns will be critical for making progress in this field. We also develop a case study on urban heat islands, where several key questions regarding hormonal flexibility and adaptation to climate change can be addressed. Understanding the mechanisms that allow animals to cope when conditions become more challenging will help in predicting which populations are vulnerable to ongoing climate change. This article is part of the theme issue 'Endocrine responses to environmental variation: conceptual approaches and recent developments'.

Single-cell transcriptome profiling implicates the psychological stress-induced disruption of spermatogenesis

Male infertility has emerged as a global issue, partly attributed to psychological stress. However, the cellular and molecular mechanisms underlying the adverse effects of psychological stress on male reproductive function remain elusive. We created a psychologically stressed model using terrified-sound and profiled the testes from stressed and control rats using single-cell RNA sequencing. Comparative and comprehensive transcriptome analyses of 11,744 testicular cells depicted the cellular landscape of spermatogenesis and revealed significant molecular alterations of spermatogenesis suffering from psychological stress. At the cellular level, stressed rats exhibited delayed spermatogenesis at the spermatogonia and pachytene phases, resulting in reduced sperm production. Additionally, psychological stress rewired cellular interactions among germ cells, negatively impacting reproductive development. Molecularly, we observed the down-regulation of anti-oxidation-related genes and up-regulation of genes promoting reactive oxygen species (ROS) generation in the stress group. These alterations led to elevated ROS levels in testes, affecting the expression of key regulators such as ATF2 and STAR, which caused reproductive damage through apoptosis or inhibition of testosterone synthesis. Overall, our study aimed to uncover the cellular and molecular mechanisms by which psychological stress disrupts spermatogenesis, offering insights into the mechanisms of psychological stress-induced male infertility in other species and promises in potential therapeutic targets.

In your CORT: Corticosterone and its receptors in the brain underlie mate choosiness in female Cope's gray treefrogs (Hyla chrysoscelis)

Selecting an attractive mate can involve trade-offs related to investment in sampling effort. Glucocorticoids like corticosterone (CORT) are involved in resolving energetic trade-offs. However, CORT is rarely studied in the context of mate choice, despite its elevated levels during reproductive readiness and the energetic transitions that characterize reproduction. Few systems are as well suited as anuran amphibians to evaluate how females resolve energetic trade-offs during mate choice. Phonotaxis tests provide a robust bioassay of mate choice that permit the precise measurement of inter-individual variation in traits such as choosiness-the willingness to pursue the most attractive mate despite costs. In Cope's gray treefrogs (Hyla chrysoscelis), females exhibit remarkable variation in circulating CORT as well as choosiness during mate choice, and a moderate dose of exogenous CORT rapidly (<1 h) and reliably induce large increases in choosiness. Here we measured the expression of glucocorticoid (GR) and mineralocorticoid (MR) receptors in the brains of females previously treated with exogenous CORT and tested for mate choosiness. We report a large decrease in GR expression in the hindbrain and midbrain of females that were treated with the moderate dosage of CORT-the same treatment group that exhibited a dramatic increase in choosiness following CORT treatment. This association, however, does not appear to be causal, as only forebrain GR levels, which are not affected by CORT injection, are positively associated with variation in choosiness. No strong effects were found for MR. We discuss these findings and suggest future studies to test the influence of glucocorticoids on mate choice.

Hormone profiles of the African pygmy mouse Mus minutoides, a species with XY female sex reversal

In mammals, most sex differences in phenotype are controlled by gonadal hormones, but recent work on transgenic mice has shown that sex chromosomes can have a direct influence on sex-specific behaviors. In this study, we take advantage of the naturally occurring sex reversal in a mouse species, Mus minutoides, to investigate for the first time the relationship between sex chromosomes, hormones, and behaviors in a wild species. In this model, a feminizing variant of the X chromosome, named X*, produces three types of females with different sex chromosome complements (XX, XX*, and X*Y), associated with alternative behavioral phenotypes, while all males are XY. We thus compared the levels of three major circulating steroid hormones (testosterone, corticosterone, and estradiol) in the four sex genotypes to disentangle the influence of sex chromosomes and sex hormones on behavior. First, we did not find any difference in testosterone levels in the three female genotypes, although X*Y females are notoriously more aggressive. Second, in agreement with their lower anxiety-related behaviors, X*Y females and XY males display lower baseline corticosterone concentration than XX and XX* females. Instead of a direct hormonal influence, this result rather suggests that sex chromosomes may have an impact on the baseline corticosterone level, which in turn may influence behaviors. Third, estradiol concentrations do not explain the enhanced reproductive performance and maternal care behavior of the X*Y females compared to the XX and XX* females. Overall, this study highlights that most of the behaviors varying along with sex chromosome complement of this species are more likely driven by genetic factors rather than steroid hormone concentrations.

Chronic non-discriminatory social defeat stress during the perinatal period induces depressive-like outcomes in female mice

Depression is more prevalent in women than in men. Perinatal stress is one of the main risk factors for depression in women. However, there is no suitable female model for perinatal depression that uses the social defeat stress (SDS) paradigm. The standard chronic SDS protocol, which is the most useful method for developing a depression-like model, is effective only in male mice. Thus, this study aimed to characterize a novel SDS method for producing a perinatal depression-like model mouse. We induced chronic SDS in perinatal female mice, wherein chronic non-discriminatory SDS (ND-SDS) was used to induce substantial stress in female mice. The female mice were placed in aggressive ICR mouse cages with sentinel male mice under ND-SDS conditions. Stressed female mice subjected to ND-SDS during the perinatal period efficiently exhibited stress-susceptible phenotypes, such as a social avoidance phenotype and anhedonic behavior, whereas stressed female mice subjected to SDS did not show depressive-like behaviors. These results indicate that chronic ND-SDS in perinatal females could be used to develop a female perinatal depression-like model that can be used to study women's health.

Effects of landscape metrics on scorpion (Arachnida: Scorpiones) assemblage in a tropical urban ecosystem

Urban landscapes restrain the distribution of forest-dwelling species, which may be related to challenging conditions that impair body condition. The dynamics in urban areas lead to the simplification of communities that inhabit forest patches in cities with the turnover of sensitive species for opportunistic ones. In this study, we investigated the effect of urbanization on the body condition and diversity of scorpions at the landscape scale. Sampling was carried out in 10 forest patches in an urban matrix in Brazil, originally covered by a tropical rainforest. The surroundings of the landscape of each forest patch were characterized through the amount of forest, agriculture, and urban land cover. Individual body length, dry, lipid, and muscular masses were used as proxies of Tityus pusillus body condition. In total, 147 scorpions were collected, belonging to the species Ananteris mauryi, T. pusillus, T. stigmurus, and T. neglectus. Forest cover explained 28% of species variation. There was a positive relationship between forest cover and T. pusillus and A. mauryi abundances, while T. stigmurus was negatively affected by forest cover. Species richness and total scorpion abundance were not influenced by landscape metrics. In terms of body condition, only females of T. pusillus were affected by landscape variables, with individuals showing higher body mass with an increase in forest cover. Our results suggest that urban forests can support scorpion assemblages. However, there is a turnover in specialist forest species for opportunistic species. Forest cover is a crucial factor in maintaining healthy scorpion populations in urban areas.

A general framework for modelling trade-offs in adaptive behaviour

An animal's behaviour can influence many variables, such as its energy reserves, its risk of injury or mortality, and its rate of reproduction. To identify the optimal action in a given situation, these various effects can be compared in the common currency of reproductive value. While this idea has been widely used to study trade-offs between pairs of variables, e.g. between energy gain versus survival, here we present a unified framework that makes explicit how these various trade-offs fit together. This unification covers a wide range of biological phenomena, highlighting similarities in their logical structure and helping to identify knowledge gaps. To fill one such gap, we present a new model of foraging under the risk of predation and damage accumulation. We conclude by discussing the use and limitations of state-dependent optimisation theory in predicting biological observations.

Multiple morphophysiological responses of a tropical frog to urbanization conform to the pace-of-life syndrome

The Pace-of-Life syndrome proposes that behavioural, physiological and immune characteristics vary along a slow-fast gradient. Urbanization poses several physiological challenges to organisms. However, little is known about how the health status of frogs is affected by urbanization in the Tropics, which have a faster and more recent urbanization than the northern hemisphere. Here, we analysed a suite of physiological variables that reflect whole organism health, reproduction, metabolic and circulatory physiology and leukocyte responses in Leptodactylus podicipinus. Specifically, we tested how leukocyte profile, erythrocyte morphometrics and germ cell density, as well as somatic indices and erythrocyte nuclear abnormalities differ throughout the adult life span between urban and rural populations. We used Phenotypic Trajectory Analysis to test the effect of age and site on each of the multivariate data sets; and a Generalised Linear Model to test the effect of site and age on nuclear abnormalities. Somatic indices, erythrocyte nuclear abnormalities, erythrocyte morphometrics and leukocyte profile differed between populations, but less so for germ cell density. We found a large effect of site on nuclear abnormalities, with urban frogs having twice as many abnormalities as rural frogs. Our results suggest that urban frogs have a faster pace of life, but the response of phenotypic compartments is not fully concerted.

Factors Associated with Reproductive Success in Captive Vancouver Island Marmots (Marmota vancouverensis)

The Vancouver Island marmot (Marmota vancouverensis) is Canada's most endangered endemic mammal. In 1997, a conservation breeding-for-release program was established to supplement wild marmot populations. Retrospective analyses of captive breeding studbook records since 2000 indicate the age of the sire and the dam significantly impacted the odds of successfully weaning a litter. Dams and sires between 5 and 7 years of age had more than double the odds of reproductive success compared to older animals. Successful reproduction by the dam in the previous year also doubled the odds of successfully weaning a litter in subsequent years. Assessment of adrenal function via fecal glucocorticoid analyses indicated established breeding pairs had decreased stress compared to new pairs (5.74 ± 0.28 ng/g vs. 7.60 ± 0.34 ng/g; p < 0.0001). Pairs that were ultimately successful at weaning pups in a breeding season had decreased stress compared to unsuccessful pairs (6.05 ± 0.34 ng/g vs. 7.22 ± 0.28 ng/g; p = 0.0006). These endocrine results suggest social buffering via familiarity and breeding/pair bond formation may be decreasing stress in established and successful pairs, respectively. The results of this study will be used to assist in the captive breeding management of this species to optimise numbers of animals produced to supplement the wild populations.

Mitochondrial function and sexual selection: can physiology resolve the 'lek paradox'?

Across many taxa, males use elaborate ornaments or complex displays to attract potential mates. Such sexually selected traits are thought to signal important aspects of male 'quality'. Female mating preferences based on sexual traits are thought to have evolved because choosy females gain direct benefits that enhance their lifetime reproductive success (e.g. greater access to food) and/or indirect benefits because high-quality males contribute genes that increase offspring fitness. However, it is difficult to explain the persistence of female preferences when males only provide genetic benefits, because female preferences should erode the heritable genetic variation in fitness that sexually selected traits signal. This 'paradox of the lek' has puzzled evolutionary biologists for decades, and inspired many hypotheses to explain how heritable variation in sexually selected traits is maintained. Here, we discuss how factors that affect mitochondrial function can maintain variation in sexually selected traits despite strong female preferences. We discuss how mitochondrial function can influence the expression of sexually selected traits, and we describe empirical studies that link the expression of sexually selected traits to mitochondrial function. We explain how mothers can affect mitochondrial function in their offspring by (a) influencing their developmental environment through maternal effects and (b) choosing a mate to increase the compatibility of mitochondrial and nuclear genes (i.e. the 'mitonuclear compatibility model of sexual selection'). Finally, we discuss how incorporating mitochondrial function into models of sexual selection might help to resolve the paradox of the lek, and we suggest avenues for future research.

Impact of stress on male fertility: role of gonadotropin inhibitory hormone

Studies have implicated oxidative stress-sensitive signaling in the pathogenesis of stress-induced male infertility. However, apart from oxidative stress, gonadotropin inhibitory hormone (GnIH) plays a major role. The present study provides a detailed review of the role of GnIH in stress-induced male infertility. Available evidence-based data revealed that GnIH enhances the release of corticosteroids by activating the hypothalamic-pituitary-adrenal axis. GnIH also mediates the inhibition of the conversion of thyroxine (T4) to triiodothyronine (T3) by suppressing the hypothalamic-pituitary-thyroidal axis. In addition, GnIH inhibits gonadotropin-releasing hormone (GnRH), thus suppressing the hypothalamic-pituitary-testicular axis, and by extension testosterone biosynthesis. More so, GnIH inhibits kisspeptin release. These events distort testicular histoarchitecture, impair testicular and adrenal steroidogenesis, lower spermatogenesis, and deteriorate sperm quality and function. In conclusion, GnIH, via multiple mechanisms, plays a key role in stress-induced male infertility. Suppression of GnIH under stressful conditions may thus be a beneficial prophylactic and/or therapeutic strategy.

Male Cope's gray treefrogs (Hyla chrysoscelis) in amplexus have elevated and correlated steroid hormones compared to solitary males

Gonadal steroid hormones are typically elevated during the breeding season-a finding known as an associated reproductive pattern. Though less studied, there is also evidence, in both sexes, for elevated adrenal/interrenal steroids, including acute elevations on the day of mating. I investigated gonadal and interrenal steroids in wild male Cope's gray treefrogs at breeding aggregations. I collected blood from males found in amplexus with female mates (amplexed males) and males sampled at the same time and location that were actively advertising vocally and without a mate (solo males). Concentrations of plasma corticosterone, testosterone, and 17β-estradiol (CORT, T and E2, respectively) were validated and measured. These two categories of males differed in four ways: (1) amplexed males exhibited significantly elevated concentrations of all three steroids compared to solo males (CORT: +347 %; T: +60 %; and E2: +43 %); (2) these hormone profiles alone accurately predicted male mating category with ca. 83 % accuracy using a discriminant function analysis; (3) amplexed males exhibited significant between-hormone correlations (T and E2 were positively correlated and CORT and E2 were negatively correlated) whereas no correlations were found in solo males; (4) amplexed males showed a negative correlation with CORT concentration and the time of night, whereas no such pattern was present in solo males. These findings suggest an acute and strong coactivation of the interrenal and gonadal axes that could drive phenotypic integration during this fitness-determining moment. I discuss these findings and suggest experiments to determine causation, including the role of motor behavior driving endocrine states and the role of female selection on endocrine profiles.

Deleterious effects of mercury contamination on immunocompetence, liver function and egg volume in an antarctic seabird

Mercury (Hg) is a globally important pollutant that can negatively impact metabolic, endocrine and immune systems of marine biota. Seabirds are long-lived marine top predators and hence are at risk of bioaccumulating high Hg concentrations from their prey. Here, we measured blood total mercury (THg) concentrations and relationships with physiology and breeding parameters of breeding brown skuas (Stercorarius antarcticus) (n = 49 individuals) at Esperanza/Hope Bay, Antarctic Peninsula. Mean blood THg concentrations were similar in males and females despite the differences in body size and breeding roles, but differed between study years. Immune markers (hematocrit, Immunoglobulin Y [IgY] and albumin) were negatively correlated with blood THg concentrations, which likely indicates a disruptive effect of Hg on immunity. Alanine aminotransferase (GPT) activity, reflecting liver dysfunction, was positively associated with blood THg. Additionally, triacylglycerol and albumin differed between our study years, but did not correlate with Hg levels, and so were more likely to reflect changes in diet and nutritional status rather than Hg contamination. Egg volume correlated negatively with blood THg concentrations. Our study provides new insights into the sublethal effects of Hg contamination on immunity, liver function and breeding parameters in seabirds. In this Antarctic species, exposure to sublethal Hg concentrations reflects the short-term risks which could make individuals more susceptible to environmental stressors, including ongoing climatic changes.

Songbirds avoid the oxidative stress costs of high blood glucose levels: a comparative study

Chronically high blood glucose levels (hyperglycaemia) can compromise healthy ageing and lifespan at the individual level. Elevated oxidative stress can play a central role in hyperglycaemia-induced pathologies. Nevertheless, the lifespan of birds shows no species-level association with blood glucose. This suggests that the potential pathologies of high blood glucose levels can be avoided by adaptations in oxidative physiology at the macroevolutionary scale. However, this hypothesis remains unexplored. Here, we examined this hypothesis using comparative analyses controlled for phylogeny, allometry and fecundity based on data from 51 songbird species (681 individuals with blood glucose data and 1021 individuals with oxidative state data). We measured blood glucose at baseline and after stress stimulus and computed glucose stress reactivity as the magnitude of change between the two time points. We also measured three parameters of non-enzymatic antioxidants (uric acid, total antioxidants and glutathione) and a marker of oxidative lipid damage (malondialdehyde). We found no clear evidence for blood glucose concentration being correlated with either antioxidant or lipid damage levels at the macroevolutionary scale, as opposed to the hypothesis postulating that high blood glucose levels entail oxidative costs. The only exception was the moderate evidence for species with a stronger stress-induced increase in blood glucose concentration evolving moderately lower investment into antioxidant defence (uric acid and glutathione). Neither baseline nor stress-induced glucose levels were associated with oxidative physiology. Our findings support the hypothesis that birds evolved adaptations preventing the (glyc)oxidative costs of high blood glucose observed at the within-species level. Such adaptations may explain the decoupled evolution of glycaemia and lifespan in birds and possibly the paradoxical combination of long lifespan and high blood glucose levels relative to mammals.

Corticosterone and immune responses to dehydration in squamate reptiles

Many environments present some degree of seasonal water limitations; organisms that live in such environments must be adapted to survive periods without permanent water access. Often this involves the ability to tolerate dehydration, which can have adverse physiological effects and is typically considered a physiological stressor. While having many functions, the hormone corticosterone (CORT) is often released in response to stressors, yet increasing plasma CORT while dehydrated could be considered maladaptive, especially for species that experience predictable bouts of dehydration and have related coping mechanisms. Elevating CORT could reduce immunocompetence and have other negative physiological effects. Thus, such species likely have CORT and immune responses adapted to experiencing seasonal droughts. We evaluated how dehydration affects CORT and immune function in eight squamate species that naturally experience varied water limitation. We tested whether hydric state affected plasma CORT concentrations and aspects of immunocompetence (lysis, agglutination, bacterial killing ability and white blood cell counts) differently among species based on how seasonally water limited they are and whether this is constrained by phylogeny. The species represented four familial pairs, with one species of each pair inhabiting environments with frequent access to water and one naturally experiencing extended periods (>30 days) with no access to standing water. The effects of dehydration on CORT and immunity varied among species. Increases in CORT were generally not associated with reduced immunocompetence, indicating CORT and immunity might be decoupled in some species. Interspecies variations in responses to dehydration were more clearly grouped by phylogeny than by habitat type.

Impacts of repeated social defeat on behavior and the brain in a cichlid fish

Social defeat is a powerful experience leading to drastic changes in physiology and behavior, many of which are negative. For example, repeated social defeat in vertebrates results in reduced reproductive success, sickness and behavioral abnormalities that threaten individual survival and species persistence. However, little is known about what neural mechanisms are involved in determining whether an individual is resilient or susceptible to repeated social defeat stress. It also remains unknown whether exclusive use of reactive behaviors after repeated social defeat is maintained over time and impacts future behaviors during subsequent contests. We used a resident-intruder experiment in the African cichlid fish Astatotilapia burtoni to investigate the behavior and neural correlates of these two opposing groups. Behavior was quantified by watching fish during defeat trials and used to distinguish resilient and susceptible individuals. Both resilient and susceptible fish started with searching and freezing behaviors, with searching decreasing and freezing increasing after repeated social defeat. After a 4 day break period, resilient fish used both searching and freezing behaviors during a social defeat encounter with a new resident, while susceptible fish almost exclusively used freezing behaviors. By quantifying neural activation using pS6 in socially relevant brain regions, we identified differential neural activation patterns associated with resilient and susceptible fish and found nuclei that co-varied and may represent functional networks. These data provide the first evidence of specific conserved brain networks underlying social stress resilience and susceptibility in fishes.

Senescence and the stress axis: a constraint or a trade-off of reproduction in mammals with fast and slow life histories

A critical time in the life of a male occurs at reproduction, when his behaviour, physiology and resources must be brought to bear for the central purpose of his life-propagating his genes. We ask whether reproduction results in dysfunction of the stress axis, is linked to life history, and causes senescence. We assessed if deterioration in the axis underlies variation in reproductive lifespan in males of five species of North American ground squirrels whose life history varies from near semelparity to iteroparity. The most stressful and energy-demanding time occurs in spring during the intense 2-3 week breeding competition just after arousal from hibernation. We compared their stress axis functioning before and after the mating period using a hormonal challenge protocol. We found no evidence of stress axis dysfunction after reproduction in any species nor was there a relationship between reproductive lifespan and stress axis functional deterioration. Moreover, there was no consistent relationship between free cortisol levels and downstream measures (energy mobilization, haematology, immunity and body indices of condition). Thus, stress axis function was not traded off to promote reproduction irrespective of life history and lifespan, and we conclude that it is a prerequisite for life. Hence, it functions as a constraint and does not undergo senescence.

Sex-specific behavioral and physiological changes during single parenting in a biparental species, Columba livia

Many species exhibit biparental care to maximize fitness. When a partner is lost, the surviving partner may alter their behavior to compensate offspring. Whether both sexes use the same physiological mechanisms to manifest their change in behavior remains elusive. We investigated behaviors and mechanisms associated with the alteration of parental care post-partner removal in a biparental avian species, the rock dove (Columba livia). We hypothesized that rock dove single parents experience sex-biased changes in neural genomic transcription and reproductive behaviors, and these changes are related to chick development. We manipulated parental partner presence and measured parental attendance, offspring growth, gene expression of glucocorticoid receptors (GR) and mineralocorticoid receptors (MR) in the pituitary, and GR, MR, and estrogen receptor beta (ER-β) in the hypothalamus. We also measured circulating plasma concentrations of the stress-associated hormone corticosterone and the parental care-associated hormone prolactin. We also quantified prolactin gene (PRL) expression changes in the pituitary, as well as prolactin receptor (PRLR) expression in the hypothalamus and pituitary. We found that single mothers and fathers maintained similar provisioning levels as paired parents, but spent less cumulative time brooding chicks. Chicks of single parents were smaller than paired-parented chicks after three days post-hatch. Mothers in both treatment groups experienced higher expression of hypothalamic GR as compared to fathers. Single parents experienced lower PRL gene expression in the pituitary as compared to paired parents. No significant differences were found for the circulating hormones or other genes listed.

Investigating relationships among stress, reproduction, and immunity in three species of watersnake

Energy is a finite resource required for all physiological processes and must be allocated efficiently among essential activities to ensure fitness and survival. During the active season, adult organisms are expected to prioritize investment in reproduction over other energetically expensive processes, such as responding to immunological challenges. Furthermore, when encountering a stressor, the balance between reproduction and immunity might be disrupted in order to fuel the stress response. Because of the distinct differences in life histories across species, watersnakes provide a unique group of study in which to examine these tradeoffs. Over a two-year period, we captured three watersnake species throughout Northeast Arkansas. Animals were subjected to restraint stress and blood samples were collected throughout the acute stress response. Blood samples were used to assess innate immunity and steroid hormone concentrations. We found the peak in corticosterone concentration is season-specific, potentially because energetic reserves fluctuate with reproductive activities. We also found body condition was positively related to acute stress and negatively related to immunity. Watersnakes evidently prioritize reproduction over immunity, especially during the energetically intensive process of vitellogenesis. Energetic tradeoffs between reproduction, immunity, and the stress response are complex, and this study contributes to our understanding of energetic shifts in free-living organisms in the context of stress.