Glucocorticoid stress hormones and the effect of predation risk on elk reproduction

Food-safety trade-offs drive dynamic behavioural antipredator responses among snowshoe hares

Prey adopt various antipredator responses to minimize the risk of predation, and the fitness costs of antipredator responses can have emergent effects on the population dynamics of prey species. While the trade-off between food acquisition and predation avoidance has long been recognized in predicting antipredator responses, less attention has been paid to the dynamics of the food-safety trade-off driven by temporal variation in multiple risk factors under changing seasonal conditions. Here, we monitored foraging and vigilance behaviour of a central prey species, snowshoe hares (Lepus americanus), at fine temporal scales over the winter with various types of predation risk, while also experimentally manipulating predation risk by attracting predators to foraging patches. Hares increased foraging and decreased vigilance over the winter, but hares under chronic risk decreased their antipredator efforts to a lesser degree, indicating that those individuals prioritized risk avoidance over food acquisition. Hares also decreased foraging and increased antipredator efforts in response to the temporal activity of predators and environmental cues of predation risk. However, the magnitude of the responses to the environmental cues was mediated by time of winter. While we did not detect a reactive response of hares to acute risk, we did find that hares exhibiting camouflage mismatch proactively increased vigilance. Overall, our results highlight the importance of species-specific traits and changing seasonal conditions in addition to temporal variation in multiple risk factors in predicting antipredator responses and the context dependence of risk effects.

Harnessing the gut microbiome: a potential biomarker for wild animal welfare

The welfare of wild animal populations is critically important to conservation, with profound implications for ecosystem health, biodiversity, and zoonotic disease transmission. Animal welfare is typically defined as the accumulated affective mental state of an animal over a particular time period. However, the assessment of animal welfare in the wild poses unique challenges, primarily due to the lack of universally applicable biomarkers. This perspective explores the potential role of the gut microbiome, a dynamic and non-invasive biomarker, as a novel avenue for evaluating animal welfare in wild animals. The gut microbiome, through interactions with the host's physiology, behavior, and cognition, offers a promising opportunity to gain insights into the well-being of animals. In this synthesis, we discuss the distinction between fitness and welfare, the complexities of assessing welfare in wild populations, and the linkages between the gut microbiome and aspects of animal welfare such as behavior and cognition. We lastly elucidate how the gut microbiome could serve as a valuable tool for wildlife managers, with the potential to serve as a non-invasive yet informative window into the welfare of wild animals. As this nascent field evolves, it presents unique opportunities to enhance our understanding of the well-being of wild animals and to contribute to the preservation of ecosystems, biodiversity, and human health.

Sensory cues of predation risk generate sex-specific changes in neural activity and behavior, but not hormones, in Trinidadian guppies

How an organism responds to risk depends on how that individual perceives such risk. Integrating cues from multiple sensory modalities allows individuals to extract information from their environment, and whether and how the brain and body respond differently to different sensory cues can help reveal mechanistic decision-making processes. Here, we assessed neural, hormonal, and behavioral responses to different sensory cues of predation risk in Trinidadian guppies (Poecilia reticulata). Adult guppies were assigned to one of four treatment groups: control, visual, olfactory, and both sensory cues combined from a natural predator, the pike cichlid (Crenicichla alta), for 2 h. We found no difference in glucocorticoid response to any cue. However, we found behavioral and neural activation responses to olfactory-only cues. In addition, we found a sex by treatment effect, where males showed greater changes in neural activation in brain regions associated with avoidance behavior, while females showed greater changes in neural activation in regions associated with social behavior and memory, mirroring sex by treatment differences in behavioral antipredator responses. Altogether, our results demonstrate that single and combinatory cues may influence risk-taking behavior differently based on sex, suggesting that perception and integration of cues can cascade into sex differences in behavior.

Moving beyond the mean: an analysis of faecal corticosterone metabolites shows substantial variability both within and across white-tailed deer populations

Glucocorticoid (GC) levels have significant impacts on the health and behaviour of wildlife populations and are involved in many essential body functions including circadian rhythm, stress physiology and metabolism. However, studies of GCs in wildlife often focus on estimating mean hormone levels in populations, or a subset of a population, rather than on assessing the entire distribution of hormone levels within populations. Additionally, explorations of population GC data are limited due to the tradeoff between the number of individuals included in studies and the amount of data per individual that can be collected. In this study, we explore patterns of GC level distributions in three white-tailed deer (Odocoileus virginianus) populations using a non-invasive, opportunistic sampling approach. GC levels were assessed by measuring faecal corticosterone metabolite levels ('fCMs') from deer faecal samples throughout the year. We found both population and seasonal differences in fCMs but observed similarly shaped fCM distributions in all populations. Specifically, all population fCM cumulative distributions were found to be very heavy-tailed. We developed two toy models of acute corticosterone elevation in an effort to recreate the observed heavy-tailed distributions. We found that, in all three populations, cumulative fCM distributions were better described by an assumption of large, periodic spikes in corticosterone levels every few days, as opposed to an assumption of random spikes in corticosterone levels. The analyses presented in this study demonstrate the potential for exploring population-level patterns of GC levels from random, opportunistically sampled data. When taken together with individual-focused studies of GC levels, such analyses can improve our understanding of how individual hormone production scales up to population-level patterns.

Direct and indirect effects of cougar predation on bighorn sheep fitness

Predation has direct effects on prey population dynamics through mortality, and it can induce indirect effects through fear. The indirect effects of predation have been documented experimentally, but few studies have quantified them in nature so that their role in prey population dynamics remains controversial. Given the expanding or reintroduced populations of large predators in many areas, the quantification of indirect effects of predation is crucial. We sought to evaluate the direct and indirect fitness effects of intense cougar (Puma concolor) predation using 48 years of data on marked bighorn sheep (Ovis canadensis) on Ram Mountain, Alberta, Canada. We compared years of intense cougar predation with years with no or occasional cougar predation. We first quantified the effects of predation on neonatal, weaning, and overwinter lamb survival, three metrics potentially affected by direct and indirect effects. We then investigated the possible indirect effects of intense cougar predation on lamb production, female summer mass gain, and lamb mass at weaning. We found strong effects of cougar predation on lamb survival, lamb production, and seasonal mass gain of lambs and adult females. In years with high predation, neonatal, weaning, and overwinter lamb survival declined by 18.4%, 19.7% and 20.8%, respectively. Indirect effects included a 14.2% decline in lamb production. Female summer mass gain decreased by 15.6% and lamb mass at weaning declined by 8.0% in years of intense cougar predation. Our findings bring key insights on the impacts of predation on prey fitness by reporting moderate to large effects on recruitment and illustrate the importance of indirect effects of predation on population dynamics.

Insights from a 31-year study demonstrate an inverse correlation between recreational activities and red deer fecundity, with bodyweight as a mediator

Human activity is omnipresent in our landscapes. Animals can perceive risk from humans similar to predation risk, which could affect their fitness. We assessed the influence of the relative intensity of recreational activities on the bodyweight and pregnancy rates of red deer (Cervus elaphus) between 1985 and 2015. We hypothesized that stress, as a result of recreational activities, affects the pregnancy rates of red deer directly and indirectly via a reduction in bodyweight. Furthermore, we expected non-motorized recreational activities to have a larger negative effect on both bodyweight and fecundity, compared to motorized recreational activities. The intensity of recreational activities was recorded through visual observations. We obtained pregnancy data from female red deer that were shot during the regular hunting season. Additionally, age and bodyweight were determined through a post-mortem examination. We used two Generalized-Linear-Mixed Models (GLMM) to test the effect of different types of recreation on (1) pregnancy rates and (2) bodyweight of red deer. Recreation had a direct negative correlation with the fecundity of red deer, with bodyweight, as a mediator as expected. Besides, we found a negative effect of non-motorized recreation on fecundity and bodyweight and no significant effect of motorized recreation. Our results support the concept of humans as an important stressor affecting wild animal populations at a population level and plead to regulate recreational activities in protected areas that are sensitive. The fear humans induce in large-bodied herbivores and its consequences for fitness may have strong implications for animal populations.

Tracking reproductive events: Hoof growth and steroid hormone concentrations in hair and hoof tissues in moose (Alces alces)

Measurements of reproductive and stress-related hormones in keratinous tissues (e.g. hair, claws, hooves, baleen) can provide a record of stress and reproductive response in wildlife. We evaluated a method to collect keratin tissue from hooves of immobilized moose (Alces alces) and validated enzyme immunoassays for measuring cortisol and progesterone in hooves and hair. We also measured the annual growth and wear rates of moose hooves. Progesterone (range: 1.0-43.7 pg/mg) and cortisol (range: 0.05-2.9 pg/mg) were measurable and showed variation among hoof samples and moose. Pregnant females had twice as high progesterone concentrations (18.00 ± 3.73 pg/mg) from hoof sample locations post breeding compared to non-pregnant moose (9.40 ± 0.25 pg/mg). Annual hoof growth differed between the front (5.58 ± 0.12 cm) and rear (4.73 ± 0.13 cm) hooves and varied by season with higher growth rates during summer which decreased into autumn and winter. Adult female hooves represented between 1.6 and 2.1 years of growth and included up to two reproductive cycles. We established a method to estimate hoof growth rate and applied this to postmortem samples and were able to detect previous pregnancies. Shoulder guard hairs grew between August and March including during late gestation; however, hair progesterone concentrations (range: 2-107.1 pg/mg) were not related to reproductive state. Hair cortisol concentrations in our study (range: 0.2-15.9 pg/mg) were within the range of values previously reported for cervids. Our study supports the use of hooves for longitudinal sampling and measuring reproductive and stress-related hormones, providing a new tool for tracking reproductive events and understanding what variables may contribute to population level changes in reproduction.

Physiological plasticity in elephants: highly dynamic glucocorticoids in African and Asian elephants

Slowly reproducing and long-lived terrestrial mammals are often more at risk from challenges that influence fitness and survival. It is, therefore, important to understand how animals cope with such challenges and how coping mechanisms translate over generations and affect phenotypic plasticity. Rapidly escalating anthropogenic challenges may further diminish an animal’s ability to reinstate homeostasis. Research to advance insights on elephant stress physiology has predominantly focused on relative or comparative analyses of a major stress response marker, glucocorticoids (GCs), across different ecological, anthropogenic, and reproductive contexts. This paper presents an extensive review of published findings on Asian and African elephants from 1980 to 2023 (May) and reveals that stress responses, as measured by alterations in GCs in different sample matrices, often are highly dynamic and vary within and across individuals exposed to similar stimuli, and not always in a predictable fashion. Such dynamicity in physiological reactivity may be mediated by individual differences in personality traits or coping styles, ecological conditions, and technical factors that often are not considered in study designs. We describe probable causations under the ‘Physiological Dynamicity Model’, which considers context–experience–individuality effects. Highly variable adrenal responses may affect physiological plasticity with potential fitness and survival consequences. This review also addresses the significance of cautious interpretations of GCs data in the context of normal adaptive stress versus distress. We emphasize the need for long-term assessments of GCs that incorporate multiple markers of ‘stress’ and ‘well-being’ to decipher the probable fitness consequences of highly dynamic physiological adrenal responses in elephants. Ultimately, we propose that assessing GC responses to current and future challenges is one of the most valuable and informative conservation tools we have for guiding conservation strategies.

Assessing the impacts of recreation on the spatial and temporal activity of mammals in an isolated alpine protected area

The management objectives of many protected areas must meet the dual mandates of protecting biodiversity while providing recreational opportunities. It is difficult to balance these mandates because it takes considerable effort to monitor both the status of biodiversity and impacts of recreation. Using detections from 45 camera traps deployed between July 2019 and September 2021, we assessed the potential impacts of recreation on spatial and temporal activity for 8 medium- and large-bodied terrestrial mammals in an isolated alpine protected area: Cathedral Provincial Park, British Columbia, Canada. We hypothesised that some wildlife perceive a level of threat from people, such that they avoid 'risky times' or 'risky places' associated with human activity. Other species may benefit from associating with people, be it through access to anthropogenic resource subsidies or filtering of competitors/predators that are more human-averse (i.e., human shield hypothesis). Specifically, we predicted that large carnivores would show the greatest segregation from people while mesocarnivores and ungulates would associate spatially with people. We found spatial co-occurrence between ungulates and recreation, consistent with the human shield hypothesis, but did not see the predicted negative relationship between larger carnivores and humans, except for coyotes (Canis latrans). Temporally, all species other than cougars (Puma concolor) had diel activity patterns significantly different from that of recreationists, suggesting potential displacement in the temporal niche. Wolves (Canis lupus) and mountain goats (Oreamnos americanus) showed shifts in temporal activity away from people on recreation trails relative to off-trail areas, providing further evidence of potential displacement. Our results highlight the importance of monitoring spatial and temporal interactions between recreation activities and wildlife communities, in order to ensure the effectiveness of protected areas in an era of increasing human impacts.

Prey life stages modulate effects of predation stress on prey lifespan, development, and reproduction in mites

The non-consumptive effects of predator-induced stress can influence a variety of life-history traits. Many previous studies focused only on short-term effects such as development and reproductive rates. Recent studies have showed that long-term predation stress (given during the whole life of the prey) and short-term predation stress (provided during the immature stage of the prey) could generate completely opposite results: the former could decrease lifespan, whereas the later could increase lifespan. However, it is still unclear whether the advantage is because of the short duration of exposure or the early stage of life during which exposure was exerted. Thus, in this study, the prey (Tyrophagus putrescentiae) was exposed to predation stress from the predator (Neoseiulus cucumeris) during different life stages (larva, protonymph, tritonymph, first 5 d of oviposition, the full lifespan or none of the above). The results showed that the predation stress supplied during larval and protonymphal stage delayed development, reduced fecundity and prolonged lifespan of the prey, while the stress given during tritonymphal stage only reduced lifespan slightly and the stress given during the first 5 d of oviposition did not change lifespan but reduced fecundity. This study indicated that the effects of predation stress are dependent on prey life stage and the predation stress experienced in the early life stages is important to lifespan modulation.

The cost of sympatry: spatio-temporal patterns in leopard dietary and physiological responses to tiger competition gradient in Rajaji Tiger Reserve, Uttarakhand, India

Apex predators have critical roles in maintaining the structure of ecosystem functioning by controlling intraguild subordinate populations. Such dominant-subordinate interactions involve agonistic interactions including direct or indirect impacts on the subordinates. As these indirect effects are often mediated through physiological processes, it is important to quantify such responses to better understand population parameters. We used a large carnivore intraguild system involving tiger (Panthera tigris) and leopard (Panthera pardus) to understand the dietary and physiological responses under a spatio-temporal gradient of tiger competition pressures in Rajaji Tiger Reserve (RTR) between 2015 and 2020. We conducted systematic faecal sampling in the winters of 2015 and 2020 from the park to assess diet and physiological measures. Analyses of leopard-confirmed faeces suggest a dietary-niche separation as a consequence of tiger competition. In 2020, we found an increased occurrence of large-bodied prey species without tiger competition in western-RTR. Physiological measures followed the dietary responses where leopards with large-sized prey in the diet showed higher fT3M and lower fGCM measures in western-RTR. In contrast, eastern-RTR leopards showed lower levels of fT3M and fGCM in 2020, possibly due to intense competition from tigers. Overall, these patterns strongly indicate a physiological cost of sympatry where competition with dominant tigers resulted in elevated nutritional stress. We recommend expansion of leopard monitoring and population estimation efforts to buffers, developing appropriate plans for human-leopard conflict mitigation and intensive efforts to understand leopard population dynamics patterns to ensure their persistence during the ongoing Anthropocene.

The Landscape of Fear as a Safety Eco-Field: Experimental Evidence

In a development of the ecosemiotic vivo-scape concept, a 'safety eco-field' is proposed as a model of a species response to the safety of its environment. The safety eco-field is based on the ecosemiotic approach which considers environmental safety as a resource sought and chosen by individuals to counter predatory pressure. To test the relative safety of different locations within a landscape, 66 bird feeders (BF) were deployed in a regular 15 × 15 m grid in a rural area, surrounded by shrubs, small trees, hedgerows, and buildings. On each of 48 days in November 2021 and February and March 2022, dried mealworms were placed on each BF and counts of larvae at each BF were made at noon and dusk. The European robin (Erithacus rubecula) and the great tit (Parus major) were the most regular visitors to the BFs. Land cover at each BF was recorded. Bird behaviour at the BFs was noted from direct video recordings of the birds at nine selected BFs, totalling 32 daily sessions in March. The different behaviours of the European robin and the great tit were observable. The safety eco-field changed according to the month and the time of day. The distance of the BF from the woodland edges seemed to be important only in the morning. In the afternoon, BFs that were more distant from the woodland edges received the highest number of visits. Weather conditions were found to influence the number of mealworms removed, but this requires further investigation. A significant relationship between land cover and the number of mealworm larvae removed from the BFs was observed. Within the grid of BF, three regions were distinguishable which were related to land cover in the safety eco-field process. The experimental framework confirms the adequacy, at least for birds that have cryptic predators, to map the landscape as a proxy of safety resource. From the video recordings it was noted that the European robin visits were distributed throughout the day without apparent temporal preferences, while the great tit visits were concentrated in the central part of the day. This result has the limitation of the short period of observation (March) and should be extended to the entire period of the experiment to eventually capture seasonal variation. The experimental evidence obtained confirms that the ecosemiotic-based models of safety eco-field are an efficient approach to explain bird feeding preferences and behaviours.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12304-023-09522-1.

Red deer Cervus elaphus blink more in larger groups

Most animals need to spend time being vigilant for predators, at the expense of other activities such as foraging. Group-living animals can benefit from the shared vigilance effort of other group members, with individuals reducing personal vigilance effort as group size increases. Behaviors like active scanning or head lifting are usually used to quantify vigilance but may not be accurate measures of this. We suggest that measuring an animal's blinking rate gives a meaningful measure of vigilance: increased blinking implies reduced vigilance, as the animal cannot detect predators when its eyes are closed. We describe an observational study of a captive population of red deer, where we measured the blinking rates of individual deer from groups of differing sizes (where mean group size ranged between 1 and 42.7 individuals). We demonstrate that as group size increases in red deer, individuals increase their blink rate, confirming the prediction that vigilance should decrease. Blinking is a simple non-invasive measure and offers a useful metric for assessing the welfare of animals experiencing an increase in perceived predation risk or other stressors.

Predation stress experienced as immature mites extends their lifespan

The early-life experience is important in modulating the late-life performance of individuals. It has been predicted that there were trade-offs between early-life fitness and late-life success. Most of the studies on senescence have focused on the trade-offs between the reproduction and lifespan, and the influences of diet, mating, and other factors. Because the negative, non-consumptive effects of predators could also modulate the behaviour and underlying mechanisms of the prey, this study aimed to examine the different effects of predator-induced stress experienced in the early life compared with later life of the prey. The prey (Tyrophagus putrescentiae) was exposed to predation stress from the predator (Neoseiulus cucumeris) during different periods of its life (immature, oviposition period, and post-oviposition period). The results showed that the predation stress experienced during immature stages delayed development by 7.3% and prolonged lifespan by 9.7%, while predation stress experienced in the adult stage (both oviposition and post-oviposition periods) decreased lifespans of T. putrescentiae (by 24.8% and 28.7%, respectively). Predation stress experienced during immature stages also reduced female fecundity by 7.3%, whereas that experienced during the oviposition period reduced fecundity of the prey by 50.7%. This study demonstrated for the first time lifespan extension by exposure to predation stress when young and highlighted the importance of early-life experience to aging and lifespan.

Experimental evidence that chronic outgroup conflict reduces reproductive success in a cooperatively breeding fish

Conflicts with conspecific outsiders are common in group-living species, from ants to primates, and are argued to be an important selective force in social evolution. However, whilst an extensive empirical literature exists on the behaviour exhibited during and immediately after interactions with rivals, only very few observational studies have considered the cumulative fitness consequences of outgroup conflict. Using a cooperatively breeding fish, the daffodil cichlid (Neolamprologus pulcher), we conducted the first experimental test of the effects of chronic outgroup conflict on reproductive investment and output. ‘Intruded’ groups received long-term simulated territorial intrusions by neighbours that generated consistent group-defence behaviour; matched ‘Control’ groups (each the same size and with the same neighbours as an Intruded group) received no intrusions in the same period. Intruded groups had longer inter-clutch intervals and produced eggs with increasingly less protein than Control groups. Despite the lower egg investment, Intruded groups provided more parental care and achieved similar hatching success to Control groups. Ultimately, however, Intruded groups had fewer and smaller surviving offspring than Control groups at 1-month post-hatching. We therefore provide experimental evidence that outgroup conflict can decrease fitness via cumulative effects on reproductive success, confirming the selective potential of this empirically neglected aspect of sociality.

Cortisol metabolites vary with environmental conditions, predation risk, and human shields in a wild primate, Cercopithecus albogularis

Environmental challenges are often associated with physiological changes in wildlife that allow animals to maintain homeostasis. Among these, scarcity in resources, and risks from predators, competitors, and humans can all result in psychological and physiological stress. Yet, for habituated species, it is not clear whether this relationship with humans still holds to a lesser degree or is outweighed by the benefits of human presence - such as serving as a buffer from competitors or predators. We investigated how human presence and environmental challenges such as resource availability, weather, predation, and competition may be associated with variation in fecal cortisol metabolite levels (FCMs) in a group of samango monkeys (Cercopithecus albogularis) in the Soutpansberg Mountains, South Africa. FCMs can often broadly track environmental challenges and perturbations. Initially, we employed an exploratory analysis comparing candidate models representing biological hypotheses and found that those incorporating information on human presence had less weight than models for food availability, thermoregulation, and water scarcity. When we examined a subset of the data that included information on intergroup competition and predator alarm calls, we found that FCMs were higher on the day following potential predator encounters but not competitive interactions. As observer numbers increased, responses to predators flattened, indicating that the presence of several humans might deter predators and/or affect samangos' perception of danger - yet we could not distinguish between these possibilities. Together, these results suggest that ecological perturbations track with FCMs in this study population and challenge long-held assumptions that human presence has negligible effects on habituated study animals.

Evaluating the summer landscapes of predation risk and forage quality for elk (Cervus canadensis)

The recovery of carnivore populations in North American has consequences for trophic interactions and population dynamics of prey. In addition to direct effects on prey populations through killing, predators can influence prey behavior by imposing the risk of predation. The mechanisms through which patterns of space use by predators are linked to behavioral response by prey and nonconsumptive effects on prey population dynamics are poorly understood. Our goal was to characterize population- and individual-level patterns of resource selection by elk (Cervus canadensis) in response to risk of wolves (Canis lupus) and mountain lions (Puma concolor) and evaluate potential nonconsumptive effects of these behavioral patterns. We tested the hypothesis that individual elk risk-avoidance behavior during summer would result in exposure to lower-quality forage and reduced body fat and pregnancy rates. First, we evaluated individuals' second-order and third-order resource selection with a used-available sampling design. At the population level, we found evidence for a positive relationship between second- and third-order selection and forage, and an interaction between forage quality and mountain lion risk such that the relative probability of use at low mountain lion risk increased with forage quality but decreased at high risk at both orders of selection. We found no evidence of a population-level trade-off between forage quality and wolf risk. However, we found substantial among-individual heterogeneity in resource selection patterns such that population-level patterns were potentially misleading. We found no evidence that the diversity of individual resource selection patterns varied predictably with available resources, or that patterns of individual risk-related resource selection translated into biologically meaningful changes in body fat or pregnancy rates. Our work highlights the importance of evaluating individual responses to predation risk and predator hunting technique when assessing responses to predators and suggests nonconsumptive effects are not operating at a population scale in this system.

Expanding the frame around social dynamics and glucocorticoids: From hierarchies within the nest to competitive interactions among species

The effect of the social environment on individual state or condition has largely focused on glucocorticoid levels (GCs). As metabolic hormones whose production can be influenced by nutritional, physical, or psychosocial stressors, GCs are a valuable (though singular) measure that may reflect the degree of "stress" experienced by an individual. Most work to date has focused on how social rank influences GCs in group-living species or how predation risk influences GCs in prey. This work has been revealing, but a more comprehensive assessment of the social environment is needed to fully understand how different features of the social environment influence GCs in both group living and non-group living species and across life history stages. Just as there can be intense within-group competition among adult conspecifics, it bears appreciating there can also be competition among siblings from the same brood, among adult conspecifics that do not live in groups, or among heterospecifics. In these situations, dominance hierarchies typically emerge, albeit, do dominants or subordinate individuals or species have higher GCs? We examine the degree of support for hypotheses derived from group-living species about whether differential GCs between dominants and subordinates reflect the "stress of subordination" or "costs of dominance" in these other social contexts. By doing so, we aim to test the generality of these two hypotheses and propose new research directions to broaden the lens that focuses on social hierarchies and GCs.

Level-dependent effects of predation stress on prey development, lifespan and reproduction in mites

In predator-prey interactions, non-consumptive effects of predators have been less studied than consumptive effects. However, non-consumptive effects may have significant influences on prey and can change different aspects of their life history such as development, reproduction and lifespan. The odour and other cues associated with a predator, without direct contact, could induce stress in prey, leading to phenotypic changes in life history traits. In this study, we investigate how mild and strong predator-induced stress could affect prey life history. The prey (Tyrophagus putrescentiae) was exposed, from hatching to death, to three different levels of predation stress from its predator (Neoseiulus cucumeris) (1, 3 or 5 predator adults in an adjacent cage separated by a mesh screen). Compared with the control, both males and females under predator-induced stress had longer developmental time and shorter lifespan when the level of predation stress increased, showing significant level-dependence. In addition, females had reduced fecundity under predation stress. Sex-specific response to predation stress was observed under a low level of predation stress: females had greater reduction in lifespan than males. Furthermore, the reduction in female lifespan was due more from the decrease in the post-oviposition period than the decrease in the oviposition period. Future studies applying even milder levels of predation press, such as exposure of prey to predator cues only during part of the prey lifespan, may provide additional insights.

Variation between species, populations, groups and individuals in the fitness consequences of out-group conflict

Out-group conflict is rife in the natural world, occurring from primates to ants. Traditionally, research on this aspect of sociality has focused on the interactions between groups and their conspecific rivals, investigating contest function and characteristics, which group members participate and what determines who wins. In recent years, however, there has been increasing interest in the consequences of out-group conflict. In this review, we first set the scene by outlining the fitness consequences that can arise immediately to contest participants, as well as a broader range of delayed, cumulative and third-party effects of out-group conflict on survival and reproductive success. For the majority of the review, we then focus on variation in these fitness consequences of out-group conflict, describing known examples both between species and between populations, groups and individuals of the same species. Throughout, we suggest possible reasons for the variation, provide examples from a diverse array of taxa, and suggest what is needed to advance this burgeoning area of social evolution. This article is part of the theme issue 'Intergroup conflict across taxa'.

“Ecology of fear” in ungulates: Opportunities for improving conservation

Because ungulates are important contributors to ecosystem function, understanding the “ecology of fear” could be important to the conservation of ecosystems. Although studying ungulate ecology of fear is common, knowledge from ungulate systems is highly contested among ecologists. Here, we review the available literature on the ecology of fear in ungulates to generalize our current knowledge and how we can leverage it for conservation. Four general focus areas emerged from the 275 papers included in our literature search (and some papers were included in multiple categories): behavioral responses to predation risk (79%), physiological responses to predation risk (15%), trophic cascades resulting from ungulate responses to predation risk (20%), and manipulation of predation risk (1%). Of papers focused on behavior, 75% were about movement and habitat selection. Studies were biased toward North America (53%), tended to be focused on elk (Cervus canadensis; 29%), and were dominated by gray wolves (40%) or humans (39%) as predators of interest. Emerging literature suggests that we can utilize predation risk for conservation with top‐down (i.e., increasing predation risk) and bottom‐up (i.e., manipulating landscape characteristics to increase risk or risk perception) approaches. It is less clear whether fear‐related changes in physiology have population‐level fitness consequences or cascading effects, which could be fruitful avenues for future research. Conflicting evidence of trait‐mediated trophic cascades might be improved with better replication across systems and accounting for confounding effects of ungulate density. Improving our understanding of mechanisms modulating the nature of trophic cascades likely is most important to ensure desirable conservation outcomes. We recommend future work embrace the complexity of natural systems by attempting to link together the focal areas of study identified herein.

Loss of an apex predator in the wild induces physiological and behavioural changes in prey

Predators can impact prey via predation or risk effects, which can initiate trophic cascades. Given widespread population declines of apex predators, understanding and predicting the associated ecological consequences is a priority. When predation risk is relatively unpredictable or uncontrollable by prey, the loss of predators is hypothesized to release prey from stress; however, there are few tests of this hypothesis in the wild. A well-studied predator-prey system between white sharks (Carcharodon carcharias) and Cape fur seals (Arctocephalus pusillus pusillus) in False Bay, South Africa, has previously demonstrated elevated faecal glucocorticoid metabolite concentrations (fGCMs) in seals exposed to high levels of predation risk from white sharks. A recent decline and disappearance of white sharks from the system has coincided with a pronounced decrease in seal fGCM concentrations. Seals have concurrently been rafting further from shore and over deeper water, a behaviour that would have previously rendered them vulnerable to attack. These results show rapid physiological and behavioural responses by seals to release from predation stress. To our knowledge, this represents the first demonstration in the wild of physiological changes in prey from predator decline, and such responses are likely to increase given the scale and pace of apex predator declines globally.

A novel field method for preserving African lion (Panthera leo) fecal samples for noninvasive hormone metabolite analysis,

The traditional methods of preserving fecal samples to suspend hormone-degrading bacteria are not always options during remote fieldwork when studying wildlife endocrinology. Our goal was to develop a field method for preserving African lion (Panthera leo) feces for hormone metabolite analysis by determining the stability of fecal hormone metabolites: 1) when exposed to the natural environment, and 2) in silica beads at ambient temperatures. We collected fresh feces from zoo-housed lions and combined them into two (male and female) homogenous samples. Each was divided into eight samples to undergo a cross-designed treatment.•

We immediately lyophilized one sample to serve as the control.

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We then exposed seven samples outside to natural environmental conditions for 0, 12, 24, 36, 48, 60, or 72 h. After outdoor exposure, we desiccated a subsample in silica beads for an additional 5, 7, or 10 days.

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We analyzed the fecal hormone metabolite concentrations in each sample using enzyme immunoassays for corticosterone, cortisol, testosterone, progesterone, and estradiol.

We determined that male and female fecal hormone metabolites in fresh African lion fecal samples are stable and comparable to a standardized desiccation method if dried in silica beads for 5 to 10 days prior to storing them at -20℃.

Do boars compensate for hunting with higher reproductive hormones?

The predation-stress hypothesis has been proposed as a general mechanism to explain the negative effect of predation risk on reproduction, through a chronic activation of the stress response. However, in some cases, stress appears to augment the reproductive potential of mammals. Wild boar (Sus scrofa) populations are on a rise worldwide, despite the high hunting pressure that they are exposed to. This hunting pressure instigates, among other effects, earlier sexual maturity in juvenile females, leading to the shortening of wild boars' generation time. The mechanism that underlies this earlier sexual maturity under high hunting pressure has not been examined to date. To explore the physiological effects that hunting has on the reproductive system and whether the stress response is involved, we examined steroid hormone levels in the hair of female wild boars in northern Israel, comparing populations exposed to high and low hunting pressure. Furthermore, we compared steroid levels in the hair of female wild boars that were roaming alone or as a part of a group. We found no hormonal signs of stress in the hunted boars. Cortisol levels were low in both the high and low hunting-pressure groups. Yet, progesterone levels were higher in females that were exposed to high hunting pressure. Females roaming in a group also had higher progesterone levels compared to females that were alone, with no distinguishable differences in cortisol levels. These elevations in reproductive hormones that were associated with hunting may lead to a higher reproductive potential in female wild boars. They further show that high hunting pressure does not necessarily lead to chronic stress that impairs the reproductive potential of female wild boars. This data suggests that a reproductive hormonal response may be one of the factors leading to the rapid wild boars population growth worldwide, despite the high hunting pressure.

The impact of variable predation risk on stress in snowshoe hares over the cycle in North America's boreal forest: adjusting to change

The boreal forest is one of the world's ecosystems most affected by global climate warming. The snowshoe hare, its predators, and their population dynamics dominate the mammalian component of the North American boreal forest. Our past research has shown the 9-11-year hare cycle to be predator driven, both directly as virtually all hares that die are killed by their predators, and indirectly through sublethal risk effects on hare stress physiology, behavior, and reproduction. We replicated this research over the entire cycle by measuring changes in predation risk expected to drive changes in chronic stress. We examined changes in hare condition and stress axis function using a hormonal challenge protocol in the late winter of 7 years-spanning all phases of the cycle from the increase through to the low (2014-2020). We simultaneously monitored changes in hare abundance as well as those of their primary predators, lynx and coyotes. Despite observing the expected changes in hare-predator numbers over the cycle, we did not see the predicted changes in chronic stress metrics in the peak and decline phases. Thus, the comprehensive physiological signature indicative of chronic predator-induced stress seen from our previous work was not present in this current cycle. We postulate that hares may now be increasingly showing behavior-mediated rather than stress-mediated responses to their predators. We present evidence that increases in primary productivity have affected boreal community structure and function. We speculate that climate change has caused this major shift in the indirect effects of predation on hares.

Food availability and long-term predation risk interactively affect antipredator response

Food availability and temporal variation in predation risk are both important determinants of the magnitude of antipredator responses, but their effects have rarely been examined simultaneously, particularly in wild prey. Here, we determine how food availability and long-term predation risk affect antipredator responses to acute predation risk by monitoring the foraging response of free-ranging snowshoe hares (Lepus americanus) to an encounter with a Canada lynx (Lynx canadensis) in Yukon, Canada, over four winters (2015-2016 to 2018-2019). We examined how this response was influenced by natural variation in long-term predation risk (2-month mortality rate of hares) while providing some individuals with supplemental food. On average, snowshoe hares reduced foraging time up to 10 h after coming into close proximity (≤75 m) with lynx, and reduced foraging time an average of 15.28 ± 7.08 min per lynx encounter. Hares tended to respond more strongly when the distance to lynx was shorter. More importantly, the magnitude of hares' antipredator response to a lynx encounter was affected by the interaction between food-supplementation and long-term predation risk. Food-supplemented hares reduced foraging time more than control hares after a lynx encounter under low long-term risk, but decreased the magnitude of the response as long-term risk increased. In contrast, control hares increased the magnitude of their response as long-term risk increased. Our findings show that food availability and long-term predation risk interactively drive the magnitude of reactive antipredator response to acute predation risk. Determining the factors driving the magnitude of antipredator responses would contribute to a better understanding of the indirect effects of predators on prey populations.

Diet Drives Differences in Reproductive Synchrony in Two Sympatric Mountain Ungulates in the Himalaya

Ungulates in higher latitudes and altitudes experience sharp seasonal changes in forage abundance and quality. In response, ungulates show varying degrees of synchrony in reproduction. Diet type has been hypothesized to be a determinant of differences in reproductive synchrony. Analyses at global scales using proxies of plant phenology such as climate, latitude and Normalized Difference Vegetation Index (NDVI) have found no evidence in support because such proxies do not capture differences in phenology among plant taxa at local scales. We compared seasonal variations in diet quality with reproductive synchrony in the Himalayan musk deer (Moschus chrysogaster), a browser, and the Himalayan goral (Naemorhedus goral), a grazer, in mid-altitude Himalaya. We also compared seasonal variations in physiological stress using fecal glucocorticoid metabolite (FGM). We identified different stages of female reproductive cycle using fecal concentrations of metabolites of estradiol, pregnanediol-3-glucuronide (PdG) and testosterone and used fecal crude protein (CP) as an indicator of diet quality. In musk deer, fecal estradiol and PdG concentrations showed a dispersed estrous and parturition, respectively. Goral had a more synchronized estrous and parturition. Estrous cycles in both species occurred when diet quality was poor, but parturition occurred when diet quality was high. Greater seasonality in reproduction in goral is driven by sharp phenological changes in graminoids on which it feeds, compared to slow changes in browse on which musk deer feeds. Thus, we show that diet type drives the differences in reproductive synchrony in these two sympatric species. Spring and summer with highest diet quality were times of highest stress in both the ungulates. We hypothesize predation pressure from feral dogs and resource competition with livestock as plausible explanations for this, which need to be tested in future. Our findings also highlight the need for studying relationships among plant phenology, diet type and reproductive biology of ungulates at local scales if we are to understand species responses to global phenomena such as climate change.

Detecting the effects of predator-induced stress on the global metabolism of an ungulate prey using fecal metabolomic fingerprinting

Few field tests have assessed the effects of predator-induced stress on prey fitness, particularly in large carnivore-ungulate systems. Because traditional measures of stress present limitations when applied to free-ranging animals, new strategies and systemic methodologies are needed. Recent studies have shown that stress and anxiety related behaviors can influence the metabolic activity of the gut microbiome in mammal hosts, and these metabolic alterations may aid in identification of stress. In this study, we used NMR-based fecal metabolomic fingerprinting to compare the fecal metabolome, a functional readout of the gut microbiome, of cattle herds grazing in low vs. high wolf-impacted areas within three wolf pack territories. Additionally, we evaluated if other factors (e.g., cattle nutritional state, climate, landscape) besides wolf presence were related to the variation in cattle metabolism. By collecting longitudinal fecal samples from GPS-collared cattle, we found relevant metabolic differences between cattle herds in areas where the probability of wolf pack interaction was higher. Moreover, cattle distance to GPS-collared wolves was the factor most correlated with this difference in cattle metabolism, potentially reflecting the variation in wolf predation risk. We further validated our results through a regression model that reconstructed cattle distances to GPS-collared wolves based on the metabolic difference between cattle herds. Although further research is needed to explore if similar patterns also hold at a finer scale, our results suggests that fecal metabolomic fingerprinting is a promising tool for assessing the physiological responses of prey to predation risk. This novel approach will help improve our knowledge of the consequences of predators beyond the direct effect of predation.

Effects of ectoparasite infestation during pregnancy on physiological stress and reproductive output in a rodent-flea system

Biotic and abiotic stressors impose various fitness costs on individuals across a variety of taxa. In vertebrates, these stressors typically trigger complex neuroendocrine responses that stimulate glucocorticoid (GC) secretion from the adrenal cortex. Short-term elevation of GCs can be adaptive as it shifts energy toward physiological processes that cope with acute stressors; however, chronic increases in GC levels could have detrimental effects on fitness. Parasitism can be considered an important biotic stressor in nature and a possible cause of reproductive failure that could substantially affect an individual's fitness. Thus, we aimed to test the effects of parasitism and maternal stress, as measured by GCs, during pregnancy and the relationship between these variables and measures of reproductive output using a rodent-flea system. Female Egyptian spiny mice (Acomys cahirinus) were randomly assigned to flea (Parapulex chephrenis) infested or uninfested treatments before and during pregnancy. The offspring of these females were flea-free. Feces were collected at five time points during the experiment to determine maternal fecal glucocorticoid metabolite (FGCM) concentrations. Overall, infested females had lower FGCM levels during gestation but higher FGCM levels post-parturition and larger mass changes than uninfested females. Additionally, models related to pup quality and quantity often included some measure of maternal investment or body condition moderating relationships between infestation and stress. This suggests that flea parasitism or high GC levels alone might not significantly impact host reproduction but rather females can experience different effects depending on their level of investment, which could be limited by body condition and/or the number of pups present in a litter.

Sum of fears among intraguild predators drives the survival of green sea turtle (Chelonia mydas) eggs

Ecologists have long theorized that apex predators stabilize trophic systems by exerting a net protective effect on the basal resource of a food web. Although experimental and observational studies have borne this out, it is not always clear what behavioural mechanisms among the trophically connected species are responsible for this stability. Fear of intraguild predation is commonly identified as one such mechanism in models and mesocosm studies, but empirical evidence in natural systems remains limited, as the complexity of many trophic systems renders detailed behavioural studies of species interactions challenging. Here, we combine long-term field observations of a trophic system in nature with experimental behavioural studies of how all the species in this system interact, in both pairs and groups. The results demonstrate how an abundant, sessile and palatable prey item (sea turtle eggs, Chelonia mydas) survives when faced by three potential predators that all readily eat eggs: an apex predator (the stink ratsnake, Elaphe carinata) and two mesopredators (the brown rat, Rattus norvegicus, and kukri snake, Oligodon formosanus). Our results detail how fear of intraguild predation, conspecific cannibalism, habitat structure and territorial behaviour among these species interact in a complex fashion that results in high egg survival.

Sex-Specific Elk Resource Selection during the Anthrax Risk Period

Anthrax, caused by the spore-forming bacterium Bacillus anthracis, is a zoonosis affecting animals and humans globally. In the United States, anthrax outbreaks occur in wildlife and livestock, with frequent outbreaks in native and exotic wildlife species in Texas, livestock outbreaks in the Dakotas, and sporadic mixed outbreaks in Montana. Understanding where pathogen and host habitat selection overlap is essential for anthrax management. Resource selection and habitat use of ungulates may be sex-specific and lead to differential anthrax exposure risks across the landscape for males and females. We evaluated female elk (Cervus canadensis) resource selection in the same study areas as male elk in a previous anthrax risk study to identify risk of anthrax transmission to females and compare transmission risk between females and males. We developed a generalized linear mixed-effect model to estimate resource selection for female elk in southwest Montana during the June to August anthrax transmission risk period. We then predicted habitat selection of female and male elk across the study area and compared selection with the distribution of anthrax risk to identify spatial distributions of potential anthrax exposure for the male and female elk. Female and male elk selected different resources during the anthrax risk period, which resulted in different anthrax exposure areas for females and males. The sex-specific resource selection and habitat use could infer different areas of risk for anthrax transmission, which can improve anthrax and wildlife management and have important public health and economic implications.

Socio-Ecological Challenges as Modulators of Women's Reproductive Trajectories

Amenorrhea, anovulatory cycles, miscarriages, and other reproductive outcomes are often seen as pathological. Life history theory, in contrast, treats those outcomes as adaptations that helped women optimize the timing of reproductive ventures across our evolutionary history. Women's bodies adjust their reproductive strategies in response to socio-ecological conditions, a process mediated by the hypothalamic-pituitary-adrenal axis (HPAA). Here, we review the links between socio-ecological conditions, HPAA activity, and the pace of women's reproductive transitions such as puberty, age at first birth, interbirth interval, and perimenopause. We also discuss the HPAA's role as a modulator of reproductive function: It not only suppresses it but may also prime women's bodies for future reproductive ventures. We conclude by reviewing challenges and opportunities within our subfield, including the need for transdisciplinary teams to develop longitudinal studies to improve our understanding of women's reproductive trajectories and outcomes from the moment they are conceived.

Bigger doesn't mean bolder: behavioral variation of four wild rodent species to novelty and predation risk following a fast-slow continuum

Background

Understanding how wild species respond to novel situations with associated risk can provide valuable insights for inter-specific behavioral variation and associations with pace-of-life (POL). Rodents, a globally distributed and diverse taxonomic group, have been the subjects of countless studies emulating risky situations. Controlled laboratory experiments with a focus on wild-caught species provide the opportunity to test fine-scale behavioral responses to contexts of risk with ecological implications. For example, assessing the importance of predator cues eliciting antipredator responses, as well as whether wild rodents embody behavioral plasticity and repertoires, illustrated by habituation and variation in behavioral traits, respectively.

Results

In this comparative study, we examined multiple behavioral responses of four rodent species in eastern Taiwan (three native species Mus caroli, Apodemus agrarius, Rattus losea, and one invasive, Rattus exulans) exposed to an unfamiliar microenvironment and novel cue from an allopatric predator, the leopard cat (Prionailurus bengalensis). All wild-caught animals were subjected to two consecutive nights of experimental trials in a laboratory setting. Behavioral responses to a novel situation during the first trial differed between species; smaller species investing more time in non-defensive behaviors compared to the larger species. More specifically, the smaller species M. caroli and A. agrarius allocated more time to exploration and foraging, whereas the larger rat species R. exulans and R. losea spent more time motionless or concealing. During the second trial, the addition of leopard cat cues did not elicit antipredator behaviors, but rather, rodents were found to exhibit increased non-defensive behaviors, specifically foraging efforts.

Conclusions

Our results suggest that these four species do largely follow a behavioral fast-slow continuum with the two smaller mice species demonstrating increased boldness in a novel context compared to the larger rat species. Also, the wild populations of rodents in eastern Taiwan may be naïve to leopard cats. Finally, the rodents in our study demonstrated habituation to the microenvironment, indicating they possess adaptive capacity.

Effect of group size and reproductive status on faecal glucocorticoid concentration and vigilance in a free-ranging population of Przewalski's gazelle

Elevated glucocorticoid (GC) concentration and increased vigilance are two common responses to predation risk in mammals. Chronic high-level GC concentration and vigilance occur at the expense of other life maintenance and reproduction activities, reflecting a trade-off between individual survival and future fecundity. Przewalski's gazelle (Procapra przewalskii) is a group-living ungulate endemic to the high-altitude Qinghai Lake region of China. Group-size effect on gazelle vigilance has been examined, yet little is known about how their GC concentration is affected by group size or reproductive status. In this study, we examined the effect of group size and reproductive status on faecal glucocorticoid metabolite (FGM) concentrations and individual vigilance during different stages of the reproduction cycle (i.e. non-breeding, lambing and rutting) in free-ranging adult female Przewalski's gazelles. Group size did not influence FGMs significantly, but mean vigilance duration increased with group size. The gazelles' FGMs and vigilance peaked in lambing season. FGMs showed no difference between rutting season and non-reproductive season, but vigilance was lowest in the rutting season. FGMs correlated with vigilance frequency and vigilance duration. Antipredator responses of female Przewalski's gazelles appear to change with reproductive status but not with group size in free-ranging females. Management measures should be taken in the lambing season to minimize stress on mother gazelles.

Effects of predation risk on egg steroid profiles across multiple populations of threespine stickleback

Predation often has consistent effects on prey behavior and morphology, but whether the physiological mechanisms underlying these effects show similarly consistent patterns across different populations remains an open question. In vertebrates, predation risk activates the hypothalamic-pituitary-adrenal (HPA) axis, and there is growing evidence that activation of the maternal HPA axis can have intergenerational consequences via, for example, maternally-derived steroids in eggs. Here, we investigated how predation risk affects a suite of maternally-derived steroids in threespine stickleback eggs across nine Alaskan lakes that vary in whether predatory trout are absent, native, or have been stocked within the last 25 years. Using liquid chromatography coupled with mass spectroscopy (LC-MS/MS), we detected 20 steroids within unfertilized eggs. Factor analysis suggests that steroids covary within and across steroid classes (i.e. glucocorticoids, progestogens, sex steroids), emphasizing the modularity and interconnectedness of the endocrine response. Surprisingly, egg steroid profiles were not significantly associated with predator regime, although they were more variable when predators were absent compared to when predators were present, with either native or stocked trout. Despite being the most abundant steroid, cortisol was not consistently associated with predation regime. Thus, while predators can affect steroids in adults, including mothers, the link between maternal stress and embryonic development is more complex than a simple one-to-one relationship between the population-level predation risk experienced by mothers and the steroids mothers transfer to their eggs.

Stress hypothesis overload: 131 hypotheses exploring the role of stress in tradeoffs, transitions, and health

Stress is ubiquitous and thus, not surprisingly, many hypotheses and models have been created to better study the role stress plays in life. Stress spans fields and is found in the literature of biology, psychology, psychophysiology, sociology, economics, and medicine, just to name a few. Stress, and the hypothalamic-pituitaryadrenal/interrenal (HPA/I) axis and sympathetic nervous system (SNS), are involved in a multitude of behaviors and physiological processes, including life-history and ecological tradeoffs, developmental transitions, health, and survival. The goal of this review is to highlight and summarize the large number of available hypotheses and models, to aid in comparative and interdisciplinary thinking, and to increase reproducibility by a) discouraging hypothesizing after results are known (HARKing) and b) encouraging a priori hypothesis testing. For this review I collected 214 published hypotheses or models dealing broadly with stress. In the main paper, I summarized and categorized 131 of those hypotheses and models which made direct connections among stress and/or HPA/I and SNS, tradeoffs, transitions, and health. Of those 131, the majority made predictions about reproduction (n = 43), the transition from health to disease (n = 38), development (n = 23), and stress coping (n = 18). Additional hypotheses were classified as stage-spanning or models (n = 37). The additional 83 hypotheses found during searches were tangentially related, or pertained to immune function or oxidative stress, and these are listed separately. Many of the hypotheses share underlying rationale and suggest similar, if not identical, predictions, and are thus not mutually exclusive; some hypotheses spanned classification categories. Some of the hypotheses have been tested multiple times, whereas others have only been examined a few times. It is the hope that multi-disciplinary stress researchers will begin to harmonize their naming of hypotheses in the literature so as to build a clearer picture of how stress impacts various outcomes across fields. The paper concludes with some considerations and recommendations for robust testing of stress hypotheses.

Active acoustic telemetry tracking and tri-axial accelerometers reveal fine-scale movement strategies of a non-obligate ram ventilator

BACKGROUND

California horn sharks (Heterodontus francisci) are nocturnally active, non-obligate ram ventilating sharks in rocky reef habitats that play an important ecological role in regulating invertebrate communities. We predicted horn sharks would use an area restricted search (ARS) movement strategy to locate dense resource patches while minimizing energetic costs of travel and nighttime activity. As ectotherms, we predicted environmental temperature would play a significant role in driving movement and activity patterns.

METHODS

Continuous active acoustic tracking methods and acceleration data loggers were used to quantify the diel fine-scale spatial movements and activity patterns of horn sharks. First passage time was used to identify the scale and locations of patches indicative of ARS. Activity was assessed using overall dynamic body acceleration (ODBA) as a proxy for energy expenditure. Behavior within a patch was characterized into three activity patterns: resting, episodic burst activity, and moderate, consistent activity.

RESULTS

After resting in daytime shelters, individuals travelled to multiple reefs throughout the night, traversing through depths of 2-112 m and temperatures of 10.0-23.8 °C. All sharks exhibited area restricted search patch use and arrived at their first patch approximately 3.4 ± 2.2 h (mean ± SD) after sunset. Sharks exhibited moderate, consistent activity in 54% of the patches used, episodic burst activity in 33%, and few (13%) were identified as resting at night. ODBA peaked while sharks were swimming through relatively deeper (~ 30 m), colder channels when traversing from one patch to the next. There was no consistent pattern between ODBA and temperature.

CONCLUSIONS

We provide one of the largest fine-scale, high-resolution paired data sets for an elasmobranch movement ecology study. Horn sharks exhibited ARS movement patterns for various activity patterns. Individuals likely travel to reefs known to have profitable and predictable patches, potentially tolerating less suitable environmental temperatures. We demonstrate how gathering high-resolution information on the movement decisions of a community resident enhances knowledge of community structure and overall ecosystem function.

Steroids, Pregnancy and Fetal Development

Maternal glucocorticoids critically rise during pregnancy reaching up to a 20-fold increase of mid-pregnancy concentrations. Concurrently, another steroid hormone, progesterone, increases. Progesterone, which shows structural similarities to glucocorticoids, can bind the intracellular glucocorticoid receptor, although with lower affinity. Progesterone is essential for the establishment and continuation of pregnancy and it is generally acknowledged to promote maternal immune tolerance to fetal alloantigens through a wealth of immunomodulatory mechanisms. Despite the potent immunomodulatory capacity of glucocorticoids, little is known about their role during pregnancy. Here we aim to compare general aspects of glucocorticoids and progesterone during pregnancy, including shared common steroidogenic pathways, plasma transporters, regulatory pathways, expression of receptors, and mechanisms of action in immune cells. It was recently acknowledged that progesterone receptors are not ubiquitously expressed on immune cells and that pivotal features of progesterone induced- maternal immune adaptations to pregnancy are mediated via the glucocorticoid receptor, including e.g., T regulatory cells expansion. We hypothesize that a tight equilibrium between progesterone and glucocorticoids is critically required and recapitulate evidence supporting that their disequilibrium underlie pregnancy complications. Such a disequilibrium can occur, e.g., after maternal stress perception, which triggers the release of glucocorticoids and impair progesterone secretion, resulting in intrauterine inflammation. These endocrine misbalance might be interconnected, as increase in glucocorticoid synthesis, e.g., upon stress, may occur in detriment of progesterone steroidogenesis, by depleting the common precursor pregnenolone. Abundant literature supports that progesterone deficiency underlies pregnancy complications in which immune tolerance is challenged. In these settings, it is largely yet undefined if and how glucocorticoids are affected. However, although progesterone immunomodulation during pregnancy appear to be chiefly mediated glucocorticoid receptors, excess glucocorticoids cannot compensate by progesterone deficiency, indicating that additional und still undercover mechanisms are at play.

Noninvasive measures of physiological stress are confounded by exposure

Glucocorticoids and glucocorticoid metabolites are increasingly used to index physiological stress in wildlife. Although feces is often abundant and can be collected noninvasively, exposure to biotic and abiotic elements may influence fecal glucocorticoid metabolite (FGM) concentrations, leading to inaccurate conclusions regarding wildlife physiological stress. Using captive snowshoe hares (Lepus americanus) and simulated environmental conditions, we evaluated how different realistic field conditions and temporal sampling constraints might influence FGM concentrations using an 11-oxoetiocholanolone-enzyme immunoassay. We quantified how fecal pellet age (i.e., 0–6 days), variable summer temperatures, and precipitation affected FGM concentrations. Fecal pellet age had a strong effect on FGM concentrations (β_Age = 0.395, s.d. = 0.085; β²_Age = −0.061, s.d. = 0.012), which were lowest at the beginning and end of our exposure period (e.g., mean_day6 = 37.7 ng/mg) and typically highest in the middle (mean_day3 = 51.8 ng/mg). The effect of fecal pellet age on FGM concentrations varied across treatments with warm-dry and cool-wet conditions resulting in more variable FGM concentrations relative to control samples. Given the confounding effects of exposure and environmental conditions, if fresh fecal pellet collection is not an option, we encourage researchers to develop a temporally consistent sampling protocol to ensure all samples are exposed to similar environmental conditions.