Reproduction alters oxidative status when it is traded-off against longevity

Oxidative status: A general but overlooked indicator of welfare across animal species?

Because of their ubiquity, plasticity, and direct effects on the nervous system, markers of oxidative status may be of great value to assess animal welfare across species and conditions in the wild. However, welfare biologists have not yet seized this opportunity, possibly because the validity of these markers as welfare indicators remains questionable. A validation process was, therefore, performed here using a meta-analytical approach considering three conditions assumed to impair the welfare of animals. With very few exceptions, two of the four considered markers consistently varied across these negatively-valenced conditions. By highlighting the current underrepresentation of markers of oxidative status in animal welfare studies, and by concretely illustrating that some of these markers can consistently reflect negative affective states, this article aims to encourage biologists to include these physiological markers in their toolbox to better measure, monitor, and perhaps also improve the welfare of animals in their natural habitat.

Increased pupal temperature has reversible effects on thermal performance and irreversible effects on immune system and fecundity in adult ladybirds

The environmental conditions an organism encounters during development vary in their lasting impact on adult phenotypes. In the context of ongoing climate change, it is particularly relevant to understand how high developmental temperatures can impact adult traits, and whether these effects persist or diminish during adulthood. Here, we assessed the effects of pupal temperature (17 °C - normal temperature, 26 °C - increased temperature, or 35 °C - heat wave) on adult Harmonia axyridis thermal stress tolerance, immune function, starvation resistance, and fecundity. The temperature during pupation significantly affected all investigated traits in fresh adults. Heat acclimation decreased adult haemocyte concentration, cold tolerance, and total egg production, and had a positive effect on heat tolerance and starvation resistance. The negative effects of heat acclimation on cold tolerance diminished after seven days. In contrast, heat acclimation had a lasting positive effect on adult heat tolerance. Our results provide a broad assessment of the effects of developmental thermal acclimation on H. axyridis adult phenotypes. The relative plasticity of several adult traits after thermal acclimation may be consequential for the future geographic distribution and local performance of various insect species.

Changes in life-history traits, antioxidant defense, energy metabolism and molecular outcomes in the cladoceran Daphnia pulex after exposure to polystyrene microplastics

Ubiquitous plastic pollution is a threat to the organisms' survival and ecosystem functions, especially in aquatic environments. Although there is increasing concern about the toxicity of microplastics, knowledge about the effects of microplastics of diverse sizes and adverse impacts on freshwater organisms is still limited. In the present study, the alteration in life-history traits, antioxidant defense and energy metabolism of the model freshwater zooplankton Daphnia pulex were assessed after chronic exposure to gradient concentrations (0.5, 1, 2 and 4 mg/L) of 500-nm polystyrene microplastics (PS-MPs). Changes in protein abundance were analyzed using proteomics after exposure to 1 mg/L of PS-MPs for 14 days. The results showed that ingested PS-MPs accumulated in the digestive tract of D. pulex. 2 and 4 mg/L of PS-MPs inhibited the survival function and 4 mg/L of PS-MPs reduced the body length of D. pulex after 14 or 21 days of exposure. The exposure did not decrease the fecundity of D. pulex. After 14 days of exposure, PS-MPs changed the antioxidant capacity in a dose-dependent way and all concentrations of PS-MPs induced lipid oxidative damage. Exposure to 500-nm PS-MPs for 14 days decreased glucose and fructose contents and disturbed the lipid transport and utilization in D. pulex. Meanwhile, PS-MPs activated DNA repair and transcription regulation but inhibited lipid metabolism and response to unfolded or misfolded proteins. These results indicated that chronic exposure to 500-nm PS-MPs negatively affected D. pulex and showed similar toxic mechanisms to smaller nano-sized microplastics. Exposure to 500-nm PS-MPs resulted in restricted resources such as inhibited antioxidant capacity or energy metabolisms and D. pulex showed a potential trade-off among life-history traits to maintain fecundity at the cost of self-maintenance. The present study offers perspectives for understanding the differences in ecological effects caused by microplastics of different sizes.

The high invasion success of fall armyworm is related to life-history strategies across a range of stressful temperatures

BACKGROUND

Insects living in unfavorably high or low temperatures are predicted to display a fast or slow life-history strategy. Here, we examined life histories of fall armyworm (FAW), a globally important invasive species with a broad ecological niche, at five constant temperatures of 13, 19, 25, 31 and 37°C, to study life-history responses to different temperatures.

RESULTS

In our experiment, FAW had lower lifetime fecundity at unfavorable temperatures, a finding that is consistent with the idea that FAW can shift resources from reproduction to other functions under stressful conditions-such as heat or cold tolerance. Given the adverse effects of stressful temperatures, life-history strategies arise from individuals having limited remaining resources to allocate towards vital functions like survival or reproduction. Here we show plasticity in life-history strategies adopted at different temperatures. Rather than simply varying along a fast-slow continuum, FAW at unfavorably high temperatures exhibited lower daily fecundity and longer reproductive lifespans, and at unfavorably low temperatures showed a shorter peak in reproduction later in life, compared with FAW at 25°C. Such patterns, if adaptive, could suggest a strategy mitigating reproductive and mortality risk in unfavorable environments, however, this remains to be tested.

CONCLUSION

Our analysis suggests that the high invasion success of FAW may result from their ability to adjust life-history strategies, across a range of stressful temperatures, in a way that reduces not only mortality, but also fecundity loss. The adoption of such strategies may be instrumental for the global invasion success of FAW. © 2022 Society of Chemical Industry.

The oxidative cost of helping and its minimization in a cooperative breeder

Cooperative actions are beneficial to the group, but presumably costly to the individual co-operators. In cooperatively breeding species, helping to raise young is thought to involve important energetic costs, which could lead to elevated exposure to reactive oxygen species, resulting in oxidative stress. However, identifying such costs can be difficult if individuals adjust their investment in helping in relation to environmental conditions or their own physiological condition. Experimental approaches are therefore required to quantify the costs of helping but, to date, these have been infrequent. Here, we combined correlational and experimental data to investigate the oxidative cost of helping-at-the-nest and how this affects helping decisions in wild sociable weavers Philetairus socius, a colonial cooperatively breeding bird. At the correlational level, we found that the probability of helping was influenced by the interaction of an individual’s oxidative state and age: compared to younger birds, older individuals were more likely to help when they had higher oxidative damage, and the opposite trend was found for younger individuals. After experimentally increasing the energetic cost of flight, manipulated helpers in breeding colonies decreased nestling feeding rates and incurred an increase in oxidative damage, which was not present in manipulated helpers in non-breeding colonies. This indicates that individuals decreased their helping behavior to minimize the associated costs. These results suggest that oxidative stress can influence helping decisions and underlie a trade-off between cooperation and self-maintenance, which is central to understanding when helping might take place in this and other species.

Irreversible impact of early thermal conditions: an integrative study of developmental plasticity linked to mobility in a butterfly species

Within populations, phenotypic plasticity may allow adaptive phenotypic variation in response to selection generated by environmental heterogeneity. For instance, in multivoltine species, seasonal changes between and within generations may trigger morphological and physiological variation enhancing fitness under different environmental conditions. These seasonal changes may irreversibly affect adult phenotypes when experienced during development. Yet, the irreversible effects of developmental plasticity on adult morphology have rarely been linked to life-history traits even though they may affect different fitness components such as reproduction, mobility and self-maintenance. To address this issue, we raised larvae of Pieris napi butterflies under warm or cool conditions to subsequently compare adult performance in terms of reproduction performance (as assessed through fecundity), displacement capacity (as assessed through flight propensity and endurance) and self-maintenance (as assessed through the measurement of oxidative markers). As expected in ectotherms, individuals developed faster under warm conditions and were smaller than individuals developing under cool conditions. They also had more slender wings and showed a higher wing surface ratio. These morphological differences were associated with changes in the reproductive and flight performances of adults, as individuals developing under warm conditions laid fewer eggs and flew larger distances. Accordingly, the examination of their oxidative status suggested that individuals developing under warm conditions invested more strongly into self-maintenance than individuals developing under cool conditions (possibly at the expense of reproduction). Overall, our results indicate that developmental conditions have long-term consequences on several adult traits in butterflies. This plasticity likely acts on life history strategies for each generation to keep pace with seasonal variations and may facilitate acclimation processes in the context of climate change.

Differential oxidative costs of locomotory and genital damage in an orb-weaving spider

In animals that regularly experience tissue loss, physiological responses may have evolved to overcome the related costs. Changes in oxidative status may reflect such self-maintenance mechanisms. Here, we investigated how markers of oxidative status vary in female orb-weaving spiders (Larinia jeskovi) by mimicking two distinct types of tissue loss they may naturally encounter: damage to their locomotory system and damage to their external genital structure (scapus), as inflicted by males during copulation (external female genital mutilation). Damage to the locomotory system resulted in a significant shift in oxidative status, reflecting investment in self-maintenance. In contrast, the loss of the scapus did not result in quantitative changes of oxidative markers. This lack of a physiological response suggests negligible physiological costs of genital mutilation for female spiders. However, not being able to remate with other males might be costly for females.

Resistance of Cowpea Genotypes to Spodoptera frugiperda (Lepidoptera: Noctuidae) and Its Relationship to Resistance-Related Enzymes

Spodoptera frugiperda (J.E. Smith) can attack cowpea plants (Vigna unguiculata [L.] Walp.) (Fabales: Fabaceae) in any growth stage but attacks primarily in the first days after plant emergence, when the plants are more sensitive to defoliation. This study was carried out to evaluate the resistance to S. frugiperda in six cowpea genotypes, of which four were cultivars (BRS Tapahium, BRS Tumucumaque, Fradinho, and Miranda), and two were landraces (Juti and Nioaque), in three different experiments. In the first experiment, adult emergence, adult weight, adult longevity, larva to adult period, numbers of injured leaves per plant canopy (upper, middle, and lower), and reduction in plant dry matter were assessed. In the second experiment, the oviposition preference of S. frugiperda for the different cowpea genotypes was evaluated under free-choice conditions. In the third experiment, levels of peroxidase (POD), superoxide dismutase (SOD), and protein content in cowpea leaves were assessed. Insects fed on landrace Juti plants showed low adult emergence, yielded a lower fitness index, and caused less plant dry matter reduction. In addition, plants of landrace Juti were less preferred for oviposition. Overall, Juti plants showed higher resistance levels in all three resistance categories and higher levels of POD and SOD in S. frugiperda injured leaves, in addition to a lower protein content. Juti will be tested in field conditions, followed by molecular characterization. This will provide additional information about its potential as an S. frugiperda resistance source in plant breeding programs.

Timescale and colony-dependent relationships between environmental conditions and plasma oxidative markers in a long-lived bat species

To increase the applicability and success of physiological approaches in conservation plans, conservation physiology should be based on ecologically relevant relationships between physiological markers and environmental variation that can only be obtained from wild populations. Given their integrative and multifaceted aspects, markers of oxidative status have recently been considered in conservation physiology, but still need to be validated across environmental conditions and locations. Here, we examined whether inter-annual variation in two oxidative markers, plasma antioxidant capacity and plasma hydroperoxides, followed inter-annual variation in temperature anomalies and associated vegetation changes in four colonies of long-lived greater mouse-eared bats (Myotis myotis) monitored over five consecutive years. We found that the plasma antioxidant capacity of bats decreased while plasma hydroperoxide concentrations increased with increasing temperature anomalies occurring in the two weeks before blood sampling. Moreover, the antioxidant defences of these bats reflected vegetation indices, which themselves reflected the thermal conditions experienced by bats in their foraging habitat. Variation in oxidative markers therefore appears to be due to variation in thermoregulatory costs and to indirect changes in foraging costs. Overall, these results validate the use of markers of oxidative status in conservation physiology to monitor thermal perturbations recently experienced by animals in their natural habitat. However, even though oxidative markers varied in the same direction in all four bat colonies across years, the amplitude of their response differed. If these different physiological responses reflect different performances (e.g. productivity, survival rate) between colonies, this implies that, if necessary, conservation measures may need to be applied at the local scale.

Clinal variation in investment into reproduction versus maintenance suggests a 'pace-of-life' syndrome in a widespread butterfly

Extreme weather events such as heat waves are predicted to increase in the course of anthropogenic climate change. Widespread species are exposed to a variety of environmental conditions throughout their distribution range, often resulting in local adaptation. Consequently, populations from different regions may vary in their capacity to deal with challenging conditions such as thermal stress. In this study, we investigated clinal variation in body size, fecundity, and oxidative markers along a pan-European latitudinal gradient in the green-veined white butterfly Pieris napi, and additionally gene expression in German individuals. We exposed butterflies from replicated Italian, German, and Swedish populations to cold, control, or hot temperatures for 24 h. Under hot conditions, molecular chaperones were up-regulated, while oxidative damage remained unaffected and levels of the antioxidant glutathione (GSH) were reduced under cold and hot conditions. Thus, the short-term exposure to heat stress did not substantially affect oxidative balance. Moreover, we found decreased body size and fecundity in cooler compared with warmer regions. Interestingly, oxidative damage was lowest in Swedish animals exhibiting (1) high levels of GSH, (2) low early fecundity, and (3) low larval growth rates. These results suggest that Swedish butterflies have a slower life style and invest more strongly into maintenance, while those from warmer regions show the opposite pattern, which may reflect a 'pace-of-life' syndrome.

Species-specific effects of thermal stress on the expression of genetic variation across a diverse group of plant and animal taxa under experimental conditions

Assessing the genetic adaptive potential of populations and species is essential for better understanding evolutionary processes. However, the expression of genetic variation may depend on environmental conditions, which may speed up or slow down evolutionary responses. Thus, the same selection pressure may lead to different responses. Against this background, we here investigate the effects of thermal stress on genetic variation, mainly under controlled laboratory conditions. We estimated additive genetic variance (V_A), narrow-sense heritability (h²) and the coefficient of genetic variation (CV_A) under both benign control and stressful thermal conditions. We included six species spanning a diverse range of plant and animal taxa, and a total of 25 morphological and life-history traits. Our results show that (1) thermal stress reduced fitness components, (2) the majority of traits showed significant genetic variation and that (3) thermal stress affected the expression of genetic variation (V_A, h² or CV_A) in only one-third of the cases (25 of 75 analyses, mostly in one clonal species). Moreover, the effects were highly species-specific, with genetic variation increasing in 11 and decreasing in 14 cases under stress. Our results hence indicate that thermal stress does not generally affect the expression of genetic variation under laboratory conditions but, nevertheless, increases or decreases genetic variation in specific cases. Consequently, predicting the rate of genetic adaptation might not be generally complicated by environmental variation, but requires a careful case-by-case consideration.

Alteration of insulin and nutrition signal gene expression or depletion of Met reduce both lifespan and reproduction in the German cockroach

In insects, nutrition and hormones coordinately regulate lifespan and reproduction, which might affect each other. We here investigated how nutrition, insulin, and juvenile hormone (JH) signal genes affect lifespan and reproduction in the German cockroach, Blattella germanica, a serious urban pest throughout the world. Starvation as well as altering insulin and nutrition signal genes by RNA interference (RNAi) knockdown of the expression of either positive or negative components in the two pathways simultaneously reduced lifespan and ootheca number of the mated female cockroaches. Meanwhile, depletion of the JH receptor Methoprene-tolerant (Met), but not kruppel homolog 1 (Kr-h1) that predominately transduces JH signaling to prevent metamorphosis, significantly reduced the two parameters. Moreover, suppressing the expression of several reproduction-related genes, including doublesex (Dsx), vitellogenin (Vg), and the Vg receptor (VgR), had little yet various effects on lifespan; nevertheless, it is likely that there are some reproduction-independent mating factors reducing lifespan. In conclusion, through blocking lifespan and reproduction in a simultaneous manner, the alteration of insulin and nutrient signal gene expression or the depletion of Met might provide a great potential for controlling the German cockroach.

Physiological dynamics, reproduction-maintenance allocations, and life history evolution

Allocation of resources to competing processes of growth, maintenance, or reproduction is arguably a key process driving the physiology of life history trade-offs and has been shown to affect immune defenses, the evolution of aging, and the evolutionary ecology of offspring quality. Here, we develop a framework to investigate the evolutionary consequences of physiological dynamics by developing theory linking reproductive cell dynamics and components of fitness associated with costly resource allocation decisions to broader life history consequences. We scale these reproductive cell allocation decisions to population-level survival and fecundity using a life history approach and explore the effects of investment in reproduction or tissue-specific repair (somatic or reproductive) on the force of selection, reproductive effort, and resource allocation decisions. At the cellular level, we show that investment in protecting reproductive cells increases fitness when reproductive cell maturation rate is high or reproductive cell death is high. At the population level, life history fitness measures show that cellular protection increases reproductive value by differential investment in somatic or reproductive cells and the optimal allocation of resources to reproduction is moulded by this level of investment. Our model provides a framework to understand the evolutionary consequences of physiological processes underlying trade-offs and highlights the insights to be gained from considering fitness at multiple levels, from cell dynamics through to population growth.

Understanding diversity in oxidative status and oxidative stress: the opportunities and challenges ahead

Oxidative stress may be of profound biological relevance. In this Commentary, I discuss some key issues faced by the emerging field of oxidative stress ecology, and seek to provide interpretations and solutions. First, I show that the way in which we define oxidative stress has far-reaching implications for the interpretation of results, and that we need to distinguish between (1) a biochemical definition in terms of the molecular outcomes of oxidative stress (e.g. generation of oxidative damage) and (2) a biological definition in terms of the fitness consequences for the organism (e.g. effects on fertility). Second, I discuss the dangers of comparing different tissues and markers. Third, I highlight the need to pay more attention to the cross-talk between oxidative stress and other important physiological costs and functions; this will allow us to better understand the mechanistic basis of fitness costs. Fourth, I propose the 'redox signalling hypothesis' of life history to complement the current 'oxidative stress hypothesis' of life history. The latter states that oxidative damage underlies trade-offs because it affects traits like growth, reproduction or cell senescence. By contrast, the redox signalling hypothesis states that a trade-off between signalling and biochemical oxidative stress underlies the regulation of reactive oxygen species production and their subsequent control. Finally, I critically appraise our current knowledge of oxidative stress ecology, highlighting key research themes and providing an optimistic overview of future opportunities for the discipline to yield considerable insight into the ecological and evolutionary meaning of oxidative stress.

Morph- and sex-specific effects of challenging conditions on maintenance parameters in the Gouldian finch

Intraspecific discrete polymorphism is associated with the use of alternative life-history strategies, reflected by distinct reproductive or copying strategies in individuals of different morphs. Yet, morph-specific costs and benefits related to different life-history strategies remain unclear. Here, we examined in the polymorphic Gouldian finch (Erythrura gouldiae) whether markers of somatic maintenance (body mass, oxidative status and telomere length) differed between red- and black-headed birds under energetically demanding conditions (during heatwaves of different intensity, and during moult or breeding following heatwaves). During heatwaves, red-headed birds showed a homogeneous response, as males and females initially tended to gain mass and had reduced plasma hydroperoxide levels (a marker of oxidative damage) irrespective of heatwave intensity. In contrast, black-headed birds showed a stronger and more heterogeneous response, as black-headed males gained mass at the beginning of the thermoneutral heatwave and showed stable oxidative status, whereas black-headed females lost mass and tended to show higher hydroperoxide levels at the end of the thermocritical heatwave. Following heatwaves, we found morph-specific oxidative costs owing to moult or reproduction, with oxidative markers varying only in black-headed birds. Again, oxidative markers varied differently in black-headed males and females, as plasma antioxidant capacity decreased in moulting or breeding females, whereas males showed higher hydroperoxide levels with larger broods. For the first time, our study highlights that within polymorphic species, some individuals appear more vulnerable than others when coping with energetically demanding conditions. In the context of climate change, such differential effects may ultimately alter the currently observed balance between morphs and sexes within natural populations.

Effects of adult temperature on gene expression in a butterfly: identifying pathways associated with thermal acclimation

BACKGROUND

Phenotypic plasticity is a pervasive property of all organisms and considered to be of key importance for dealing with environmental variation. Plastic responses to temperature, which is one of the most important ecological factors, have received much attention over recent decades. A recurrent pattern of temperature-induced adaptive plasticity includes increased heat tolerance after exposure to warmer temperatures and increased cold tolerance after exposure to cooler temperatures. However, the mechanisms underlying these plastic responses are hitherto not well understood. Therefore, we here investigate effects of adult acclimation on gene expression in the tropical butterfly Bicyclus anynana, using an RNAseq approach.

RESULTS

We show that several antioxidant markers (e.g. peroxidase, cytochrome P450) were up-regulated at a higher temperature compared with a lower adult temperature, which might play an important role in the acclamatory responses subsequently providing increased heat tolerance. Furthermore, several metabolic pathways were up-regulated at the higher temperature, likely reflecting increased metabolic rates. In contrast, we found no evidence for a decisive role of the heat shock response.

CONCLUSIONS

Although the important role of antioxidant defence mechanisms in alleviating detrimental effects of oxidative stress is firmly established, we speculate that its potentially important role in mediating heat tolerance and survival under stress has been underestimated thus far and thus deserves more attention.

Mitotype Interacts With Diet to Influence Longevity, Fitness, and Mitochondrial Functions in Adult Female Drosophila

Mitochondrial DNA (mtDNA) and the dietary macronutrient ratio are known to influence a wide range of phenotypic traits including longevity, fitness and energy production. Commonly mtDNA mutations are posited to be selectively neutral or reduce fitness and, to date, no selectively advantageous mtDNA mutations have been experimentally demonstrated in adult female Drosophila. Here we propose that a ND V161L mutation interacted with diets differing in their macronutrient ratios to influence organismal physiology and mitochondrial traits, but further studies are required to definitively show no linked mtDNA mutations are functionally significant. We utilized two mtDNA types (mitotypes) fed either a 1:2 Protein: Carbohydrate (P:C) or 1:16 P:C diet. When fed the former diet, Dahomey females harboring the V161L mitotype lived longer than those with the Alstonville mitotype and had higher climbing, basal reactive oxygen species (ROS) and elevated glutathione S-transferase E1 expression. The short lived Alstonville females ate more, had higher walking speed and elevated mitochondrial functions as suggested by respiratory control ratio (RCR), mtDNA copy number and expression of mitochondrial transcription termination factor 3. In contrast, Dahomey females fed 1:16 P:C were shorter lived, had higher fecundity, walking speed and mitochondrial functions. They had reduced climbing. This result suggests that mtDNA cannot be assumed to be a strictly neutral evolutionary marker when the dietary macronutrient ratio of a species varies over time and space and supports the hypothesis that mtDNA diversity may reflect the amount of time since the last selective sweep rather than strictly demographic processes.

Dietary antioxidants, but not courtship effort, affect oxidative balance in the testes and muscles of crickets

Recent interest has focused on the role of reactive oxygen species (ROS) as universal constraints in life-history evolution. Empirical studies have examined the oxidative costs of reproduction for females, with little work conducted on males. The male germline is thought to be particularly susceptible to oxidative damage because the testes, and the sperm themselves, can be prolific producers of ROS. We tested the hypothesis that protection of the male germline from oxidative damage represents a cost of reproduction for males. We fed male crickets, Teleogryllus oceanicus, with one of two experimental diets in which we manipulated the availability of dietary antioxidants, and we induced variation in their expenditure on courtship effort by manipulating access to females. We measured the total antioxidant capacity, levels of ROS production and the amount of oxidative damage to proteins in both testis and thoracic muscle tissues. Dietary antioxidants contributed to positive oxidative balance in both tissue types. Although the testes had greater antioxidant defences than muscle tissue, they also produced considerably higher levels of ROS and sustained higher levels of oxidative damage. Courtship effort had no impact on any measure of oxidative balance. Our data confirm that the male germline is especially susceptible to oxidative stress and that dietary antioxidants can alleviate this oxidative cost of reproduction.

Hormetic benefits of prior anoxia exposure in buffering anoxia stress in a soil-pupating insect

Oxygen is essential for most animals, and exposure to a complete lack of oxygen, i.e. anoxia, can result in irreparable damage to cells that can extend up to the organismal level to negatively affect performance. Although it is known that brief anoxia exposure may confer cross-tolerance to other stressors, few data exist on the biochemical and organismal consequences of repeated intermittent bouts of anoxia exposure. In nature, the Caribbean fruit fly, Anastrepha suspensa (Diptera: Tephritidae), is frequently exposed to heavy tropical rainfall while pupating in the soil, equating to multiple exposures to hypoxia or anoxia during development. Here, we tested whether prior anoxia exposures during pupal development can induce a beneficial acclimation response, and we explored the consequences of prior exposure for both whole-organism performance and correlated biochemical metrics. Pharate adults (the last developmental stage in the pupal case) were most sensitive to anoxia exposure, showing decreased survival and fertility compared with controls. These negative impacts were ameliorated by exposure to anoxia in earlier pupal developmental stages, indicating a hormetic effect of prior anoxia exposure. Anoxia exposure early in pupal development reduced the oxygen debt repaid after anoxia exposure relative to pharate adults experiencing anoxia for the first time. Lipid levels were highest in all pupal stages when exposed to prior anoxia. Prior anoxia thus benefits organismal performance and relocates resources towards lipid storage throughout pupal-adult development.

Age-related sex differences in body condition and telomere dynamics of red-sided garter snakes

Life-history strategies vary dramatically between the sexes, which may drive divergence in sex-specific senescence and mortality rates. Telomeres are tandem nucleotide repeats that protect the ends of chromosomes from erosion during cell division. Telomeres have been implicated in senescence and mortality because they tend to shorten with stress, growth and age. We investigated age-specific telomere length in female and male red-sided garter snakes, Thamnophis sirtalis parietalis We hypothesized that age-specific telomere length would differ between males and females given their divergent reproductive strategies. Male garter snakes emerge from hibernation with high levels of corticosterone, which facilitates energy mobilization to fuel mate-searching, courtship and mating behaviours during a two to four week aphagous breeding period at the den site. Conversely, females remain at the dens for only about 4 days and seem to invest more energy in growth and cellular maintenance, as they usually reproduce biennially. As male investment in reproduction involves a yearly bout of physiologically stressful activities, while females prioritize self-maintenance, we predicted male snakes would experience more age-specific telomere loss than females. We investigated this prediction using skeletochronology to determine the ages of individuals and qPCR to determine telomere length in a cross-sectional study. For both sexes, telomere length was positively related to body condition. Telomere length decreased with age in male garter snakes, but remained stable in female snakes. There was no correlation between telomere length and growth in either sex, suggesting that our results are a consequence of divergent selection on life histories of males and females. Different selection on the sexes may be the physiological consequence of the sexual dimorphism and mating system dynamics displayed by this species.

Socially-induced variation in physiological mediators of parental care in a colonial bird

Social facilitation of reproduction occurs in humans and animals, and may represent one of the bases of reproduction in groups. However, its underlying physiological mechanisms remain largely unexplored. Here, we found in a colonial bird, the Adélie penguin (Pygoscelis adeliae), that the number of parental interactions (nest relief ceremonies) performed by breeding individuals on the colony was positively related to prolactin levels in other breeding individuals exposed to these interactions (i.e. focal individuals). As prolactin is typically involved in the expression of parental behaviour in birds, this suggests that parental interactions by conspecifics represent social cues that might increase parental motivation in focal individuals. Moreover, parental interactions were not related to corticosterone levels in focal individuals, suggesting that these social cues were not stressful for penguins. However, social stimulation still had a cost for focal individuals, as it was negatively related to their antioxidant defences (a component of self-maintenance). As social stimulation was also positively related to prolactin levels, this highlights the fact that social stimulation acts on the trade-off between reproduction and self-maintenance. For the first time, the results of the current study shed light on the physiological factors potentially underlying social facilitation of parental care. Importantly, they suggest that, even though social facilitation of parental care may increase breeding performance, it can also negatively affect other fitness components.

Feeding on ripening and over-ripening fruit: interactions between sugar, ethanol and polyphenol contents in a tropical butterfly

In ripe fruit, energy mostly derives from sugar, while in over-ripe fruit, it also comes from ethanol. Such ripeness differences may alter the fitness benefits associated with frugivory if animals are unable to degrade ethanol when consuming over-ripe fruit. In the tropical butterfly Bicyclus anynana, we found that females consuming isocaloric solutions mimicking ripe (20% sucrose) and over-ripe fruit (10% sucrose, 7% ethanol) of the palm Astrocaryum standleyanum exhibited higher fecundity than females consuming a solution mimicking unripe fruit (10% sucrose). Moreover, relative to butterflies consuming a solution mimicking unripe fruit, survival was enhanced when butterflies consumed a solution mimicking either ripe fruit supplemented with polyphenols (fruit antioxidant compounds) or over-ripe fruit devoid of polyphenols. This suggests that (1) butterflies have evolved tolerance mechanisms to derive the same reproductive benefits from ethanol and sugar, and (2) polyphenols may regulate the allocation of sugar and ethanol to maintenance mechanisms. However, variation in fitness owing to the composition of feeding solutions was not paralleled by corresponding physiological changes (alcohol dehydrogenase activity, oxidative status) in butterflies. The fitness proxies and physiological parameters that we measured therefore appear to reflect distinct biological pathways. Overall, our results highlight that the energy content of fruit primarily affects the fecundity of B. anynana butterflies, while the effects of fruit consumption on survival are more complex and vary depending on ripening stage and polyphenol presence. The actual underlying physiological mechanisms linking fruit ripeness and fitness components remain to be clarified.

Royal Darwinian Demons: Enforced Changes in Reproductive Efforts Do Not Affect the Life Expectancy of Ant Queens

One of the central tenets of life-history theory is that organisms cannot simultaneously maximize all fitness components. This results in the fundamental trade-off between reproduction and life span known from numerous animals, including humans. Social insects are a well-known exception to this rule: reproductive queens outlive nonreproductive workers. Here, we take a step forward and show that under identical social and environmental conditions the fecundity-longevity trade-off is absent also within the queen caste. A change in reproduction did not alter life expectancy, and even a strong enforced increase in reproductive efforts did not reduce residual life span. Generally, egg-laying rate and life span were positively correlated. Queens of perennial social insects thus seem to maximize at the same time two fitness parameters that are normally negatively correlated. Even though they are not immortal, they best approach a hypothetical "Darwinian demon" in the animal kingdom.

Overproduction of superoxide dismutase and catalase confers cassava resistance to Tetranychus cinnabarinus

To explore the role of protective enzymes in cassava (Manihot esculenta Crantz) resistance to mites, transgenic cassava lines overproducing copper/zinc superoxide dismutase (MeCu/ZnSOD) and catalase (MeCAT1) were used to evaluate and molecularly confirm cassava resistance to Tetranychus cinnabarinus. Laboratory evaluation demonstrated that, compared with the control cultivar TMS60444 (wild type, WT), the survival, reproduction, development and activities of SOD and CAT in T. cinnabarinus feeding on transgenic cassava lines SC2, SC4, and SC11 significantly inhibited. Furthermore, the activities of SOD and CAT in transgenic cassava lines SC2, SC4, and SC11 damaged by T. cinnabarinus significantly increased. These findings were similar to the results in the mite-resistant cassava cultivars. Besides, field evaluation indicated that the transgenic cassava lines SC2, SC4, and SC11 were slightly damaged as the highly mite-resistant control C1115, while the highly mite-susceptible WT was severely damaged by T. cinnabarinus. Laboratory and field evaluation demonstrated that transgenic cassava lines were resistant to T. cinnabarinus, which directly confirmed that the increase in SOD and CAT activities was positively related to cassava resistance to T. cinnabarinus. These results will help in understanding the antioxidant defense responses in the cassava-mite interaction and molecular breeding of mite-resistant cassava for effective pest control.

Keeping up with the Red Queen: the pace of aging as an adaptation

For decades, a vast majority of biogerontologists assumed that aging is not and cannot be an adaptation. In recent years, however, several authors opposed this predominant view and repeatedly suggested that not only is aging an adaptation but that it is the result of a specific aging program. This issue almost instantaneously became somewhat controversial and many important authors produced substantial works refuting the notion of the aging program. In this article we review the current state of the debate and list the most important arguments proposed by both sides. Furthermore, although classical interpretations of the evolution of aging are in sharp contrast with the idea of programmed aging, we suggest that the truth might in fact very well lie somewhere in between. We also propose our own interpretation which states that although aging is in essence inevitable and results from damage accumulation rather than from a specific program, the actual rate of aging in nature may still be adaptive to some extent.

Elevated reproduction does not affect telomere dynamics and oxidative stress

ABSTRACT

Oxidative stress and telomere dynamics are considered to be powerful biomarkers quantifying a potential trade-off between current reproduction and self-maintenance. Recent studies confirmed the negative impact of elevated reproduction on telomeres, but the evidence for the cost of reproduction in terms of oxidative stress remains equivocal. In order to induce reproductive costs, we experimentally manipulated reproductive effort by increasing brood size in captive zebra finches (Taeniopygia guttata) and additionally challenged all birds by a low ambient temperature to facilitate detection of these costs. We were not able to show any negative effects of elevated reproductive effort on telomere dynamics and oxidative stress among parents, although brood enlargement was effective in terms of total mass and number of fledged young. Interestingly, irrespective of brood size treatment, we found a significant increase in antioxidant capacity at peak breeding while oxidative damage did not change with time. Our results may suggest that reproduction, instead of generating costs, may stimulate physiological functions promoting self-maintenance in terms of higher protection against free radicals. Possibly, opportunistic breeders such as zebra finches may not impede their future performance for the sake of current reproduction.

SIGNIFICANCE STATEMENT

This study interrogates a molecular background behind one of the most intriguing trade-offs that potentially occurs between self-maintenance and reproduction. We manipulated breeding effort in zebra finches to understand if the cost of reproduction can be mediated by telomere dynamics and oxidative stress. In our study system, we did not detect the direct reproductive costs in terms of parental oxidative damage and telomere loss; instead, these costs were paid by the offspring in terms of their inhibited growth rate. Moreover, we found that entering into the reproductive state strongly stimulated self-maintenance by increasing antioxidant capacity in parents. Our results emphasize that current reproductive success is not always prioritized over investment in body maintenance preventing the oxidative cost of reproduction.

Larval nutrition-induced plasticity affects reproduction and gene expression of the ladybeetle, Cryptolaemus montrouzieri

Background

Organisms may develop into multiple phenotypes under different nutritional environments by developmental plasticity, whereas the potential costs and mechanisms of such plasticity are poorly understood. Here we examined the fitness and gene expression of nutrition-induced phenotypes in the ladybeetle, Cryptolaemus montrouzieri after having experienced varying larval food regimes.

Results

We found that C. montrouzieri adults undergoing a variable larval food regime achieved a similar developmental time, survival, body mass and egg production as those undergoing a high larval food regime. The survival, developmental time, body mass and fecundity of the adults from a restricted larval food regime were inferior to those from the high and variable larval food regimes. However, the adults from this restricted larval food regime had a higher expression level of genes encoding immune- and antioxidant-related enzymes than those from the high and variable larval food regimes when exposed to starvation and pesticide conditions in adult life.

Conclusions

These results suggest that larval food availability in C. montrouzieri not only triggers adult phenotypic differences but also affects reproduction and expression level of genes in adult life, indicating that the larval nutritional conditions can affect adult fitness and resistance to stressful conditions through developmental plasticity.

Testing the Effects of DL-Alpha-Tocopherol Supplementation on Oxidative Damage, Total Antioxidant Protection and the Sex-Specific Responses of Reproductive Effort and Lifespan to Dietary Manipulation in Australian Field Crickets (Teleogryllus commodus)

The oxidative stress theory predicts that the accumulation of oxidative damage causes aging. More generally, oxidative damage could be a cost of reproduction that reduces survival. Both of these hypotheses have mixed empirical support. To better understand the life-history consequences of oxidative damage, we fed male and female Australian field crickets (Teleogryllus commodus) four diets differing in their protein and carbohydrate content, which have sex-specific effects on reproductive effort and lifespan. We supplemented half of these crickets with the vitamin E isoform DL-alpha-tocopherol and measured the effects of nutrient intake on lifespan, reproduction, oxidative damage and antioxidant protection. We found a clear trade-off between reproductive effort and lifespan in females but not in males. In direct contrast to the oxidative stress theory, crickets fed diets that improved their lifespan had high levels of oxidative damage to proteins. Supplementation with DL-alpha-tocopherol did not significantly improve lifespan or reproductive effort. However, males fed diets that increased their reproductive investment experienced high oxidative damage to proteins. While this suggests that male reproductive effort could elevate oxidative damage, this was not associated with reduced male survival. Overall, these results provide little evidence that oxidative damage plays a central role in mediating life-history trade-offs in T. commodus.