Biology subjects

Westrick, S. E.

Publications and source records attributed to Westrick, S. E..

10 recordsLinked to original sources

bioRxiv2025

Partner cues and individual variation underlie sex-reversed parental care in poison frogs

Flexible parental care strategies are widespread in nature and factor into conflict between the sexes and the realization of sex roles. While adaptive explanations abound, the mechanisms underlying flexible sex-reversal of care are less clear. We enlist a biparental frog (Ranitomeya imitator) with flexible parental care to investigate the extrinsic and intrinsic mechanisms underpinning parental decisions. Using mate removal experiments in the laboratory, we show that members of the primary caregiving sex (males) show less variation than the flexible sex (females) in their propensity to provide care, and that care propensity in females is affected by extrinsic partner cues as well as individual variability. Indeed, individual repeatability in parental effort is high in both typically caregiving and flexible parents. To investigate the underpinnings of differences in care propensity, we sequenced RNA from whole brains of caregiving and non-caregiving frogs of both sexes. While actively caregiving females showed minimal differential gene expression compared to actively caregiving males, females that failed to provide care showed distinct patterns of gene expression. Our findings offer an initial glimpse into the environmental and genetic regulation of individual variation in sex-reversed parental care.

animal behavior and cognition↗

bioRxiv2024

Early development of the glucocorticoid stress response in poison frog tadpoles

In vertebrates, the glucocorticoid "stress" response (corticosterone or cortisol) through the hypothalamic-pituitary-adrenal (HPA) axis influences many essential functions, including behavior, metabolism, immunity, and ontogenetic transitions. During development, stress responses can be adaptive if they facilitate antipredator behavior and modulate developmental speed to adjust to environmental conditions; however, these same responses can be maladaptive when energetic costs become too high and developmental speed trades-off with size and health at maturity. Thus, the timing of HPA-axis development may be aligned with specific developmental challenges and opportunities presented by a species life history strategy. In anurans (frogs and toads), corticosterone plays critical roles in development and behavior, and concentrations can fluctuate in response to environmental stressors. Given the role of corticosterone in ontogenetic changes and behaviors, we studied the development of the glucocorticoid stress response in tadpoles of the dyeing poison frog (Dendrobates tinctorius), a species with a unique life history that includes transport to water after hatching on land and aggressive and cannibalistic behavior. We measured the excretion rate and whole-body concentration of corticosterone and the corticosterone response to adrenocorticotropic hormone (ACTH) in free-swimming tadpoles after transport and throughout metamorphosis. We found no significant differences across development in excretion rates or whole-body concentration of corticosterone, nor corticosterone response to ACTH, indicating that that the glucocorticoid response develops early in ontogeny. This pattern differs from those in other species, suggesting the unique ecological pressures faced by D. tinctorius have shaped the development of the glucocorticoid stress response in this species. More broadly, this study illustrates how life history strategies and tradeoffs impact the timing of the development of stress responsivity.

physiology↗

bioRxiv2024

Timing-dependent effects of elevated maternal glucocorticoids on offspring brain gene expression in a wild small mammal

An increase in maternal stress during offspring development can have cascading, life-long impacts on offspring behavior and physiology, which can vary depending on the timing of exposure to the stressor. By responding to stressors through increasing production of glucocorticoids (GCs), the hypothalamic-pituitary-adrenal (HPA) axis is a key mediator of maternal effects - both on the side of the mother and the offspring. At a molecular level, maternal effects are thought to be mediated through modifying transcription of genes, particularly in the brain. To better understand the evolutionary implications of maternal effects, more studies are needed on mechanisms of maternal effects in wild populations. To test how the timing of maternal stress impacts gene expression in the brains of offspring, we treated free-ranging North American red squirrels (Tamiasciurus hudsonicus) with GCs during late pregnancy or early lactation and collected brains from offspring around weaning. We used RNA-sequencing to measure gene expression in the hypothalamus and hippocampus. We found small differences in gene expression between GC-treated and control individuals suggesting long-term effects of the GC treatment on neural gene transcription. The general patterns of gene regulation across the transcriptome were consistent between the pregnancy and lactation-treated individuals. However, the number of significantly differentially expressed genes was higher in the lactation treatment group. These results support the idea that maternal stress affects neural gene expression in offspring, and these effects are dependent on timing. Our findings add valuable insight into the impact of maternal hormones on neural transcriptomics in a wild population.

ecology↗

bioRxiv2023

Why not both? A case study measuring cortisol and corticosterone in poison frogs

A general tenet in stress physiology is that the hypothalamic-pituitary-adrenal (HPA) axis predominantly produces one glucocorticoid (GC) in response to stressors. However, most vertebrates produce both cortisol and corticosterone, and these steroids show variation across species in absolute levels, relative proportions, and stress responsivity and regulate much more than just stress physiology. Therefore, focusing on a single GC within a species may not capture the whole story. In the present study, we set out to validate non-invasive waterborne hormone measurements in our focal species, the dyeing poison frog Dendrobates tinctorius. In pursuing this goal, we uncovered unexpected patterns of GC abundance within and across species of poison frogs. D. tinctorius had higher amounts of corticosterone than cortisol in both plasma and waterborne samples, and corticosterone was responsive to adrenocorticotropic hormone (ACTH) as canonically assumed. However, corticosterone and cortisol levels were surprisingly similar in D. tinctorius, and cortisol was more abundant than corticosterone in water samples from four additional poison frog species. These results challenge the broadly accepted assumption that corticosterone is always more abundant in amphibians and add to the growing literature highlighting the importance of measuring both GCs to understand (stress) physiology.

physiology↗

bioRxiv2020

Maternal glucocorticoids do not influence HPA axis activity or behavior of juvenile wild North American red squirrels

Environmental factors experienced during development can affect the physiology and behavior of offspring. Maternal glucocorticoids (GCs) may convert environmental cues experienced by the mother into a cue triggering adaptive developmental plasticity in offspring. In North American red squirrels (Tamiasciurus hudsonicus), females exhibit increases in GCs when conspecific density is elevated, and selection favors more aggressive and perhaps more active mothers under high density conditions. We experimentally elevated maternal GCs during gestation or early lactation to test the hypothesis that elevated maternal GCs cause shifts in offspring aggression and activity that may prepare them for high density conditions. When offspring were weaned, we measured two behavioral traits (activity and aggression) using a standardized behavioral assay. Because maternal GCs may influence offspring hypothalamic-pituitary-adrenal (HPA) axis activity and HPA axis activity may in turn affect offspring behavior, we also measured the impact of our treatments on offspring HPA axis activity (adrenal reactivity and negative feedback) and the association between offspring HPA axis activity and behavior. Increased maternal GCs during lactation, but not gestation, only slightly elevated activity levels in offspring. Offspring aggression, adrenal reactivity, and negative feedback did not differ between GC-treated and control groups. Offspring with higher adrenal reactivity did exhibit lower aggression, but the relationship between adrenal reactivity and aggression was not affected by treatment with maternal GCs. These results suggest maternal GCs during gestation or early lactation alone may not be a sufficient cue to produce changes in behavioral and physiological stress responses in offspring in natural populations. Summary StatementWe found maternal glucocorticoid levels do not influence offspring personality or HPA axis dynamics in North American red squirrels. Regardless of maternal glucocorticoid treatment, more aggressive squirrels exhibited lower adrenal reactivity.

animal behavior and cognition↗

bioRxiv2019

Maternal stress promotes offspring growth without oxidative costs in wild red squirrels

Elevations in glucocorticoid levels (GCs) in breeding females may induce adaptive shifts in offspring life histories. Offspring produced by mothers with elevated GCs may be better prepared to face harsh environments where a faster pace of life is beneficial. We examined how experimentally elevated GCs in pregnant or lactating North American red squirrels (Tamiasciurus hudsonicus) affected offspring postnatal growth, structural size, oxidative stress levels (two antioxidants and oxidative protein damage) in three different tissues (blood, heart, liver), and liver telomere lengths. We predicted that offspring from mothers treated with GCs would grow faster but would also have higher levels of oxidative stress and shorter telomeres, which may predict reduced longevity. Offspring from mothers treated with GCs during pregnancy were 8.3% lighter around birth but grew (in body mass) 17.0% faster than those from controls, whereas offspring from mothers treated with GCs during lactation grew 34.8% slower than those from controls and did not differ in body mass around birth. Treating mothers with GCs during pregnancy or lactation did not alter the oxidative stress levels or telomere lengths of their offspring. Fast-growing offspring from any of the treatment groups did not have higher oxidative stress levels or shorter telomere lengths, indicating that offspring that grew faster early in life did not exhibit oxidative costs after this period of growth. Our results indicate that elevations in maternal GCs may induce plasticity in offspring growth without long-term oxidative costs to the offspring that might result in a shortened lifespan. Summary StatementWe show that experimental increases in glucocorticoids in breeding female North American red squirrels affects offspring postnatal growth but not levels of oxidative damage and antioxidants or telomere lengths.

evolutionary biology↗

bioRxiv2019

Fitness benefits of a motivated mom

Parental investment theory predicts that observed levels of parental care afforded to offspring are set by the benefits (to offspring quality and survival) relative to the costs (to parental survival or future reproduction). Although difficult to document in mammals, there is often substantial individual-variation in the amount of parental care within species. We measured the impact of individual variation in maternal care (\"attentiveness\" towards offspring or maternal motivation) on offspring growth and survival in a wild population of North American red squirrels (Tamiasciurus hudsonicus). We used latency to return to pups following a nest intrusion as a measure of maternal attentiveness to pups. We found this behavior to be repeatable within individuals suggesting this behavior is a personality trait or a \"maternal style\". In this population, postnatal growth rate is important for pup overwinter survival. Pups from large litters grew faster if they had a highly attentive mother, indicating that maternal care behavior can mitigate the trade-off between litter size and offspring growth and potentially improve survival of pups. Additionally, more attentive mothers had slightly higher lifetime reproductive success than less attentive mothers. These results highlight important fitness effects of having a highly attentive mother and show that maternal care behavior can alter a fundamental life history trade-off between offspring quantity and quality.\n\nLay SummaryIt pays to be attentive to your pups as a squirrel mom. In a long-term study of a wild population of North American red squirrels, we observed repeatable individual variation in maternal attentiveness towards offspring. Mothers who returned faster to pups following a nest intrusion produced faster growing pups and were able to produce larger fast-growing litters. Over their entire lifetime, attentive mothers also had more offspring recruit into the breeding population.

evolutionary biology↗

bioRxiv2018

Stress activity is not predictive of coping style in North American red squirrels

Individuals vary in their behavioral and physiological responses to environmental changes. These behavioral responses are often described as coping styles along a proactive-reactive continuum. Studies in laboratory populations often, but not always, find that behavioral responses and physiological responses to stressors covary, where more proactive (more aggressive and active) individuals have a lower physiological stress response, specifically as measured by hypothalamic-pituitary-adrenal (HPA) axis activity. These studies support the possibility of hormonal pleiotropy underlying the presentation of behaviors that make up the proactive-reactive phenotype. However, recent research in wild populations is equivocal, with some studies reporting the same pattern as found in many controlled laboratory studies, whereas others do not. We tested the hypothesis that physiological and behavioral stress responses are correlated in wild adult North American red squirrels (Tamiasciurus hudsonicus). We used fecal cortisol metabolites (FCMs) as a non-invasive, integrated estimate of circulating glucocorticoids for our measurement of HPA axis activity. We found that FCM concentrations were not correlated with three measures of behavioral coping styles (activity, aggression, and docility) among individuals. This does not support the hypothesis that hormonal pleiotropy underlies a proactive-reactive continuum of coping styles. Instead, our results support the \"two-tier\" hypothesis that behavioral and physiological stress responses are independent and uncorrelated traits among individuals in wild populations that experience naturally varying environments rather than controlled environments. If also found in other studies, this may alter our predictions about the evolutionary consequences of behavioral and endocrine coping styles in free-living animals.\n\nSignificance StatementIndividuals vary in how they respond to stressors through behavior and physiology, but we find the two responses are independent in wild animals. Many laboratory studies find links between the behavioral and physiological stress responses, however studies conducted with wild populations are less conclusive. In wild North American red squirrels, independence between the physiological response and behavioral response may allow adaptive responses to a changing environment without pleiotropic constraint.

animal behavior and cognition↗

bioRxiv2018

Experimental increases in glucocorticoids alter function of the neuroendocrine stress axis in wild red squirrels without negatively impacting survival and reproduction

Hormones such as glucocorticoids (colloquially referred to as "stress hormones") have important effects on animal behavior and life history traits, yet most of this understanding has come through correlative studies. While experimental studies offer the ability to assign causality, there are important methodological concerns that are often not considered when manipulating hormones, including glucocorticoids, in wild animals. In this study, we examined how experimental elevations of cortisol concentrations in wild North American red squirrels (Tamiasciurus hudsonicus) affected their hypothalamic-pituitary-adrenal (HPA) axis reactivity, and life history traits including body mass, litter survival, and adult survival. The effects of exogenous cortisol on plasma cortisol concentrations depended on the time between treatment consumption and blood sampling. In the first nine hours after consumption of exogenous cortisol, individuals had significantly higher true baseline plasma cortisol concentrations, but adrenal gland function was impaired as indicated by their dampened response to capture and handling and to injections of adrenocorticotropic hormone compared to controls. Approximately 24 hours after consumption of exogenous cortisol, individuals had much lower plasma cortisol concentrations than controls, but adrenal function was restored. Corticosteroid binding globulin (CBG) concentrations were also significantly reduced in squirrels treated with cortisol. Despite these profound shifts in the functionality of the HPA axis, squirrel body mass, offspring survival, and adult survival were unaffected by experimental increases in cortisol concentrations. Our results highlight that even short-term experimental increases in glucocorticoids can affect adrenal gland functioning and CBG concentrations but without other side-effects.

zoology↗

bioRxiv2018

Differences In Neural Activity, But Not Behavior, Across Social Contexts In Guppies, Poecilia reticulata

Animals are continually faced with the challenge of producing context-appropriate social behaviors. In many instances, animals produce unrelated behaviors across contexts. However, in some instances the same behaviors are produced across different social contexts, albeit in response to distinct stimuli and with distinct purposes. We took advantage of behavioral similarities across mating and aggression contexts in guppies, Poecilia reticulata, to understand how patterns of neural induction differ across social contexts when behaviors are nonetheless shared across contexts. While these is growing interest in understanding behavioral mechanisms in guppies, resources are sparse. As part of this study, we developed a neuroanatomical atlas of the guppy brain as a research community resource. Using this atlas, we found that neural activity in the preoptic area reflected social context, whereas individual differences in behavioral motivation paralleled activity in the posterior tuberculum and ventral telencephalon (teleost homologs of the ventral tegmental area and lateral septum, respectively). Our findings suggest independent coding of social salience versus behavioral motivation when behavioral repertoires are shared across social contexts.\n\nSummary statementActivity in distinct brain regions reflects behavioral context versus social motivation in a in which behavioral repertoires are shared across social contexts (Trinidadian guppies, Poecilia reticulata).

animal behavior and cognition↗