Concurrent threats and extinction risk in a long-lived, highly fecund vertebrate with parental care.

Detecting declines and quantifying extinction risk of long-lived, highly fecund vertebrates, including fishes, reptiles, and amphibians, can be challenging. In addition to the false notion that large clutches always buffer against population declines, the imperiled status of long-lived species can often be masked by extinction debt, wherein adults persist on the landscape for several years after populations cease to be viable. Here we develop a demographic model for the eastern hellbender (Cryptobranchus alleganiensis), an imperiled aquatic salamander with paternal care. We examined the individual and interactive effects of three of the leading threats hypothesized to contribute to the species' demise: habitat loss due to siltation, high rates of nest failure, and excess adult mortality caused by fishing and harvest. We parameterized the model using data on their life history and reproductive ecology to model the fates of individual nests and address multiple sources of density-dependent mortality under both deterministic and stochastic environmental conditions. Our model suggests that high rates of nest failure observed in the field are sufficient to drive hellbender populations toward a geriatric age distribution and eventually to localized extinction but that this process takes decades. Moreover, the combination of limited nest site availability due to siltation, nest failure, and stochastic adult mortality can interact to increase the likelihood and pace of extinction, which was particularly evident under stochastic scenarios. Density dependence in larval survival and recruitment can severely hamper a population's ability to recover from declines. Our model helps to identify tipping points beyond which extinction becomes certain and management interventions become necessary. Our approach can be generalized to understand the interactive effects of various threats to the extinction risk of other long-lived vertebrates. As we face unprecedented rates of environmental change, holistic approaches incorporating multiple concurrent threats and their impacts on different aspects of life history will be necessary to proactively conserve long-lived species.

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

The behavioral endocrinology associated with reproduction and uniparental male care has been studied in teleosts, but little is known about hormonal correlates of uniparental male care in other ectotherms. To address this gap, we are the first to document the seasonal steroid endocrinology of uniparental male hellbender salamanders during the transition from pre-breeding to nest initiation, and through the subsequent eight months of paternal care. In doing so, we investigated the correlates of nest fate and clutch size, exploring hellbenders' alignment with several endocrinological patterns observed in uniparental male fish. Understanding the endocrinology of hellbender paternal care is also vital from a conservation perspective because high rates of nest failure were recently identified as a factor causing population declines in this imperiled species. We corroborated previous findings demonstrating testosterone and dihydrotestosterone (DHT) to be the primary androgens in hellbender reproduction, and that cortisol circulates as the most abundant glucocorticoid. However, we were unable to identify a prolactin or a "prolactin-like" peptide in circulation prior to or during parental care. We observed âˆ¼ 80 % declines in both primary androgens during the transition from pre-breeding to nest initiation, and again as paternal care progressed past its first month. In the days immediately following nest initiation, testosterone and DHT trended higher in successful individuals, but did not differ with males' clutch size. We did not observe meaningful seasonality in baseline glucocorticoids associated with breeding or nesting. In contrast, stress-induced glucocorticoids were highest at pre-breeding and through the first two months of care, before declining during the latter-most periods of care as larvae approach emergence from the nest. Neither baseline nor stress-induced glucocorticoids varied significantly with either nest fate or clutch size. Both stress-induced cortisol and corticosterone were positively correlated with total length, a proxy for age in adult hellbenders. This is consistent with age-related patterns in some vertebrates, but the first such pattern observed in a wild amphibian population. Generally, we found that nesting hellbenders adhere to some but not all of the endocrinological patterns observed in uniparental male teleosts prior to and during parental care.

Filial Cannibalism Leads to Chronic Nest Failure of Eastern Hellbender Salamanders (Cryptobranchus alleganiensis).

AbstractIn species that provide parental care, parents will sometimes cannibalize their own young (i.e., filial cannibalism). Here, we quantified the frequency of whole-clutch filial cannibalism in a species of giant salamander (eastern hellbender; Cryptobranchus alleganiensis) that has experienced precipitous population declines with unknown causes. We used underwater artificial nesting shelters deployed across a gradient of upstream forest cover to assess the fates of 182 nests at 10 sites over 8 years. We found strong evidence that nest failure rates increased at sites with low riparian forest cover in the upstream catchment. At several sites, reproductive failure was 100%, mainly due to cannibalism by the caring male. The high incidence of filial cannibalism at degraded sites was not explained by evolutionary hypotheses for filial cannibalism based on poor adult body condition or low reproductive value of small clutches. Instead, larger clutches at degraded sites were most vulnerable to cannibalism. We hypothesize that high frequencies of filial cannibalism of large clutches in areas with low forest cover could be related to changes in water chemistry or siltation that influence parental physiology or that reduce the viability of eggs. Importantly, our results identify chronic nest failure as a possible mechanism contributing to population declines and observed geriatric age structure in this imperiled species.

Pre-breeding androgen and glucocorticoid profiles in the eastern hellbender salamander (Cryptobranchus alleganiensis alleganiensis).

Seasonally breeding species exhibit cyclical changes in circulating steroid hormone profiles that correspond with changes to their reproductive behavior and ecology. Such information is critical to the conservation of imperiled and data-deficient species, such as the eastern hellbender salamander (Cryptobranchus alleganiensis alleganiensis). We determined changes in plasma testosterone (T), dihydrotestosterone (DHT), 11-ketotestosterone (11-KT), 11-ketoandrostenedione (11-KA), dehydroepiandrosterone (DHEA), cortisol, corticosterone, and progesterone (P4) during a four-month period preceding breeding in adult male and female eastern hellbenders. This pre-breeding period is characterized by increased diel movement and aggression by both sexes, follicular development and yolk production in females, and sperm production, territoriality, and nest site establishment in males. In both males and females, we observed a progressive increase in circulating T and DHT during the pre-reproductive season, both peaking in August (17 days before breeding), but concentrations of both hormones were higher in males. Conversely, 11-KT was higher in females, but did not vary significantly by date. These results suggest that T and DHT are the predominant androgens in eastern hellbenders and are likely important regulators of reproductive processes in both males and females. The detection of significant quantities of DHT and 11-KT in females is particularly interesting, considering that unlike T, neither of these androgens can be converted to estrogens. Therefore, it seems possible that aggression or some aspect of reproduction in the female eastern hellbender may be directly mediated by androgen signaling. Baseline cortisol did not vary throughout the pre-breeding period but was higher in females than males, and also became highly variable in females leading up to breeding. Progesterone, 11-KA, DHEA, and corticosterone were rarely or never detected, and thus, do not appear to be important during the pre-reproductive season. This study provides a physiological framework for future studies of hellbender reproductive biology, which could ultimately be important for their conservation.

Cortisol is the predominant glucocorticoid in the giant paedomorphic hellbender salamander (Cryptobranchus alleganiensis).

Corticosterone is widely regarded to be the predominant glucocorticoid produced in amphibians. However, we recently described unusually low baseline and stress-induced corticosterone profiles in eastern hellbenders (Cryptobranchus alleganiensis alleganiensis), a giant, fully aquatic salamander. Here, we hypothesized that hellbenders might also produce cortisol, the predominant glucocorticoid used by fishes and non-rodent mammals. To test our hypothesis, we collected plasma samples in two field experiments and analyzed them using multiple analytical techniques to determine how plasma concentrations of cortisol and corticosterone co-varied after 1) physical restraint and 2) injection with adrenocorticotropic hormone (ACTH), the pituitary hormone responsible for triggering the release of glucocorticoids from amphibian interrenal glands. Using liquid chromatography-mass spectrometry, we found that baseline and restraint-induced plasma concentrations of cortisol were more than five times those of corticosterone. We then demonstrated that plasma concentrations of both glucocorticoids increased in response to ACTH in a dose-dependent manner, but cortisol concentrations were consistently higher (up to 10-fold) than corticosterone. Cortisol and corticosterone concentrations were not correlated with one another at basal or induced conditions. The extremely low plasma concentrations of corticosterone in hellbenders suggests that corticosterone could simply be a byproduct of cortisol production, and raises questions as to whether corticosterone has any distinct physiological function in hellbenders. Our results indicate that hellbenders produce cortisol as their predominant glucocorticoid, supporting a small and inconclusive body of literature indicating that some other amphibians may produce appreciable quantities of cortisol. We hypothesize that the use of cortisol by hellbenders could be an adaptation to their fully aquatic life history due to cortisol's ability to fulfill both mineralocorticoid and glucocorticoid functions, similar to its functions in fishes. Given the large number of amphibian species that are fully aquatic or have aquatic life stages, we suggest that the broadly held assumption that corticosterone is the predominant glucocorticoid in all amphibians requires further scrutiny. Ultimately, multi-species tests of this assumption will reveal the ecological factors that influenced the evolution of endocrine adaptations among amphibian lineages, and may provide insight into convergent evolution of endocrine traits in paedomorphic species.

Prolactin is related to incubation constancy and egg temperature following a disturbance in a precocial bird.

To maximize fitness, parents may trade-off time and energy between parental care and self-maintenance. In vertebrates, prolactin and corticosterone are two important hormones that regulate parental investment because they stimulate parental care and mobilize energy, respectively. Further, concentrations of both hormones change in response to disturbances. One of the most important parental care behaviors in birds is incubation, since small changes in egg temperature have large effects on offspring. We investigated how prolactin and corticosterone may mediate parental incubation constancy (i.e., the daily amount of time spent incubating eggs) and regulation of egg temperature. We collected blood samples from female wood ducks (Aix sponsa) near the start and end of the incubation period to measure baseline and stress-induced (30 min after capture and restraint) hormone concentrations. We also quantified incubation constancy and egg temperature using artificial egg temperature loggers. As expected, prolactin decreased and corticosterone increased after 30 min of capture and restraint. Corticosterone concentrations (baseline and stress-induced) were negatively related to body mass, but were not related to incubation constancy. In contrast, prolactin concentrations (baseline and stress-induced) were higher at the end than the start of the incubation period, and stress-induced prolactin concentrations were positively related to incubation constancy following a nest disturbance (i.e., capture). Further, prolactin (baseline and stress-induced) concentrations were positively related to egg temperatures, but only after the disturbance. These results suggest that prolactin may be associated with the regulation of parental incubation constancy and resulting heat-transfer after a disturbance, which may ultimately affect offspring development.

Ultraviolet-assisted oiling assessment improves detection of oiled birds experiencing clinical signs of hemolytic anemia after exposure to the Deepwater Horizon oil spill.

While large-scale oil spills can cause acute mortality events in birds, there is increasing evidence that sublethal oil exposure can trigger physiological changes that have implications for individual performance and survival. Therefore, improved methods for identifying small amounts of oil on birds are needed. Because ultraviolet (UV) light can be used to identify thin crude oil films in water and on substrate that are not visually apparent under normal lighting conditions, we hypothesized that UV light could be useful for detecting small amounts of oil present on the plumage of birds. We evaluated black skimmers (Rynchops niger), brown pelicans (Pelecanus occidentalis), clapper rails (Rallus crepitans), great egrets (Ardea alba), and seaside sparrows (Ammodramus maritimus) exposed to areas affected by the Deepwater Horizon oil spill in the Gulf of Mexico as well as from reference areas from 20 June, 2010 to 23 February, 2011. When visually assessed without UV light, 19.6% of birds evaluated from areas affected by the spill were determined to be oiled (previously published data), whereas when examined under UV light, 56.3% of the same birds were determined to have oil exposure. Of 705 individuals examined in areas potentially impacted by the spill, we found that fluorescence under UV light assessment identified 259 oiled birds that appeared to be oil-free on visual exam, supporting its utility as a simple tool for improving detection of modestly oiled birds in the field. Further, UV assessment revealed an increase in qualitative severity of oiling (approximate % of body surface oiled) in 40% of birds compared to what was determined on visual exam. Additionally, black skimmers, brown pelicans, and great egrets exposed to oil as determined using UV light experienced oxidative injury to erythrocytes, had decreased numbers of circulating erythrocytes, and showed evidence of a regenerative hematological response in the form of increased reticulocytes. This evidence of adverse effects was similar to changes identified in birds with oil exposure as determined by visual examination without UV light, and is consistent with hemolytic anemia likely caused by oil exposure. Thus, UV assessment proved useful for enhancing detection of birds exposed to oil, but did not increase detection of birds experiencing clinical signs of anemia compared to standard visual oiling assessment. We conclude that UV light evaluation can help identify oil exposure in many birds that would otherwise be identified visually as unexposed during oil spill events.

Effects of Echinostoma trivolvis metacercariae infection during development and metamorphosis of the wood frog (Lithobates sylvaticus).

Many organisms face energetic trade-offs between defense against parasites and other host processes that may determine overall consequences of infection. These trade-offs may be particularly evident during unfavorable environmental conditions or energetically demanding life history stages. Amphibian metamorphosis, an ecologically important developmental period, is associated with drastic morphological and physiological changes and substantial energetic costs. Effects of the trematode parasite Echinostoma trivolvis have been documented during early amphibian development, but effects during later development and metamorphosis are largely unknown. Using a laboratory experiment, we examined the energetic costs of late development and metamorphosis coupled with E. trivolvis infection in wood frogs, Lithobates [=Rana] sylvaticus. Echinostoma infection intensity did not differ between tadpoles examined prior to and after completing metamorphosis, suggesting that metacercariae were retained through metamorphosis. Infection with E. trivolvis contributed to a slower growth rate and longer development period prior to the initiation of metamorphosis. In contrast, E. trivolvis infection did not affect energy expenditure during late development or metamorphosis. Possible explanations for these results include the presence of parasites not interfering with pronephros degradation during metamorphosis or the mesonephros compensating for any parasite damage. Overall, the energetic costs of metamorphosis for wood frogs were comparable to other species with similar life history traits, but differed from a species with a much shorter duration of metamorphic climax. Our findings contribute to understanding the possible role of energetic trade-offs between parasite defense and host processes by considering parasite infection with simultaneous energetic demands during a sensitive period of development.

Mercury alters initiation and construction of nests by zebra finches, but not incubation or provisioning behaviors.

Mercury is an environmental contaminant that impairs avian reproduction, but the behavioral and physiological mechanisms underlying this effect are poorly understood. The objective of this study was to determine whether lifetime dietary exposure to mercury (1.2 µg/g wet weight in food) impacted avian parental behaviors, and how this might influence reproductive success. To distinguish between the direct effects of mercury on parents and offspring, we created four treatment groups of captive-bred zebra finches (Taeniopygia guttata), with control and mercury-exposed adults raising cross-fostered control or mercury-exposed eggs (from maternal transfer). Control parents were 23% more likely to fledge young than parents exposed to mercury, regardless of egg exposure. Mercury-exposed parents were less likely to initiate nests than controls and spent less time constructing them. Nests of mercury-exposed pairs were lighter, possibly due to an impaired ability to bring nest material into the nestbox. However, nest temperature, incubation behavior, and provisioning rate did not differ between parental treatments. Unexposed control eggs tended to have shorter incubation periods and higher hatching success than mercury-exposed eggs, but there was no effect of parental exposure on these parameters. We accidentally discovered that parent finches transfer some of their body burden of mercury to nestlings during feeding through secretion in the crop. These results suggest that, in mercury-exposed songbirds, pre-laying parental behaviors, combined with direct exposure of embryos to mercury, likely contribute to reduced reproductive success and should be considered in future studies. Further research is warranted in field settings, where parents are exposed to greater environmental challenges and subtle behavioral differences might have more serious consequences than were observed in captivity.

Short-Term Exposure to Coal Combustion Waste Has Little Impact on the Skin Microbiome of Adult Spring Peepers (Pseudacris crucifer).

UNLABELLED: Disruptions to the microbiome can impact host health as can exposure to environmental contaminants. However, few studies have addressed how environmental contaminants impact the microbiome. We explored this question for frogs that breed in wetlands contaminated with fly ash, a by-product of coal combustion that is enriched in trace elements. We found differences in the bacterial communities among a fly ash-contaminated site and several reference wetlands. We then experimentally assessed the impacts of fly ash on the skin microbiome of adult spring peepers (Pseudacris crucifer). Frogs were exposed to fly ash in the laboratory for 12 h, the duration of a typical breeding event, and the skin microbiome was assessed after 5 days (experiment 1) or after 5 and 15 days (experiment 2). We examined bacterial community structure using 16S rRNA gene amplicon sequencing and metabolite profiles using high-pressure liquid chromatography-mass spectrometry (HPLC-MS). We found little impact as the result of acute exposure to fly ash on the bacterial communities or metabolite profiles in either experiment, suggesting that the bacterial symbiont communities of adults may be relatively resistant to brief contaminant exposure. However, housing frogs in the laboratory altered bacterial community structure in the two experiments, which supports prior research suggesting that environmental source pools are important for maintaining the amphibian skin microbiome. Therefore, for contaminants like fly ash that may alter the potential source pool of symbionts, we think it may be important to explore how contaminants affect the initial assembly of the amphibian skin microbiome in larval amphibians that develop within contaminated sites. IMPORTANCE: Animals are hosts to many symbiotic microorganisms, collectively called the microbiome, that play critical roles in host health. Therefore, environmental contaminants that alter the microbiome may impact hosts. Some of the most widespread contaminants, produced worldwide, are derived from the mining, storage, and combustion of coal for energy. Fly ash, for example, is a by-product of coal combustion. It contains compounds such as arsenic, selenium, cadmium, and strontium and is a recognized source of ground and surface water contamination. Here, we experimentally investigated the impacts of short-term fly ash exposure on the skin microbiome of spring peepers, one of many species of amphibian that sometimes breed in open fly ash disposal ponds. This research provides a look into the potential impacts of fly ash on an animal's microbiome and suggests important future directions for research on the effects of environmental contaminants on the microbiome.

Incubation temperature causes skewed sex ratios in a precocial bird.

Many animals with genetic sex determination are nonetheless capable of manipulating sex ratios via behavioral and physiological means, which can sometimes result in fitness benefits to the parent. Sex ratio manipulation in birds is not widely documented, and revealing the mechanisms for altered sex ratios in vertebrates remains a compelling area of research. Incubation temperature is a key component of the developmental environment for birds, but despite its well-documented effects on offspring phenotype it has rarely been considered as a factor in avian sex ratios. Using ecologically relevant manipulations of incubation temperature within the range 35.0-37.0°C, we found greater mortality of female embryos during incubation than males regardless of incubation temperature, and evidence that more female than male embryos die at the lowest incubation temperature (35.0°C). Our findings in conjunction with previous work in brush turkeys suggest incubation temperature is an important determinant of avian secondary sex ratios that requires additional study, and should be considered when estimating the impact of climate change on avian populations.

Relationships among plumage coloration, blood selenium concentrations and immune responses of adult and nestling tree swallows.

In a number of taxa, males and females both display ornaments that may be associated with individual quality and could be reliable signals to potential mates or rivals. We examined the iridescent blue/green back and white breast of adult tree swallows (Tachycineta bicolor) to determine whether plumage reflectance is related to adult or offspring immune responses. We simultaneously addressed the influence of blood selenium levels and the interaction between blood selenium and plumage coloration on adult and nestling immunity. Selenium is a well-known antioxidant necessary for mounting a robust immune response but its importance in wild birds remains poorly understood. In females, the brightness of white breast coloration was positively associated with bactericidal capacity, but there was no association with blood selenium. In contrast, male bactericidal capacity was associated with an interactive effect between dorsal plumage coloration and blood selenium concentration. Males with bluer hues and greater blue chroma showed increased bactericidal capacity as blood selenium concentrations increased, while bactericidal capacity declined in greener males at higher blood selenium concentrations. In nestlings, bactericidal capacity was positively associated with nestling blood selenium concentrations and white brightness of both social parents. These results suggest that white plumage reflectance is indicative of quality in tree swallows and that greater attention should be paid to the reflectance of large white plumage patches. Additionally, the role of micronutrients, such as selenium, in mediating relationships between physiology and signals of quality, should be explored further.

Evidence of ectoparasite-induced endocrine disruption in an imperiled giant salamander, the eastern hellbender (Cryptobranchus alleganiensis).

Parasitic leeches and trypanosomes release chemical signals into their hosts to evade immuno-detection, but it is unknown whether these compounds manipulate host behavior or endocrine physiology. We determined whether parasitic infections with leeches and/or trypanosomes affected the immune and stress response of an imperiled giant species of amphibian, the eastern hellbender (Cryptobranchus alleganiensis Daudin). We monitored corticosterone and white blood cell counts in response to restraint and injection with adrenocorticotropin hormone (ACTH) or saline for up to 50 h. The presence of leeches dampened hellbender corticosterone responses to restraint and reduced diel patterns of plasma corticosterone. Injection with ACTH restored the normal inter-renal responses of hellbenders, suggesting that leeches, possibly through neurotransmitters in leech saliva, cause down-regulation of corticosterone release at the level of the pituitary or hypothalamus. Infection with leeches also increased the relative abundance of eosinophils, white blood cells often recruited into circulation in response to parasitic infection. Lastly, neutrophil to lymphocyte (N:L) ratios increased in all animals after 24 h of capture and remained elevated for up to 50 h, but these temporal dynamics did not differ with parasite infection. Trypanosome infection did not affect any aspect of hellbender physiology that we measured. Our findings reveal a previously undocumented host-parasite dynamic. While the functional significance to the parasite is unclear, the physiological and behavioral implications for the host are great, given the important role of glucocorticoids in regulating physiology and behavior.

Reproduction and hatchling performance in freshwater turtles associated with a remediated coal fly-ash spill.

In 2008 an impoundment retaining wall failed at the Tennessee Valley Authority's coal burning plant in Kingston, Tennessee, releasing large quantities of coal-fly ash into the Emory River. Following extensive remediation of the spill, we captured (in 2011 and 2012) gravid turtles of multiple species in three rivers (two impacted and one reference) within the vicinity of the spill to determine whether there was evidence of the spill influencing reproduction. There was little evidence that river of origin affected reproductive output, hatching success, hatchling size, or hatchling locomotor performance. Although hatching success and hatchling righting ability of pond sliders, Trachemys scripta, was higher in our reference river than in the Emory or Clinch River, respectively, these differences could not be attributed to differences in individual element concentrations in turtle tissues and effect sizes were relatively small. For example, hatching success was reduced by 11% in the spill zone compared to the reference river, an effect that is unlikely substantial enough to influence local population dynamics in light of turtle life history. Our results suggest that residual contamination that remains in the Emory-Clinch system after its remediation poses low risk of excessive element exposure and limited adverse reproductive effects to freshwater turtles. Future monitoring could reveal whether the observed reduction in hatching success gradually attenuates with time, or whether any long-term effects of chronic exposure to low-level contamination emerge over time.

The effects of a remediated fly ash spill and weather conditions on reproductive success and offspring development in tree swallows.

Animals are exposed to natural and anthropogenic stressors during reproduction that may individually or interactively influence reproductive success and offspring development. We examined the effects of weather conditions, exposure to element contamination from a recently remediated fly ash spill, and the interaction between these factors on reproductive success and growth of tree swallows (Tachycineta bicolor) across nine colonies. Females breeding in colonies impacted by the spill transferred greater concentrations of mercury (Hg), selenium (Se), strontium, and thallium to their eggs than females in reference colonies. Parental provisioning of emerging aquatic insects resulted in greater blood Se concentrations in nestlings in impacted colonies compared to reference colonies, and these concentrations remained stable across 2 years. Egg and blood element concentrations were unrelated to reproductive success or nestling condition. Greater rainfall and higher ambient temperatures during incubation were later associated with longer wing lengths in nestlings, particularly in 2011. Higher ambient temperatures and greater Se exposure posthatch were associated with longer wing lengths in 2011 while in 2012, blood Se concentrations were positively related to wing length irrespective of temperature. We found that unseasonably cold weather was associated with reduced hatching and fledging success among all colonies, but there was no interactive effect between element exposure and inclement weather. Given that blood Se concentrations in some nestlings exceeded the lower threshold of concern, and concentrations of Se in blood and Hg in eggs are not yet declining, future studies should continue to monitor exposure and effects on insectivorous wildlife in the area.

The habitat quality paradox: loss of riparian forest cover leads to decreased risk of parasitism and improved body condition in an imperiled amphibian.

Amphibian declines are a global phenomenon but responses of populations to specific threats are often context dependent and mediated by individual physiological condition. Habitat degradation due to reduced riparian forest cover and parasitism are two threats facing the hellbender salamander (Cryptobranchus alleganiensis), but their potential to interact in nature remains largely unexplored. We investigated associations between forest cover, parasitic infection and physiology of hellbenders to test the hypotheses that physiological condition responds to infection and/or habitat degradation. We sampled 17 stream reaches in southwest Virginia, USA, on a year-round basis from 2013 to 2016 and recorded 841 captures of 405 unique hellbenders. At each capture we documented prevalence of two blood-associated parasites (a leech and trypanosome) and quantified up to three physiological condition indices (body condition, hematocrit, white blood cell [WBC] differentials). We used generalized linear mixed models to describe spatiotemporal variation in parasitic infection and each condition index. In general, living in the most heavily forested stream reaches, where hellbender density was highest, was associated with the greatest risk of parasitism, elevated neutrophil-to-lymphocyte (N:L) ratios and eosinophils, slightly lower hematocrit and lower mean body condition in hellbenders. All condition indices fluctuated temporally in a manner consistent with seasonal variation in hellbender metabolic demands and breeding phenology and were associated with land use during at least part of the year. Paradoxically, relatively low levels of forest cover appeared to confer a potential advantage to individuals in the form of release from parasites and improved body condition. Despite improved body condition, individuals from less forested areas failed to exhibit fluctuating body condition in response to spawning, which was typical in hellbenders from more forested habitats. We postulate this lack of fluctuation could be due to reduced conspecific competition or reproductive investment and/or high rates of filial cannibalism in response to declining forest cover.

Energetic constraints and parental care: is corticosterone indicative of energetic costs of incubation in a precocial bird?

Suppression of the adrenocortical response (e.g., corticosterone release) to an acute stressor is a physiological adjustment thought to decrease the likelihood of avian parents abandoning their nests. However, some periods of parental care, like incubation, are energetically costly, thus corticosterone could increase during these stages to allow incubating parents to utilize energy reserves. Wood ducks (Aix sponsa) have ~30 day incubation periods and only the female incubates the eggs. We hypothesized that corticosterone would be important in regulating energy availability during incubation in this species. Because resources invested in reproduction increase with clutch size, we also hypothesized that clutch size would influence plasma corticosterone during incubation. We measured baseline and stress-induced corticosterone in incubating females during early and late stages of incubation. At both stages of incubation all hens had low baseline corticosterone levels. However, we found that stress-induced corticosterone was 105% greater late in incubation than early in incubation. We also detected a significant negative correlation between female body mass and stress-induced corticosterone late in incubation, but not during the early stages of incubation. Furthermore, we found a significant positive relationship between stress-induced corticosterone and clutch size. These lines of evidence support the hypothesis that incubation in wood ducks is energetically costly and corticosterone is important in supporting the energetic demands of incubating hens. Our findings suggest that corticosterone's role in supporting parental care behaviors are dynamic and are influenced by several factors and that there is a greater physiological cost associated with incubating larger clutches.

Like mother, like offspring: maternal and offspring wound healing correlate in snakes.

Immune function early in life can be influenced by parental effects and the environment, but it remains unclear how these two factors may interact to influence immunocompetence. We evaluated maternal and environmental contributions to offspring healing ability in a viviparous reptile, the northern watersnake (Nerodia sipedon). We measured wound healing rates, a highly integrative and biologically relevant measure of innate immunity, of females and their offspring collected from sites contaminated with a toxic heavy metal and compared them with those of individuals from reference sites. We found that female watersnakes that healed the fastest produced offspring that also exhibited faster healing rates. However, we detected no influence of environmental pollution on maternal or offspring healing rates. To our knowledge, our study is the first to correlate maternal and offspring wound healing ability in a wild vertebrate.

Deposition of pathogenic Mycoplasma gallisepticum onto bird feeders: host pathology is more important than temperature-driven increases in food intake.

Although ambient temperature has diverse effects on disease dynamics, few studies have examined how temperature alters pathogen transmission by changing host physiology or behaviour. Here, we test whether reducing ambient temperature alters host foraging, pathology and the potential for fomite transmission of the bacterial pathogen Mycoplasma gallisepticum (MG), which causes seasonal outbreaks of severe conjunctivitis in house finches (Haemorhous mexicanus). We housed finches at temperatures within or below the thermoneutral zone to manipulate food intake by altering energetic requirements of thermoregulation. We predicted that pathogen deposition on bird feeders would increase with temperature-driven increases in food intake and with conjunctival pathology. As expected, housing birds below the thermoneutral zone increased food consumption. Despite this difference, pathogen deposition on feeders did not vary across temperature treatments. However, pathogen deposition increased with conjunctival pathology, independently of temperature and pathogen load, suggesting that MG could enhance its transmission by increasing virulence. Our results suggest that in this system, host physiological responses are more important for transmission potential than temperature-dependent alterations in feeding. Understanding such behavioural and physiological contributions to disease transmission is critical to linking individual responses to climate with population-level disease dynamics.

Evaluating the effects of anthropogenic stressors on source-sink dynamics in pond-breeding amphibians.

Although interwetland dispersal is thought to play an important role in regional persistence of pond-breeding amphibians, few researchers have modeled amphibian metapopulation or source-sink dynamics. Results of recent modeling studies suggest anthropogenic stressors, such as pollution, can negatively affect density and population viability of amphibians breeding in isolated wetlands. Presumably population declines also result in reduced dispersal to surrounding (often uncontaminated) habitats, potentially affecting dynamics of nearby populations. We used our data on the effects of mercury (Hg) on the American toad ( Bufo americanus) as a case study in modeling the effects of anthropogenic stressors on landscape-scale amphibian dynamics. We created a structured metapopulation model to investigate regional dynamics of American toads and to evaluate the degree to which detrimental effects of Hg contamination on individual populations can disrupt interpopulation dynamics. Dispersal from typical American toad populations supported nearby populations that would otherwise have been extirpated over long time scales. Through support of such sink populations, dispersal between wetland-associated subpopulations substantially increased overall productivity of wetland networks, but this effect declined with increasing interwetland distance and decreasing wetland size. Contamination with Hg substantially reduced productivity of wetland-associated subpopulations and impaired the ability of populations to support nearby sinks within relevant spatial scales. Our results add to the understanding of regional dynamics of pond-breeding amphibians, the wide-reaching negative effects of environmental contaminants, and the potential for restoration or remediation of degraded habitats.