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Summary There is growing need for reliable biomarkers of the physiological stress response in basic ecological investigations and conservation‐specific applications. One effect of stress hormone secretion is the alteration of circulating leucocytes, specifically an increase in the heterophil : lymphocyte ratio (HLR). There have been numerous studies and reviews of the relationship between the stress response and HLR, yet the data have not been systematically analysed across studies. Here, we performed meta‐analyses of studies in which paired values of plasma corticosterone (CORT) and HLR were available to investigate the relationship between these parameters. Specifically, we analysed CORT and HLR as baseline measures between treatment (or ‘stressed’ populations) and control (or ‘reference’ populations). Additionally, we investigated the relationship within CORT and HLR to identify temporal patterns of the response as a result of the duration of the stressor. Across studies, we identified that CORT and HLR are significantly elevated in populations subjected to environmentally stressful conditions. While not significantly different, CORT tended to be more elevated than HLR in the stressed populations. We found that there is a significant, negative relationship between CORT and the temporal duration of environmental stress. Additionally, we found a significant break point in this response at 85 days of stress duration, above which there is not a clear relationship between CORT and duration. This indicates that the CORT response to environmental stress attenuates. We found a small but positive significant relationship between HLR and temporal duration of environmental stress. This suggests that the elevation of HLR in response to environmental stress does not decrease over time. Our data identified that data gaps of wild populations of species exist and that more studies pairing physiological stress responses will further our understanding of how populations respond to environmental challenges. We found that CORT and HLR responded differently to stress, depending on captivity status, whether the study population was the domestic chicken, and the sex of the study population. Lay Summary

Endocrine disrupting chemicals are present in the environment and/or in consumer products. These agents have the capacity to mimic and/or antagonize endogenous hormones and thus perturb the endocrine axis. The male reproductive tract expresses steroid hormone (androgen and estrogen) receptors at high levels and is a major target for endocrine disrupting chemicals. In this study, Long–Evans male rats were exposed to dichlorodiphenyldichloroethylene, a metabolite of dichlorodiphenyltrichloroethane and a chemical present in the environment, in drinking water at 0.1 and 10 µg/L for 4 weeks. At the end of exposure, we measured steroid hormone secretion and analyzed steroidogenic proteins, including 17β-hydroxysteroid dehydrogenase, 3β-hydroxysteroid dehydrogenase, steroidogenic acute regulatory protein, aromatase, and the LH receptor. We also analyzed Leydig cell apoptosis (poly-(ADP-ribose) polymerase) and caspase-3 in the testes. Testicular testosterone (T) and 17β-estradiol (E2) were both affected by exposure to dichlorodiphenyldichloroethylene by displaying altered steroidogenic enzyme expression. Dichlorodiphenyldichloroethylene exposure also increased the expression of enzymes mediating the pathway for programmed cell death, including caspase 3, pro-caspase 3, PARP, and cleaved PARP. Altogether, the present results demonstrate that dichlorodiphenyldichloroethylene directly and/or indirectly can target specific proteins involved in steroid hormone production in the male gonad and suggest that exposure to environmentally relevant dichlorodiphenyldichloroethylene levels has implications for male reproductive development and function. Summary Sentence Exposure to environmentally relevant DDE levels has implications for male reproductive development and activity due to disruption of testicular T and E2 secretion.

Sex ratio theory suggests that females should bias offspring sex ratios based on maternal condition and the availability of critical food resources. Work in birds indicates that females do, indeed, bias sex ratios according to maternal condition and food quality and quantity. Yet it is unknown whether these sex ratio skews occur due to fluctuations in particular micro‐ or macro‐nutrients, caloric content overall or even the perception of food availability. We hypothesized that dietary fats may drive biases in offspring sex ratios, because measures of maternal condition often reflect fat reserves, and fats are critical for the process of egg‐laying in birds. To test this, we provided breeding Japanese quail, a species that biases sex ratios in response to maternal condition, with either a control breeding diet or a diet supplemented with two oils (safflower oil and flaxseed oil). These oils were chosen for their high omega‐3 and omega‐6 fatty acid content as well as their importance in mammalian sex allocation. We then measured influences of these diets on the sex ratio of offspring, the change in maternal weight, and the laying rates of female quail. The dietary oil supplements increased weight gains in quail but decreased the number of eggs laid during the experiment. There was no influence of the oil supplements on offspring sex ratios. This indicates that fat may not be a macro‐nutrient involved in the process of sex ratio adjustment in quail.

Organisms possess a range of thermoregulatory strategies that may vary in response to sickness, thereby driving important life-history consequences. Because the immune system is vital to maintaining organism function, understanding the suite of immune responses to infection indicates basic costs and benefits of physiological strategies. Here, we assessed consequences of thermoregulation and seasonality on immune function in both immunologically stimulated and nonstimulated gopher tortoises (Gopherus polyphemus). An ectothermic vertebrate was used as an experimental model because the effects of thermoregulation on immunity remain understudied and are of increasing importance in light of anthropogenic alterations to thermal environments. We found that G. polyphemus increased body temperature (T b) at 1 h after injection with lipopolysaccharide (LPS) when compared with saline controls (P = 0.04), consistent with behavioral fever. LPS increased plasma bactericidal ability (BA; P = 0.006), reduced plasma iron concentration (P = 0.041), and increased heterophil:lymphocyte ratios (P < 0.001). In nonstimulated animals, thermoregulatory strategy had a strong effect on innate immunity, which demonstrated that individuals have the ability to facultatively adjust immune function when infection burden is low; this relationship was not present in LPS-injected animals, which suggested that animals stimulated with LPS maximize bactericidal ability independently of temperature. Seasonal acclimation state did not influence responses to LPS, although baseline plasma iron was significantly lower in animals acclimated to winter. These results support that a trade-off exists between immunity and other conflicting physiological interests. Moreover, these results clearly demonstrate the ability of individuals to modulate immune function as a direct result of thermoregulatory decisions.

Physiological tradeoffs occur in organisms coping with their environments, which are likely to increase as populations reach peripheries of established ranges. Invasive species offer opportunities to study tradeoffs that occur, with many hypotheses focusing on how immune responses vary during dispersal. The cane toad (Rhinella marina) is a well-known invasive species. Populations near the expanding edge of the Australian invasion have altered immune responses compared to toads from longer-established core populations, although this has not been well-documented for Florida populations. In this study, cane toads from a northern edge [New Port Richey (NPR)] and southern core (Miami) population in Florida were collected and injected with lipopolysaccharide (LPS) to compare immune responses. Core population individuals injected with LPS showed greater metabolic increases compared to their baseline rates that were higher compared to those from the edge population. In addition, LPS-injected core individuals had different circulating leukocyte profiles compared to saline-injected cane toads while edge individuals did not. There was a significant interaction between plasma bacteria-killing capability (BKA) and treatment, such that BKA decreased with time in saline compared to LPS-injected individuals, and saline-injected toads from the edge population had lower BKA compared to LPS-injected edge toads at 20 h post-injection. There was also a significant interaction between location and time on circulating corticosterone (CORT) levels following injections with saline or LPS, with CORT decreasing more with time in core population toads. The differential CORT response indicates that differential stress responses contribute to the tradeoffs observed with immunity and dispersal.

Cane Toads (Rhinella marina) are an invasive species introduced to southern Florida, USA, and populations have spread northward through the state. Populations established near expanding edges of their distributions are predicted to have greater endurance, an indicator of dispersal capability, than longer established populations. To assess endurance, we collected Cane Toads from a northern (edge) and southern (core) population in Florida, placed them into a track, and prodded them to hop. The number of prods (taps), hops, and time spent hopping were recorded, along with the total distance each toad moved on the track. Edge population toads were less willing to move and did not travel as far in the track as those from the core population. To further evaluate endurance, we placed an additional set of toads inside a treadmill, where movement was required to maintain equilibrium. Toads moved on the treadmill until reaching exhaustion. We measured blood lactate levels from each toad upon exhaustion and during a 3-h recovery period. After the treadmill trials, there was no population effect on the distances traveled by toads. There was also no population effect on lactate levels of toads when reaching exhaustion or during recovery. Overall, Cane Toads from our sampled northern edge population showed no differences in endurance compared to those sampled from the southern population in this study. This finding may indicate that further dispersal is limited in the northernmost populations of the Cane Toad range in Florida. Furthermore, the reluctance of Cane Toads to move in the track trials may indicate that selective pressures differ for edge populations in Florida.

Anecdotal observations suggest that visual obstruction after capture will calm crocodilians, leading many to hypothesize that eye covering reduces physiological stress. However, this has yet to be tested empirically. To investigate this, we randomly divided 20 juvenile American Alligators (Alligator mississippiensis) into two treatments (visual obstruction [VO] and no obstruction [NO]) and took blood samples immediately after capture (baseline) and 30 min after treatment to determine the effects of visual obstruction on alligator corticosterone (CORT) levels. We found that baseline and post treatment CORT levels were similar between both NO-treated and VO-treated alligators; however, CORT levels were significantly elevated 30 min after capture relative to baseline in both NO and VO alligators. Our results indicate that visual obstruction does not prevent or reduce handling stress after capture in crocodilians and that any observed behavioral alterations are independent of changes in CORT levels.

Researchers have documented significant skews in the primary sex ratios of avian offspring in relation to a variety of environmental and social cues. Zebra finches Taeniopygia guttata, in particular, adjust offspring sex ratio according to both the quality and quantity of available food, as well as male attractiveness. The mechanisms behind such manipulation of offspring sex remain elusive. Recent studies suggest that females with chronically elevated corticosterone levels (both naturally and artificially) produce significantly female biased offspring sex ratios. We tested the effects of a pharmacological dose of corticosterone or progesterone administered at the time of sex chromosome segregation on the primary sex ratio of zebra finch offspring to determine whether one or both hormones act on offspring sex at this critical period. Females were injected with 20 μg of corticosterone or 20 μg of progesterone five hours prior to the predicted time of ovulation of the 3rd or 4th ovulating follicle. A third group of females were unmanipulated. The corticosterone treated group produced 72% males while the control group produced 37.5% in the 3rd or 4th ovulation of the sequence. Progesterone injections disrupted ovulation and oviposition in 90% of females. Corticosterone administration did not adversely affect oviposition or ovulation. Females injected with corticosterone had significantly elevated levels of corticosterone 20 min, 1 h and 2.5 h post-injection and produced significantly more males compared to untreated females. Our results suggest that offspring sex ratios may be influenced at the time of meiotic division by acute exposure to corticosterone and provides evidence for the timing of this effect.

This study investigated the effects of railway noise across distinct freshwater fishes to predict species-specific susceptibility as well further define noise as an environmental detriment. Results revealed that while predicting susceptibility is difficult, the impacts experienced further distinguish anthropogenic noise as a relevant stressor to the species effected.AbstractWhile the expansion of anthropogenic noise studies in aquatic habitats has produced conservation-based results for a range of taxa, relatively little attention has been paid to the potential impacts on stream fishes. Recent work has shown responses to road noise in single species of stream fish; however, assemblage-wide effects of anthropogenic noise pollution have not yet been investigated. By examining five metrics of disturbance across four ecologically and evolutionarily disparate species of stream fishes, a series of laboratory experiments aimed to describe the effects of and species susceptibility to anthropogenic noise playback. Each species studied represented a unique combination of hearing sensitivity and water column position. Physiological and behavioral metrics were compared across the presence and absence of rail-noise noise playback in four target species. Through repeated subsampling, the temporal dynamics of cortisol secretion in response to noise in two target species were additionally described. Rail-noise playback had no statistically significant effect on blood glucose or water-borne cortisol levels, with the exception of decreased cortisol in noise-exposed largescale stoneroller (Campostoma oligolepis). Time-course cortisol experiments revealed rapid secretion and showed minimal effects of noise at most observation points. The presence of noise produced significant changes in ventilation rate and swimming parameters in a portion of the four species observed representing the most conserved responses. Overall, effects of noise were observed in species contrary to what would be hypothesized based on theoretical hearing sensitivity and water column position demonstrating that predicting susceptibility to this type of stressor cannot be accomplished based off these course considerations alone. More importantly, we show that anthropogenic noise can disrupt a variety of behavioral and physiological processes in certain taxa and should be further investigated via measures of fitness in the wild.

Bats are known reservoirs for numerous emerging infectious diseases, occupy unique ecological niches, and occur globally except for Antarctica. Given their impact on human and agricultural health, it is critical to understand the mechanisms underlying immunocompetence in this reservoir host. To date, few studies have examined immune function in the Order Chiroptera, particularly among natural colonies of bats. The phytohemagglutinin (PHA) skin test has been widely used to measure delayed-type cellular immune response in a wide variety of vertebrates, and has been routinely employed in immunoecological studies. Although this test is frequently described as a measure of T cell proliferation, recent studies indicate it may represent a combination of immune responses. In mammals, the immune response is differentially, temporally and spatially regulated, therefore, we characterized the infiltrating leukocyte response to the PHA skin test in bats by examining a time-series of histological sections from PHA and saline injection areas in 41 Brazilian free-tailed bats (Tadarida brasiliensis). Results suggest that bats exhibit diverse leukocyte traffic within 6 h, and up to 24 h following subcutaneous PHA injection. There was a significant presence of lymphocytes and neutrophils, as well as eosinophils, basophils, and macrophages observed in the PHA-injected tissues, compared with saline-injected control tissues. We observed a highly significant negative correlation between the number of lymphocytes and neutrophils in PHA-injected tissue, with peak lymphocyte response at 12 h, and peak neutrophil response at 24 h post-injection. These results indicate substantial variation in the immune response of individuals, and may aid our understanding of disease emergence in natural populations of bats.