Conservation Physiology最新文献

Increasing variable hydroperiods may leave ectotherms with complex life cycles more vulnerable to the impacts of environmental drying. While developmental plasticity may enable some species to escape drying ponds, this plasticity might result in trade-offs with performance and subsequent fitness in adults. Here, we used rice paddy frogs (Fejervarya limnocharis) to test how pond drying influences the developmental plasticity of tadpoles, and the resulting carryover effects on body size and jumping performance. We predicted that tadpoles under simulated drought conditions (2-0.25 cm depth) compared to low stable water level conditions (0.25 cm depth) would develop faster, and the resulting metamorphs would be smaller and exhibit lower jumping performance. We show that tadpoles in drying conditions had a faster developmental rate than tadpoles in stable low water level treatments. The size of metamorphs from the drying treatment was similar to the high-water treatments (2 cm depth), but maximum jumping distance of individuals from the drying condition was lower than that of the high-water treatment. These results indicate that drying conditions for F. limnocharis increase development rate without a reduction in size at metamorphosis, but with poorer mass-independent locomotor performance, which can potentially impact their survival.

Ongoing amphibian population declines are caused by factors such as climate change, habitat destruction, pollution and infectious diseases not limited to chytridiomycosis. Unfortunately, action is taken against these factors once population collapses are underway. To avoid these post hoc responses, wildlife endocrinology aims to analyse physiological mediators that predict future population declines to inform wildlife management. Mediators typically investigated are stress hormones known as glucocorticoids, which are produced by the Hypothalamus-Pituitary-Interrenal axis (HPI axis). The HPI axis is the part of the endocrine system that helps amphibians cope with stress. Chronic increases in glucocorticoids due to stress can lead to immune dysfunction, which makes amphibians more susceptible to infectious diseases. Despite this predictive potential of glucocorticoids, interpretation of glucocorticoid data is confounded by sampling design and type. Glucocorticoid monitoring classically involves blood sampling, which is not widely applicable in amphibians as some are too small or delicate to sample, and repeated samples are often valued. To address this, we tried to validate skin swabbing via corticosterone (CORT) and adrenocorticotropin hormone (ACTH) injections in adults of two amphibian species: Eastern red-spotted newts, Notophthalmus viridescens viridescens, with natural skin infections with Batrachochytrium dendrobatidis (Bd) upon collection in the field, and Northern leopard frogs, Rana (Lithobates) pipiens, raised in captivity and naïve to Bd exposure. Further, we determined the predictive potential of skin glucocorticoids on Bd load in the field via correlations in Eastern red-spotted newts. We found that hormones present in the skin are not related to the HPI axis and poorly predict infection load; however, skin hormone levels strongly predicted survival in captivity. Although skin swabbing is not a valid method to monitor HPI axis function in these species, the hormones present in the skin still play important roles in organismal physiology under stressful conditions relevant to wildlife managers.

For aquatic and semi-aquatic vertebrates like amphibians, it is possible to estimate excreted hormone levels using non-invasive methods such as waterborne and salivary sampling. These techniques allow monitoring of endocrine activity over varying, repeated and simultaneous integration periods while minimizing handling-related stress that can 'contaminate' hormone estimates, including estimates of baseline glucocorticoids. Here we have validated the extraction and quantification of three steroid hormones (corticosterone, CORT; 17-b estradiol, E₂; testosterone, TST) in Couch's spadefoots (Scaphiopus couchii)-a desert-adapted anuran of special interest for physiology, evolution and conservation-using non-invasive waterborne and minimally invasive salivary hormone methods. We combined extraction and enzyme immunoassay methods to conduct conventional technical validations of parallelism, recovery and time-course. Next, we carried out biological validations by testing the correlation between excreted and circulating concentrations and conducting pharmacological challenges. We found that all three hormones can be precisely estimated from 60-min water baths, exhibit robust parallelism, and have high recoveries. Further, we demonstrated that secretory responses to pharmacological challenges can be detected in waterborne CORT in male and female frogs; in TST and E₂ in male frogs, but not consistently for TST or E₂ in female frogs. Lastly, plasma hormone concentrations were consistently correlated with their waterborne complements for CORT (both sexes), as well as TST and E₂ in males (but not females). Plasma CORT was also positively correlated with salivary CORT. Together, our findings suggest that sampling waterborne and salivary hormones offers a minimally invasive method that field endocrinologists and conservation physiologists can use to obtain biologically informative endocrine estimates from desert-adapted amphibians.

Sturgeon are threatened by anthropogenic changes to river systems, including entrainment or impingement at water diversions (i.e. the unwanted passage of fish through a water intake or physical contact with a barrier screen, likely caused by high intake velocities). Though there are no universally accepted protocols to determine water diversion risk, previous studies on sturgeon suggest that laboratory evaluations of swimming performance are an effective way to describe susceptibility to entrainment or impingement. The swimming performance of juvenile Green Sturgeon (~5 cm fork length), Acipenser medirostris, was quantified for fish acclimated to 13 and 18°C for 2 weeks using fixed water velocity endurance tests. Water velocities ranged from 25 to 55 cm s^-1, and time-to-fatigue was measured at 5 cm s^-1 increments. Green Sturgeon were quicker to exhaust at the lower acclimation temperature (13°C) compared to fish acclimated to 18°C, for example at 40 cm s^-1 13°C acclimated fish impinged ~7.7 times faster than 18°C acclimated fish and ~41.3 times quicker at water velocities of 45 cm s^-1. Whole-body cortisol grouped by time-to-fatigue (i.e. sustained swimming: time-to-fatigue >200 min, prolonged swimming: time-to-fatigue between 5 and 200 min, rapid swimming: time-to-fatigue <5 min, and non-swimming: control fish) was highest following the swimming experiment for fish utilizing prolonged swimming strategies regardless of temperature exposure. Furthermore, whole body lactate was elevated in fish utilizing prolonged and rapid swimming strategies compared to sustained and control non-swimming fish. Taken together, when swimming to exhaustion, these results suggest that Green Sturgeon were upregulating stress markers and relying on anaerobic metabolism, although both the above trends were driven by 18°C acclimated fish. The time-to-fatigue data suggest that the risk of entrainment was reduced to zero at water speeds ≤ 29.4 cm s^-1 for 18°C and ≤ 22.6 cm s^-1 for 13°C acclimated fish.

Understanding wildlife reproductive seasonality is crucial for effective management and long-term monitoring of species. This study investigates the seasonal variability of testosterone in male Pacific Coast Feeding Group (PCFG) gray whales, using an eight-year dataset (2016-2023) of individual sightings, drone-based photogrammetry and endocrine analysis of faecal samples. We analyzed the relationship between faecal testosterone levels and total body length (TL), body condition (body area index, BAI), sexual maturity and day of the year using generalized additive mixed models. Our findings reveal a significant increase in faecal testosterone levels in mature males (MM) towards the end of the foraging season. This increase was not observed in JM, highlighting age-dependent development of sexual characteristics. No significant relationship was found between testosterone levels and TL. Additionally, BAI was not significantly associated with testosterone levels. Our results suggest that the increasing testosterone levels in MM gray whales may indicate preparation for mating before the southbound migration. These findings provide valuable insights into the reproductive biology of PCFG gray whales and underscore the importance of non-invasive faecal sampling for studying reproductive seasonality in large whales. Our approach not only provides further insights into the seasonality of male reproduction for the PCFG gray whales but also offers tools to enhance the understanding of male reproduction in baleen whales broadly with non-invasive approaches.

Human landscape modification is amongst the greatest drivers of biodiversity loss. Measuring faecal glucocorticoid metabolites (FGM) in wildlife is of great value to measure the impact of human activities on local biodiversity because FGM offer a non-invasive way of measuring an animal's response to changes in its environment in the form of adrenocortical activity. Here, we measure the concentration of FGM in three native Australian mammal species belonging to different trophic levels: the Tasmanian devil (Sarcophilus harrisii) and the spotted-tailed quoll (Dasyurus maculatus), both carnivores, and an omnivore that is primarily an arboreal folivore, the brushtail possum (Trichosurus vulpecula), and compare the FGM concentrations across three major land uses: agricultural, plantation and National Parks. We find that land use influences the FGM concentration in all three species and that general patterns emerge in FGM concentrations across multiple species and trophic levels in relation to land use. Specifically, plantation landscapes are associated with the lowest median and range of variation of FGM concentration in all species with several plausible explanations depending on the species. Our results suggest that measuring FGM in multiple species can offer a time- and cost-efficient snapshot of how different animals experience the same environment, potentially simplifying FGM interpretation. This study is the first to apply a community approach to understand how multiple species of different trophic levels respond collectively, and separately, to different land use types.

[This corrects the article DOI: 10.1093/conphys/coae084.].

Faecal cortisol metabolites (FCMs) are increasingly used to index physiological stress in wildlife. Cortisol and other stress hormones act to mobilize glucose, providing energy for the organism to respond to environmental perturbations. Cortisol, the predominant glucocorticoid (GC) in most mammals, is metabolized by the liver and excreted as FCMs. For FCMs to serve as a meaningful physiological index of stress in brown bears (Ursus arctos), we sought to quantify the relationship between blood cortisol and FCM concentrations. Consequently, we conducted an adrenocorticotropic hormone (ACTH) challenge on nine unanaesthetized captive brown bears at the Washington State University Bear Research, Education, and Conservation Center. We collected 10 ml of blood at 0, 3, 6, 24, 48 and 72 h post-injection to measure changes in blood cortisol concentrations. Faecal samples were collected between 7:00 am and 8:00 pm from 24 h prior to injection through 72 h post ACTH challenge. We found that FCM concentration was positively correlated with blood cortisol concentrations and that peak blood cortisol concentrations occurred between 3 and 6 h following an ACTH challenge, whereas FCMs peaked between 10 and 27 h after injection.

Assessing how at-risk species respond to co-occurring stressors is critical for predicting climate change vulnerability. In this study, we characterized how young-of-the-year White Sturgeon (Acipenser transmontanus) cope with warming and low oxygen (hypoxia) and investigated whether prior exposure to one stressor may improve the tolerance to a subsequent stressor through "cross-tolerance". Fish were acclimated to five temperatures within their natural range (14-22°C) for one month prior to assessment of thermal tolerance (critical thermal maxima, CTmax) and hypoxia tolerance (incipient lethal oxygen saturation, ILOS; tested at 20°C). White Sturgeon showed a high capacity for thermal acclimation, linearly increasing thermal tolerance with increasing acclimation temperature (slope = 0.55, adjusted R² = 0.79), and an overall acclimation response ratio (ARR) of 0.58, from 14°C (CTmax = 29.4 ± 0.2°C, mean ± S.E.M.) to 22°C (CTmax = 34.1 ± 0.2°C). Acute warming most negatively impacted hypoxia tolerance in 14°C-acclimated fish (ILOS = 15.79 ± 0.74% air saturation), but prior acclimation to 20°C conferred the greatest hypoxia tolerance at this temperature (ILOS = 2.60 ± 1.74% air saturation). Interestingly, individuals that had been previously tested for thermal tolerance had lower hypoxia tolerance than naïve fish that had no prior testing. This was particularly apparent for hypoxia-tolerant 20°C-acclimated fish, whereas naïve fish persisted the entire 15-h duration of the hypoxia trial and did not lose equilibrium at air saturation levels below 20%. Warm-acclimated fish demonstrated significantly smaller relative ventricular mass, indicating potential changes to tissue oxygen delivery, but no other changes to red blood cell characteristics and somatic indices. These data suggest young-of-the-year White Sturgeon are resilient to warming and hypoxia, but the order in which these stressors are experienced and whether exposures are acute or chronic may have important effects on phenotype.