Glucocorticoid steroid hormones (GCs) coordinate physiology and behavior across immediate, developmental, and evolutionary timescales. There are two main GCs produced by vertebrates, cortisol and corticosterone, and, based on taxonomic relationships, species are generally assumed to have one of the two as their primary GC. However, growing evidence demonstrates that GC abundance and regulation are more complex than previously thought, with the potential for variation across tissues, developmental time, and context. To understand GC patterns across the life cycle of Northern Glassfrogs (Hyalinobatrachium fleischmanni), we quantified both cortisol and corticosterone across seven life stages, from egg to adult, and two sampling methods, non-invasive waterborne sampling and invasive body sampling. As predicted for amphibians, we found that corticosterone was generally more abundant than cortisol. However, the magnitude of this difference varied across life stages and sampling method. Counter to expectations that water hormone levels consistently reflect those in the body, we found that this relationship differed across life stages. Our results emphasize the context-dependent nature of GCs, highlighting exciting avenues for future research and important considerations for researchers interested in non-invasive GC sampling.
Keratin matrixes are a highly relevant tissue for measuring and evaluating the accumulation of endogenous and exogenous substances across a wide variety of species. In this context, the carapace of marine turtles is a valuable source of information. In this study, we collected carapace samples from two species of marine turtles to analyze metals and metalloids. Nine elements (As, Ag, Cd, Cr, Cu, Fe, Pb, Mn, Zn) were measured, with Zn, Pb, Fe, Cu, and As being the elements that showed the highest concentrations. Significant correlations were observed in Green Turtles between morphometric variables and elements such as Ag (carapace width) and Cu (body mass). In Hawksbill Turtles, these variables demonstrated correlations with Ag. No significant differences were found between species except for Cu concentrations. Our study demonstrates that the carapace of sea turtles is a valuable tissue in the research and conservation efforts for these species. It has generated new information on the accumulation of pollutant elements (metals and metalloids) in keratinized matrixes and will be helpful in evaluating their long-term exposure.
Animal body coloration plays a crucial role in a wide range of ecological functions, including communication, predator avoidance, and thermoregulation. Being able to change color can further enhance these functions, as it allows organisms to fine-tune their appearance to deal with environmental heterogeneity or changes in their environment. Organisms frequently encounter conditions where requirements of camouflage and thermoregulation conflict, potentially forcing a trade-off in which function to emphasize. This may elucidate whether predator avoidance or metabolic demands represent a greater potential cost to survival and are thus under stronger selection. We examined the ecology of environment- and temperature-dependent color change in Eastern Gray Treefrogs (Dryophytes versicolor) under naturalistic conditions by allowing frogs to position themselves freely within a large outdoor enclosure filled with natural perches. We first corroborated that frogs were indeed capable of changing color and that any frog-background match was not due to environmental color preferences. We show that measures of frog coloration (luminosity, saturation, and hue) correlate strongly and consistently with the coloration of their environment, but that only frog hue significantly correlates with temperature. We also found no evidence that frogs simultaneously optimize camouflage and thermoregulation by choosing light backgrounds on warm days and dark backgrounds on cold days. Overall, our results suggest that under average temperature conditions, Eastern Gray Treefrogs predominantly adjust body coloration for camouflage.
The home range of an individual is the spatial area in which it moves to meet its needs for survival and reproduction. Studies of snake movement and home range show a geographic and taxonomic bias toward the Northern Hemisphere, limiting our understanding of how snakes in other regions interact with their environments. We examined movement patterns of Cape cobras (Naja nivea) at Tswalu Kalahari Reserve (Northern Cape Province, South Africa). We telemetered 37 cobras and analyzed movement data from 33 individuals, collecting 1,960 locations between January 2018 and September 2021. We estimated home ranges using dynamic Brownian Bridge Movement Models, which generated a 99% probability contour for each snake. We tested effects of sex, body size and tracking duration on home range area, and examined variation in mean monthly displacement relative to sex and season, accounting for inter-annual variation. Home ranges differed significantly between sexes with females occupying smaller areas (75 ± 72 ha) than males (147 ± 101 ha). We found a significant interaction between sex and season in snake movement, with males moving farther than females in spring. Cape Cobras conform qualitatively to patterns described for northern hemisphere snakes, but the home ranges we report are far larger than those of elapids studied in other arid systems, and movement was suppressed in summer as well as winter—a pattern inconsistent with the temperate expectation that warm seasons promote activity. Existing literature appears to predict the direction but not the magnitude or seasonal structure of movement in arid-zone African elapids.
Certain anuran species display distinctive foraging behaviors, including a phenomenon known as toe twitchingrhythmic movement of the longest toe on the hind legs to induce movement in prey. In this study, we developed and analyzed a novel agent-based model for a system of frogs (Kaloula pulchra) and roaches (Blaptica dubia), which quantifies the role of toe twitching in prey capture and allows for testing of the hypothesis that this behavior is triggered when prey are nearby but not within a frog's visual field. By incorporating observed behaviors, the model serves as a tool to determine whether toe twitching is a direct physical result of predator-prey interactions or whether a more complex behavior is present. This work provides a framework for evaluating the functional significance of toe twitching in predator-prey dynamics and lays the groundwork for future experimental validation.
