Effects of climate change on reptiles with temperature-dependent sex determination and potential adaptation via maternal nest-site choice

Reptiles with temperature-dependent sex determination may be particularly threatened by climate change, as increasing temperatures could lead to skewed sex ratios. A potential compensatory mechanism is nest-site choice, with females selecting nest sites to match incubation conditions to climatic conditions. I studied nest-site choice in painted turtles (Chrysemys picta) to determine the extent to which behavioral plasticity in nest-site choice can compensate for the effects of climate change. In a common-garden experiment, gravid females from five populations across the species\u27 range were collected and nest-site choice was compared among populations to evaluate variation in nesting phenology, shade cover over the nest, nest depth, incubation regime, and offspring sex ratio. Populations differed in nesting phenology and nest depth, but not in shade cover over nests; thus, when exposed to novel climatic conditions, females from transplanted populations chose nest-sites with similar shade cover to those of local females, thereby producing similar offspring sex ratios. The performance of hatchlings produced in this experiment declined with decreasing mean temperature of the mother\u27s site of origin, and nests with greater variation in daily temperature range produced hatchlings that performed faster and more readily than nests with less variable incubation temperatures. Therefore, selection of shadier nest-sites may be a mechanism by which female turtles could compensate for climatic warming, and the increase in temperature fluctuations predicted by climate change models may result in the production of faster hatchling turtles with enhanced righting ability. In an experiment manipulating nest depth, I found that nest depth affected the magnitude of daily temperature fluctuation, but neither mean nest temperature nor sex ratio were affected by depth. The adjustment in nest depth that would be required to affect sex ratio in this species is biologically unfeasible, and therefore female adjustment of nest depth is unlikely to compensate for climate change. Finally, I compared used vs. available nesting habitat between a southern and central population of painted turtles. Compared to the central population, turtles from southern population were more limited in the available range of accessible shade cover under which to nest. As shade cover is an easily-manipulated feature, land managers can adjust the range of shade cover available to nesting turtles in order to preserve populations in the face of climate change. Overall, this research is fundamental to understanding processes in evolutionary ecology in general, and to contemporary climate change biology specifically

Temperature-Dependent Sex Determination under Rapid Anthropogenic Environmental Change: Evolution at a Turtle’s Pace?

Organisms become adapted to their environment by evolving through natural selection, a process that generally transpires over many generations. Currently, anthropogenically driven environmental changes are occurring orders of magnitude faster than they did prior to human influence, which could potentially outpace the ability of some organisms to adapt. Here, we focus on traits associated with temperature-dependent sex determination (TSD), a classic polyphenism, in a model turtle species to address the evolutionary potential of species with TSD to respond to rapid climate change. We show, first, that sex-ratio outcomes in species with TSD are sensitive to climatic variation. We then identify the evolutionary potential, in terms of heritability, of TSD and quantify the evolutionary potential of 3 key traits involved in TSD: pivotal temperature, maternal nest-site choice, and nesting phenology. We find that these traits display different patterns of adaptive potential: pivotal temperature exhibits moderate heritable variation, whereas nest-site choice and nesting phenology, with considerable phenotypic plasticity, have only modest evolutionary potential to alter sex ratios. Therefore, the most likely response of species with TSD to anthropogenically induced climate change may be a combination of microevolution in thermal sensitivity of the sex-determining pathway and of plasticity in maternal nesting behavior

Genomic Correlates of Virulence Attenuation in the Deadly Amphibian Chytrid Fungus, Batrachochytrium dendrobatidis.

Emerging infectious diseasespose a significant threat to global health, but predicting disease outcomes for particular species can be complicated when pathogen virulence varies across space, time, or hosts. The pathogenic chytrid fungus Batrachochytrium dendrobatidis (Bd) has caused worldwide declines in frog populations. Not only do Bd isolates from wild populations vary in virulence, but virulence shifts can occur over short timescales when Bd is maintained in the laboratory. We leveraged changes in Bd virulence over multiple generations of passage to better understand mechanisms of pathogen virulence. We conducted whole-genome resequencing of two samples of the same Bd isolate, differing only in passage history, to identify genomic processes associated with virulence attenuation. The isolate with shorter passage history (and greater virulence) had greater chromosome copy numbers than the isolate maintained in culture for longer, suggesting that virulence attenuation may be associated with loss of chromosome copies. Our results suggest that genomic processes proposed as mechanisms for rapid evolution in Bd are correlated with virulence attenuation in laboratory culture within a single lineage of Bd. Moreover, these genomic processes can occur over extremely short timescales. On a practical level, our results underscore the importance of immediately cryo-archiving new Bd isolates and using fresh isolates, rather than samples cultured in the laboratory for long periods, for laboratory infection experiments. Finally, when attempting to predict disease outcomes for this ecologically important pathogen, it is critical to consider existing variation in virulence among isolates and the potential for shifts in virulence over short timescales

Road avoidance and its energetic consequences for reptiles

CITATION: Paterson, J. E., et al. 2019. Road avoidance and its energetic consequences for reptiles. Ecology and Evolution, 9(17):9794-9803, doi:10.1002/ece3.5515.The original publication is available at https://onlinelibrary.wiley.comRoads are one of the most widespread human-caused habitat modifications that can increase wildlife mortality rates and alter behavior. Roads can act as barriers with variable permeability to movement and can increase distances wildlife travel to access habitats. Movement is energetically costly, and avoidance of roads could therefore impact an animal's energy budget. We tested whether reptiles avoid roads or road crossings and explored whether the energetic consequences of road avoidance decreased individual fitness. Using telemetry data from Blanding's turtles (Emydoidea blandingii; 11,658 locations of 286 turtles from 15 sites) and eastern massasaugas (Sistrurus catenatus; 1,868 locations of 49 snakes from 3 sites), we compared frequency of observed road crossings and use of road-adjacent habitat by reptiles to expected frequencies based on simulated correlated random walks. Turtles and snakes did not avoid habitats near roads, but both species avoided road crossings. Compared with simulations, turtles made fewer crossings of paved roads with low speed limits and more crossings of paved roads with high speed limits. Snakes made fewer crossings of all road types than expected based on simulated paths. Turtles traveled longer daily distances when their home range contained roads, but the predicted energetic cost was negligible: substantially less than the cost of producing one egg. Snakes with roads in their home range did not travel further per day than snakes without roads in their home range. We found that turtles and snakes avoided crossing roads, but road avoidance is unlikely to impact fitness through energetic expenditures. Therefore, mortality from vehicle strikes remains the most significant impact of roads on reptile populations.https://onlinelibrary.wiley.com/doi/full/10.1002/ece3.5515Publisher's versio