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

Effects of a novel climate on stress response and immune function in painted turtles (Chrysemys picta)

Climate change may subject animals to increasingly stressful environmental conditions, which could have negative physiological consequences if stress levels are elevated for long periods. We conducted a manipulative experiment to determine the effects of a novel climate on stress levels and immune function in a model reptile species, the painted turtle. We collected turtles from four populations across the species' geographic range and housed them in a common-garden in one population's local climate. We measured levels of the stress hormone corticosterone and tested two aspects of innate immune function, bactericidal capacity and natural antibody agglutination, at the time of capture (baseline) and three additional time points over 1 year. The four populations did not differ in corticosterone levels over the course of 1 year, and corticosterone levels were also similar at each sampling period except that post-hibernation corticosterone levels were significantly lower than the previous three time points. Furthermore, we found no evidence that elevated corticosterone depressed immune function in the painted turtle. Our study suggests that turtles exposed to novel climatic conditions did not display a detectable stress response, nor did the novel climate depress immune function in the transplanted populations. Therefore, in terms of innate immune function, turtles may be relatively resilient to at least small changes in climatic conditions.Fil: Refsnider, Jeanine M.. University Of California Berkeley; Estados UnidosFil: Palacios, María Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico.; ArgentinaFil: Reding, Dawn M.. Luther College. Department of Biology; Estados UnidosFil: Bronikowski, Anne M.. Iowa State University. Department of Ecology, Evolution and Organismal Biology.; Estados Unido

Behavioural plasticity may compensate for climate change in a long-lived reptile with temperature-dependent sex determination

How are organisms responding to climate change? The rapidity with which climate is changing suggests that, in species with long generation times, adaptive evolution may be too slow to keep pace with climate change, and that alternative mechanisms, such as behavioural plasticity, may be necessary for population persistence. Species with temperature-dependent sex determination may be particularly threatened by climate change, because altered temperatures could skew sex ratios. We experimentally tested nest-site choice in the long-lived turtle Chrysemys picta to determine whether nesting behaviour can compensate for potential skews in sex ratios caused by rapid climate change. We collected females from five populations across the species′ range and housed them in a semi-natural common garden. Under these identical conditions, populations differed in nesting phenology (likely due to nesting frequency), and in nest depth (possibly due to a latitudinal cline in female body size), but did not differ in choice of shade cover over the nest, nest incubation regime, or in resultant nest sex ratios. These results suggest that choice of nest sites with particular shade cover may be a behaviourally plastic mechanism by which turtles can compensate for change in climatic temperatures during embryonic development, provided that sufficient environmental variation in potential nest microhabitat is available

Rock glaciers in central Colorado, U.S.A., as indicators of Holocene climate change

We measured thalli diameters of the lichen Rhizocarpon subgenus Rhizocarpon on 48 individual lobes of 18 rock glaciers and rock glacier complexes in the Elk Mountains and Sawatch Range of central Colorado. Cumulative probability distribution and K-means clustering analyses were used to separate lichen thalli measurements into statistically-distinct groups, each interpreted as representing a discrete episode of rock glacier activity driven by an interval of cooler climate. Lichen ages for these episodes were assigned using a growth curve developed for Rhizocarpon geographicum in the nearby Front Range. An early Neoglacial episode, ca. 3080 yr BP, is correlative to other glacial and periglacial activity in the southern Rocky Mountains and surrounding areas and broadly corresponds to an interval of climatic deterioration evident in several other proxies of Holocene climate. The younger two episodes, ca. 2070 and 1150 yr BP, are also coeval with regional (Audubon) glacial and periglacial activity but are thus far not widely recognized in other climate proxies

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

Home Range and Site Fidelity of Imperiled Ornate Box Turtles (Terrapene ornata) in Northwestern Illinois

The destruction of prairies has led to the decline of the ornate box turtle (Terrapene ornate) across much of its range. Land management agencies are considering translocation programs to restore populations to areas from which they have been extirpated. For these conservation efforts to be successful, long-term posttranslocation monitoring is necessary to ensure that translocated individuals behave and use habitat similarly to unmanipulated individuals. We conducted a 3-yr radiotelemetry study of a potential source population of ornate box turtles to provide baseline data on home range size and site fidelity pretranslocation. Adult males and females did not differ in minimum convex polygon home range size (mean 4.0 ha), 95% fixed kernel home ranges (mean 2.6 ha), or 50% fixed kernel home ranges (mean 0.4 ha). Both sexes showed high site fidelity to annual home ranges and to previously used overwintering sites, although distance between subsequent overwintering sites was less for females than for males. At our study site, ornate box turtles have relatively small home ranges and exhibit strong site fidelity. Translocation programs for this species should closely monitor movements of translocated individuals to assess whether they are successfully establishing new home ranges or attempting to return to their site of origin. Moreover, the high site fidelity exhibited by this species suggests that newly translocated individuals may be at increased mortality risk because they are unfamiliar with suitable overwintering and/or nesting sites in their new location. The results of our study will be used to ensure that sites to which animals are translocated are comparable to the site of origin in terms of home range size requirements and important habitat features. In addition, our data serve as a critical baseline to which the habitat use and movement patterns of monitored animals posttranslocation can be directly compared to assess the success of the translocation

Reconstructing Quaternary ice sheet erosion and dynamics across Baffin Island, Arctic Canada

Evidence is poorly preserved in the geologic record for the evolution of Laurentide Ice Sheet (LIS) erosion, dynamics, and basal thermal regime patterns. It has been hypothesized that changes in LIS subglacial conditions and erosional efficiency drove the enigmatic mid-Pleistocene transition (MPT) from 41- to 100-ka climate cyclicity. In this dissertation, a variety of archives and tools are used to explore the 2.7+ Ma history of ice-sheet erosion on Baffin Island in the eastern Canadian Arctic and the possible role of the LIS in the MPT. We compile till geochemistry and cosmogenic radionuclide data to identify a coherent spatial pattern of fresh till and older, more weathered till on the landscape. We interpret the presence of such weathered till to be the result of an expansion in cold-based ice cover prior to 1 Ma, and by that time the fiorded Baffin Island coastline must have developed close to its modern configuration. Subglacially precipitated calcite crusts preserved at several sites on the interior plateaux of Baffin Island provide unique insight into LIS erosion during the last glaciation. U-series dating and O, C, and Sr isotope analyses reveal that the majority of erosion during the last glaciation must have occurred prior to 25-15 ka, and the extent of cold-based ice expanded during deglaciation. The Clyde Foreland Formation (CFF) records at least seven Plio-Pleistocene glaciations. Combining amino acid racemization and 10Be-26Al isochron burial dating, we construct the first absolute chronological framework for the CFF. The oldest sediments are Early Pleistocene or latest Pliocene and contain an exceptionally high meteoric 10Be inventory consistent with regolith erosion. Younger tills both pre- and post-dating the MPT contain no detectable geochemical or mineralogical evidence of regolith erosion. Regolith was most likely removed from beneath the Foxe Dome of the LIS prior to the MPT, and the subglacial deformation of such sediment was not responsible for any regional changes in ice sheet dynamics related to the MPT. However, changes in the LIS basal thermal regime on Baffin Island occurred coincident with or prior to the MPT and may have contributed to the MPT

Variation in glacier length and ice volume of Rabots Glaciar, Sweden, in response to climate change, 1910–2003

Historical records, photographs, maps and measurements were used to determine changes in the length, geometry and volume of Rabots Glaciar, Sweden, in response to a warming that occurred early in the 20th century

Experimental assessment of winter conditions on turtle nesting behaviour

Background: Many reptiles have temperature-dependent sex determination (TSD), and thus are potentially directly influenced by climate change. Where and when a reptile nests can influence nest temperature and offspring characteristics (including sex). Understanding how nesting behaviours are affected by climate is important, particularly in these temperature-sensitive species. Aim: Long-term field research in painted turtles (Chrysemys picta) has identified several nesting behaviours that correlate with air temperature during the preceding winter. Since painted turtles hibernate in water, we sought to observationally and experimentally test whether this correlation is mediated through differences in the duration of ice cover, specifically, the spring ice-off date. Methods: We performed a 25-year observational study of painted turtle nesting, and explored whether the timing of nesting (phenology) was related to ice-off dates recorded in the region. With a complementary experiment, we exposed female painted turtles to conditions simulating different ice-off dates and monitored nesting phenology, nest-site choice, and nest depth. Results and conclusions: Our study identified a significant, positive correlation between ice-off dates and nesting phenology of turtles, with turtles initiating nesting later in years where winter conditions persisted for longer. Contrary to expectations, however, turtles did not differ in nesting behaviours between the ‘early’ and ‘late’ ice-off treatments in the experiment. Thus, variation in these traits in the wild likely is driven by other factors. These results highlight the complexity of understanding how animal behaviours will be altered as climate changes

Geographic variation in thermal sensitivity of early life traits in a widespread reptile

Taxa with large geographic distributions generally encompass diverse macroclimatic conditions, potentially requiring local adaptation and/or phenotypic plasticity to match their phenotypes to differing environments. These eco‐evolutionary processes are of particular interest in organisms with traits that are directly affected by temperature, such as embryonic development in oviparous ectotherms. Here we examine the spatial distribution of fitness‐related early life phenotypes across the range of a widespread vertebrate, the painted turtle (Chrysemys picta). We quantified embryonic and hatchling traits from seven locations (in Idaho, Minnesota, Oregon, Illinois, Nebraska, Kansas, and New Mexico) after incubating eggs under constant conditions across a series of environmentally relevant temperatures. Thermal reaction norms for incubation duration and hatchling mass varied among locations under this common‐garden experiment, indicating genetic differentiation or pre‐ovulatory maternal effects. However, latitude, a commonly used proxy for geographic variation, was not a strong predictor of these geographic differences. Our findings suggest that this macroclimatic proxy may be an unreliable surrogate for microclimatic conditions experienced locally in nests. Instead, complex interactions between abiotic and biotic factors likely drive among‐population phenotypic variation in this system. Understanding spatial variation in key life‐history traits provides an important perspective on adaptation to contemporary and future climatic conditions