COS 211-4 - Is the future female for turtles? Adaptive capacity in the face of climate change and the influence of landscape structure on freshwater turtle sex ratios

Background/Question/Methods

For decades, scientists have raised alarm over the potential for climate change to skew sex ratios in taxa such as turtles that largely express temperature-dependent sex determination. However, limited evidence exists that this phenomenon is occurring in natural settings. For species that are vulnerable to anthropogenic land-use practices, differential mortality rates among sexes may also skew sex ratios. Through a highly collaborative effort, we sampled spotted turtle populations across a majority of the species distribution (Florida to Maine) with the goal of understanding the factors influencing population sex ratios.

Results/Conclusions

We present evidence that suggests recent climate change has skewed the adult sex ratio of spotted turtles, with populations indeed following the predicted pattern of increased female bias with warming trends, but only within the hottest areas sampled. At sites with intermediate historic temperatures there was no apparent relationship with climate, while in the coolest areas there was in fact the opposite trend, with populations becoming more male-biased with increasing temperatures. Our findings also demonstrate that spotted turtles have a context-dependent and multi-scale relationship with agriculture. We observed a negative relationship between male proportion and the amount of agricultural cover within 300 m when wetlands were spatially dispersed; however, when wetlands were aggregated, sex ratios remained roughly constant. This pattern may reflect sex-specific patterns in movement that render males more vulnerable to agricultural machinery and other threats. This study highlights the complexity of species responses to both climate change and land use, and emphasizes the important role that landscape structure can play in shaping wildlife population demographics.