Predicting the fate of a living fossil: how will global warming

(1302 articles) evolution (1176 articles) ecology (92 articles) developmental biology Articles on similar topics can be found in the following collections Email alerting service here right-hand corner of the article or click Receive free email alerts when new articles cite this article-sign up in the box at the top How will climate change affect species' reproduction and subsequent survival? In many egg-laying reptiles, the sex of offspring is determined by the temperature experienced during a critical period of embryonic development (temperature-dependent sex determination, TSD). Increasing air temperatures are likely to skew offspring sex ratios in the absence of evolutionary or plastic adaptation, hence we urgently require means for predicting the future distributions of species with TSD. Here we develop a mechanistic model that demonstrates how climate, soil and topography interact with physiology and nesting behaviour to determine sex ratios of tuatara, cold-climate reptiles from New Zealand with an unusual developmental biology. Under extreme regional climate change, all-male clutches would hatch at 100% of current nest sites of the rarest species, Sphenodon guntheri, by the mid-2080s. We show that tuatara could behaviourally compensate for the male-biasing effects of warmer air temperatures by nesting later in the season or selecting shaded nest sites. Later nesting is, however, an unlikely response to global warming, as many oviparous species are nesting earlier as the climate warms. Our approach allows the assessment of the thermal suitability of current reserves and future translocation sites for tuatara, and can be readily modified to predict climatic impacts on any species with TSD. 1. INTRODUCTION The ecological impact of increasing air temperatures on terrestrial animals is mediated by complex interactions between climatic variables, terrain and vegetation, as well as the animal's morphology, behaviour and physiology. Translating a predicted air temperature increase into a survival probability for a species ideally requires a mechanistic understanding of these underlying processes. For oviparous species, the most vulnerable part of an animal's life cycle is often the embryo, since eggs are typically left unattended in fixed locations throughout their development (e.g. Feder 1997). Elevated nest temperatures can cause death, but, more subtly, can also influence hatchling sex ratios in species with temperature-dependent sex determination (TSD). TSD is widespread in reptiles (Valenzuela & Lance 2004) with recent discoveries including viviparous species (Robert et al. 2003), making it increasingly important that we develop mechanistic, spatially explicit approaches for predicting the impact of global warming on sex …