Abstract
Climate change is expected to disrupt biological systems. Particularly susceptible are species with temperature-dependent sex determination (TSD), as in many reptiles. While the potentially devastating effect of rising mean temperatures on sex ratios in TSD species is appreciated, the consequences of increased thermal variance predicted to accompany climate change remain obscure. Surprisingly, no study has tested if the effect of thermal variance around high-temperatures (which are particularly relevant given climate change predictions) has the same or opposite effects as around lower temperatures. Here we show that sex ratios of the painted turtle (Chrysemys picta) were reversed as fluctuations increased around low and high unisexual mean-temperatures. Unexpectedly, the developmental and sexual responses around female-producing temperatures were decoupled in a more complex manner than around male-producing values. Our novel observations are not fully explained by existing ecological models of development and sex determination, and provide strong evidence that thermal fluctuations are critical for shaping the biological outcomes of climate change.
Highlights
Climate helps determine many fundamental traits of organisms, from geographic distributions to life history patterns
While most concern has focused on rising mean temperatures (e.g. [4,5]), research on temperature-dependent sex determination (TSD) reptiles indicates that natural sex ratios produced under daily temperature fluctuations may differ from those produced at constant incubation (e.g. [6,7,8], and references therein)
Our results indicate that while increasing the variance around the male producing mean (26uC) had little effect in developmental rate, sex ratio was decoupled from the thermal effect on development under the largest fluctuations, whereas around the female producing mean (31uC) both the developmental rate and the sex ratios were affected by the thermal variance experienced
Summary
Climate helps determine many fundamental traits of organisms, from geographic distributions to life history patterns Whether a similar variance experienced around high (female-producing) temperature induces females, males, or is lethal remains untested experimentally. It is unclear if enhancing the thermal variance around both unisexual means has the same or opposite effects on sex ratios. We address this question, which is critical for understanding the impact of climate change as the frequency of higher temperatures and the variance around those values increases, using the emerging model TSD turtle, Chrysemys picta [14]
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