Do covariances between maternal behavior and embryonic physiology drive sex-ratio evolution under environmental sex determination?

Date
2019-01-01
Authors
Janzen, Fredric
Delaney, David
Janzen, Fredric
Mitchell, Timothy
Warner, Daniel
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Abstract

Fisherian sex-ratio theory predicts sexual species should have a balanced primary sex ratio. However, organisms with environmental sex determination (ESD) are particularly vulnerable to experiencing skewed sex ratios when environmental conditions vary. Theoretical work has modeled sex-ratio dynamics for animals with ESD with regard to two traits predicted to be responsive to sex-ratio selection: (1) maternal oviposition behavior and (2) sensitivity of embryonic sex determination to environmental conditions, and much research has since focused on how these traits influence offspring sex ratios. However, relatively few studies have provided estimates of univariate quantitative genetic parameters for these two traits, and the existence of phenotypic or genetic covariances among these traits has not been assessed. Here, we leverage studies on three species of reptiles (two turtle species and a lizard) with temperature-dependent sex determination (TSD) to assess phenotypic covariances between measures of maternal oviposition behavior and thermal sensitivity of the sex-determining pathway. These studies quantified maternal behaviors that relate to nest temperature and sex ratio of offspring incubated under controlled conditions. A positive covariance between these traits would enhance the efficiency of sex-ratio selection when primary sex ratio is unbalanced. However, we detected no such covariance between measures of these categories of traits in the three study species. These results suggest that maternal oviposition behavior and thermal sensitivity of sex determination in embryos might evolve independently. Such information is critical to understand how animals with TSD will respond to rapidly changing environments that induce sex-ratio selection.

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<p>This is a manuscript of an article published as Janzen, Fredric J., David M. Delaney, Timothy S. Mitchell, and Daniel A. Warner. "Do covariances between maternal behavior and embryonic physiology drive sex-ratio evolution under environmental sex determination?." <em>Journal of Heredity </em>(2019). doi: <a href="https://doi.org/10.1093/jhered/esz021">10.1093/jhered/esz021</a>.</p>
Keywords
environmental change, microevolution, nesting behavior, pivotal temperature, quantitative genetics, reptile
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