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Updated: Feb 15, 2026

Visually Sexing Loggerhead Shrike Lanius Ludovicianus Using Plumage Coloration and Pattern
Published on: March 8, 2020
Sexual antagonism and the instability of environmental sex determination
Pavitra Muralidhar1, Carl Veller2,3
1Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, USA. pmuralidhar@g.harvard.edu.
Abstract:
The sex of an organism can be determined by its genetics or its early environment. Across the animal kingdom, genetic sex determination (GSD) is far more common than environmental sex determination (ESD). Here, we propose an explanation for this pattern: the coupling of genes that bias offspring sex ratios towards one sex with genes that are beneficial in that sex but costly in the other. Gradual strengthening of the sex-specific tendency of this association eventuates in a neo-sex chromosome; that is, GSD. Our model predicts to which system of heterogamety ESD will evolve when nesting behaviour is an important determinant of brood sex ratios. It explains the puzzling observation in some GSD species of sex reversal induced by extreme environments. The model also suggests an approach to discovering sex-determining genes in ESD species.
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