Temperature Sex Reversal Implies Sex Gene Dosage in a Reptile

TLDR

Reptile sex is governed either by sex chromosomes or by incubation temperature. The authors propose that a dosage‑sensitive male‑determining gene on the Z chromosome is inactivated by high temperatures. High incubation temperatures convert ZZ males into phenotypic females, indicating the W chromosome is not required for female development and suggesting that temperature‑dependent sex determination may evolve via dosage‑sensitive Z‑linked genes in many reptiles.

Abstract

Sex in reptiles is determined by genes on sex chromosomes or by incubation temperature. Previously these two modes were thought to be distinct, yet we show that high incubation temperatures reverse genotypic males (ZZ) to phenotypic females in a lizard with ZZ and ZW sex chromosomes. Thus, the W chromosome is not necessary for female differentiation. Sex determination is probably via a dosage-sensitive male-determining gene on the Z chromosome that is inactivated by extreme temperatures. Our data invite a novel hypothesis for the evolution of temperature-dependent sex determination (TSD) and suggest that sex chromosomes may exist in many TSD reptiles.