Sex reversal, a mismatch between phenotypic and genetic sex, can be induced by chemical
and thermal insults in ectotherms. Therefore, climate change and environmental pollution
may increase sex-reversal frequency in wild populations, with wide-ranging implications
for sex ratios, population dynamics, and the evolution of sex determination. We propose
that reconsidering the half-century old theory "Witschi's rule" should facilitate
understanding the differences between species in sex-reversal propensity and thereby
predicting their vulnerability to anthropogenic environmental change. The idea is
that sex reversal should be asymmetrical: more likely to occur in the homogametic
sex, assuming that sex-reversed heterogametic individuals would produce new genotypes
with reduced fitness. A review of the existing evidence shows that while sex reversal
can be induced in both homogametic and heterogametic individuals, the latter seem
to require stronger stimuli in several cases. We provide guidelines for future studies
on sex reversal to facilitate data comparability and reliability.
