Evidence for sex microchromosomes in a species with temperature-influenced sex determination (Crotaphytus collaris)

The characteristics of a species’ evolution can be powerfully influenced by its mode of sex determination and, indeed, sex determination mechanisms vary widely among eukaryotes. In non-avian reptiles, sex was long thought to be determined bimodally, either by temperature or genetics. Here we add to the growing evidence that sex determining mechanisms in reptiles fall along a continuum rather than existing as a mutually exclusive dichotomy. Using qPCR, we demonstrate that the lizard Crotaphytus collaris possesses sex-based gene dosage consistent with the presence of sex michrochromosomes, despite that extreme incubation temperatures can influence hatchling sex ratio. Our results suggest a temperature override that switches genotypic females to phenotypic males at high and low temperatures.