A new pair of primers for molecular sexing of the Pallas squirrel, Callosciurus erythraeus, and variation in fetal sex ratio

Abstract

The Pallas squirrel, Callosciurus erythraeus, is an introduced species to Japan where a male-biased sex ratio has been reported at the weaning stage in the field. For further examination of their earlier (fetal) sex ratio, a new PCR primer set was designed to amplify a portion of the Sry (sex-determining region Y) gene. This successfully produced sex-specific PCR profiles for known-sex adult samples. Using this technique we could determine the sex of fetal samples dissected out of mothers shot as pests on Izu-Oshima Island, Tokyo, Japan. The fetal sex ratio was significantly male-biased in 2000, but not in other years. The sex ratio tending towards male-bias in this squirrel is discussed from a local resource competition theory.