Epigenetic Asymmetry as an Ecological Indicator in Muskrats

Abstract

Fluctuating asymmetry in numbers of nerve foramina in the skull was studied in nine Finnish populations of the muskrat, Ondatra zibethicus (n = 555). A high negative correlation (r =−0.94) was found between the population means of asymmetry and suitability of habitat as reflected in growth indices (carcass weight/age) of the animals. This relationship is weaker among individuals within populations. The results support the idea of stress-induced interference in the synchronization of normal ontogeny of bilaterally symmetric structures during embryonic or suckling stages, although this still needs to be confirmed experimentally. Genetic differences among populations seem improbable as an explanation of fluctuating asymmetry.