Morphometric study of sex differences and static variation in the skull of Indochinese ground squirrel, Menetes berdmorei (Rodentia: Sciuridae)

Abstract

Sexual dimorphism, a common morphological phenomenon in rodents, has often been explained as the result of both sexual and natural selection. However, few studies have focused on detailed patterns of sexual dimorphism in squirrels. In this study, we investigated the patterns of sex differences and static variation in the skull of Indochinese ground squirrel (Menetes berdmorei) using linear morphometrics. A total of 24 adult skulls (15 males and 9 females) were measured, of which males showed slightly larger mean size in 19 measurements. Univariate analyses demonstrated significant differences between the sexes in few variables, while discriminant analysis indicated well distinctiveness in craniomandibular morphology. The coefficient of variation showed an inverse relationship with the mean values of skull traits. This trend might be caused by real biological phenomena, as previously reported in several studies. Although coefficient of variation tended to be larger in anterior part of the viscerocranium and smaller in posterior of the neurocranium, similar variability patterns were observed in most of the skull trails. These trends were also supported by the alternative index of the coefficient of variation and coefficients of bivariate allometry. Even though, existence of developmental factors is suggested by the patterns of variability, higher integration is denoted in major subdivisions of the skull. In conclusion, our results demonstrate a slight male-biased sexual size dimorphism in M. berdmorei. Besides, variability patterns might indicate higher morphological integration in major components of the skull.