Abstract
Among Vespertilionidae species, sexual size dimorphism is very well documented, in which females are larger than males. The differences are mainly in body weight, skull measurements and forearm length. Studies have discussed some hypothesis for this phenomenon. However, very little information is known about sexual size dimorphism in Myotis nigricans (Schinz, 1821) in Brazil. In this sense, the goal of this paper is to present a study of this phenomenon in the species. For this, we present a quantitative analysis of sexual size dimorphism assessed by traditional morphometrics. Ten skull measurements in addition to the forearm length of adult specimens were taken. Results of traditional morphometrics revealed sexual size dimorphism in five skull measurements and in the forearm length. Females were larger than males. These differences can be attributed to natural selection on large female size for increase fecundity. Bat females of the Vespertilionidae family are usually larger than males in order to perform parental care appropriately and to provide a successful reproductive process.
Highlights
Among Chiroptera, mouse-eared bats (Myotis, Vespertilionidae) represent the largest genus, with more than 100 species worldwide (Simmons, 2005)
Multivariate analysis of the Principal Components was not sensitive enough to detect sexual dimorphism, and no a priori group formed by gender was detected
There is a trend demonstrated by the regression of the Principal Component Analysis (PCA) residuals against the logarithm from the forearm length, suggesting that size (PC1) covariates with the forearm length (Figure 3)
Summary
Among Chiroptera, mouse-eared bats (Myotis, Vespertilionidae) represent the largest genus, with more than 100 species worldwide (Simmons, 2005). Myotis is distributed in all continents (except the Antarctic), from the boreal to sub-Antarctic zones, tropical rain forests, or semi-desert habitats. Ruedi and Mayer (2001) concluded that the numerous species of Myotis suffered independent evolution in the different biogeographic regions with subsequent convergent adaptive radiation. The same ecomorph appears to have evolved several times independently (Ruedi and Mayer, 2001). The genus represents one of the most diverse and successful radiations even among mammals
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