Wing shape: Description, evolution, and correlation with ecology among North American vespertilionid bats.

Abstract

Calling different bat wing shapes adaptive demands a phylogenetic approach. This study shows that history is not responsible for the diversity of wing shapes within a small subset of the Vespertilionidae. Similar wing shapes are found on distantly related bats. In addition, these wing-shape similarities are evident using either of two methods of morphological description: principal component analysis of traditional length and area measurements, and landmark data modelled using the morphometrics of the thin-plate spline. Descriptions of wing shape are substantially improved using landmark-based morphometrics. Both the location and the degree of difference can be modelled and displayed using the thin-plate spline. Inferring shape difference from the loading patterns of a principal components analysis does not provide a description of shape with the visual clarity provided by the spline. In addition, the spline analysis provides information about both large and small scale changes on the form, which principal components cannot. Ecological features of bats show different patterns of evolution. Habitat preferences are broadly described in the literature and are difficult to characterize with specificity. Broadly defined groups (generalist forager, gleaner, high-level aerial pursuer) identify generalist foragers as the most common (but not ancestral when compared to the outgroup), with gleaners possibly paraphyletic. The evolution of prey preference, although variable within species, shows that eating Lepidoptera (moths) is pleisiomorphic and eating Coleoptera (beetles) is derived. These newer morphometric methods provide evidence for convergent morphology among species, but they are also useful for identifying geographic and sexual variation within species. In big brown bats, litter size has been shown to be correlated with the amount of sexual dimorphism between males and females. Females with larger litters were shown to be relatively larger than their resident males. In this study, I found no difference in shape between male and female wings, yet large geographical variation in both wing size and shape among three populations. Furthermore, the degree of difference between the sexes was greater where bats had smaller litters. These findings do not support the hypothesis that female E. fuscus are larger than males in order to compensate aerodynamically for the demands placed on them by carrying young.