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Continuous phenotypic variation reflecting geographical clines can be difficult to distinguish from subspecific discontinuities when specimens are few and heterogeneously distributed. Nonetheless, increases in the holdings of museum collections over recent decades contribute to our ability to resolve more fine-scaled phenotypic gradients for many species. Although the big-eared woolly bat (Chrotopterus auritus) is not commonly encountered and thus poorly represented in museum collections, sufficient numbers have accumulated to allow an assessment of subspecific, sexual, spatial and environmental components of phenotypic variation. I examined 123 specimens from across the distribution of C. auritus and characterized the phenotype based on external, cranial and mandibular characteristics. I decomposed variation into components based on univariate and multivariate statistical analyses. All components accounted for significant phenotypic variation. Nonetheless, when examined together and after accounting for correlated variation among components, only sexual, spatial and environmental components accounted for significant unique variation. This, combined with the observation that all qualitative characteristics used to define subspecies of C. auritus can be observed throughout its geographical range, suggest that phenotypic variation is clinal and not characterized by discontinuities reflective of subspecies. Clinal variation was most strongly related to temperature and its seasonality, highlighting the important role played by these climatic characteristics in many aspects of the biology of Phyllostomidae. [ABSTRACT FROM AUTHOR]

Morphological integration of skull modules can explain the outstanding morphological diversity of the rostrum in phyllostomids, the largest radiation of bats in the Western Hemisphere. However, the covariation of the rostral and caudal modules within adaptive zones, where specializations may impose constraints on morphological diversification, remains unknown. Here we used phylogenetic linear models and accounted for phylogenetic uncertainty to examine the evolutionary relationship between brain volume—as a proxy for neurocranium size—and palate morphology in 42 species of specialized frugivores of the subfamily Stenodermatinae. We found that the palate surface area increased and became relatively wider as brain size increased. This pattern may be pervasive in frugivorous phyllostomids, although different lineages may show different rates of covariation. These results demonstrate that the tight relationship between the two main modules of the skull is consistent at different macroevolutionary scales, providing new insights into the macroevolutionary dynamics of the largest group of Neotropical frugivorous bats. [ABSTRACT FROM AUTHOR]

Divergence in acoustic signals plays an important role in the production and maintenance of biodiversity in numerous taxa. In this study, we assess patterns of acoustic divergence in geographically isolated and sympatric subspecies of barn swallows (Hirundo rustica), including analyses of whether song differentiation varies with geographical isolation, genetic distance and climatic distance. We provide the first description of geographical variation in song among five of six currently recognized barn swallow subspecies. Temporal traits describing terminal trills were the most distinct song traits among subspecies, adding to growing evidence that trills are important in speciation among many birds, insects and fish. Across a ~6000 km transect of Russia, acoustic distance was predicted by genetic and geographical distance, but not climatic distance. We also found no reproductive character displacement of song traits in a contact zone between H. r. rustica and H. r. tytleri. Based on patterns discovered in this study, we infer an important role of sexual selection, genetic and/or cultural drift in the gradual build-up of acoustic divergence, which is accelerated in small populations. [ABSTRACT FROM AUTHOR]