Abstract
BackgroundThe phyllostomid bats present the most extensive ecological and phenotypic radiation known among mammal families. This group is an important model system for studies of cranial ecomorphology and functional optimisation because of the constraints imposed by the requirements of flight. A number of studies supporting phyllostomid adaptation have focused on qualitative descriptions or correlating functional variables and diet, but explicit tests of possible evolutionary mechanisms and scenarios for phenotypic diversification have not been performed. We used a combination of morphometric and comparative methods to test hypotheses regarding the evolutionary processes behind the diversification of phenotype (mandible shape and size) and diet during the phyllostomid radiation.ResultsThe different phyllostomid lineages radiate in mandible shape space, with each feeding specialisation evolving towards different axes. Size and shape evolve quite independently, as the main directions of shape variation are associated with mandible elongation (nectarivores) or the relative size of tooth rows and mandibular processes (sanguivores and frugivores), which are not associated with size changes in the mandible. The early period of phyllostomid diversification is marked by a burst of shape, size, and diet disparity (before 20 Mya), larger than expected by neutral evolution models, settling later to a period of relative phenotypic and ecological stasis. The best fitting evolutionary model for both mandible shape and size divergence was an Ornstein-Uhlenbeck process with five adaptive peaks (insectivory, carnivory, sanguivory, nectarivory and frugivory).ConclusionsThe radiation of phyllostomid bats presented adaptive and non-adaptive components nested together through the time frame of the family's evolution. The first 10 My of the radiation were marked by strong phenotypic and ecological divergence among ancestors of modern lineages, whereas the remaining 20 My were marked by stasis around a number of probable adaptive peaks. A considerable amount of cladogenesis and speciation in this period is likely to be the result of non-adaptive allopatric divergence or adaptations to peaks within major dietary categories.
Highlights
The phyllostomid bats present the most extensive ecological and phenotypic radiation known among mammal families
Structure of morphological and dietary variation The distribution of dietary preferences along the phylogenetic tree of phyllostomids (Figure 1) indicate that most dietary shifts occurred only once during the evolution of the family, but nectarivory seems to have evolved twice independently and a return to insectivory is observed in the ancestor of Trinycteris and Glyphonycteris
A principal component analysis (PCA) of dietary preferences, shows a strong correlation between carnivory and insectivory as a feature of the first diet principal components (PCs), suggesting that they might be considered a single group of animalivores
Summary
The phyllostomid bats present the most extensive ecological and phenotypic radiation known among mammal families. The Phyllostomidae (leaf-nosed bats) is the dominant family of bats in Central and South America This family has undergone an adaptive radiation unparalleled among other mammals in terms of ecological and morphological diversity [1]. Starting from an insectivore ancestor in the late Eocene [2,3,4], the 53 extant genera in this family have diversified into specialized forms for insectivory, carnivory, frugivory, granivory, nectarivory, and sanguivory ( many species have mixed diets) [5,6,7] This ecological diversity and specialisation originates from an intricate partitioning of resources [8,9], and is probably responsible for the high local species richness (ranging between 31-49 syntopic species [10,11]) observed for leaf-nosed bats. The feeding behaviour is relevant to the understanding of the biomechanics of feeding and resource partitioning in bats [14,20], but is less studied than morphology
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