This article attempts to address the issue: why do some lineages consist of many species with a large degree of variation where as others have only a few species, with little variation? By using phylogenetic methods this question is investigated using large datasets on bats. This is because the order Chiroptera is one of the most diverse families of mammals and includes the family Phyllostomidae, or the leaf-nosed bat. These bats are from the New World and consist of nearly 200 species however, only include 10 species of their closest relatives were produced in the same time span. The difference between these families is that the majority of bats eat insects whilst the Phyllostomidae have a more diverse diet which includes nectar, fruit, frogs and lizards.
By looking at diet, cranial morphology and the bite force the authors were able to test the hypothesis ‘that the evolution of frugivory and a skull phenotype that improved biting performance within this feeding habit is associated with increasing diversification rates in this family’ (Dumont e al 2012). In order to test this they analysed thousands of evolutionary trees spanning over 150 species and measuring 600 bat skulls bellowing to 85 species. These bite force of 500 bats from 39 species was also tested.
The results from the research found that a new skull shape in these New World bats emerged about 15 million years ago, leading to an explosion of many new bat species. This skull was lower and broader allowing for high bite forces to be produced, even for small bats. This increase in bite force is needed in order to process hard fruits. As a new ecological niche could be exploited and as the new skull shape evolved there was an increase in the birth rate of new species.
These ‘morphological innovations’ allows for resources to be exploited and therefore an increase in the evolution of new species. This new skull phenotype led to the evolution of frugivory and a higher degree of speciation within the phyllostomids. This is a lovely example of how new species can arise in the response to exploiting a new resource.
University of Massachusetts at Amherst. “Studying bat skulls, evolutionary biologists discover how species evolve.” ScienceDaily. ScienceDaily, 28 November 2011. <www.sciencedaily.com/releases/2011/11/111123133520.htm>.
Elizabeth R. Dumont, Liliana M. Dávalos, Aaron Goldberg, Sharlene E. Santana, Katja Rex, and Christian C. Voigt (2012) ‘Morphological innovation, diversification and invasion of a new adaptive zone’ in Proc. R. Soc. B 279 1734 1797-1805; published ahead of print November 23, 2011, doi:10.1098/rspb.2011.2005 1471-2954