Bats are a diverse bunch, making up one of the largest groups of mammals with more than 1,300 species worldwide. Up close, bat species look quite different from one another. While some have significant eras, other sport elaborate noses or long jaws. Bats have so many morphological varieties, and they represent an opportunity to learn what types of evolutionary forces shape the shape of animals.
In a paper published in Nature Communications, a group of biologists at the University of Washington has been using bats to do just that. Postdoctoral researchers Jessica Arbour and Abigail Curtis, and Sharlene Santana, UW associate professor of biology and curator of mammals at the UW's Burke Museum of Natural History and Culture, focused on the diversity among bat skulls.
The team performed high-resolution microCT scans of the skulls of more than 200 bat species. They used the scans as well as information on the evolutionary relationships among at species to analyze the types of physical changes that evolved in bat skulls over tens of millions of years and correlate them with specific events in bat evolution including when a lineage switched diets or adapted to a new ecological niche. The outcome of the researchers' study reported that two major forces had shaped bat skulls over their evolutionary history and they are echolocation and diet. The team was even able to determine when in the past these forces were dominant.
Santana explained that their research sought to address a significant question about the evolution of diversity in the bat skull. What defines the large number of differences that they observed in the skull shape? They discovered that echolocation is a major, and ancient, contributor to skull shape. Diet is also essential but generally more recent.
The analyses of the team indicated that early in the evolution of the bat, from about 58 million to 34 million years ago, echolocation was a primary driver of skull shape across bat families. They also found that starting from about 26 million years ago, the diet became the more dominant driving force behind skull shape evolution, but not in all bats.
Santana maintained that the leaf-nosed bats stand out for their extraordinary diversity in skull shape and diet. Over a relatively short period, they evolved a suite of skull adaptation as they radiated into different dietary niches.
The researchers are continuing this work as part of a more considerable effort funded by the National Science Foundation to compare the evolutionary forces that shape skull diversity among different groups of mammals such as bats, primates and carnivores.
