Charles Darwin, known for his contributions to evolutionary theory, would have turned 205 years old this month. While his description of natural selection certainly sealed his place in history, he was by no means the first to study evolution and definitely not the last.

Dr. Liliana Dávalos studies natural selection in bats in the Department of Ecology and Evolution here at Stony Brook University .

There are over 1200 different species of bats, and nearly 70 percent of these species survive on insects.  Only two groups have evolved to eat plants, making these bats very unusual.

The New World leaf-nosed bats are one of these groups.  Found from Arizona to Argentina and comprised of approximately 150 different species, this group of bats is very diverse. Dávalos wants to know if this diversity is due to random genetic changes or directed changes resulting from natural selection.

As described in their recent study published in Evolution, Dávalos and her colleagues at the University of Massachusetts Amherst tackled this problem on two fronts.

First, they engineered a computer program that allowed them to model the skulls of 85 different species of New World leaf-nosed bats. The program not only allowed them to look at the physical representations of the skull, but also to calculate the mechanics of the skull and the power of the bats’ bite.

Second, the diets of each of these bat species were studied and then compared to the information on skull mechanics determined by the computer program.

Dávalos and her colleagues found that based on their diets and bite force, the 85 species of bats can be clearly sorted into three groups. At two extremes are the groups that have incredibly weak and incredibly strong bite force.

Those with weak bite force are the bats whose diets consist of nectar and subsequently have very long, skinny snouts—similar to a hummingbird’s beak. The low mechanical advantage of the skull is traded for the skinny snout that allows it to feed on nectar.

At the other extreme are the approximately eight different species of what are known as short-faced bats, whose skulls feature very high mechanical advantage. Their snouts are incredibly short and wide and their skulls provide them with a powerful bite, allowing them to eat very hard things like figs. This makes them part of the rare group of bats that have evolved to eat plants.

The rest of the 85 species studied fit into the third group, which sits in between the two extremes and survives mainly on insects.

That these bat species clearly fit into three categories based on the mechanical advantage of the skull—or, the strength of the bite—suggests that the diversity of the New World leaf-nosed bats is not due to randomness, but due to natural selection and skull mechanics in particular.

Moreover, this evolution took place over a rather short period of time. “The evolution of the short-faced bat alone has occurred over only approximately 10 million years,” Dávalos said.

The next question Dávalos would like to answer is why so few bats have evolved to eat plants. Are there mechanical limitations?  Are there issues with incorporating new foods into the diet? Further, she would like to determine whether the bats’ genes reflect natural selection the way their anatomy so clearly does.

The next step Dávalos and her colleagues plan to take is to improve the computer model of the bat skulls, programming it to incorporate even more species and providing this field with a very powerful research tool.