Brazilian free-tailed bats, one of the most abundant mammals in North America, are expert flyers. They migrate hundreds of miles and regularly travel more than 30 miles a night. So researchers were surprised when their recent work uncovered a dramatic genetic rift between populations of Tadarida brasiliensis on either side of an ocean channel that cuts across the Bahamas and is just 35 miles across at its most narrow point.
“Based on their mainland population behavior, we know they’re able to disperse much farther than the distances between islands in the Caribbean,” said Kelly Speer, the study’s lead author and a student in the comparative biology doctoral program at the Museum’s Richard Gilder Graduate School, “It doesn’t seem like distance is the factor, and there’s no association with wind direction. We don’t have any idea why they don’t cross this channel.”
The research team was led by Speer while she was a master’s student at the Florida Museum of Natural History and by David Reed, Florida Museum curator of mammals and associate director of research and collections.
They sampled and compared the genetics of free-tailed bats from Florida and the Bahamas, thinking the DNA would bear out their original hypothesis: With long, narrow-tipped wings well suited for swift flight in open spaces and at high altitudes, the bats should have had no trouble spreading throughout the Bahamas.
When they sequenced a bat from one of the southern islands, however, its genetics were so different from bats on the northern islands that they thought they had tested the wrong animal. But further sampling gradually revealed a clear divide between populations on either side of the channel.
The new study, published in Ecology and Evolution, reveals that the bat populations on either side of Northwest and Northeast Providence Channels last shared an ancestor hundreds of thousands of years ago.
The bats are so genetically and morphologically distinct from one another that the populations on the southern islands may be a different species, Speer said.
“We need to do more work to confirm that, but we think the population on the southern islands might belong to a broader Caribbean species of free-tailed bat that has never been described,” she said. “The nice thing about science is that when you make a hypothesis and your data tell you it’s wrong, you still find something we didn’t know before.”