Hurricanes Blow Away Bats, Spread Genes to New Islands

Matt Kaplan
for National Geographic News
November 25, 2008
Strong hurricanes have been known to wipe out bird and bat populations, but a new study has discovered a silver lining in those storm clouds.

Hurricanes may actually blow helpless bats in the Caribbean from one island to another, eventually reconnecting geographically isolated species and boosting genetic diversity, the research found.

"After Hurricane Ivan slammed into the West Indies, we were not particularly surprised to find bat populations depressed," said study lead author Ted Fleming at the University of Miami in Florida.

"With such powerful winds, there was going to be high mortality, but we never expected to find what we found."

Fleming and colleague Kevin Murray analyzed bat species in the West Indies before and after Hurricane Ivan slammed into the region in 2004.

The team used nets and tools to collect small bits of live bats' wing tissue for DNA analysis.

While all species showed population declines following the event, one population of the common fruit bat on Grand Cayman Island actually showed an increase in genetic diversity.

(Related: "Katrina, Rita Actually Helped Wetlands, Study Says" [September 21, 2006].)

The results will appear in the journal Biotropica in January 2009.

Winds of Change

Before the storm, only one genetic variant of the fruit bat was common on Grand Cayman, Fleming said, but afterward, two other variants appeared.

The only other island where these different bats lived was Cayman Brac, 87 miles (140 kilometers) away.

There is little chance that the bats voluntarily flew this distance over water, the team said, which suggests that the hurricane literally picked up a few bats off Cayman Brac and plopped them on Grand Cayman.

"When you hear about winds distributing animals, it is typically anecdotal," Fleming said.

"We got lucky and just happened to be analyzing the right animals at the right time."

Genetic diversity is important for keeping animal populations robust. For example, if a population has little genetic variation, offspring become weaker and may eventually become inbred.

Biologist Scott Pedersen at South Dakota State University in Brookings was not involved in the study.

"It's good work and is a very welcome bit of data that we all pretty much suspected, [because] our own radio-tracking shows that bats are not moving amongst islands on their own," Pedersen said.

Perfect Storm

Fleming cautioned that hurricanes do not always have this distributing effect.

In the Bahamas, for instance, bats did not become more genetically diverse after Hurricanes Frances and Jeanne.

Clearly, a perfect storm of factors—the right bat populations on the right islands in the right storm—must exist for hurricanes to help bats.

"It looks like it takes really powerful storms to get the job done," added South Dakota State's Pedersen.

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