Hoary bats arrived in islands in two waves

It wasn’t just the human population of Hawaii that arrived in different waves.

A study published Wednesday found that the opeapea, or Hawaiian hoary bat, also made its way here in at least two separate migrations.

Using genetic sequencing, researchers determined the migrations were separated by nearly 9,000 years, with the most recent wave happening about 800 years ago.

“The fact that there were two different dispersals was astonishing,” said Dr. Amy Russell, an associate professor at Grand Valley State University in Michigan and lead author of “Two Tickets to Paradise: Multiple Dispersal Events in the Founding of Hoary Bat Populations in Hawaii.”

Russell and other researchers on the mainland looked at mitochondrial data to establish the “clear signal” of two genetic populations in the Hawaiian hoary bat. Field work was carried out by researchers at the Hawaii Cooperative Studies Unit at the University of Hawaii at Hilo and the U.S. Geological Survey.

The opeapea is the only land mammal endemic to the islands. Like so many other Hawaii species, it became genetically distinct from its mainland relative — in this case, the North American hoary bat — after millennia of adapting to its island environment.

“They’re purely Hawaiian,” USGS wildlife biologist and study co-author Frank Bonaccorso said. “They have sequences of DNA that are found in no hoary bats in continental North America.”

Bonaccorso’s previous research established that the tiny bat, which weighs no more than 18 grams, was nevertheless capable of making the overwater flight from the Pacific Coast. On the mainland, the North American hoary bat makes annual north-south migrations, relying on reserves of fat to sustain it on the trip.

If the bats were properly hydrated before embarking on an oceanic flight, “They could do it quite easily in two and a half to three days,” Bonaccorso said. “There are many small birds that do it all over the world; there’s no physical reason why bats that can store fats couldn’t do this.”

The first colonization took place about 10,000 years ago, according to the molecular analysis. Bats in that genetic group have a different fur color and are smaller than the North American hoary bat, Bonaccorso said.

“That lineage has diversified through natural selection and genetic drift,” he said.

Bats descended from the second migration group 800 years ago show more genetic affiliation to the mainland bat.

Genetic studies are becoming a key resource for scientists studying the opeapea because the animal is elusive in its natural habitat. The bat is on the Endangered Species List, but nobody knows for sure how many there are.

“They’re difficult species to study in the wild,” said Corinna Pinzari, a graduate student with the HCSU. “There’s a lot of work to be done understanding their biology and their ecology — I don’t think we’re going to have another group of bats flying over anytime soon.”

Pinzari is continuing the studies by looking at possible island-to-island migration and whether each island has genetically unique bat populations. Most research on existing populations has been done on the Big Island, but there are also opeapea specimens from Kauai, Oahu, and Maui included in the “Two Tickets to Paradise” work.

“Maui is a really interesting place, genetically,” Russell said. “Both of those [migration] lineages were present on Maui to a great extent, and I think that might be a key area to look at in the future.”

A complete genomic study is also in the works, to see if more differences between the ancient-descended and modern-descended bats can be found.

The discovery also holds implication for conservation efforts, since the current conservation plan doesn’t account for two different evolutionary pools.

“It opens up questions for wildlife management,” Bonaccorso said. “What’s the importance of conserving both lineages?”

E-mail Ivy Ashe at iashe@hawaiitribune-herald.com.