Origins of the Hawaiian Hoary Bat Revealed

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ISLAND OF HAWAI‘I, Hawaii — The use of sophisticated DNA sequencing by a team of scientists has determined that Hawaii's state land mammal, the Hawaiian hoary bat, migrated to the islands from the Pacific coast of North America in two separate waves more than 9,000 years apart.

“Because the Hawaiian hoary bat is the only living native land mammal in Hawai‘i and is on the U.S. Fish and Wildlife Service’s endangered species list we want to know everything possible about its genetic history, relationships to other bats, and if there are unique subpopulations on different Hawaiian islands,” said Dr. Amy Russell, Associate Professor of Biology at Grand Valley State University and lead author of the study.

This feat represents the longest overwater flight followed with the founding of a new population for any bat, of which there are 1300 species.  The new study estimates that these migrations from mainland North America happened around 800 years ago and 10,000 years ago. 

Until recently, little was known about the genetics or ecology of Hawai‘i’s only native terrestrial mammal, and while many questions still remain this study provides insight previously not possible using just morphology or fossil data. “We used tiny bits of wing tissue and powerful DNA sequencing and analytical tools to estimate both the time and place of origin for this unique and cryptic mammal,” said Dr. Kevin Olival, Senior Research Scientist at EcoHealth Alliance and study co-author.

DNA sampling of Hawaiian hoary bats for conservation genetics studies began in 2004 and is ongoing. “Future genetic studies will also help us to better understand local population structure and the potential for bat migration between islands of the archipelago,” said Corinna Pinzari, a researcher with the Hawaii Cooperatives Studies Unit at the University of Hawai‘i at Hilo.

Frank Bonaccorso, a wildlife ecologist from the U.S. Geological Survey, and colleague Liam McGuire now at Texas Tech University had previously modeled the path that hoary bats might have taken in a successful colonization flight scenario, and found that the shortest possible flight distance from San Francisco to Maui, approximately 3,600 kilometers, is highly feasible with normal tailwind assistance from the prevalent Trade Winds. This flight to Hawai‘i would only have required that the bat had stored the normal complement of fat that hoary bats accumulate for their annual migration through North America. While long-distance overwater colonization might seem unlikely, it actually happened once before with another bat species that went extinct in the islands a few thousand years ago.

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“Our present findings will be useful for the re-evaluation of the bat’s conservation status,” said Bonaccorso, a co-author on the study, “because we demonstrate that there are two evolutionarily distinct groups of Hawaiian hoary bats with one group a more ancient arrival.”

“This is another example of how basic research can provide valuable information that is relevant for conservation and management” said Dr. Maarten Vonhof, an Associate Professor of Biological Sciences and Environmental and Sustainability Studies at Western Michigan University and a study co-author, “Asking questions about the distribution of genetic variation and the number of unique lineages is fundamental to our understanding of the biology and conservation of this endangered animal.”

The Hawaiian Islands are extremely isolated, and their wildlife has long served as a model for scientists to determine how birds, insects, and snails disperse into areas like this. Due to their isolation, all native plant and animal species originally colonized the Hawaiian Islands by long-distance dispersal via sea or air. For example, seeds or small animals may have hitched a ride on ocean debris, attached to bird feathers or feet, or drifted by air currents (spiders and very small insects).

The journal article “Two Tickets to Paradise: Multiple Dispersal Events in the Founding of Hoary Bat Populations in Hawai'i” was published today by the journal PLOS ONE. Researchers contributing to this effort represent the following institutions: Grand Valley State University, University of Hawai'i at Hilo, Western Michigan University, EcoHealth Alliance, U.S. Geological Survey.