An international team of genetic researchers has sequenced and analyzed the complete genomes of three separate populations of aye-ayes (Daubentonia madagascariensis), a type of lemur that is found only on the island of Madagascar.
The aye-aye has a long, thin, and flexible middle finger to extract insect larvae from trees, filling the ecological niche of a woodpecker (Edward Louis / Omaha Zoo)
“The aye-aye is one of the world’s most unusual and fascinating animals,” said Prof George Perry from Penn State University, lead author of a paper reporting the results of the genome-sequence analyses in the Proceedings of the National Academy of Sciences.
“Aye-ayes use continuously growing incisors to gnaw through the bark of dead trees and then a long, thin, and flexible middle finger to extract insect larvae, filling the ecological niche of a woodpecker. Aye-ayes are nocturnal, solitary, and have very low population densities, making them difficult to study and sample in the wild.”
Prof Perry added that he and other scientists are concerned about the long-term viability of aye-ayes as a species, given the loss and fragmentation of natural forest habitats in Madagascar.
“Aye-aye population densities are very low, and individual aye-ayes have huge home-range requirements. As forest patches become smaller, there is a particular risk that there won’t be sufficient numbers of individual aye-ayes in a given area to maintain a population over multiple generations. We were looking to make use of new genomic-sequencing technologies to characterize patterns of genetic diversity among some of the surviving aye-aye populations, with an eye towards the prioritization of conservation efforts.”
The scientists worked to locate aye-ayes and collect DNA samples from three separate regions of Madagascar: the northern, eastern, and western regions. To discover the extent of the genetic diversity in present-day aye-ayes, they generated the complete genome sequences of 12 individual aye-ayes. They then analyzed and compared the genomes of the three populations.
They found that, while eastern and western aye-ayes are somewhat genetically distinct, aye-ayes in the northern part of the island and those in the east show a much more significant amount of genetic distance, suggesting an extensive period of time during which interbreeding has not occurred between the populations in these regions.
Aye-ayes in the northern part of the island of Madagascar show a significant amount of genetic distance from the populations in the east and west, suggesting an extensive period of time during which northern aye-ayes have not interbred with other populations (Edward Louis / Omaha Zoo)
“Our next step was to compare aye-aye genetic diversity to present-day human genetic diversity,” said Prof Webb Miller, also from Penn State University. “This analysis can help us to gauge how long the aye-aye populations have been geographically separated and unable to interbreed.”
To make the comparison, the team gathered 12 complete human DNA sequences – the same number as the individual aye-aye sequences generated – from publicly available databases for three distinct human populations: African agriculturalists, individuals of European descent, and Southeast Asian individuals. Using Galaxy – an open-source, web-based computer platform designed at Penn State for data-intensive biomedical and genetic research – the team developed software to compare the two species’ genetic distances. They found that present-day African and European human populations have a smaller amount of genetic distance than that found to exist between northern and eastern aye-aye populations, suggesting that the aye-aye populations were separated for an especially lengthy period of time by geographic barriers.
“We believe that northern aye-ayes have not been able to interbreed with other populations for some time. Although they are separated by a distance of only about 160 miles, high and extensive plateaus and major rivers may have made intermingling relatively infrequent,” Prof Miller said. “The results of the team’s data further suggest that the separation of the two aye-aye populations stretches back much longer than 2,300 years, which is when human settlers first arrived on the island and started burning the aye-ayes’ forest habitat and hunting lemurs.”
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Bibliographic information: George H. Perry et al. Aye-aye population genomic analyses highlight an important center of endemism in northern Madagascar. PNAS, published online before print March 25, 2013; doi: 10.1073/pnas.1211990110
