Research
I. Genetic diversity and population structure of the endangered Japanese golden eagle
The Japanese golden eagle (Aquila chrysaetos japonica) is an endangered subspecies, inhabiting Japan and parts of the Korean peninsula. Their reproductive success has been declining continuously over the past decades, and there are only about 500 individuals remaining in the wild. They are also bred in captivity, as part of conservation efforts led by the Ministry of the Environment (link to site in Japanese).
My collaborators and I have been monitoring genetic diversity of Japanese golden eagles using non-invasively collected specimens from wild individuals, such as fallen feathers, pellets, and feces, in addition to blood and skin cell samples from captive individuals.
Our results from diversity analyses using mitochondrial DNA, nuclear microsatellites, and the major histocompatibility complex (MHC) gene region show that the wild population is not inbred, even when compared to non-endangered golden eagle subspecies. However both wild and captive populations had a relatively low number of alleles at neutral and functional loci, suggesting the possibility of an early population bottleneck. Wild individuals from north, central, and west Japan belong to one genetic cluster, meaning they should be treated as a single conservation unit. The captive population appeared to be genetically compatible with the wild population as well. Click here to access our paper about this project (or contact me if you would like a PDF copy!).
Long-term monitoring is necessary to detect any sudden declines in genetic diversity and changes in genetic structure. I therefore plan to continue this research and hope to apply my results towards in-situ and ex-situ conservation efforts.
II. Genetic underpinnings of reproductive success in the golden eagle
A species' survival depends strongly on its ability to produce fit offspring. Reproductive success of the Japanese golden eagles has been declining in the wild but the reasons are not clear. In captivity, breeding success is also limited to three major family lineages, despite efforts to pair individuals from various background.
As the second focus of my PhD project, I decided to study the major histocompatibility complex (MHC) gene region. The MHC region plays an important role in the immune response and mate choice in vertebrates. MHC-dependent disassortative mating has been observed in several mammal, bird, reptile, and fish species, where individuals choose mates with dissimilar MHC genotypes to maximize their offspring's immunocompetence. Using decades worth of reproduction data from 16 captive Japanese golden eagle pairs, we found that breeding success is positively correlated with dissimilarity of MHC Class II DRB alleles. This suggests that MHC-dependent disassortative mating may have fitness benefits in golden eagles. We also found the age of the male to negatively affect breeding success.
III. Population genetics/genomics of the mountain hawk eagle
The mountain hawk eagle (Nisaetus nipalensis orientalis) is another endangered apex predator inhabiting mountainous regions of Japan. Unlike the golden eagle, they can hunt in forests and prey on a wider variety of animals. Their population size is estimated at ca. 2000 individuals, but human encroachment has led to a reduction in reproductive success in the past few decades.
Although they are distributed across most of Japan (from Hokkaido to Kyushu), it is said that mountain hawk eagles do not disperse very far after fledging. To clarify conservation units and patterns of connectivity between populations, it is important to survey the genetic diversities and structures of populations across the country. In this project, I am collaborating with conservation ecologists in the field to collect and analyze samples from wild individuals. So far, I have analyzed a region of the mitochondrial DNA, and found high diversity in populations from east, west, and south Japan.
I am currently examining genome-wide single nucleotide polymorphisms (SNPs) to get a higher resolution snapshot of genetic diversity and structure.
