Molecular ecology of population crash in the sika deer.

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The objectives of the research are to examine genetic consequences of the population crash of the sika deer (Cervus nippon) on Kinkazan Island, northern Japan. We captured 130 sika deer on the island five times during two-year research period, and collected blood samples. Genetic analyses using nine microsatellite DNA markers revealed local genetic differentiation within a population ; allele frequencies differ between eastern and northwestern local groups. The result indicates that the population on Kinkazan Island is subdivided into local groups even they are not separated geographically. Individual distance is correlated to genetic relatedness measured by microsatellite markers, suggesting that not only hinds but stags are likely to be philopatric to some extent. To study the influence of population crash on the genetic diversity, we analyzed the correlation between individual heterozygosity and fitness measures such as number of offspring before and after the crash. The result showed no significant correlation between the measures, which suggest that the neutral markers such as microsatellite are not diagnostic to detect the selection that could have occurred during the crash. In the next step, therefore, we attempted to isolate novel genetic markers that are selected positively during the population crash. Blood samples collected during the field survey were preserved in RNAlater and taken to lab without freezing. RT-PCR was carried out to amplify the partial sequence of the major histocompatibility complex (MHC) gene. We successfully isolated clones of MHC-DRB exon2 sequences from several individuals. Phylogenetic analysis demonstrated that the sika deer has two paralogous MHC-DRB sequences. It is also shown that the two sequences had been diverged prior to the speciation of the sika deer and red deer. The clone we isolated for MHC-DRB will be utilized in the study of the natural selection during the population crash of the sika deer population.