title: Spatial and temporal variation at major histocompatibility complex class IIB genes in the endangered Blakiston's fish owl.
abstract: BACKGROUND
  Quantifying intraspecific genetic variation in functionally important genes, such as those of the major histocompatibility complex (MHC), is important in the establishment of conservation plans for endangered species. The MHC genes play a crucial role in the vertebrate immune system and generally show high levels of diversity, which is likely due to pathogen-driven balancing selection. The endangered Blakiston's fish owl (Bubo blakistoni) has suffered marked population declines on Hokkaido Island, Japan, during the past several decades due to human-induced habitat loss and fragmentation. We investigated the spatial and temporal patterns of genetic diversity in MHC class IIβ genes in Blakiston's fish owl, using massively parallel pyrosequencing.
  
  
  RESULTS
  We found that the Blakiston's fish owl genome contains at least eight MHC class IIβ loci, indicating recent gene duplications. An analysis of sequence polymorphism provided evidence that balancing selection acted in the past. The level of MHC variation, however, was low in the current fish owl populations in Hokkaido: only 19 alleles were identified from 174 individuals. We detected considerable spatial differences in MHC diversity among the geographically isolated populations. We also detected a decline of MHC diversity in some local populations during the past decades.
  
  
  CONCLUSIONS
  Our study demonstrated that the current spatial patterns of MHC variation in Blakiston's fish owl populations have been shaped by loss of variation due to the decline and fragmentation of populations, and that the short-term effects of genetic drift have counteracted the long-term effects of balancing selection.
authors.affiliation: Department of Natural History Sciences, Faculty of Science, Hokkaido University, Sapporo, 060-0810 Japan.
authors.forename: Tetsuo I
authors.initials: TI
authors.lastname: Kohyama
authors.affiliation: Department of Natural History Sciences, Graduate School of Science, Hokkaido University, Sapporo, 060-0810 Japan.
authors.forename: Keita
authors.initials: K
authors.lastname: Omote
authors.affiliation: Department of Natural History Sciences, Faculty of Science, Hokkaido University, Sapporo, 060-0810 Japan.
authors.forename: Chizuko
authors.initials: C
authors.lastname: Nishida
authors.affiliation: FILIN, Hachiken 2 Jo Nishi 2, Nishi-ku, Sapporo 063-0842 Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Takenaka
authors.affiliation: Institute for Raptor Biomedicine, Kushiro, 084-0922 Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Saito
authors.affiliation: Kushiro Zoo, Kushiro, 085-0201 Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Fujimoto
authors.affiliation: Department of Natural History Sciences, Faculty of Science, Hokkaido University, Sapporo, 060-0810 Japan.
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Masuda
keywords: Balancing selection; Bubo blakistoni; Genetic drift; MHC class IIβ; Pyrosequencing