TREEセミナー＠東邦大学理学部

石田　聖二　Seiji ISHIDA
Department of Biology, University at Buffalo, The State University of New York

要旨(発表は日本語です)

Quaternary glacial cycles have drastically changed the Holarctic biota. However, the effect of glaciation as a source of biodiversity remains unclear for most of taxonomic groups. Here we assess the effects of glaciation on the evolution of Holarctic Daphnia. First, I addressed the systematic biology of the subgenus Daphnia, and estimated the phylogenetic position of D. curvirostris by performing the combination of genetical and morphological analyses. The Japanese 'curvirostris' was found to be a new divergent lineage in the subgenus Daphnia and possess distinctive morphological characteristics from D. curvirostris in Europe and North America. Second, I assessed the effects of glaciation on Daphnia galeata with apparently marked dispersal capacity and a widespread hybrid lineage in North America. I analyzed the samples of this species from 148 Holarctic lakes using the nuclear and mitochondrial gene sequences, and tested predictions for hypotheses that account for the origin and spread of North American D. galeata. The genetic results supported the hypothesis that North American D. galeata underwent introgression with the native lineages of Daphnia rosea s.l., with dispersal being enhanced by glaciations. Finally, I addressed the history of population differentiation and ongoing gene flow in Daphnia rosea s.l., by comparing population and regional divergences in mature unglaciated areas with younger previously glaciated areas. I analyzed the sample of this species complex from 84 Holarctic lakes and ponds using the nuclear and mitochondrial gene sequences, and examined the timing and paths of colonization in previously-glaciated areas to assess the dispersal limitations of D. rosesa s.l. Mitochondrial phylogeny revealed three geographically restricted and divergent clades: European; Siberian; and Japanese/American. The Japanese/ American clade showed marked population genetic structure that was weakly associated with geographical distance. The evidence agrees with negligible gene flow after founding, and the accumulation of genetic divergence with habitat age. My results consistently showed that older unglaciated habitats have preserved ancient lineages, and agreed with the accumulation of genetic divergence with habitat age. Widespread geographical sampling is critical to understand Holarctic diversity. The primacy of local selective regimes has implications for population genetics and conservation biology.


セミナーでは，周北極地域のミジンコの分布が氷河期の影響をどのように受けてきたかについて，分子系統情報を用いて検証した研究の話をして頂きます。時空間スケールのとても大きな話で、生物の分布、進化について考えさせられる興味深い内容です。皆様、ぜひご来聴ください。なおご講演は日本語で行われます。

2007年11月6日のポスター