Abstract
BackgroundClimatic changes during glacial periods have had a major influence on the recent evolutionary history of living organisms, even in temperate forests on islands, where the land was not covered with ice sheets. We investigated the phylogeographical patterns of the weevil Curculio sikkimensis (Curculionidae), a generalist seed predator of Fagaceae plants living in both deciduous oak and evergreen forests of Japan. Its genetic structure was compared to that of another host-specific seed predator, C. hilgendorfi, inhabiting only evergreen forests.ResultsWe examined 921 bp of mitochondrial DNA for 115 individuals collected from 33 populations of C. sikkimensis from 11 plant species of three genera, Quercus, Lithocarpus, and Castanopsis. An analysis of molecular variance revealed that a large proportion (almost 50%, P < 0.001) of the total genetic variance could be explained by differences between two geographical regions, the southwestern and northeastern parts of the main islands of Japan. In contrast, no significant genetic differentiation of the weevil was observed among vegetation types of their utilized host plant species. The phylogeographical patterns of the generalist and the host-specific seed predator exhibited a congruent genetic boundary in the Chugoku-Shikoku region.ConclusionOur results suggest that geology and historical environment have contributed to shaping the present genetic structure of C. sikkimensis. The geographical patterns of genetic differentiation in the Chugoku-Shikoku region observed in the two types of Fagaceae-associated Curculio in this study have also been observed in several plant species growing in warm and cool temperate zones of Japan. The occurrence of this common pattern suggests that deciduous oak and evergreen forests of Japan survived together, or adjacent to each other, in small refugia during glacial ages, in the southwestern and northeastern parts of the main islands, although these two types of forests are presently distributed in cool and warm temperate zones of Japan, respectively.
Highlights
Climatic changes during glacial periods have had a major influence on the recent evolutionary history of living organisms, even in temperate forests on islands, where the land was not covered with ice sheets
Phylogeographical patterns in C. sikkimensis The observed gap between the SW and NE clades with respect to the mitochondrial DNA (mtDNA) sequences of C. sikkimensis (Fig. 1) suggests that the southwestern and northeastern insect populations have been isolated for a long time, probably through several glacial and interglacial periods; the genetic groups have not been in contact for several thousands of years since the last glacial period; and long-distance migration of the weevil has been rare, resulting in negligible interpopulation genetic exchange events
Our data suggest that geology and historical environment have contributed to shaping the recent genetic structure of C. sikkimensis in temperate forests of Japan
Summary
Climatic changes during glacial periods have had a major influence on the recent evolutionary history of living organisms, even in temperate forests on islands, where the land was not covered with ice sheets. The current distribution of biological diversity cannot be understood without information about how organisms responded to historical geological and climatic conditions. BMC Evolutionary Biology 2009, 9:103 http://www.biomedcentral.com/1471-2148/9/103 shaping the distribution of biodiversity among current populations, even in warm temperate zones, where the land was not covered with ice sheets [1,2]. Several landbridges between Japan and surrounding areas, which formed or disappeared in response to glacial-interglacial climatic changes, have played important roles in determining the current distribution of Japanese biological diversity
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