MBE Advance Access published online on April 9, 2008
Molecular Biology and Evolution, doi:10.1093/molbev/msn086
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Research Article |
Unequal Rates of Y chromosome Gene Divergence during Speciation of the Family Ursidae
1 Division of Biological Science, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan
2 Laboratory of Genomic Diversity, National Cancer Institute-Frederick, Frederick, MD, 21782 USA
3 Department of Genome Dynamics, Creative Research Initiative "Sousei", Hokkaido University, Sapporo 060-0810, Japan
* Corresponding author: Tel/ Fax. +81-11-706-3588 E-mail: masudary{at}ees.hokudai.ac.jp
Received for publication March 11, 2008. Accepted for publication March 26, 2008.
Evolution of the bear family Ursidae is well investigated in terms of morphological, paleontological, and genetic features. However, several phylogenetic ambiguities occur within the subfamily Ursinae (the family Ursidae excluding the giant panda and spectacled bear), which may correlate with behavioral traits of female philopatry and male-biased dispersal which form the basis of the observed matriarchal population structure in these species. In the process of bear evolution, we investigate the premise that such behavioral traits may be reflected in patterns of variation among genes with different modes of inheritance: matrilineal mitochondrial DNA (mtDNA), patrilineal Y-chromosome, biparentally inherited autosomes, and the X-chromosome. In the present study, we sequenced three Y-linked genes (3,453 bp) and four X-linked genes (4,960 bp), and re-analyzed previously published sequences from autosome genes (2,347 bp) in ursid species to investigate differences in evolutionary rates associated with patterns of inheritance. The results describe topological incongruence between sex-linked genes and autosome genes, and between nuclear DNA and mtDNA. In more ancestral branches within the bear phylogeny, Y-linked genes evolved faster than autosome and X-linked genes, consistent with expectations based on male-driven evolution. However, this pattern changes among branches leading to each species within the lineage of Ursinae whereby the evolutionary rates of Y-linked genes have fewer than expected substitutions. This inconsistency between more recent nodes of the bear phylogeny with more ancestral nodes may reflect the influences of sex-biased dispersal, as well as molecular evolutionary characteristics of the Y-chromosome, and stochastic events in species natural history and phylogeography unique to ursine bears.
Key Words: Ursidae • sex-linked genes • male-biased dispersal • female philopatry • matriarchal structure
Current address: Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Kashiwa 277-8562, Japan