MBE Advance Access published online on October 13, 2004
Molecular Biology and Evolution, doi:10.1093/molbev/msi016
Molecular Biology and Evolution © Society for Molecular Biology and Evolution 2004; all rights reserved
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1 Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan
* To whom correspondence should be addressed. E-mail: yudai{at}sys.bot.kyoto-u.ac.jp.
Interspecific hybridization is one of the major factors leading to phylogenetic incongruence among loci, but the knowledge is still limited about the potential of each locus to introgress between species. By directly sequencing three DNA regions: chloroplast DNAs (matK gene and trnL-F noncoding region), nuclear ribosomal external transcribed spacer (ETS) region, and internal transcribed spacer (ITS) regions, we construct three phylogenetic trees of Asian species of Mitella (Saxifragaceae), a genus of perennials in which natural hybrids are commonly observed. Within this genus, there is a significant topological conflict between chloroplast and nuclear phylogenies, and also between the ETS and ITS ones, which can be attributed to frequent hybridization within the lineage. Chloroplast DNAs show the most extensive introgression pattern, ITS regions show a moderate pattern, and ETS region shows no evidence of introgression. Nonuniform concerted evolution best explains the difference in the introgression patterns between the ETS and ITS regions, as the sequence heterogeneity of the ITS region within an individual genome is estimated to be twice that of an ETS in this lineage. Significant gene conversion patterns between two hybridizing taxa were observed in contiguous arrays of cloned ETS-ITS sequences, further confirming that only ITS regions have introgressed bidirectionally. The relatively slow concerted evolution in the ITS regions probably allows the coexistence of multiple alleles within a genome, whereas the strong concerted evolution in the ETS regions rapidly eliminates heterogeneous alleles derived from other species, resulting in species delimitations highly concordant with those based on morphology. This finding indicates that the use of multiple molecular tools has the potential to reveal detailed organismal evolution processes involving interspecific hybridization, as individual loci vary greatly in its potential to introgress between species.
Research Article
Nonuniform Concerted Evolution and Chloroplast Capture: Heterogeneity of Observed Introgression Patterns in Three Molecular Data Partition Phylogenies of Asian Mitella (Saxifragaceae)
2 Makino Herbarium, Graduate School of Science, Tokyo Metropolitan University, Hachioji, Japan
3 Department of Biology, Aichi University of Education, Kariya, Japan
4 Department of Botany, Graduate School of Science, Kyoto University, Kyoto, Japan
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