title: Tempo of speciation in a butterfly genus from the Southeast Asian tropics, inferred from mitochondrial and nuclear DNA sequence data.
abstract: Molecular systematics is frequently beset with phylogenetic results that are not fully resolved. Researchers either state that the absence of resolution is due to character conflict, explosive speciation, or some combination of the two, but seldom do they carefully examine their data to distinguish between these causes. In this study, we exhaustively analyze a set of nuclear and mitochondrial nucleotide data for the Asian tropical butterfly genus Arhopala so as to highlight the causes of polytomies in the phylogenetic trees, and, as a result, to infer important biological events in the history of this genus. We began by using non-parametric statistical methods to determine whether the ambiguously resolved regions in these trees represent hard or soft polytomies. In addition we determined how this correlated to number of inferred changes on branches, using parametric maximum likelihood estimations. Based on congruent patterns in both mitochondrial and nuclear DNA sequences, we concluded that at two stages in the history of Arhopala there have been accelerated instances of speciation. One event, at the base of the phylogeny, generated many of the groups and subgroups currently recognized in this genus, while a later event generated another major clade consisting of both Oriental and Papuan species groups. Based on comparisons of closely related taxa, the ratio of instantaneous rate of evolution between mitochondrial and nuclear DNA evolution is established at approximately 3:1. The earliest radiation is dated between 7 and 11 Ma by a molecular clock analysis, setting the events generating much of the diversity of Arhopala at well before the Pleistocene. Periodical flooding of the Sunda plateau during interglacial periods was, therefore, not responsible for generating the major divisions in the genus Arhopala. Instead, we hypothesize that large-scale climatic changes taking place in the Miocene have induced the early acceleration in speciation.
authors.affiliation: Institute of Evolutionary and Ecological Sciences, Leiden University, Leiden, The Netherlands. hendrik-jens.megens@wur.nl
authors.forename: Hendrik-Jan
authors.initials: HJ
authors.lastname: Megens
authors.forename: Coline H M
authors.initials: CH
authors.lastname: van Moorsel
authors.forename: William H
authors.initials: WH
authors.lastname: Piel
authors.forename: Naomi E
authors.initials: NE
authors.lastname: Pierce
authors.forename: Rienk
authors.initials: R
authors.lastname: de Jong
mesh_terms: D000818:Animals; D001210:Asia, Southeastern; D001483:Base Sequence; D002080:Butterflies / Q000235:genetics*; D002467:Cell Nucleus / Q000235:genetics* / Q000378:metabolism; D004272:DNA, Mitochondrial; D019143:Evolution, Molecular; D016013:Likelihood Functions; D008928:Mitochondria / Q000378:metabolism; D008969:Molecular Sequence Data; D010802:Phylogeny; D013045:Species Specificity; D013998:Time Perception
chemical_list: D004272:DNA, Mitochondrial