Colonization and diversification of the species Brachyderes rugatus (Coleoptera) on the Canary Islands: evidence from mitochondrial DNA COII gene sequences.

The genus Brachyderes Schönherr (Coleoptera: Curculionidae) is represented by the species B. rugatus Wollaston on the Canary Islands, with one subspecies on each of the islands of Gran Canaria, Tenerife, La Palma, and El Hierro. These four subspecies are associated with the endemic pine tree Pinus canariensis, and their distributions are broadly coincident. Eighty-eight individual Canarian Brachyderes, sampled from across the distributions of each subspecies, have been sequenced for 570 bp of the mitochondrial DNA (mtDNA) cytochrome oxidase II gene (COII). No mitotypes are shared among islands. Both maximum-likelihood and distance-based phylogenetic analyses have shown that: Tenerife is composed of a single monophyletic clade of mitotypes, El Hierro is composed of a single monophyletic clade occurring within a larger clade comprising all the La Palma mitotypes, and the mitotypes of these three islands form a monophyletic group distinct from Gran Canaria. New methods for estimating divergence times without the assumption of rate constancy have been used to reconstruct the direction and approximate timing of colonizations among the islands. Colonization has occurred from older to progressionally younger islands, and these colonizations are estimated to have occurred less than 2.6 million years ago, although the timing of the initial colonization of the archipelago is not discernable. New methods for the estimation of diversification rates that use branching times as the analyzed variable have been applied to each island fauna. Hypothesized effects of different levels of recent volcanism among islands were not apparent. All islands exhibit a gradually decreasing rate of genetic diversification that is marked by periodic sudden changes in rate.