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

The genus Brachyderes Schonherr (Coleoptera: Curculionidae) is represented by the species B. rugatus Wollaston on the Canary Islands, with one subspec ies on each of the islands of Gran Canaria, Tenerife, La Palma, and El Hier ro. These four subspecies are associated with the endemic pine tree Pinus c anariensis, and their distributions are broadly coincident. Eighty-eight in dividual Canarian Brachyderes, sampled from across the distributions of eac h subspecies, have been sequenced for 570 bp of the mitochondrial DNA (mtDN A) cytochrome oxidase II gene (COII). No mitotypes are shared among islands . Both maximum-likelihood and distance-based phylogenetic analyses have sho wn that: Tenerife is composed of a single monophyletic clade of mitotypes, El Hierro is composed of a single monophyletic clade occurring within a lar ger clade comprising all the La Palma mitotypes, and the mitotypes of these three islands form a rnonophyletic group distinct from Gran Canaria. New m ethods for estimating divergence times without the assumption of rate const ancy have been used to reconstruct the direction and approximate timing of colonizations among the islands. Colonization has occurred from older to pr ogressionally younger islands, and these colonizations are estimated to hav e occurred less than 2.6 million years ago, although the timing of the init ial colonization of the archipelago is not discernable. New methods for the estimation of diversification rates that use branching times as the analyz ed 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.