Phylogenetic relationships within Diadasia, a group of specialist bees

We estimated phylogenetic relationships among species of the bee genus Diad asia, a group of new world, specialist bees. We sequenced similar to2 kb of the mitochondrial genes cytochrome oxidase subunit I and II and tRNA leuci ne and similar to1 kt, of the nuclear gene elongation factor 1-alpha for 24 North American Diadasia species, 4 South American species, and five outgro up genera. Parsimony analyses of the two data sets were highly congruent. A combined analysis produced a well-resolved phylogenetic hypothesis that su pported the monophyly of Diadasia, but not that of traditional subgenera: D iadasia s. sfr. was paraphyletic in all analyses. With one exception, the N orth and South American species formed separate clades, supporting previous hypotheses that two lineages of Diadasia have dispersed from South to Nort h America: a more recent dispersal of D. ochracea and an older dispersal of the ancestor to all other North American species. Different species of Dia dasia specialize on pollen from at least five different plant families; the phylogeny presented here, along with known host affinities, indicates that host-switching has been rare. (C) 2001 Academic Press.