COMPARATIVE PHYLOGENETIC HISTORIES OF TWO LOUSE GENERA FOUND ON CATHARUS THRUSHES AND OTHER BIRDS

The louse genera Brucelia (Ischnocera) and Myrsidea (Amblycera) are broadly codistributed on songbirds (Passeri-formes), but differ in a variety of life history characteristics. We used mitochondrial and nuclear DNA sequences to assess levels of genetic divergence and reconstruct phylogenies of these 2 genera. focusing especially oil Catharus thrushes in North America. We then qualitatively compared the phylogenies and levels of divergence within these 2 genera of codistributed parasites. Neither Brueelia nor Myrsidea appears to cospeciate with Catharus thrushes or passerine birds ill general. The Myrsidea phylogeny exhibits significant levels of biogeographic structure, whereas the Brueelia phylogeny does not. Myrsidea and Brucelia also differ in their levels of infra-generic genetic divergence. with Myrsidea showing higher levels of genetic divergence and host specificity than Brueelia. Our generic data support traditional morphology-based taxonomy ill several instances in which the sank species of Brueelia has been reported oil multiple host taxa, e.g., all migrant Catharus spp. carry B. antiqua, with little haplotype divergence. Myrsidea found on each Catharus sp. are in general genetically distinct, except for M. incerta, which parasitizes both Catharsis ustulatus and Catharsis minimus. The strong biogeographic signal ill the Myrsidea phylogeny and higher relative levels of host specificity of Myrsidea slip. suggest that infrequent host-switching, followed by speciation is shaping the evolutionary of this group. Ill contrast, the relatively lower host specificity of Brueelia spp. suggests that host-switching combined with more frequent ongoing dispersal. has been more important in the evolutionary history of Brueelia.