Molecular Phylogenetics of the Avian GenusPipiloand a Biogeographic Argument for Taxonomic Uncertainty

Abstract

We sequenced 1709 base pairs (bp) of mitochondrial DNA including parts of cytochromeb, ND 2, and the control region (CR I, II) for seven members of the avian genusPipilo(towhees),Melozone kieneri(rusty-crowned ground-sparrow), andArremonops rufivirgatus(olive sparrow). A total of 457 bp was variable and 257 bp were potentially phylogenetically informative. All gene regions were similarly variable (20.2 to 28.4%) except for CR II (38.4%); third position transitions were as common as substitutions in the CR. Tree topology was sensitive to choice of outgroup(s) and individual sequences used as exemplars. Six trees were considered viable phylogenetic hypotheses based on maximum parsimony and maximum likelihood analyses. These trees generally supported two groups of towhees (rufous-sided group, brown towhee group), a sister taxon relationship forP. abertiandP. crissalis,and a sister taxon relationship forP. ocaiandP. maculatus.The occurrence ofM. kierneiwithinPipiloin three trees challenges the monophyly of the latter; the other species ofMelozoneand other outgroups require study to resolvePipilomonophyly. The relationships ofP. albicollisandP. fuscuswere ambiguous, as they were with previous data sets (allozymes, mtDNA restriction sites); they could be sister species or either one could be the basal species in the brown towhee group. We suggest that this taxonomic uncertainty obtains from the contemporaneous origin ofP. fuscus, P. albicollis,and the ancestor ofP. aberti/P. crissalis.We favor a “star” phylogeny because species in unrelated lineages found in the same region asP. albicollisare similarly difficult to resolve phylogenetically. Synapomorphies from coding genes and the CR did not preferentially support basal and terminal nodes, and hence did not provide different windows of taxonomic resolution, which might be expected from the apparent rapid rate of CR evolution. Phylogenetic trees inferred from allozymes, restriction sites, and mtDNA sequences were congruent, suggesting that each is a useful source of phylogenetic information.