Seabird and louse coevolution: Complex histories revealed by 12S rRNA sequences and reconciliation analyses

We investigated the coevolutionary history of seabirds (orders Procellariif ormes and Sphenisciformes) and their lice (order Phthiraptera). Independent trees were produced for the seabirds (tree derived from 12S ribosomal RNA, isoenzyme, and behavioral data) and their lice (trees derived from 12S rRN A data). Brook's parsimony analysis (BPA) supported a general history of co speciation (consistency index = 0.84, retention index = 0.81). We inferred that the homoplasy in the BPA was caused by one intrahost speciation, one p otential host-switching, and eight or nine sorting events. Using reconcilia tion analysis, we quantified the cost of fitting the louse tree onto the se abird tree. The reconciled trees postulated one host-switching, nine cospec iation, three or four intrahost speciation, and 11 to 14 sorting events. Th e number of cospeciation events was significantly more than would be expect ed from chance alone (P < 0.01). The sequence data were used to test for ra te heterogeneity for both seabirds and lice. Neither data set displayed sig nificant rate heterogeneity. An examination of the codivergent nodes reveal ed that seabirds and lice have cospeciated synchronously and that lice have evolved at similar to 5.5 times the rate of seabirds. The degree of sequen ce divergence supported some of the postulated intrahost speciation events (e.g., Halipeurus predated the evolution of their present hosts). The seque nce data also supported some of the postulated host-switching events. These results demonstrate the value of sequence data and reconciliation analyses in unraveling complex histories between hosts and their parasites.