Co-phylogeography and comparative population genetics of the threatened Galápagos hawk and three ectoparasite species: ecology shapes population histories within parasite communities

Comparative microevolutionary studies of multiple parasites occurring on a single host species can help shed light on the processes underlying parasite diversification. We compared the phylogeographical histories, population genetic structures and population divergence times of three co-distributed and phylogenetically independent ectoparasitic insect species, including an amblyceran and an ischnoceran louse (Insecta: Phthiraptera), a hippoboscid fly (Insecta: Diptera) and their endemic avian host in the Galápagos Islands. The Galápagos hawk (Aves: Falconiformes: Buteo galapagoensis) is a recently arrived endemic lineage in the Galápagos Islands and its island populations are diverging evolutionarily. Each parasite species differed in relative dispersal ability and distribution within the host populations, which allowed us to make predictions about their degree of population genetic structure and whether they tracked host gene flow and colonization history among islands. To control for DNA region in comparisons across these phylogenetically distant taxa, we sequenced ~1 kb of homologous mitochondrial DNA from samples collected from all island populations of the host. Remarkably, the host was invariant across mitochondrial regions that were comparatively variable in each of the parasite species, to degrees consistent with differences in their natural histories. Differences in these natural history traits were predictably correlated with the evolutionary trajectories of each parasite species, including rates of interisland gene flow and tracking of hosts by parasites. Congruence between the population structures of the ischnoceran louse and the host suggests that the ischnoceran may yield insight into the cryptic evolutionary history of its endangered host, potentially aiding in its conservation management.