Tales of the flying earth: The effect of host flyways on the phylogeny of shorebird lice (Phthiraptera: Ischnocera)

摘要

On the wings, bodies, and heads of most birds there are lice. These lice spend their whole lives ontheir host, with the exception of the few lice that get the opportunity to transfer from one host toanother, typically when the hosts come into physical contact with each other. In shorebirds(Charadriiformes), such opportunities are unevenly distributed over the year. The hosts are spread outover vast areas in their Arctic breeding grounds during the Arctic summer, but form dense, multispeciesflocks in the tropics and subtropics during the Arctic winter. During autumn and spring, whenthe hosts migrate between the Arctic to the tropics, they follow more or less well-defined routes, calledflyways. In this thesis, the impact of this host migration pattern on the phylogeny of shorebird lice isevaluated. More specifically, two complementary hypotheses of pattern formation in the evolutionaryhistory of shorebird lice, flyway homogenisation and flyway differentiation, are tested by phylogeneticreconstruction of the evolutionary history of two genera of lice (Lunaceps and Carduiceps) thatparasitize the same group of sandpiper (Scolopacidae: Calidrinae) hosts. Flyway homogenisation isfounded on the assumption that opportunities for lateral spread of lice between hosts of differentspecies are prevalent in flyways, which will facilitate gene flow between louse populations ondifferent host species, and prevent speciation of lice on host species that use the same stop-over pointsand wintering grounds. Over evolutionary time, this would cause a pattern of host species migratingalong the same flyways having genetically similar or identical louse populations. Flywaydifferentiation is, conversely, the hypothesis that the division of a widely spread host species intodiscrete populations that each follow different flyways during migration will work as an isolatingmechanism on the lice. If the generation time of the lice is significantly shorter than that of their hosts,this would result in a pattern where the same Holarctic-breeding host species is parasitized bygenetically different louse populations in different parts of the world. Extrapolating from datapublished on other groups of lice, flyway homogenisation is expected to be more pronounced in winglice (Lunaceps) than in body lice (Carduiceps) as these are topologically better placed on the host totake advantage of opportunities of lateral transfer to novel host species. Flyway differentiation isexpected to be more pronounced in Carduiceps than in Lunaceps, as wing lice of vagrant hostsmigrating along the “wrong” flyway would transfer to novel hosts more easily, and could preventcomplete isolation between flyways. While no evidence is found in either genus for flywaydifferentiation, there is evidence for flyway homogenisation in Lunaceps, with three Lunaceps speciesoccurring on multiple host species using the same flyways. Surprisingly, most Carduiceps collectedacross the world are genetically almost identical, and thus less isolated on their hosts than areLunaceps. Both Lunaceps and Carduiceps show some partial evidence of a division between lice onNew World hosts and those on Old World hosts. This division in echoed in a larger molecular studyon the proposed louse family Rallicolidae, where several species group together according to hostbiogeography rather than host relationships, thus contradicting the so-called Fahrenholz’ rule thatstates that parasite phylogeny should come to mirror host phylogeny. In the same phylogeny, evidenceis presented that the genus Quadraceps, widely distributed on most groups of shorebirds, isparaphyletic with regards to most other louse genera on shorebirds, and is in need of further study.Finally, the genus Lunaceps is revised morphologically. Six new species and one new subspecies aredescribed, and all old species are re-described and illustrated, several for the first time. Five previouslyrecognised species are placed as synonyms to other species, one species is transferred to the genusQuadraceps, one species is resurrected from synonymy, one species is considered a nomen dubiumand three populations are placed as incerta sedis.