| Summary: | On the wings, bodies, and heads of most birds there are lice. These lice spend their whole lives on their host, with the exception of the few lice that get the opportunity to transfer from one host to another, 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 out over vast areas in their Arctic breeding grounds during the Arctic summer, but form dense, multispecies flocks in the tropics and subtropics during the Arctic winter. During autumn and spring, when the hosts migrate between the Arctic to the tropics, they follow more or less well-defined routes, called flyways. In this thesis, the impact of this host migration pattern on the phylogeny of shorebird lice is evaluated. More specifically, two complementary hypotheses of pattern formation in the evolutionary history of shorebird lice, flyway homogenisation and flyway differentiation, are tested by phylogenetic reconstruction of the evolutionary history of two genera of lice (Lunaceps and Carduiceps) that parasitize the same group of sandpiper (Scolopacidae: Calidrinae) hosts. Flyway homogenisation is founded on the assumption that opportunities for lateral spread of lice between hosts of different species are prevalent in flyways, which will facilitate gene flow between louse populations on different host species, and prevent speciation of lice on host species that use the same stop-over points and wintering grounds. Over evolutionary time, this would cause a pattern of host species migrating along the same flyways having genetically similar or identical louse populations. Flyway differentiation is, conversely, the hypothesis that the division of a widely spread host species into discrete populations that each follow different flyways during migration will work as an isolating mechanism 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 ...
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