Document Type



Doctor of Philosophy


Biology, Ecology

Date of Defense


Graduate Advisor

Patricia Parker, PhD


Ricklefs, Robert

Marquis, Robert

Johnson, Kevin


My dissertation focused on understanding the factors behind host-parasite specificity and parasite diversification, using Galapagos seabirds and their ectoparasites as the study system. This system comprised the seabird hosts (magnificent and great frigatebirds, Nazca, blue-footed and red-footed boobies) and nine species of ectoparasitic lice (one Pectinopygus ischnoceran louse species infecting each host, two species of Colpocephalum amblyceran lice, one on each frigatebird species, and two shared amblyceran lice, Eidmanniella albescens found on Nazca and blue-footed boobies and Fregatiella aurifasciata found on the two frigatebirds). Using as focal species Eidmanniella albescens and Fregatiella aurifasciata, which infect multiple hosts, I analyzed how the spatial location within a mixed colony and the movement of host individuals between colonies relate to parasite diversification. I found that host species identity was the only factor explaining patterns of genetic clustering in both parasite species. In the case of Fregatiella aurifasciata, the pattern of genetic divergence suggests a concordant evolutionary history with their hosts. In contrast, the genetic structure found in Eidmanniella albescens suggests a host-switching event, where Nazca booby parasites colonized blue-footed boobies. I analyzed the factors behind host-switching events that are thought to start by successive “straggling” parasites until they establish a breeding population. I found that the presence of host and potential host in the same locality, together with the specifics of lice attachment, are the main factors behind straggling frequency and thus also behind potential successful host-switching. Host-parasite specificity and parasite diversity seem to be driven by host conspecific and heterospecific interactions. Differences in nesting microhabitat may limit the potential for parasite exchange favoring divergence in parasite species that infect multiple hosts. Moreover, behaviors such as the kleptoparasitism observed in frigatebirds and something as specific as the way lice attach to the host feathers, may drive which parasite species has the potential to colonize a novel host and possibly diverge into a different species.

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