Disease ecology in the Galápagos Hawk (Buteo galapagoensis): host genetic diversity, parasite load and natural antibodies.

An increased susceptibility to disease is one hypothesis explaining how inbreeding hastens extinction in island endemics and threatened species. Experimental studies show that disease resistance declines as inbreeding increases, but data from in situ wildlife systems are scarce. Genetic diversity increases with island size across the entire range of an extremely inbred Galápagos endemic bird, providing the context for a natural experiment examining the effects of inbreeding on disease susceptibility. Extremely inbred populations of Galápagos hawks had higher parasite abundances than relatively outbred populations. We found a significant island effect on constitutively produced natural antibody (NAb) levels and inbred populations generally harboured lower average and less variable NAb levels than relatively outbred populations. Furthermore, NAb levels explained abundance of amblyceran lice, which encounter the host immune system. This is the first study linking inbreeding, innate immunity and parasite load in an endemic, in situ wildlife population and provides a clear framework for assessment of disease risk in a Galápagos endemic.

Phylogeography of the Galápagos hawk (Buteo galapagoensis): a recent arrival to the Galápagos Islands.

Galápagos hawks (Buteo galapagoensis) are one of the most inbred bird species in the world, living in small, isolated island populations. We used mitochondrial sequence and nuclear minisatellite data to describe relationships among Galápagos hawk populations and their colonization history. We sampled 10 populations (encompassing the entire current species range of nine islands and one extirpated population), as well as the Galápagos hawk's closest mainland relative, the Swainson's hawk (B. swainsoni). There was little sequence divergence between Galápagos and Swainson's hawks (only 0.42% over almost 3kb of data), indicating that the hawks colonized Galápagos very recently, likely less than 300,000 years ago, making them the most recent arrivals of the studied taxa. There were only seven, closely related Galápagos hawk haplotypes, with most populations being monomorphic. The mitochondrial and minisatellite data together indicated a general pattern of rapid population expansion followed by genetic isolation of hawk breeding populations. The recent arrival, genetic isolation, and phenotypic differentiation among populations suggest that the Galápagos hawk, a rather new species itself, is in the earliest stages of further divergence.

Cryptic host specificity of an avian skin mite (Epidermoptidae) vectored by louseflies (Hippoboscidae) associated with two endemic Galapagos bird species.

Host specificity of vectors is an important but understudied force shaping parasite evolution and the relationship between hosts and parasites. Low vector specificity may allow a vectored parasite to invade new host species, whereas high specificity of vectors may reduce the host range of the parasite and favor specialization. The 'generalist' and widely distributed avian skin mite Myialges caulotoon Speiser (Acari: Epidermoptidae) is unusual because females require an insect vector to complete their life cycle. Myialges caulotoon was previously reported from 2 lousefly (Diptera: Hippoboscidae) species, Olfersia sordida and Icosta nigra, parasitizing flightless cormorants (Phalacrocorax harrisi) and Galápagos hawks (Buteo galapagoensis), respectively, within the Galápagos Islands. This is a surprising distribution, given that the 2 lousefly species involved are relatively host-specific. Mitochondrial DNA sequences revealed 2 reciprocally monophyletic Myialges clades that sorted out perfectly with respect to their vector species, regardless of whether they were in allopatry or sympatry. One clade was restricted to flies of hawks and the other to flies of cormorants. Females of the 2 Myialges groups were also separated consistently by the shape of the sternal surface sclerotization. Mites of hawk flies were more abundant than those of cormorant flies. Within the Myialges clade associated with hawks, genetic differentiation between 2 island populations mirrored its host's patterns of differentiation.

Effects of host sociality on ectoparasite population biology.

Theory predicts a positive relationship between parasite infection intensity and host density. However, this generalization is complicated in natural systems by differences in life history among parasite taxa, e.g., transmissibility. Accordingly, predictions relating host density to parasite load should be specific to each parasite taxon. To illustrate this, we studied parasites that differed greatly in life history in the context of the Galapagos hawk's (Buteo galapagoensis) variably cooperative mating system. Two louse (Phthiraptera) species were collected: Colpocephalum turbinatum (Amblycera), with 53 host species, and Degeeriella regalis (Ischnocera), with 10 host species, although B. galapagoensis was the only known Galapagos host. Sixty territorial adult male hawks from 26 groups of 1-6 males were quantitatively sampled for lice. Average abundance and intensity of C. turbinatum but not D. regalis were significantly larger in large groups of hawks than small groups. Males from the same polyandrous group harbored significantly correlated abundances of C. turbinatum but not D. regalis. Prevalence, average abundance, and intensity of C. turbinatum were significantly higher than D. regalis. These are the first results to demonstrate significant differences in a suite of population responses between these louse suborders in the context of host sociality.

Differences in straggling rates between two genera of dove lice (Insecta: Phthiraptera) reinforce population genetic and cophylogenetic patterns.

Differences in dispersal abilities have been implicated for causing disparate evolutionary patterns between Columbicola and Physconelloides lice (Insecta: Phthiraptera). However, no study has documented straggling (when lice are found on atypical hosts) rates within these lineages. We used the fact that the Galapagos Hawk, Buteo galapagoensis (Gould) (Falconiformes) feeds on the Galapagos Dove Zenaida galapagoensis Gould (Columbiformes) within an ecologically simplified setting. The Galapagos Dove is the only typical host of Columbicola macrourae (Wilson) and Physconelloides galapagensis (Kellogg and Huwana) in Galapagos. We quantitatively sampled and found these lice on both bird species. A DNA barcoding approach confirmed that stragglers were derived from Galapagos doves. We also collected a Bovicola sp. louse, likely originating from a goat (Capra hircus). On hawks, C. macrourae was significantly more prevalent than P. galapagensis. On doves, the two lice were equally prevalent and abundant. Differences in prevalence on hawks was a function of differences in straggling rate between lice, and not a reflection of their relative representation within the dove population. This provides further evidence that differences in dispersal abilities may drive differences in the degree of cospeciation in Columbicola and Phyconelloides lice, which have become model systems in evolutionary biology.