Santa Cruz Island Reserve

19 May, 04 AM - 21 May, 08 AM

The Biogeography and Community Structure of Parasites of Channel Island Deer Mice (Peromyscus maniculatus) on the California Channel Islands Paul Durst, Duke University Introduction and Objectives Parasitism is the most common consumer strategy among organisms (1), yet we remain largely ignorant of the impact parasites have on ecology and evolution. A recent study that quantified the total biomass in three estuarine systems found that parasite biomass exceeded the biomass of top predators within the system (2). As biologists begin to put parasites into an ecological and evolutionary context, fundamental questions arise regarding the way they interact with the world. Do parasites follow the same ecological rules as other organisms? How do parasites affect other trophic levels? How do these interactions shape the ecological communities and to what degree does the evolution of parasite communities reflect the evolutionary history of their hosts? Islands, as test tubes for evolution, often provide a starting point for addressing evolutionary and ecological questions (3), but what constitutes an island for a parasite? Each individual host can, in essence, act as an island, but parasites on physical islands can provide unique insights into parasite ecology and community structure. For example, several studies of non-parasitic animals have suggested that random assemblages are more likely to be seen in small-bodied organisms such as parasites (4). The argument is that low mobility and low population densities lessen the effects of interspecific competition, resulting in a less structured community. Parasite community studies treating individual hosts as islands have reflected these findings to some degree (5). On physical islands, however, population densities are often extremely high, even for small-bodied organisms (3). For parasites, these high densities might reveal a community structure not seen on the mainland which could, in turn, provide insight into the role different parasite species play in the formation of mainland parasite communities. Insular parasites can help answer questions about mainland parasite communities, but they can provide insight into the history of their insular hosts as well. Smith and Carpenter (2006) surveyed the parasites of deer mice on Anacapa Island, an island previously inhabited by invasive black rats, and they found that two years after the extirpation of black rats on the island, the deer mice were still infected with several black rat parasites. Parasites can provide information about the colonization history of their hosts based on the pattern of nestedness (5) between different islands, they can reveal gene flow between islands and the mainland based on differences in the parasite communities, and, as they did in Smith and Carpenter?s study, they can even provide evidence of extinct island occupants . The broad goal of this study is to gain a better understanding of how communities of parasites on insular mammals form, how they differ from their mainland counterparts, and how their evolutionary histories shed light on that of their hosts. To achieve this, I will sample deer mouse (Peromyscus maniculatus) populations on the California Channel Islands and perform a comprehensive survey of the metazoan parasite communities associated with these mice on each island and the nearby mainland. The data will be used to test for non-random assemblages of parasites and to explore the colonization history of the parasites and their host across the Channel Islands. Study Site and Host Species The California Channel Islands present an excellent opportunity to address questions about the community structure of parasites as well as the ecological history of their hosts. The Channel Islands consist of four northern islands off the coast of Santa Barbara, and four southern islands off the coast of Los Angeles. The islands represent one of the only coastal Mediterranean-type ecosystems in North America and they harbor a unique suite of plants and animals. The deer mouse, Peromyscus maniculatus, is the only mammal native to all eight Channel Islands (6), and each island houses a unique subspecies (6). While some of the islands were colonized directly from the mainland, others are believed to have been colonized from other islands (6). Samples of deer mice will be taken from all eight islands as well as from two mainland populations close to the northern and southern Channel Island groups. The abundance of deer mice on each island is relatively high (Paul Collins, Curator of Vertebrate Zoology, SBMNH, personal communication) and adequate samples can be obtained anywhere on the island, so island sampling sites will be restricted to the area surrounding public campgrounds or other accommodations to minimize the disturbance to the environment. On the mainland, coastal sage scrub sites previously sampled by the Santa Barbara Museum of Natural History will be revisited. Methods Parasite Survey: On each island as well as on the mainland, transects of Sherman live traps will be set up. Twenty deer mice will be sacrificed immediately after capture and any additional rodents (P. maniculatus on the islands as well as other spp. on the mainland) will be released after being measured and weighed. The sacrificed individuals will then be combed for ectoparasites using the methods employed by Soliman et al (2001). After being frozen and shipped back to Duke University, the individuals will be examined for endoparasites following the procedures set forth by Smith and Carpenter (2006). Parasites will be identified to the lowest possible taxonomic level. Phylogeographic Analysis: I will sequence several mtDNA loci for the mice and the parasites. These sequences will be used to infer phylogenetic relationships among the island populations of the deer mice and of each parasite species, and these phylogenies will be compared against each other and used to test different colonization hypotheses (any congruence between phylogenies will add resolution to the deer mouse phylogeny). Statistical phylogeographic analyses utilizing the IM model (7) will also be used to estimate divergence times and gene flow between islands. Parasite Community Analysis: Different measures of diversity (abundance, richness, evenness) will be calculated for all the islands, and the Simpson and Jaccard indices (8) will be employed to analyze the degree of similarity between the communities on different islands and to test for patterns in the parasite assemblages (e.g. nestedness or deviations from expectations of randomness). C-scores and V-ratios will be calculated to examine the co-variance of parasite species (4), and phylogenetic beta diversity (9) will be calculated to measure the effect of local (within island) processes and to examine how these processes affect regional (all of the islands plus the mainland) diversity. The results of these tests along with the results from the phylogeographic analyses will be used to compare parasite community structure against the null expectation (each island representing a random sampling of the mainland parasite pool) and to evaluate colonization hypotheses for the deer mice, for individual parasite species and for the parasite community as a whole. References 1) Lafferty, K. D., S. Allesina, M. Arim, C. J. Briggs, G. De Leo, A. P. Dobson, J. A. Dunne, P. T. J. Johnson, A. M. Kuris, D. J. Marcogliese, N. D. Martinez, J. Memmott, P. A. Marquet, J. P. McLaughlin, E. A. Mordecai, M. Pascual, R. Poulin, and D. W. Thieltges. 2008. Parasites in food webs: the ultimate missing links. Ecology Letters 11:533-546. 2) Kuris, A. M., R. F. Hechinger, J. C. Shaw, K. L. Whitney, L. Aguirre-Macedo, C. A. Boch, A. P. Dobson, E. J. Dunham, B. L. Fredensborg, T. C. Huspeni, J. Lorda, L. Mababa, F. T. Mancini, A. B. Mora, M. Pickering, N. L. Talhouk, M. E. Torchin, and K. D. Lafferty. 2008. Ecosystem energetic implications of parasite and free-living biomass in three estuaries. Nature 454:515-518. 3) Whittaker, R.J., and J.M. Fernandez-Palacios. Island Biogeography: Ecology, Evolution and Conservation. New York: Oxford University Press, 2007. 4) Krasnov, B. R., S. Matthee, M. Lareschi, N. P. Korallo-Vinarskaya, and M. V. Vinarski. Co-occurrence of ectoparasites on rodent hosts: null model analyses of data from three continents. Oikos 119:120-128. 5) Poulin, R. 2007. Are there general laws in parasite ecology? Parasitology 134: 763-776. 6) Pergams, O.R.W., Lacy, R.C. & Ashley, M.V. Conservation and management of Anacapa Island deer mice. Conservation Biology, 14, 819?832. 7) Nielsen, R., and J. Wakeley. Distinguishing migration from isolation: a Markov Chain Monte Carlo approach. Genetics 158:885-96. 8) Fallaw, W.C. A Test of the Simpson Coefficient and Other Binary Coefficients of Faunal Similarity. Journal of Paleontology 53:4:1029-1034. 9) Graham, C.H. and P.V.A. Fine. Phylogenetic beta diversity: linking ecological and evolutionary processes across space in time. Ecology Letters 11:1265-1277. 10) Soliman, S., A.J. Main, A.S. Marzouk, and A.A. Montasser. 2001. Seasonal studies on commensal rats and their ectoparasites in a rural area of Egypt: the relationship of ectoparasites to the species, locality, and relative abundance of the host. Journal of Parasitology 87:3:545-553 11) Smith, K.F., and S.M. Carpenter. 2006. Potential spread of introduced black rat (Rattus rattus) parasites to endemic deer mice (Peromyscus maniculatus) on the California Channel Islands. Diversity and Distributions 12:742-748

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The Biogeography and Community Structure of Parasites of Deer Mice (Peromyscus maniculatus) on the California Channel Islands

graduate_student - Duke University

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Paul Durst May 19 - 21, 2012 (3 days)

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