Browsing by Subject "Parasites"
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Item Competition across space : from metacommunities to social body-snatching trematodes(2019-09-13) Resetarits, Emlyn Jane; Jha, Shalene; Bolnick, Daniel; Farrior, Caroline E; Leibold, Mathew A; Mueller, Ulrich GThis dissertation is composed of two sections. The first section focuses on experimentally testing the keystone community concept using protist microcosms. I found that habitat loss can cause structural changes in how communities are assembled, even when diversity measures appear unchanged. This work has important implications for reserves management and conservation efforts. The second section is composed of three chapters on social body-snatching trematodes residing in the California horn snail. First, I investigated the tradeoff between reproduction and defense to determine if social trematode colonies increase their soldier investment in areas of high intraguild predation (IGP). I found that colonies appear to respond to IGP as predicted and do so at the site-level. Second, I conducted a reciprocal transplant experiment to determine if differences in soldier investment are due to phenotypic plasticity. Unfortunately, our results were inconclusive but provided us with valuable information on natural variation in these colonies within an estuary. Finally, I investigated how individual soldier attributes and colony composition might explain a linear competitive dominance hierarchy between six species of social body-snatching trematodes. I found that the dominance hierarchy was not explained by attributes of the colony that we measured. All totaled, there are over 20,000 trematode species, in league with the diversity of social insect groups, like ants. The trematode system is rich with opportunity to study the evolution and ecology of sociality outside of insects.Item Local adaptation to parasites and selection on major histocompatibility genes in ecologically divergent populations of three-spine stickleback (Gasterosteus aculeatus)(2013-08) Stutz, William Edward; Bolnick, Daniel; Kirkpatrick, Mark, 1956-As individuals and populations diverge ecologically, they become exposed to new parasites and pathogens with potentially harmful fitness consequences. Populations are therefore expected to evolve resistance, possibly at a cost of less resistance to parasites rarely encountered parasites. This trade-off in resistance should generate local adaptation to parasites in different habitats. In chapter one, I show how local adaptation can potentially evolve in response to variation in parasite exposure among eighteen ecologically variable populations of threespine stickleback (Gasterosteus aculeatus). Within populations infection appeared to reflect morphology/diet based exposure differences among individuals. Among populations, however, these patterns were absent or reversed, consistent with the evolution of local adaptation. In chapters two and three I set out to test whether variation major histocompatibility (MHC) genes can underly such local adaptation in stickleback. MHC genes are important components of vertebrate immunity; however, there is little direct empirical support for spatially divergent selection driving local adaptation on MHC loci in the wild. In chapter two I tested for the action of parasite mediated balancing and divergent selection on on MHC loci using naturally infected stickleback in three replicate lake-stream pairs. Despite consistent divergence in parasites and MHC alleles, lakes tended to show decreased parasite burdens with increased allelic richness (consistent with balancing selection), while streams showed some support for divergent selection between lake and stream types. In chapter three I use the same lake-stream pairs to investigate how divergent selection could instead be reflected in variation in the effects of individual MHC alleles among populations. When comparing parapatric populations experiencing gene flow, MHC alleles maintained at relatively high frequency in one population were more likely to be associated with reduced, rather than increased, parasite abundances in that population. Allopatric populations experiencing no gene flow showed no such general relationship between allele frequency and resistance. These results are only consistent with spatially divergent selection, and imply that gene flow and environmental heterogeneity can be important for maintaining MHC diversity.