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Lookup NU author(s): Dr Mark Shirley
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Theory suggests that a population in a patchy environment will persist longer than in a homogeneous environment. Persistence of the population is necessary for the evolution of resistance, which here occurs under strong selection pressure from heavy metal pollution. Here we investigate the factors promoting persistence and check the theoretical expectation that, given persistence, evolution will occur fastest under high selection pressure and small metapopulation size. We report a replicated study of the metapopulation dynamics of the fruit fly Drosophila melanogaster undergoing evolutionary change over 12 generations in patchy environments. Environments were composed of two types of patch: polluted and unpolluted, the former being contaminated with cadmium. Metapopulation performance was examined in relation to patch connectivity and in relation to the ratio of polluted to unpolluted patches. The ancestral population contained a small proportion of genes that allowed improved performance on the polluted patches containing cadmium. An initial experiment showed that metapopulation connectivity was essential for metapopulation persistence in polluted patches; without it, extinct patches could not be recolonized. By the twelfth generation the resistant allele had spread in all of the metapopulations, so that all evolved resistance to cadmium. This evolution of resistance substantially increased carrying capacity in polluted patches, and these carrying capacities were in fact indistinguishable from those of unpolluted patches, so that eventual metapopulation sizes did not differ between treatments. Contrary to expectation, evolution took longer in metapopulations living in environments containing more polluted patches, as measured by time taken to achieve full patch occupancy. A metapopulation structure of connected patches was essential for the evolution of resistance, and systems with a high proportion of polluted patches evolved slower than systems containing less polluted patches. With increasing landscape fragmentation, the long-term survival of localized and endangered species may depend on our understanding of metapopulation evolution and dynamics in patchy environments.
Author(s): Shirley MDF; Sibly RM
Publication type: Article
Publication status: Published
ISSN (print): 0012-9658
ISSN (electronic): 1939-9170
Publisher: Ecological Society of America
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