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SEPG 2373 - Date Awarded 2004
Genetic bottlenecks and the geographic distribution of sexual and asexual organisms
Christoph Haag and Deborah Charlesworth
Abstract
Geographic parthenogenesis describes the well-known pattern that asexual (parthenogenetic) organisms often live in more marginal (as opposed to core) habitats than their closely related sexual counterparts. Although several hypotheses exist, the reasons for this pattern are not well understood, yet they are potentially crucial to understanding the maintenance of sexual reproduction. We initiated the investigation of a recently published hypothesis, which states that inbreeding depression following genetic bottlenecks may be responsible for geographic parthenogenesis. There is evidence that genetic bottlenecks are more frequent and severe in marginal than in core habitats. These bottlenecks may result in inbreeding in sexual organisms, leading to increased homozygosity, and often reducing fitness. In asexuals, with no mating or segregation, this does not happen. Therefore the fitness of asexuals relative to sexuals may be higher in marginal than in core habitats. To test this hypothesis, we planned an experiment using Daphnia pulex, which occurs in a cyclical parthenogenetic (sexual) and obligate parthenogenetic (asexual) form. We found 73 sexual, 12 asexual and one mixed populations in our study area in southern Finland. Animals from sexual populations were used to establish three types of experimental populations in large outdoor containers: bottlenecked, non-bottlenecked (natural inbreeding level), and outbred. Additionally, asexual populations were established. These populations will be used in 2006 to test the key prediction of our hypothesis, namely that the success of asexual immigrants, which will be experimentally introduced into sexual populations, will depend on the degree of bottlenecking of the sexual population.
Full report: SEPG2373
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