TAILIEUCHUNG - Population structure attributable to reproductive time: isolation by time and adaptation by time

Many populations are composed of a mixture of individuals that reproduce at different times, and these times are often heritable. Under these conditions, gene flow should be limited between early and late reproducers, even within populations having a unimodal temporal distribution of reproductive activity. This temporal restriction on gene flow might be called ‘isolation by time’ (IBT) to acknowledge its analogy with isolation by distance (IBD). IBD and IBT are not exactly equivalent, however, owing to differences between dispersal in space and dispersal in time. We review empirical studies of natural populations that provide evidence for IBT based on heritabilities of reproductive time and on molecular genetic differences. | Molecular Ecology 2005 14 901-916 doi INVITED REVIEW Population structure attributable to reproductive time isolation by time and adaptation by time ANDREW P. HENDRY and TROY DAY t Redpath Museum and Department of Biology McGill University 859 Sherbrooke St. W. Montreal Québec H3A 2K6 Canada Department of Mathematics and Department of Biology Queen s University Kingston Ontario K7L 3 N6 Canada Abstract Many populations are composed of a mixture of individuals that reproduce at different times and these times are often heritable. Under these conditions gene flow should be limited between early and late reproducers even within populations having a unimodal temporal distribution of reproductive activity. This temporal restriction on gene flow might be called isolation by time IBT to acknowledge its analogy with isolation by distance IBD . IBD and IBT are not exactly equivalent however owing to differences between dispersal in space and dispersal in time. We review empirical studies of natural populations that provide evidence for IBT based on heritabilities of reproductive time and on molecular genetic differences associated with reproductive time. When IBT is present variation in selection through the reproductive season may lead to adaptive temporal variation in phenotypic traits adaptation by time ABT . We introduce a novel theoretical model that shows how ABT increases as i selection on the trait increases ii environmental influences on reproductive time decrease iii the heritability of reproductive time increases and iv the temporal distribution of reproductive activity becomes increasingly uniform. We then review empirical studies of natural populations that provide evidence for ABT by documenting adaptive temporal clines in phenotypic traits. The best evidence for IBT and ABT currently comes from salmonid fishes and flowering plants but we expect that future work will show these processes are more widespread. Keywords .

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