Journal
PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES
Volume 364, Issue 1523, Pages 1533-1542Publisher
ROYAL SOC
DOI: 10.1098/rstb.2009.0007
Keywords
adaptational constraints; eco-evolutionary dynamics; migration load; migrational meltdown; species' range
Categories
Funding
- Natural Sciences and Engineering Research Council of Canada
- Canada Graduate Scholarship
- Natural Environment Research Council [cpb010001] Funding Source: researchfish
- NERC [cpb010001] Funding Source: UKRI
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Dispersal and gene flow can have both positive and negative effects on population size, but little empirical support from nature exists for the negative effects. We test for such effects in a stream population of threespine stickleback (Gasterosteus aculeatus L.) that is subject to high gene flow from a lake and is thus maladapted to stream conditions. In this system, maladaptation increases with distance along the stream, and this increase is associated with decreasing population densities until stickleback are no longer present (2.5 km from the lake). We conducted field experiments to inform whether this association might reflect a negative role for gene flow in constraining population size and therefore causing a local range limit. We specifically tested predictions deriving from theory: peripheral populations should show partial local adaptation, be under strong selection and not simply be maintained by dispersal. First, a transplant experiment suggested a weak home-site advantage in the peripheral population. Second, a mark-recapture study showed directional selection for a stream-adapted phenotype in 1 of 2 years. Third, another mark-recapture experiment showed that dispersal is limited to the point that positive demographic effects of dispersal are probably minimal. We conclude that, although gene flow does constrain morphological maladaptation in the outlet stream population, the evidence for its contribution to population size and range limits is mixed. We discuss the implications of our work for the study of factors influencing the evolution of species' ranges.
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