Evolutionary Consequences of Asymmetric Dispersal Rates

Abstract

We study the consequences of asymmetric dispersal rates (e.g., due to wind or current) for adaptive evolution in a system of two habitat patches. Asymmetric dispersal rates can lead to overcrowding of the "downstream" habitat, resulting in a source-sink population structure in the absence of intrinsic quality differences between habitats or can even cause an intrinsically better habitat to function as a sink. Source-sink population structure due to asymmetric dispersal rates has similar consequences for adaptive evolution as a source-sink structure due to habitat quality differences: natural selection tends to be biased toward the source habitat. We demonstrate this for two models of adaptive evolution: invasion of a rare allele that improves fitness in one habitat but reduces it in the other and antagonistic selection on a quantitative trait determined by five additive loci. If a habitat can sustain a population without immigration, the conditions for adaptation to that habitat are most favorable if there is little or no immigration from the other habitat; the influence of emigration depends on the magnitude of the allelic effects involved and other parameters. If, however, the population is initially unable to persist in a given habitat without immigration, our model predicts that the population will be most likely to adapt to that habitat if the dispersal rates in both directions are high. Our results highlight the general message that the effect of gene flow upon local adaptation should depend profoundly on the demographic context of selection.

Mating system and gene flow in the red seaweed Gracilaria gracilis: effect of haploid–diploid life history and intertidal rocky shore landscape on fine-scale genetic structure

“…In the absence of differences in survival, fecundity or extinction probabilities and even habitat quality, biased spore dispersal may generate directional gene flow (cf. Stanton et al, 1997;Kawecki and Holt, 2002). If the transport of spores and gametes occurs predominantly at low tide when small streams flow from high-to lower-shore pools, higher pools will be relatively isolated from gene flow compared to lower pools.…”

Bringing the Hutchinsonian niche into the 21st century: Ecological and evolutionary perspectives

“…Details of genetic architecture matter. For instance, for alleles of small effect, increasing bidirectional movement usually facilitates adaptation to a sink (83), but for alleles of large effect, intermediate rates of movement are least favorable for their retention (84,85).…”

Integrating across Life‐History Stages: Consequences of Natal Habitat Effects on Dispersal

“…However, asymmetry in local adaptation provides potential pitfalls for researchers; habitat-induced asymmetry in dispersal may lead to com pletely asymmetrical adaptation, so that populations in two environments do not differ in genetic composition, but one is locally adapted and the other is maladapted (Ronce and Kirkpatrick 2001;Kawecki and Holt 2002). Under these conditions, standard tests for local adaptation, such as reciprocal transplant experiments or common garden experiments, would be unable to discriminate this from a failure of both populations to become locally adapted, because the populations are not genetically differentiated.…”

“…Under these con ditions, the allele frequencies of propagules from higherquality environments can swamp the frequency of alleles from lower-quality environments in both habitats. Ka wecki and Holt (2002) evaluated the effect of asymmetry in dispersal rate between two patches on the probability of fixation of alleles that were advantageous in one patch but disadvantageous in another. Under two different sets of genetic assumptions, they found that local adaptation was more likely to occur in the population with a higher emigration rate.…”

“…By al tering the traits or quantity of dispersers between different environments, phenotypic plasticity induced by natal hab itat conditions can have profound consequences for meta population and metacommunity dynamics as well as ge netic differentiation and adaptation of populations. These effects include strongly reducing the ability of metapop ulations to persist (Vuilleumier and Possingham 2006), skewing estimates of connectivity between populations, and creating unidirectional gene flow and thus asymme tries in the geographic patterns of local adaptation and maladaptation Kawecki and Holt 2002). While natal habitat-induced plasticity of adult phe notypes has received considerable attention by ecologists working at local scales (e.g., Roach and Wulff 1987;Pech enik 2006), how those developmental environments may affect the quality and quantity of dispersing individuals has received very little attention Clobert et al 2004).…”