Abstract
Local adaptation to rare habitats is difficult due to gene flow, but can occur if the habitat has higher productivity. Differences in offspring phenotypes have attracted little attention in this context. We model a scenario where the rarer habitat improves offspring's later competitive ability - a carryover effect that operates on top of local adaptation to one or the other habitat type. Assuming localised dispersal, so the offspring tend to settle in similar habitat to the natal type, the superior competitive ability of offspring remaining in the rarer habitat hampers immigration from the majority habitat. This initiates a positive feedback between local adaptation and trait divergence, which can thereafter be reinforced by coevolution with dispersal traits that match ecotype to habitat type. Rarity strengthens selection on dispersal traits and promotes linkage disequilibrium between locally adapted traits and ecotype-habitat matching dispersal. We propose that carryover effects may initiate isolation by ecology.
Highlights
What allows a population in a heterogeneous landscape to become locally adapted? One well-studied consideration is a tug-of-war between divergent selection and the homogenising effects of gene flow (Hendry et al 2002)
In the scenario where there was no carryover effect upon competitive ability (Fig. 1b), the reproductive trait remained highly-adapted to the majority habitat type, and maladapted to the minority habitat type (Fig. 2a)
The key model findings were that: (1) local adaptation to a minority habitat can occur when the minority habitat type confers a competitive advantage to offspring as a carryover effect, and (2) dispersal traits that promote matching between ecotype and habitat type can coevolve with and strengthen local adaptation and trait divergence
Summary
What allows a population in a heterogeneous landscape to become locally adapted? One well-studied consideration is a tug-of-war between divergent selection and the homogenising effects of gene flow (Hendry et al 2002). Stanton et al 1997) if high-quality habitat is relatively common in the landscape; if it is rare, local adaptation to the low-quality habitat type may occur All these results depend on dispersal, which will influence gene flow and the pattern of spatial genetic variation and ecological dynamics. Individuals are outcrossing hermaphrodites that form breeding pairs on territories, and have an evolvable trait that determines their local adaptedness This trait determines number of offspring raised, and since an individual cannot be locally adapted to both habitat types, high reproduction in one habitat type implies low reproduction in the other. To be able to include carryover effects (the focus of our model), an individual’s natal habitat type is assumed to determine its ability to compete for breeding territories.
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