Microhabitat contributes to microgeographic divergence in threespine stickleback

Abstract

Since the New Synthesis, most migration-selection balance theory has predicted that there should be negligible differentiation over small spatial scales (relative to dispersal), because gene flow should erode any effect of divergent selection. Nevertheless, there are classic examples of microgeographic divergence, which theory suggests can arise under specific conditions: exceptionally strong selection, phenotypic plasticity in philopatric individuals, or nonrandom dispersal. Here, we present evidence of microgeographic morphological variation within lake and stream populations of threespine stickleback (Gasterosteus aculeatus). It seems reasonable to assume that a given lake or stream population of fish is well-mixed. However, we found this assumption to be untenable. We examined trap-to-trap variation in 34 morphological traits measured on stickleback from 16 lakes and 16 streams. Most traits varied appreciably among traps within populations. Both between-trap distance and microhabitat characteristics such as depth and substrate explained some of the within-population morphological variance. Microhabitat was also associated with genotype at particular loci but there was no genetic isolation by distance, implying that heritable habitat preferences may contribute to microgeographic variation. Our study adds to growing evidence that microgeographic divergence can occur across small spatial scales within individuals' daily dispersal neighborhood where gene flow is expected to be strong. K E Y W O R D S : dispersal neighborhood, Gasterosteus aculeatus, migration-selection balance.

Habitat‐linked genetic variation supports microgeographic adaptive divergence in an island‐endemic bird species

“…Recent evidence indicates that adaptive divergence driven by strong divergent selection is also possible in highly mobile animals with significant levels of dispersal and gene flow (e.g., Hohenlohe et al, 2010;Mikles et al, 2020;Nacci et al, 2016;Torres-Dowdall et al, 2012;Urban et al, 2017). While many studies clearly demonstrate phenotypic and genetic variation consistent with hypotheses of microgeographic adaptive evolution (e.g., Charmantier et al, 2016;Maciejewski et al, 2020;Pequeno et al, 2021), determining the environmental factors and evolutionary and genetic mechanisms driving these patterns remains a difficult challenge (Barrett & Hoekstra, 2011;Hoban et al, 2016). Studies that are successful at showing both genomic evidence of divergent selection and a genetic basis to diverging phenotypes at fine spatial scales are generally restricted to traits controlled by few genes of large effect (e.g., Laurent et al, 2016;Linnen et al, 2013;Nosil et al, 2018;Pfeifer et al, 2018).…”

Interactions between microenvironment, selection and genetic architecture drive multiscale adaptation in a simulation experiment

“…Indeed, despite the intuitive idea that adaptation should be impeded by strong local gene flow, there is increasing empirical evidence that groups of individuals within the reach of gene flow can adapt to microgeographic environmental variations (e.g. Audigeos et al, 2013 ; Barth et al, 2017 ; Brousseau et al, 2013 , 2021 ; DeMarche et al, 2016 ; Gauzere et al, 2020 ; Jain & Bradshaw, 1966 ; Lind et al, 2017 ; Maciejewski et al, 2020 ; Scotti et al, 2016 ; Szulkin et al, 2016 ; Turner et al, 2010 ). As within‐ and between‐populations scales have generally been considered separately, our objective here is to investigate local adaptation simultaneously at both scales, using simulation experiments in hierarchical population structures where environmental conditions differ both among populations and within each population.…”

Scale‐dependent effects of host patch traits on species composition in a stickleback parasite metacommunity

“…More generally, spatial variation in the diversity and identity of terminal hosts can generate among‐population differences in multiple parasite species that use those terminal hosts (Hechinger and Lafferty 2005). A caveat here is that although abiotic and biotic differences between host populations are obvious and large, there may be appreciable abiotic and biotic variation within a supposedly well‐mixed population (Maciejewski et al 2020), which may yield comparable effects at the within‐population scale.…”