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Conditionally deleterious mutation load accumulates in genomic islands but can be purged with sufficient genotypic redundancy
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Mee, Jonathan; Carson, Bryce; Yeaman, Sam — 2024-02-20 <p>Local adaptation frequently evolves in patches or environments that are connected via migration. In these cases, genomic regions that are linked to a locally adapted locus experience reduced effective migration rates. Via individual-based simulations of a two-patch system, we show that this reduced effective migration results in the accumulation of conditionally deleterious mutations, but not universally deleterious mutations, adjacent to adaptive loci. When there is redundancy in the genetic basis of local adaptation (i.e. genotypic redundancy), turnover of locally adapted polymorphisms allows conditionally deleterious mutation load to be purged. The amount of mutational load that accumulates adjacent to locally adapted loci is dependent on redundancy, recombination rate, migration rate, population size, strength of selection, and the phenotypic effect size of adaptive alleles. Our results highlight the need to be cautious when interpreting patterns of local adaptation at the level of phenotype or fitness, as the genetic basis of local adaptation can be transient, and evolution may confer a degree of maladaptation to non-local environments.</p>
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Pelvic spine reduction affects diet but not gill raker morphology in two polymorphic brook stickleback (Culaea inconstans) populations
Mee, Jonathan; Yap, Emily; Wuitchik, Daniel — 2023-11-01 <p>Pelvic spine polymorphism occurs in several species in the stickleback family (<em>Gasterosteidae</em>). Given parallel selection driving similar phenotypic polymorphisms in multiple stickleback species, we sought to determine the extent of parallelism in the ecological consequences of pelvic spine reduction. Based on a metabarcoding analysis of brook stickleback gut contents in two polymorphic populations, we found a shift towards a planktonic diet was associated with pelvic spine reduction. These results contrast with those found in threespine stickleback where pelvic spine reduction is associated with a shift towards a benthic diet. Hence, we found non-parallel consequences of spine polymorphism across species. Furthermore, a change in gill raker morphology has been consistently implicated in the change in diet in pelvic-reduced threespine stickleback. But we found no evidence of any difference in gill raker morphology associated with pelvic spine polymorphism in brook stickleback.</p>

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(Author: Mee, Jonathan)

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