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Dryad

Weak response to selection on stigma-anther distance in a primarily selfing population of yellow monkeyflower

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May 14, 2024 version files 18.73 MB

Abstract

Stebbins hypothesized that selfing lineages are evolutionary dead ends because they lack adaptive potential. While selfing populations often harbor limited nucleotide variability compared to closely related outcrossers, reductions in the genetic variability of quantitative characters remain unclear, especially for key traits determining selfing rates. Yellow monkeyflower (Mimulus guttatus) populations generally outcross and maintain extensive quantitative genetic variation in floral traits. Here, we study the Joy Road population (Bodega Bay, California, USA) of M. guttatus, where individuals exhibit stigma-anther distances typical of primarily selfing monkeyflowers. We show that this population is closely related to nearby conspecifics on the Pacific coast with a modest 33% reduction in genome-wide variation compared to a more highly outcrossing population. A five-generation artificial selection experiment challenged the hypothesis that the Joy Road population harbors comparatively low evolutionary potential in the stigma-anther distance, a critical determinant of selfing rate in Mimulus. Artificial selection generated a weak phenotypic response, with low realized heritabilities (0.020-0.028) falling 84% below those measured for floral characters in more highly outcrossing M. guttatus. These results demonstrate substantial declines in evolutionary potential with a transition toward selfing. Whether these findings explain infrequent reversals to outcrossing or general limits on adaptation in selfers requires further investigation.