Abstract
Color polymorphisms have long been of evolutionary interest for their diverse roles, including mate choice, predator avoidance, and pollinator attraction. While color variation is often under strong selection, some taxa demonstrate unexpectedly high frequencies of presumed deleterious color forms. Here we show that a genetic variant underlying complete loss of anthocyanin pigmentation has risen to an unexpectedly high frequency of >0.2 in a natural population of the plant Mimulus guttatus. Decreased expression of MYB5 transcription factor is associated with unpigmented morphs. While the allele was found only in heterozygote adults in the wild, suggesting negative selection, experiments were unable to demonstrate a fitness cost for unpigmented plants, suggesting a cryptic selection pressure in the wild. However, life-history differences among morphs suggests that unpigmented individuals benefit from later flowering and clonal growth. Overall, our study highlights the complex interplay of factors maintaining variation in nature, even for genes of major effect.
Highlights
The maintenance of polymorphisms at genes of major phenotypic effect has long interested evolutionary biologists
We show that a genetic variant underlying complete loss of anthocyanin pigmentation has risen to an unexpectedly high frequency of 10.2 in a natural population of the plant Mimulus guttatus
Thin-layer chromatographic analysis of floral and leaf extracts from four pigmented and four unpigmented plants confirmed that unpigmented plants do not produce detectable levels of pigment with a retention factor (Rf) in the range expected of anthocyanin, in contrast to the
Summary
The maintenance of polymorphisms at genes of major phenotypic effect has long interested evolutionary biologists. A recent series of articles and discussion (Forsman et al 2008; Wennersten and Forsman 2012; Bolton et al 2015, 2016; Forsman 2016) illustrates that the direct and indirect effects of color polymorphism on fitness can be complicated, and whether such polymorphism contributes to population persistence is contentious These articles were focused on animal examples, plants too show dramatic variation in coloration of vegetative and floral structures, and there are many notable cases where variation is present between closely related species (Rausher 2008) or among populations (Sobral et al 2015) or show segregation within populations (Brown and Clegg 1984)
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