Inheritance of somatic mutations can affect fitness in monkeyflowers

Abstract

Plants possess the unique ability to transmit mutations to progeny that arise both through meiotic and mitotic (somatic) cell divisions. This is because the same meristem cells responsible for vegetative growth also generate gametes for sexual reproduction. Despite the potential for somatic mutations to be an additional source of genetic variation for adaptation, their role in plant evolution remains largely unexplored. We performed multiple experiments in the bush monkeyflower (Mimulus aurantiacus) to determine the fitness effects of somatic mutations inherited across generations. We tracked somatic mutations transmitted to progeny by generating self-pollinations within a flower (autogamy) or between stems of the same plant (geitonogamy). Autogamy and geitonogamy lead to different segregation patterns of somatic mutations among stems, making it possible to compare average fitness due to somatic variants. We found increased fecundity following autogamy, as well as significant impacts on drought tolerance, survival, and biomass. The variance in fitness was also greater following autogamy, consistent with the effects of somatic mutations impacting fitness. Effect sizes were small, but predictable, given that M. aurantiacus is a long-lived, drought-adapted shrub. These results reveal the importance of inherited somatic mutations as a source of genetic variation that can be relevant for plant adaptation.