Research Article

Selective trade-offs maintain alleles underpinning complex trait variation in plants

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Science  03 Aug 2018:
Vol. 361, Issue 6401, pp. 475-478
DOI: 10.1126/science.aat5760

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Fluctuating selection in nature

Natural environmental variation can lead to individuals within a species experiencing different selective parameters. Seep monkeyflower (Mimulus guttatus) populations are constrained by local moisture availability and the onset of summer drought. This results in a selective tradeoff between the amount of seed set, which is determined by plant size, and the timing of reproduction. Troth et al. sequenced and phenotyped 187 M. guttatus plants and identified genetic variants associated with plant and flower size and rapid flowering. In wild populations surveyed over 3 years, the magnitude of selection changed depending on the rainfall patterns. Thus, fluctuating selection may maintain genetic variation in this species.

Science, this issue p. 475

Abstract

To understand evolutionary factors that maintain complex trait variation, we sequenced genomes from a single population of the plant Mimulus guttatus, identifying hundreds of nucleotide variants associated with morphological and life history traits. Alleles that delayed flowering also increased size at reproduction, which suggests pervasive antagonistic pleiotropy in this annual plant. The “large and slow” alleles, which were less common in small, rapidly flowering populations, became more abundant in populations with greater plant size. Furthermore, natural selection within the field population favored alternative alleles from year to year. Our results suggest that environmental fluctuations and selective trade-offs maintain polygenic trait variation within populations and also contribute to the geographic divergence in this wildflower species.

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