Journal Article

Tests for the joint evolution of mating system and drought escape in <i>Mimulus</i>

Christopher T. Ivey and David E. Carr

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 109, issue 3, pages 583-598
Published in print February 2012 | ISSN: 0305-7364
Published online August 2011 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcr160
Tests for the joint evolution of mating system and drought escape in Mimulus

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry

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Background and Aims

Self-fertilizing taxa are often found at the range margins of their progenitors, where sub-optimal habitats may select for alternative physiological strategies. The extent to which self-fertilization is favoured directly vs. arising indirectly through correlations with other adaptive life history traits is unclear. Trait responses to selection depend on genetic variation and covariation, as well as phenotypic and genetic responses to altered environmental conditions. We tested predictions of the hypothesis that self-fertilization in Mimulus arises through direct selection on physiological and developmental traits that allow seasonal drought escape.

Methods

Phenotypic selection on mating system and drought escape traits was estimated in field populations of M. guttatus. In addition, trait phenotype and phenotypic selection were compared between experimental wet and dry soil in two greenhouse populations each of M. guttatus and M. nasutus. Finally, genetic variation and covariation for traits were compared between wet and dry soil treatments in a greenhouse population of M. guttatus.

Key Results

Consistent with predictions, selection for early flowering was generally stronger than for mating system traits, and selection for early flowering was stronger in dry soil. Inconsistent with predictions, selection for water-use efficiency was largely absent; selection for large flowers was stronger than for drought escape in the field; and most drought escape and mating system traits were not genetically correlated. A positive genetic correlation between flowering time and flower size, which opposed the adaptive contour, emerged only in wet soil, suggesting that variation in water availability may maintain variation in these traits. Plastic responses to soil moisture treatments supported the idea that taxonomic divergence could have been facilitated by plasticity in flowering time and selfing.

Conclusions

The hypothesis that plant mating systems may evolve indirectly via selection on correlated life history characteristics is plausible and warrants increased attention.

Keywords: Developmental rate; drought escape; floral evolution; flowering time; genetic correlation; heritability; Mimulus; mating system; phenology; phenotypic plasticity; phenotypic selection; water-use efficiency

Journal Article.  10584 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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