Tests for the joint evolution of mating system and drought escape in Mimulus

Area of Science:

• Evolutionary Biology
• Plant Sciences
• Ecology

Background:

• Self-fertilizing species often occur at the edges of their ranges.
• Sub-optimal habitats may favor unique physiological adaptations.
• The role of direct selection versus correlated traits in self-fertilization evolution is unclear.

Purpose of the Study:

• To test if self-fertilization in Mimulus arises from direct selection on drought escape traits.
• To investigate the indirect evolution of self-fertilization through correlated life history traits.

Main Methods:

• Estimated phenotypic selection on mating system and drought escape traits in field populations of Mimulus guttatus.
• Compared trait phenotypes and selection between wet and dry soil conditions in greenhouse experiments.
• Assessed genetic variation and covariation for traits under different soil moisture treatments.

Main Results:

• Selection favored early flowering, especially in dry conditions, more than mating system traits.
• Water-use efficiency selection was minimal; large flowers were selected for more than drought escape in the field.
• Plasticity in flowering time and selfing potentially facilitated species divergence.

Conclusions:

• The evolution of plant mating systems may occur indirectly through selection on correlated life history traits.
• This indirect evolutionary pathway warrants further investigation.