Graduation Year


Document Type

Open Access Senior Thesis

Degree Name

Bachelor of Arts


Environmental Analysis

Reader 1

Findley Finseth

Reader 2

Colin Robins

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The ‘time limitation hypothesis’ is an evolutionary theory regarding evolution in angiosperms. The theory attributes ephemeral drought stress to transitions from a perennial to annual life history and an animal- to self-pollinating mating style. The most influential edaphic parameter on water availability is soil texture (i.e. grain size) due to its controls on porosity. Adhesion weakens with coarseness allowing for expedited rates of water loss via evaporation and percolation. The potential implications of coarse soil textures on major transitions in angiosperms due to drought mediation as the ‘time-limitation hypothesis’ proposes has yet to be thoroughly examined. Here, we grew two sympatric species of Mimulus with distinct mating styles on varying sand textures with equal water inputs and measured their response to increasing texture-mediated drought. Texture was shown to moderate both water retention in the soils and the felt effects of drought by overlying plants. In terms of species response to intermittent droughts, the selfing species was more drought resilient and enacted drought escape behaviors where the animal-pollinator appeared to be more drought avoidant. These findings suggest a potential underlying causal link between soil texture and mating style transitions in angiosperms which is of interest given that historic drought events are expected to occur more frequently under climate change.

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Evolution Commons