Phenotypic plasticity in mating-system traits in the annual Collinsia verna

Variation in abiotic factors can influence the selective advantage of selfing and expression of the mating system if mating-system modifier traits are phenotypically plastic. However, relative to biotic factors, the role of abiotic conditions in driving variation in and evolution of plant mating systems is rarely addressed. We use an experimental approach to evaluate the extent to which genetic and environmental variation influence the expression of mating-system traits in the annual Collinsia verna. We subjected families to two environmental treatments in the greenhouse that varied in light and water availability, simulating natural and short flowering-season conditions, and examined the following: autonomous fruit set, flower number, flower size, rate of anther dehiscence, floral longevity, and timing of selfing. Our results demonstrate plasticity in nearly all traits examined. Compared with natural-season conditions, plants under short-season conditions produced fewer, smaller flowers and selfed approximately one day later due to slower anther dehiscence rates. Autonomous fruit set was similar across treatments, but there was genetic variation for plasticity in this important trait. Further, we show genetic variation in autonomous fruit set, timing of selfing, and flower number and size. Given the effects of global climate change on the duration of growing season, our results suggest that plasticity in mating-system traits will affect mating-system variation and, thus, opportunities for selection.