DEVELOPMENTAL PLASTICITY OF SHOOT ARCHITECTURE: MORPHOLOGICAL EXPRESSION AND ECOLOGICALLY RELEVANT ONSET IN LOCALLY ADAPTED POPULATIONS OF MIMULUS GUTTATUS

Premise of research.Shoot architecture profoundly affects vegetative and reproductive features of plants. Perennial dunes (DUN) and annual Iron Mountain (IM) populations of Mimulus guttatus are adapted to locales with different water availability regimes and have drastically different patterns of shoot architecture. Plants from both populations exhibit plastic responses to water availability, although plastic responses in shoot architecture have not been investigated in these populations. Because plants grow indeterminately and plastic responses accrue over developmental time, an ontogenetic approach is essential to understanding the expression and ecological relevance of plastic responses.Methodology.Seeds from multiple families of both populations were collected from the field, grown in a common environment, and allowed to self. Selfed seeds were then grown under wet or dry conditions. Morphological data were recorded weekly to describe ontogenetic changes in shoot architecture.Pivotal results.Plants from both populations exhibited phenotypic plasticity in response to water availability; however, the morphological expression, magnitude, and onset differed between populations.Conclusions.Our ontogenetic study demonstrates that plastic responses in M. guttatus architecture are expressed at ecologically relevant times during ontogeny. In particular, IM plants behave like aggressive annuals while DUN plants exhibit more conservative growth rates and delayed plastic responses. Plastic responses in the IM population included increased flower production, indicating a potential adaptive role for phenotypic plasticity in this population.