Multiple effects of drought on pollination and mating-system traits in Dalechampia scandens

Premise of research - Selfing rates in mixed-mating plant species are often found to fluctuate greatly across time and space. Environmentally induced changes in floral traits may mediate changes in selfing rates through several mechanisms, including direct effects via changes in traits influencing autofertility rates, and indirect effects via changes in traits affecting the rate of pollinator visitation and/or the efficiency of cross-pollination. In this study we tested how experimentally induced drought affected traits related to these three components of plant mating systems.
Methodology - We subjected two populations from each of two species in the Dalechampia scandens species complex to a series of experimental drought events in the greenhouse. We measured drought effects on advertisement (signaling) traits, reward traits, herkogamy, dichogamy, autofertility, and pollination accuracy, and compared these across populations and species.
Pivotal results. Blossom size (advertisement and reward traits) and dichogamy were consistently reduced under dry conditions. In contrast, the effects of drought on herkogamy and autofertility were population specific. Similarly, despite consistent effects of drought on traits functionally related to pollen transfer, changes in pollination accuracy differed among populations. When plants were returned to a benign moisture environment, phenotypic changes were largely reversed.
Conclusions - These results show that environmental variation may simultaneously affect multiple traits related to plant mating systems, and thus mediate spatial and temporal variation in selfing rates. However, except for size reductions in advertisement and reward traits, these effects tend to be population-specific and therefore difficult to predict.