Drought and temperature stresses impact pollen production and autonomous selfing in a California wildflower, Collinsia heterophylla

Abstract

AbstractOngoing climatic changes have altered growing conditions for plants by limiting water availability and inducing unprecedented temperature increases, eliciting plant functional responses that compromise floral trait expression, reduce pollen production and promote early self‐pollination. In a controlled greenhouse study, plants of Collinsia heterophylla, an annual mixed‐mated hermaphrodite, were grown under temperature and water stresses. Floral trait responses and related effects on plant reproductive success were recorded. Plants grown under temperature and water stresses were shorter and had fewer leaves at flowering than control plants. Temperature‐stressed plants flowered earlier and had smaller flowers that produced fewer per capita pollen grains than control and water‐stressed plants. While lifetime flower production in plants experiencing temperature stress alone or water stress alone was similar to control plants, those receiving combined temperature and water stresses had significantly lower lifetime flower production. Abiotic stress did not affect investment in female traits such as ovule number per flower, but impacted male traits seen as fewer pollen grains per flower. In plants experiencing abiotic stress, an increase in autonomous self‐pollination was facilitated through a compromise in herkogamy, a sexual interference mechanism that promotes cross‐pollination. Spatial separation between stigma and anther, a measure of herkogamy was zero or negative in stressed plants. Thus, abiotic stress responses in plants did not compromise plant reproductive success as autonomous selfing was augmented. In nature, such responses will likely reduce available nutrition for pollinators through decreased flower and pollen production.