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

Authors: Seshadri, Arathi; SMITH, TYLER - Nature Conservancy

Submitted to: Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2023
Publication Date: 7/19/2023
Citation: Seshadri, A.H., Smith, T. 2023. Drought and temperature stresses impact pollen production and autonomous selfing in a California wildflower, Collinsia heterophylla. Ecology and Evolution. 13(7). Article e10324. https://doi.org/10.1002/ece3.10324.
DOI: https://doi.org/10.1002/ece3.10324

Interpretive Summary: Unprecedented changes to climatic conditions, including drought and temperature extremes, have become common place. Plants growing under these extreme climate scenarios are responding in a variety of ways, tiding through the extremes to eke out reproductive success. We subjected plants of Collinsia heterophylla, a wildflower native to California, to drought and temperature stresses, observed their responses and surmised the implications of plant stress responses on pollinators that depend on plants. Some of the strategies plants exhibited include early flowering, reduced number of flowers and fewer pollen grains per flower, all of which directly impact pollinators by reducing amount and access to nutrition. In addition, plants experiencing abiotic stress exhibited smaller flowers and reduced stigma-anther separation (herkogamy). Reduced herkogamy is beneficial for plants as the flowers can self-pollinate and maintain reproductive success under stressful conditions by advancing self-pollination and limiting the time to which flowers need to remain open for pollinator visitation. Our study demonstrates that plants are able to rapidly change floral traits under stressful conditions, maximize reproduction while reducing resource intensive floral traits such as flower number, size and pollen grain production. Such plant stress responses directly impact pollinators through reduced nutrition, even as the pollinators are having to deal with the same abiotic stresses to raise their own offspring. Our results suggest that, understanding plant stress responses is critical to develop appropriate management strategies to support pollinators during extreme temperature and drought stress conditions.

Technical Abstract: Ongoing 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, limit pollinator-related floral benefits 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 plant 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 does not appear to compromise plant reproductive success but will likely reduce available nutrition for pollinators through decreased flower and pollen production.