Seminar by international scientist at the Department of Botany and Zoology

Prof Susan Mazer from the University of California in Santa Barbara will present a seminar on “The evolution of mating system, life history, and physiological performance in Clarkia sister taxa: does selection for drought-avoidance drive the evolution of selfing?” at the Department of Botany & Zoology.

DATE: 23 August

TIME: 13:00 – 14:00

VENUE: Science Building, Broom Lecture Hall (Room 2020)

ENQUIRIES: trobins@sun.ac.za/ lwillems@sun.ac.za, 021 808 3236

More about Prof Mazer’s talk: 

Plant mating systems are highly evolutionarily labile; in the annual wildflower genus Clarkia, for example, the shift between outcrossing and self-fertilization has occurred > 12 times among ~40 taxa. In addition to exhibiting lower pollen:ovule ratios and smaller flowers, regularly selfing Clarkia taxa flower earlier and have faster floral development rates than their outcrossing counterparts. The most common explanations for the evolution of selfing focus on its direct advantages. For example, selection may favor selfing where pollinators are scarce or unreliable, where plants with large, attractive flowers are at risk of desiccation, or where short growing seasons require rapid reproduction (which is promoted by selfing). But selfing could also evolve as a “by-product” of selection on genetically correlated traits, even if there is no direct advantage to selfing. Currently, we’re investigating genetic correlations between flowering date and traits that influence mating system (e.g., the degree of herkogamy and dichogamy). If these correlations are sufficiently strong, with early flowering associated with rapidly developing flowers with low herkogamy and dichogamy, then selfing may evolve in Clarkia not (only) because of its direct advantages, but as a correlated response to selection favoring earlier flowering (e.g., where the growing season is short). If this is generally the case, then adaptation of annual spring wildflowers to earlier or unpredictable summer drought could involve a rapid increase in selfing rates (and inbreeding depression), potentially reducing their adaptive potential. We’re also examining whether the shorter life span of selfing Clarkia is reflected in their physiological performance. Selfing taxa appear to achieve their earlier flowering through faster photosynthetic rates, but this comes with higher rates of evapotranspiration. Consequently, the evolution of selfing may assume both physiological as well as genetic risks, and therefore be restricted to certain habitats or environmental conditions.