Costs and benefits of self-fertility in Asclepias exaltata (Apocynaceae)1

Abstract

Himes, S. L. (Department of Biology, Western Carolina University, Cullowhee, NC 28723) and R. Wyatt (Highlands Biological Station, 265 Sixth Street, P.O. Box 580, Highlands, NC 28741). Costs and benefits of self-fertility in Asclepias exaltata (Apocynaceae). J. Torrey Bot. Soc. 132: 24–32. 2005.–Variation in levels of self-fertility exists among populations of Asclepias exaltata, despite traditional characterization of this species as self-sterile. The costs and benefits associated with self-fertility were investigated by comparing fruit-set, seed number, and progeny fitness from self-pollinations, single-donor cross-pollinations, and multiple-donor cross-pollinations. Single-donor cross-pollinations were expected to produce fewer fruits than multiple-donor cross-pollinations as a result of mate selection by maternal plants, but this was not the case. Outcrossed fruits from self-fertile plants contained significantly fewer seeds than did outcrossed fruits from self-sterile plants, but overall fitnesses of self-fertile and self-sterile plants were essentially equal. There was variability among self-fertile plants in their propensity to mature selfed fruits, but, on the whole, selfed fruit-set was very low compared to outcrossed fruit-set. Furthermore, seed number, percent seed germination, and plant survival were significantly lower for selfed versus outcrossed progeny on self-fertile plants, suggesting strongly that selfed progeny suffer greatly from inbreeding depression. Because selfing is rare and the overall fitnesses of self-fertile and self-sterile plants are essentially equal, frequencies of self-fertile individuals in these populations may differ simply due to random processes.