Abstract Detail

Ecology

Hove, Alisa A [1], Mazer, Susan J [2], Ivey, Christopher T [3].

Seed set variation in wild Clarkia populations: Teasing apart the effects of seasonal resource depletion, pollen quality, and pollen quantity.

In habitats that experience predictable, seasonal resource declines during the growing season, natural selection may favor individuals that flower early or engage in a mixed mating strategy that reduces dependence on pollinators for reproduction. Under such ephemerally favorable conditions, late blooming species may be particularly vulnerable to resource limitation of seed production. Nonetheless, late flowering may be adaptive if it ameliorates the negative effects of early-season pollen-limitation on fitness. In California (USA), a region prone to seasonal drought, members of the annual, self-compatible wildflower genus Clarkia are among the last herbaceous species to bloom in their plant communities. We compared pollen limitation of seed set and self-fertilization rates within seasons in two mixed-mating Clarkia taxa. For three years, we conducted a pollen supplementation experiment in multiple field populations of each taxon. We hand-pollinated one flower on each of 1240 individual plants Early (near the onset of flowering) and Late (near the end of flowering), and compared seed set to adjacent, open-pollinated flowers on the same stem. To assess the contribution of pollen quality to pollen limitation, we first (2008) used allozymes to estimate outcrossing rates of seeds produced by Early and Late open-pollinated flowers. Second (2009), we conducted an anther-removal experiment to estimate autogamous (within-flower), geitonogamous (between flowers on the same individual), and xenogamous (between individuals) pollen deposition. Seed set in C. unguiculata was not pollen-limited. Clarkia xantiana ssp. xantiana, however, was pollen-limited in 2008 and 2010, but not 2009. Pollen-limitation did not differ between Early and Late treatments, however, for either taxon in any year. Fruits from Early flowers consistently had higher seed set than Late flowers, but not because the latter were pollen-limited. Reproduction in both taxa was generally pollinator-dependent — most pollen deposition was xenogamous and outcrossing rates were > 0.7 in both taxa — but it did not differ between Early and Late periods. These results suggest that in the Clarkia populations studied here, pollen receipt and pollen quality (estimated as the proportion of selfed versus outcrossed offspring) remain consistent across the growing season. By contrast, within individuals, the resources necessary to provision seeds decline over the season, reducing the fitness benefits associated with resource allocation to ovules.

1 - Warren Wilson College, Biology Department, PO Box 9000, Asheville, NC, 29915-9000, United States
2 - University Of California Santa Barbara, Department Of Ecology & Marine Biology, 4119 Life Sciences Building, Santa Barbara, CA, 93106, USA
3 - California State University, CENTER FOR BIODIVERSITY-INHS, California State University, Chico, 400 W 1st St., Chico, CA, 95929-0515, USA

Keywords:
resource limitation
self-fertilization
pollen limitation.

Presentation Type: Poster
Session: P, Ecology Section Posters
Location: Exhibit Hall/Savannah International Trade and Convention Center
Date: Monday, August 1st, 2016
Time: 5:30 PM This poster will be presented at 5:30 pm. The Poster Session runs from 5:30 pm to 7:00 pm. Posters with odd poster numbers are presented at 5:30 pm, and posters with even poster numbers are presented at 6:15 pm.
Number: PEC019
Abstract ID:507
Candidate for Awards:None