Abstract Detail

Ecological Section

Hersh, Evan [1], Grimm, Jaime [2], Whitton, Jeannette [1].

The clone wars: sexual-asexual dynamics in the Crepis agamic complex.

Hybridization between closely related plant species can often lead to new forms on the landscape, and may result in the displacement of the progenitor species. This dynamic is particularly exemplified in agamic complexes, systems with closely related sexual and apomictic taxa. The Crepis agamic complex contains a wide array of polyploid apomicts that rarely co-occur with sexual types. Theory predicts that asymmetrical reproductive interference will lead to an asexual sweep in mixed populations, which may explain why mixed populations are so rarely found. We identified one of these rare mixed populations in northern Washington, and conducted a crossing experiment between sexual diploid C. atribarba and apomictic polyploid (ca. 8x) C. barbigera, using the apomict as the pollen donor. Maternal recipient C. atribarba individuals received: (i) manual pollinations from sexual diploid pollen donors, and (ii) manual pollinations from apomictic polyploid pollen donors. In addition, both (iii) open pollinated and (iv) pollinator exclusion controls were preformed. The resulting seeds were counted and weighed, and the ploidy of a sample of apparently viable embryos was assessed using flow cytometry. Seed set was high for all treatments, and as predicted, diploid-diploid crosses produced all diploid offspring. Diploid-polyploid crosses, however, produced mainly polyploidy offspring, demonstrating the potential for asymmetric gene flow to interfere with the production of diploid offspring. Just as importantly, a small proportion of seeds from open pollinations of diploids was also polyploid, indicating that the co-occurrence of apomicts and sexuals can result in unidirectional hybridization under natural conditions. Our results provide evidence for asymmetric reproductive interference, with polyploid C. barbigera negatively impacting the fitness of diploid C. atribarba. Although the fitness and reproductive mode of the hybrids are not known, individuals of intermediate morphology and ploidy were detected in the population, and sexual polyploids are not known from either of these taxa. Based on our results, unless mechanisms of prezygotic isolation are strengthened, mixed sexual-asexual populations are expected to be transient, eventually leading to a clonal sweep and eradication of sexual individuals from the population.

Related Links:
Whitton Lab Website

1 - University Of British Columbia, Department Of Botany, 3529-6270 Univ Blvd, Vancouver, BC, V6T 1Z4, Canada
2 - University of British Columbia, 2212 Main Mall, Vancouver, BC, V6T1Z4, Canada

Keywords:
Agamic complex
apomixis
clones
reproductive interference
Polyploidy.

Presentation Type: Oral Paper:Papers for Sections
Session: 52
Location: Salon 6/The Shaw Conference Centre
Date: Tuesday, July 28th, 2015
Time: 2:45 PM
Number: 52005
Abstract ID:891
Candidate for Awards:Ecological Section Best Graduate Student Paper