Monday, August 4, 2008

PS 14-159: Reproductive allocation and resource limitation in selfing and outcrossing desert annual plants

Katharine Gerst and D. Lawrence Venable. University of Arizona

Background/Question/Methods
Annual plants are thought to be critically important in the function and diversity of desert ecosystems. This life history strategy may potentially play a central role in the evolution of self-fertilization, as most self-fertilizing plants are annuals. Despite the severe time limitation in which to reproduce, many desert annual plants appear to invest heavily in reproduction and we see a spectrum of co-existing reproductive strategies from complete self-fertilization to complete outcrossing. An ideal system in which to examine the ecology of reproductive strategies in desert ecosystems is within the genus Camissonia (Onagraceae). Self-fertilization has evolved many times in this group and there are multiple examples of sister species with contrasting reproductive strategies that overlap in their range distributions. This study utilizes niche modelling in addition to field and greenhouse studies to explore the relationship between mating system, range size, and allocation strategies within Camissonia.
Results/Conclusions
We have found that allocation to reproductive structures relative to vegetative structures and floral longevity is reduced in selfing species. Selfing species are found to have greater range sizes and occupy a greater breadth of environmental conditions. In addition, within this group we found a trade-off between flower size, seed size, and seed number in relation to mating system. Field studies are being used to examine the relative importance of pollen and resource limitation in constraining seed production in co-occurring selfing and outcrossing species. Preliminary results indicate that the strength of pollen and resource limitation shift throughout the flowering season. Results have important consequences for expanding our understanding of the costs and benefits of selfing and outcrossing reproductive strategies in variable environments.

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