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Ecological Section

Emms, Simon K [1], Croteau, Clare [1], Bresee, Karen [1], Churchill, Stephanie [1], Duxbury, Nicole [1], Kaster, Colleen [1].

Resource Limitation and Patterns of Sex Allocation in Prairie Larkspur, Delphinium virescens..

The majority of angiosperms are cosexual, reproducing through both male and female pathways. However, if reproductive resources are limited there should be a trade-off in the allocation of these resources to male vs. female reproductive structures. Animal-pollinated plants also need to allocate resources to floral traits for pollinator attraction and reward, resulting in a three-way trade-off between male, female, and attractive structures. Sex allocation theory shows that the optimal allocation strategy depends on the marginal fitness returns on investment in each type of structure, and that the optimal strategy may change with floral blooming rank as the opportunities for male and female reproduction change. We studied patterns of sex allocation in Prairie Larkspur Delphinium virescens at three sites in southeast Minnesota between 2000 and 2003. All populations showed substantial among-plant variation in allocation to stamens, pistils, and attractive structures, although CVs for female allocation were substantially greater than those for male or attractive structure allocation. Within plants, female allocation declined significantly with floral blooming rank in all populations. Changes in male allocation differed significantly among years and populations, but the overall effect was an increase in proportional allocation to male structures with blooming rank in all populations and years. Experimental removal of early-blooming flowers showed that this change in allocation was due to declining opportunities for female reproduction in late-blooming flowers because of resource limitation. Allocation to attractive structures declined with blooming rank in all populations, but changes in proportional allocation differed significantly among populations. Among plants there was no evidence of a phenotypic trade-off in biomass allocation to stamens vs. pistils. However, there were clear biomass allocation trade-offs between stamens and pistils within flowers at all three sites, once differences in resource availability among plants and blooming rank trends in allocation to flowers were controlled for statistically.

1 - University of St. Thomas, Biology, OWS 390, 2115 Summit Avenue, St. Paul, Minnesota, 55105, USA

Floral traits
Flower size
Ovule number
Pollen-ovule ratio
Resource allocation
Sex allocation
sexual systems
Stamen number

Presentation Type: Paper
Session: 40-4
Location: Wasatch (Cliff Lodge)
Date: Tuesday, August 3rd, 2004
Time: 3:15 PM
Abstract ID:717

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