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Abstract Detail

Ecological Section

Hannan, Gary L. [1], Benedict, Andrea L. [2].

Interpopulation differences in floral phenology in response to shading in the androdioecious herb Mercurialis annua (Euphorbiaceae).

Mercurialis annua, an annual androdioecious species, exhibits intraspecific variation in sexual function associated with polyploidy. Diploid populations are dioecious, polyploids are monoecious, with some hexaploid populations being androdioecious. Sex expression is also phenotypically plastic, with population density and light intensity affecting allocation to male vs. female function. Cosexual plants growing in shade in the field reduce their allocation to female function, but effects of shading on timing of production of staminate vs. pistillate flowers is unknown. We hypothesized that if allocation to female function is reduced in shaded plants and flowering phenology is affected similarly, then shade-grown plants will exhibit delayed pistillate flower anthesis. Shading delayed onset of flowering, and most sun-grown plants produced only staminate flowers at the lowest node, but the difference in time between first pistillate flower and first staminate flower maturing at subsequent nodes did not differ between sun and shade plants. However, not all plants produced flowers of each sex at each node during the 90-day study, and the proportion of plants in each population that produced flowers of each sex at different nodes in response to shading were population-specific. Among sun-grown plants, more produced staminate flowers and fewer produced pistillate flowers at lower nodes than expected if light and node position were independent factors, whereas the converse was found for upper nodes. Among shade-grown plants, no significant interaction between light and node position was found. In general, interpopulation differences in sexual function were reflected in some aspects of the phenology of flowering, and phenotypic plasticity in response to shading was also observed. The extreme variation in reproductive function among populations offers wide latitude in response to selection pressures.

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1 - Eastern Michigan University, Biology, 316 Mark Jefferson Bldg., Ypsilanti, MI, 48197, USA
2 - Johns Hopkins University School of Medicine, Department of Pharmacology and Molecular Sciences, 725 N. Wolfe Street, WBSB 302, Baltimore, MD, 21205, USA

Sex allocation
phenotypic plasticity.

Presentation Type: Poster:Posters for Sections
Session: P
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM
Number: P49023
Abstract ID:1794

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