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Abstract Detail

Pollination Biology

Penny, Rebecca [1].

Sterile pollen and stamens in females of a cryptically dioecious angiosperm do not increase pollen receipt or seed set.

The presence of sterile reproductive structures within cryptically dioecious species presents an opportunity to address fundamental questions about the evolution of separate sexes and the potential benefits of hermaphroditic morphologies. Thalictrum macrostylum (Small & A. Heller) is a morphologically androdioecious but functionally dioecious species. Females produce flowers with variable numbers of both uniovulate pistils and stamens that contain only inaperturate, non-germinating pollen. Previous evidence suggests that a negative relationship may exist between pistil and stamen number in some conditions. Thus, if stamens do not increase female fitness - for instance by increasing pollen receipt - they are expected to be lost. Using nested pollinator exclusion and stamen-removal treatments, I examined the relationship between stamen number, pollen receipt, and seed set in females to test hypotheses for the maintenance of stamens and sterile pollen in females of two natural populations of T. macrostylum. I found no effect of stamen presence on wind-borne pollen receipt and only a marginally significant positive effect on open pollination in females. Average pollen capture per flower did not differ significantly between bagged and open-pollinated flowers, suggesting that insect pollination does not represent a significant source of pollen receipt for females. There is a positive relationship between stamen number and seed set; however, the distribution of variance in seed set was significantly broader for flowers with few stamens. Taken within the context of no effect of stamen number on pollen receipt, I suggest that stamen number may be an indicator of female quality or resource availability, rather than a direct cause of increased seed set. Thus, I reject the pollinator attraction hypothesis for the maintenance of sterile stamens in females and look to other forces (such as genetic constraints) to explain the maintenance of sterile pollen and stamens in females of T. macrostylum.

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1 - Indiana University, Biology, Jordan Hall, Rm 142, Bloomington, IN, 47405, USA

cryptic dioecy
Thalictrum macrostylum
pollinator attraction
wind pollination.

Presentation Type: Oral Paper:Papers for Topics
Session: 45
Location: Melrose/Riverside Hilton
Date: Wednesday, July 31st, 2013
Time: 2:00 PM
Number: 45003
Abstract ID:558
Candidate for Awards:None

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