09/07/07, 13:00 - 14:00 at Room 3631 (6th floor of building 3 of the Faculty of Sciences)

Gynodioecy describes populations of females and hermaphrodites. Gynodioecy is the second most common breeding system among angiosperms after hermaphroditism. Gynodioecy typically arises because of mitochondrial cytoplasmic male sterility genes (CMS) which create the female phenotype. Gynodioecy persists if the ecological context selects for females and thereby maintains the CMS mitotype. Despite the widespread occurence of gynodioecy and more than 100 years of research on how females are maintained, current models can not adequately predict gynodioecious sex ratios, nor can they explain the dramatic sex ratio variation observed in gynodioecious populations. Pollinators' role in maintaining females in a population should be further examined as females require access to quality pollination services to persist. I use complimentary empirical and theoretical experiments to understand the role pollinator behavior may play in sex ratio evolution of gynodioecious plants. I will discuss my fieldwork exposing replicate *Silene vulgaris* populations to various pollinators and measuring female relative seed fitness. I will also present my theoretical work to be conducted this summer at Kyushu University, using simulation-based and analytical modeling approaches to understand the relationship between pollinator behavior and gynodioecious sex ratios. This work suggests a pollinator-shift could act as a sex ratio distorter and that there are limited pollinator contexts in which gynodioecy can evolve.

Sex change evolution of Arisaema triphyllium in areas of high deer density

Mollie Brooks
(University of Florida)

09/07/07, 14:00 - 15:00 at Room 3631 (6th floor of building 3 of the Faculty of Sciences)

This summer I will try to determine what might be causing Jack-in-the-pulpit (JITP: Arisaema triphyllum) populations to have skewed sex ratios in forests with high densities of white-tailed deer (Odocoileus virginianus). Due to hunting policies that preserve female deer and reduce predators, deer populations in the northeastern US have been increasing for the past century and are drastically changing the forest understory. Deer rarely eat JITP, and it is unclear from field observations, what aspect of JITP’s life history is being affected. There are several competing hypotheses including increased seedling mortality due to trampling and decreased asexual reproduction due to soil compaction. JITP are sequential hermaphrodites, first being non-reproductive, then male, then switching to be female if they grow large enough. Some populations have up to 5 males per female. Evolution should reduce the switch size to maintain a more equal sex ratio. JITP sex allocation has previously been predicted with a size-advantage model, but it matches our system poorly because our focus populations are pollinator limited. I plan to use dynamic optimization modeling and a growth-rate-advantage model to understand the relationship between evolution and life history changes in JITP by accounting for the tradeoffs among growth, survival, and reproduction. I will also predict the switch size that is evolutionarily stable.

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