Acorn barnacles are simultaneous hermaphrodites, functioning as both males and females at once. The species from this dissertation, Semibalanus balanoides and Balanus glandula, mate with long penises during brief mating seasons in the fall and winter. Barnacles are ideal organisms for studies of reproductive investment, function and success. They are sessile, allowing for manipulation of populations and transplant experiments. Their anatomy is well suited for comparisons of allocation to the sex roles. Potential mates and levels of mating competition can be assessed because they are limited by the reach of the penis. Fertilized eggs are brooded for several weeks until the development of free-swimming larvae; during this time mating success can be measured. I used field observations and experiments to answer several questions about barnacle reproductive dynamics. I investigated variation in the functional morphology of the penis of the barnacle. I observed that barnacles from dense patches had on average shorter penises than those from sparse aggregations. I also observed that in sites exposed to ocean waves barnacles had thicker penises than those in protected, calm sites. Barnacles in these calm sites were consistently able to reach more distant mates than those from wavy sites. I performed transplant experiments that showed that this difference was the result of phenotypic plasticity and that these morphologies increased ability to successfully mate at the sites in which they develop. I performed experiments that demonstrate that observed differences in penis length are a result of the settlement density of the barnacles and not mate distance alone. Sex allocation theory predicts that as mating group size increases, barnacles should make greater investments into the male role to remain competitive and that this should tradeoff against investments to female function. My experiments show that greater settlement density does lead to increases in allocation to male function, but that increases in mate numbers do not. The assumption of a tradeoff with female function was not supported. My results indicate that the major factor underlying allocation to female function is body size and brood space.
|Advisor:||Levinton, Jeffrey S.|
|School:||State University of New York at Stony Brook|
|School Location:||United States -- New York|
|Source:||DAI-B 71/04, Dissertation Abstracts International|
|Subjects:||Evolution and Development|
|Keywords:||Hermaphroditic barnacles, Mating success, Reproductive behavior, Sex allocation|
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