Title

A Preliminary Study of Variation in Penis Characteristics and Other Reproductive Traits in Barnacles

Event Name/Location

Benthic Ecology Meeting 2005, Williamsburg, Virginia, April 6-10, 2005

Document Type

Conference Proceeding

Publication Date

4-2005

Abstract

Barnacles are an appropriate model system for studies of sex allocation. Because they are sessile and copulate, mating group size is easily controlled. Selection should favor longer penises to reach a greater number of mates, but this may be constrained by environmental factors such as wave energy regime. Sex allocation theory predicts that the amount of resources allocated to male versus female function depend on mating group size. The reach of the penis defines the mating group of a focal barnacle, the physical environment may limit the ability of barnacles to seek and inseminate mates. Limitation of penis reach may result in reduced mating group size and lessen investment into male function. If free from this limitation, barnacles may optimize penis length based on population density. Control of mating group size may give barnacles greater ability to optimize sex ratio. Semibalanus balanoides were sampled from calm sites and compared to similar collections from the exposed coast. Variation of penis length to body size, mass of egg lamellae and other reproductive characters are compared. Penis length seems to vary with population density, but not environment. Preliminary results suggest that egg masses are relatively larger for barnacles from low population densities. These data should demonstrate the relative difference in strength of biotic and abiotic factors in altering sex allocation and provide a contrast between the strength of sexual selection and environmental limitation on reproductive characters.

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