Additional Participants

Graduate Student

Sheri Johnson
Aimee Phillippi

Undergraduate Student

William Gensheimer
Dan Pinho

Organizational Partners

University of New Orleans

Project Period

January 1, 2002-July 31, 2004

Level of Access

Open-Access Report

Grant Number


Submission Date



This proposal is an extension of previous work aimed at understanding the effects of reproductive biology on patterns of life history evolution in a colonial marine tunicate, Botryllus schlosseri. The project will test five hypotheses about factors that may determine male reproductive success in natural spawns of this colonial invertebrate. The five hypotheses specifically aim to explore the effects of timing of sperm release, relatedness of mates, population density, and allocation to male function on fertilization success in field and experimental populations of Botryllus.

Previous work has shown that there is a narrow temporal window in which fertilization can result in a viable embryo, and there may be a gametic incompatibility system. Furthermore, fertilizing sperm are generally the product of nearby colonies; colonies exhibit variation in sperm production, and high levels of sperm production only increase local reproductive success when sperm competition occurs.

This preliminary information suggests that male reproductive success in natural populations is a complex function of timing relative to the reproductive cycles of other colonies, gametic compatibility, sperm production, and population density.

The proposed research will consist of field and laboratory studies, with preliminary work focused to maximize the information yield of a suite of nine polymorphic microsatellite loci. These genetic markers will then be used to assay paternity in natural spawns and test the series of five hypotheses about the determinants of male reproductive success.

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