Factors That Determine Male Reproductive Success in Natural Spawns of a Colonial Marine Invertebrate

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National Science Foundation, $335,739, January 2002 through December 2005.

Principal Investigators
Phil Yund, Ph.D., Director
Marine Science Education and Research Center
University of New England
Biddeford, ME		   Paul Rawson, Ph.D.
School of Marine Sciences
University of Maine
Orono, ME

Problem

Virtually all sessile and sedentary invertebrate marine animals (those that either live their lives glued to the bottom, or have limited powers of locomotion) reproduce by releasing sperm into the surrounding water (free-spawning). Recent work on the ecology of fertilization in free-spawners has focused largely on processes that determine how many eggs are fertilized. However, far less is known about the flip side of the problem; what makes one male more successful than another male at fertilizing eggs?

Approach

yund6This project is using an egg-brooding colonial sea squirt (Botryllus schlosseri) as a model system to test a series of hypotheses about what makes a male a successful dad. Colonies vary greatly in the amount of sperm they produce, and increased sperm production would seem likely to improve paternal success. However, model predictions suggest that high levels of sperm production may only be advantageous when males are competing for access to eggs (i.e., when sperm competition occurs). In the absence of sperm competition, a male may be able to fertilize most nearby eggs with relatively little sperm. If so, levels of sperm production may vary with population density, which ultimately determines the degree of sperm competition. This and related hypotheses will be tested by using a set of genetic markers (similar to the DNA fingerprints used for human paternity testing) to assay paternity in natural spawns.
    
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