Fertilization in Sea Urchins – How Gamete Properties Interact with Hydrodynamic Regimes

imageThis project is supported by a pair of grants from the National Science Foundation ($327,976 to the University of New England and $298,835 to the University of South Florida), from August 1, 2004, through July 31, 2007.

Principal Investigators

Phil Yund, Ph.D., Director
Marine Science Education and Research Center
University of New England
Biddeford, ME		   Flo Thomas, Ph.D.
Dept. of Biology
University of South Florida
Tampa, FL

Problem

Like many other invertebrate marine animals, sea urchins reproduce by releasing eggs and sperm into the seawater. Sea urchin spawning is easy to manipulate, and sea urchin eggs produce an easy-to-see membrane when fertilized. Consequently, urchins have become a prominent model system for addressing questions about fertilization in nature. A large body of literature on sea urchin fertilization suggests that fertilization may only be successful when urchins spawn simultaneously, in close proximity, and under nearly ideal flow conditions.

yund5However, past experimental work on sea urchin fertilization has largely by-passed some of the reproductive characteristics that may have evolved to enable successful fertilization. Gametes are often released from syringes or held in mesh bags, and fertilization is assumed to be very short-term process that occurs entirely in the water column. But the reality of sea urchin spawning differs greatly from these experimental conditions. Gametes are released in sticky, viscous fluids that cling to animals; sperm and egg slowly diffuse away for hours. Boundary layer flows around the animals cause eddies to form downstream of the sea urchins, and gametes may re-circulate in these eddies and interact for prolonged periods of time.

Approach

Laboratory flow tanks will be used to explore the effect of variation in hydrodynamic regime on the location of sperm:egg contact (i.e., the site of fertilization) and the proportion of eggs that are fertilized. We will explore fertilization processes in both unidirectional flow and the oscillatory flow typical of wave-exposed habitats. Previous fertilization experiments have largely ignored oscillatory flow. In addition, a field survey of natural populations will determine the subset of our laboratory flow conditions under which spawning actually occurs in nature.
    
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