Term of Award

Summer 2003

Degree Name

Master of Science

Document Type and Release Option

Thesis (restricted to Georgia Southern)

Department

Department of Biology

Committee Chair

Daniel F. Gleason

Committee Member 1

Alan W. Harvey

Committee Member 2

Lorne M. Wolfe

Abstract

Hermaphroditism has often been described as a mechanism of enhancing fertilization success in sessile organisms, but may also be advantageous because allocation to male and female function can be manipulated to maximize fitness when energy availability limits reproduction. Sex allocation theory has been primarily developed in plants, but may be applicable to other sessile organisms that are subject to similar selective pressures. Like plants, reef building corals depend on photosynthesis for most of their energy, yet they inhabit a wide range of depths. Along this gradient, light availability may limit the amount of energy available for reproduction. The objectives of the present study are to describe the reproductive biology of the hermaphroditic coral Porites astreoides, and to determine whether sex allocation varies with colony size or along a light-energy gradient. Tissue samples were collected at depths of 6, 13, 18 and 27 m and the surface area of each colony was measured. Tissue samples were histologically sectioned and mounted on slides for quantification of spermary and ovum area. Results indicate that allocation to female function is positively correlated with colony size and allocation to male function is negatively correlated with colony size. The pattern of sex allocation varying with colony size indicates that allocation to female function is delayed, possibly because female function is more costly or represents a greater time commitment than male function. Allocation to female function varies among depths, but not in a pattern consistent with the light gradient. Porites astreoides may have the ability to compensate for reduced light availability within a certain depth range, but not beyond a specific threshold depth. However, other environmental factors may explain the differences in sex allocation among depths, such as population density, current velocity or heterotrophic feeding.

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