Date of Award

Spring 2003

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

Program/Concentration

Biology

Committee Director

Mark J. Butler, IV

Committee Member

R. James Swanson

Committee Member

Kent E. Carpenter

Call Number for Print

Special Collections LD4331.B46 H44 2003

Abstract

The population size structure of the Caribbean Spiny Lobster, Panulirus argus, in the Florida Keys, Florida (USA) has undergone a dramatic shift as a result of fishing pressure on the large individuals of the population. Male lobsters are affected most by fishing because of sexual dimorphism in size and other studies have shown that male size has direct impacts on reproductive output (i.e., number of fertilized eggs/clutch) that are independent of female size. To assess more precisely the impact of male size on fertilization success, I conducted laboratory experiments and field observations to examine various male reproductive attributes over a range of male sizes. These experiments confirm that large males produce sperm packets (spermatophores) with more sperm and a greater quantity of spermatophore matrix. The distribution of sperm cells within the spermatophore is not uniform and indicates that the production of multiple clutches from one spermatophore is unlikely. Evaluation of sperm within spermatophores collected from female lobsters in fished and unfished areas also yielded estimates of operational sperm:egg ratios. The calculated sperm:egg ratio was low in both fished (21.5 ± 10.6 mean ± 95% confidence intervals; C.I.) and unfished (37.4 ± 18.3 mean ± 95% C.I.) lobster populations, but reduced in fished areas where males are smaller. Results from laboratory mate inhibition experiments suggest that female mating receptivity is suspended upon their receipt of a spermatophore, but can be re-established if the spermatophore is removed, either artificially or by female or male lobsters. This experiment did not permit me to determine if a chemical stimulus alone was sufficient to inhibit further mating or if a concurrent physical presence of a spermatophore was necessary. However, contact between the spermatophore and the female sternum is a necessary stimulus for mating inhibition. The evidence gathered in this study suggests that reduced male size in the Florida Keys could potentially limit population fecundity.

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DOI

10.25777/0exm-5y27

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