Publication Date


Advisor(s) - Committee Chair

Dr. Steve Huskey (Director), Dr. Philip Lienesch, Dr. Michael Collyer

Degree Program

Department of Biology

Degree Type

Master of Science


Phenotypic plasticity, the capacity of a single genotype to exhibit variable phenotypes in different environments, is common in many species. A sample of wild caught Archosargus probatocephalus, also known as sheepshead, from Florida was randomly divided into two treatment groups: one group was fed soft prey, Mercenaria sp. muscle tissue, and the other group was fed hard prey, Mercenaria sp. in the shell, for 365 days. It was hypothesized that the sheepshead fed hard prey would have a thicker tooth enamel layer containing more calcium, and therefore be stronger than the tooth enamel layer of those fed soft prey items. Additionally, the mean functional jaw surface area, the percentage of tooth coverage of functional jaw surface, number of teeth per jaw, correlation between standard length and mean total tooth height, and the combined surface area of the teeth, when compared between the two treatments, should be greater in the hard prey treatment.

The seventeen jaws of two prey groups were acquired postmortem and each jaw was divided into four quadrants. The largest tooth in each quadrant was removed from the jaw, longitudinally sectioned, and examined using scanning electron microscopy (SEM) to measure the enamel and dentin layers. Using the SEM backscatter electron detector the elemental composition of the different layers was determined at multiple locations. Finally, data was analyzed using analyses of variance (ANOVA’s) to compare mean tooth height, calcium content in enamel and dentin layers, mean functional jaw number of teeth per jaw, and upper to lower jaw overall enamel and dentin thickness between each treatment.

Phenotypic plasticity was identified in three areas: percentage of jaw surface covered by teeth, a positive correlation between total tooth height and enamel height in hard prey treatment, and a positive correlation between total tooth height and soft prey treatment dentin height; but not in the other areas studied. It is apparent that phenotypic plasticity can increase an individual’s ability to survive in a variable food resource environment by changing some aspects of tooth morphology, but the ability to change in response to stimuli was not found in all areas of tooth structure. i


Evolution | Marine Biology | Terrestrial and Aquatic Ecology