Date of Award
Thesis open access
Michele A. Johnson
The major function of the testes is sperm production. Sperm morphology is incredibly diverse both within and across species, and this variation results in part from differences in the duration and patterns of cell division during sperm development, or spermatogenesis. To produce this diversity, testis architecture may evolve in correlation with sperm morphology, as for example, sperm length is correlated with the evolution of thicker epithelia of the seminiferous tubules in birds. In this study, I examined relationships between sperm morphology and testis size and architecture in a group of 18 species of Anolis lizards from the Dominican Republic and Puerto Rico. Using cryosectioned testis tissues, I measured the cross-sectional area (CSA) of each testis, the seminiferous tubules within the testis, and the lumina of the tubules, and used the latter two measures to calculate the CSA of the epithelium. Moreover, I used a grid to identify the proportions of cells belonging to the lumen, epithelium, and interstitial space. Lastly, I obtained measures of sperm head, midpiece, and tail lengths for each species (Kahrl 2017, PhD dissertation, University of Virginia). After controlling for body size, I found that species with larger testes had larger tubules with larger lumina (not epithelia) and that larger testes produced sperm with longer heads. Additionally, seminiferous tubules with larger lumina and thicker epithelia produced sperm with longer tails. Lastly, I found that the proportion of epithelial cells within the testis was not associated with any measure of sperm length or testis size or architecture. These results show that future studies of sperm morphology should consider measurements of sperm tail, midpiece, and head lengths (instead of only studying overall sperm length), as these components show differing relationships with testis architecture, and that the evolutionary relationships between testis architecture and sperm morphology differ between birds and lizards.
Hall, Hannah R., "The Evolution of Testis Architecture and Sperm Morphology in Anolis Lizards" (2018). Biology Honors Theses. 25.
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