Degree Name

Master of Science (MS)

Semester of Degree Completion

1973

Thesis Director

Edward O. Moll

Abstract

Seasonal changes within the tubular and interstitial areas of the testes in Sternotherus odoratus are investigated, histologically and histochemically. Forty specimens were collected in Illinois, Tennessee and Louisiana between May, 1969 and August, 1972.

Many of the histological and macroscopic observations made by Risley (1938) on the spermatogenic cycle of S. odoratus in Michigan are confirmed. Contrary to his findings, fluctuations in interstitial cell nuclear diameters are observed during spermatogenesis. Greatest diameters coincide with what Risley has considered " . . . period of most active breeding." Sertoli cell nuclear diameters undergo similar fluctuations being greatest during spring breeding and fall steatogenesis.

The testes undergo a sequence of well-defined cyclical events. These include a tubular and interstitial lipid cycle correlated with spermatogenesis and a PA/S-glycogenic cycle which can be traced within the Sertoli elements. Roughly, an inverse correlation exists between the two lipid cycles. Lipid concentrations decrease as spermatogenesis advances and accumulate during the interim between cycles. The Sertoli cell is the intratubular locus of lipid accumulation while the interstitial cell is the intertubular locus. Sertoli lipids accumulate more rapidly than do interstitial lipids and are present for a longer time. Whereas interstitial lipids become depleted as secondary spermatocytes are forming, Sertoli lipids remain through the spermatid stage. In the PA/S-gylcogenic cycle, glycogen and carbohydrate materials accumulate within the Sertoli cytoplasm in granular form during the fall and spring. These substrates become depleted during the early stages of spermiogenesis.

Latitudinal geographic variation in the timing of spermatogenic, glycogenic and lipid cycles is evident. Spermatogenesis in Illinois is two to three weeks ahead of that found in Michigan, two weeks behind the cycle in Tennessee and five weeks behind in specimens from Louisiana. The PA/S-glycogenic cycle in Illinois is two weeks behind that found in Tennessee and four weeks behind that in Louisiana specimens. Intertubular lipid cycles in Tennessee and Louisiana are similar to those found in Illinois for corresponding spermatogenic stages. The Sertoli lipid cycle follows the same pattern of timing but differs in that lipids are retained for a longer time in turtles from more southerly locations.

Spring spermatogenesis accelerates with increasing temperature and photoperiod. Following the summer solstice and despite decreasing photoperiod, the cycle continues unabated. With the onset of cooler temperatures in the fall, the cycle regresses and stops. These facts suggest that temperature is the main environmental factor regulating spermatogenesis once it has started.

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