Changes in the seminiferous epithelium of the lizard – Liolaemus cuyanus – during reproductive cycle

Abstract

The arid regions have a heterogeneous availability of resources in space and time because of the marked climatic seasonality. As a strategy to guarantee reproductive success, vertebrates are adapted to hostile environments presenting a circannual rhythm. They possessed a single reproductive period, relatively short, followed by a stage of complete sexual inactivity, with resting gonads. The objective of this work is to describe the changes of the seminiferous epithelium of the lizard Liolaemus cuyanus, from the Monte Desert, San Juan, throughout its reproductive cycle. Twenty one adult male specimens were collected between October 2017 and March 2018. Both gonads were isolated and then fixed by immersion of small pieces in a fixing solution (phosphate buffered saline, containing 2% paraformaldehyde and 2% glutaraldehyde, depending on whether it is for light (MO) or transmission electron microscopy (MET), respectively). Once the samples were processed by routine histological/ultrastructural techniques, they were observed with an upright microscope - Nikon 80i for histological architecture or with a Zeiss EM 900 for ultrastructural characterization. Pictures were taken and analyzed with Image J, version 1.37v. At the beginning of the reproductive season, seminiferous tubules with developing epithelium and abundant interstitial space were observed. In the following three months, a remarkable increase of the surface of the seminiferous tubules was observed, with luminal spaces decreased, almost filled with released sperm. The interstitial space in this period was scarce due to tubular development. Towards the end of mating season, we appreciated a fall of the seminiferous epithelium, corresponding to cessation of cell differentiation that occurs during spermatogenesis and spermiogenesis. Observing the MET images, we appreciated different stages of chromatin condensation, elongation of the nucleus and formation of complex structures over the months of activity. In conclusion, the seminiferous epithelium presents circannual rhythmicity for a successful reproduction adapted to desert conditions.