Spermatogenesis and plasma testosterone levels under field conditions, in males of the common toad (Rhinella arenarum Hensel, 1867), from the Monte Desert, Argentina

Abstract

The reproductive function in anurans depends on interactions between the hypothalamus, adenohypophysis and gonads, which are mediated by an endocrine circuit. We studied the relationship between reproductive and histological parameters, variation in spermatogenic activity, and plasma testosterone concentration cycle for a population of Rhinella arenarum under field conditions in the Monte Desert of Argentina. We captured 28 adult male R. arenarum from December 2009 to November 2010, and define two seasons (wet and dry seasons). We performed histological analyses of the testes and used radioimmunoassay to determine plasma testosterone concentrations. Our results showed no difference in testicular volume between the wet and dry seasons, but found that changes in the fat body mass were higher in the dry season. The spematogenic cycle was characterized by the prominent presence of spermatogonia at the end of the dry season and the wet season. We also observed a higher percentage of primary spermatocytes in the wet season. In addition, we found that R. arenarum showed a continuous spermatogenic cycle, and spermatogenesis produced a high percentage of sperm bundles in the dry season, concordant with high levels of testosterone. Testosterone levels were highest during the dry season (33.89 ± 7.85ng/ml). Our data indicate that plasma testosterone showed a "dissociation" from reproductive activity such that the two parameters are asynchronous during the reproductive season. The characteristics of the reproductive cycle of R. arenarum allow this species the plasticity to colonize different environments, from tropical regions to deserts.