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

Lorena Quiroga,Miguel Fornés,Eduardo Sanabria,Graciela Jahn

doi:10.26496/bjz.2018.20

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 ± 7.85 ng/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.

Highlights

Anurans exhibit some of the most diverse reproductive strategies and adaptations known among vertebrates including, internal and external fertilization, oviparity and viviparity, direct and indirect development, and many forms of parental care such as the eggs or young are carried on or embedded in their backs, in pouches, and even in vocal sacs and stomachs (Duellman & Trueb 1994; Stebbins & Cohen 1997; Wells 2007; Crump 2015)
There was no significant relationship between testicular volume (TV) and SVL (P > 0.09), and FBM was correlated with TV (Spearman Correlation: R = 0.47, P > 0.01, n = 28)
SPT were more abundant in September, and the sperm bundles were more abundant in May and July before breeding (Fig. 4B)

Summary

Introduction

Anurans exhibit some of the most diverse reproductive strategies and adaptations known among vertebrates including, internal and external fertilization, oviparity and viviparity, direct and indirect development, and many forms of parental care such as the eggs or young are carried on or embedded in their backs, in pouches, and even in vocal sacs and stomachs (Duellman & Trueb 1994; Stebbins & Cohen 1997; Wells 2007; Crump 2015). Due to the diverse environments in which anurans live, they have developed a diverse range of reproductive strategies. These reproductive strategies are optimal combinations of morphological, physiological, behavioral, and life history traits that maximize reproductive success under particular environmental and evolutionary constraints (Perotti 1997). Adaptation to varied environments requires some adjustments of the reproductive cycle to produce offspring during the period of the year in which the majority of offspring have the greatest chance of survival (Callard et al 1978; De Souza Santos 2006). One of the main factors that triggers reproductive behavior is rain (Duellman & Trueb 1994)

Objectives

Methods

Results

Conclusion