Spermatogenic and Testosterone Cycles in a Desert-Adapted Amphibian Odontophrynus barrioi from the Monte Desert, Argentina

Abstract

Few studies have characterized the reproductive cycles of desert anurans, particularly species from South America. This has hampered efforts to identify broad patterns in anuran reproduction, which are known to vary both phylogenetically and throughout climatic gradients. We studied the reproductive cycle of male Odontophrynus barrioi, a small (∼20 g) terrestrial toad from the Monte Desert of San Juan, Argentina. The main goal of this work was to determine spermatogenic activity, plasma testosterone concentrations, and reproductive parameters during prereproductive (preR), reproductive (R), and postreproductive (postR) periods. We determined the plasma testosterone concentrations in male toads by radioimmunoassay (RIA). We performed histological analyses of the testes of males with the use of the hematoxylin and eosin method, and also examined the testes with a light microscope. During the preR and R periods, spermatogenesis in O. barrioi showed substantial development of the late stages (sperm bundles), coincident with high sperm percentage (spermiation) in the seminiferous tubules. Spermiation occurred when testosterone levels were high. This species exhibits a continuous spermatogenic cycle, with maximum levels of testosterone during the dry season. Therefore, O. barrioi is a desert-adapted anuran exhibiting an "associated" reproductive strategy given its association between breeding season and high plasma testosterone concentrations. This reproductive strategy likely evolved to coordinate the reproductive cycle with brief rains in summer as an adaptation to the challenging climate imposed by the desert environment, as well as Monte Desert.