Variability of testes morphology and the presence of testis-ova in the European blind cave salamander (Proteus anguinus)

Abstract

The European blind cave salamander, Proteus anguinus, is a neotenic, permanently aquatic amphibian with a very long life span, late sexual maturity, and the ability to reproduce for at least 30 years. Proteus is considered to be vulnerable species, and yet very little is known about its reproductive biology. The objective of this study is to describe the detailed morphology of the testes of adult Proteus and determine the maturation state of the gonads and gametogenesis with respect to body size and seasonality. This research showed that testis size increases with adult male body length, but the shape and meiotic condition of the testes are highly variable and independent of the length of the specimen. The testis of Proteus has a simple cystic type of organization in which cysts are enclosed in lobules, with synchronous maturation of the germ cells within each cyst. Spermatogenesis progresses in a caudocephalic direction within the testis, as in other salamanders, and appears to be seasonal, despite the fact that Proteus is a cave animal living in stable environmental conditions. Surprisingly, the testes of approximately one third of the specimens, regardless oftheir morphology or meiotic condition, contained testis-ova located randomly among groups of spermatogonia and spermatocytes. These testes-ova contained germinal vesicles with lampbrush chromosomes, and thus correspond to primary oocytes. Thepresence of testis-ova may be related to a sex-chromosome turnover involving X-Y translocation that was recently discovered in Proteus.