Endocrine regulation of reproductive behavior in the newt Cynops pyrrhogaster

Possible hormonal interaction for eliciting courtship behavior in the male newt, Cynops pyrrhogaster

Reproductive behavior in amphibians, as in other vertebrate animals, is under the control of multiple hormonal substances. Prolactin (PRL), arginine vasotocin (AVT), androgen, and 7α-hydroxypregnenolone (7α-OH PREG), four such substances with hormonal activity, are known to be involved in the expression of the tail vibration behavior which is the initial step of courtship performed by the male newt, Cynops pyrrhogaster. As current information on the interaction(s) between these hormones in terms of eliciting tail vibration behavior is limited, we have investigated whether the decline of expression of tail vibration behavior due to suppression of the activity of any one of these hormones can be restored by supplying any one of the other three hormones exogenously. Expression of the behavior was determined in terms of incidence (% of test animals exhibiting the behavior) and frequency (number of times that the behavior was repeated during the test period). Neither PRL nor androgen restored the decline in the incidence and frequency of the tail vibration behavior caused by the suppression of the activity of any one of other three hormones. AVT completely restored both the anti-PRL antibody-induced and flutamide (an androgen receptor antagonist)-induced, but not ketoconazole (an inhibitor of the steroidogenic CYP enzymes)-induced decline in the incidence and frequency of the tail vibration behavior. The neurosteroid, 7α-OH PREG, failed to restore flutamide-induced decline in the incidence and frequency of the behavior. However, it was able to restore both anti-PRL antibody-induced and AVT receptor antagonist-induced decline in the incidence, but not in the frequency of the behavior. In another experiment designed to see the activity of hormones enhancing the frequency of the tail vibration behavior, AVT was revealed to be more potent than 7α-OH PREG. The role of each hormonal substance in determining the expression of the tail vibration behavior was discussed based on the results.

Multiple sex pheromone genes are expressed in the abdominal glands of the smooth newt (Lissotriton vulgaris) and Montandon's Newt (L. montandoni) (Salamandridae)

The smooth newt (Lissotriton "Triturus" vulgaris) and Montandon's newt (L."T." montandoni) are sister species exhibiting pronounced differences in male secondary sexual traits but nevertheless hybridizing and producing fertile hybrids in nature. Since pheromonal communication is an important aspect of the reproductive biology of urodeles, structural differentiation of peptide pheromones and their receptors may contribute to incipient reproductive isolation. The aim of the study was the identification of genes encoding putative courtship pheromone precursors in two newt species and the reconstruction of phylogenetic relationships among them. Our analyses were based on cDNA obtained from the transcripts from the abdominal glands of male newts. We identified five unique cDNA sequences encoding the putative pheromone precursors in L. vulgaris and three additional unique sequences in L. montandoni. The results indicate that in the abdominal glands of Lissotriton newts more than one pheromone-encoding gene is expressed and that these loci form a gene family. Phylogenetic analysis indicates that the divergence of at least some of these genes predates the radiation of European newts.