Hormonal control of spawning in amphibians

TRUDEAU V.L.; SCHUELER, FREDERICK W.; SOMOZA M.G.; NATALE G.S.; SALGADO COSTA C.; THONEY, DENNIS; MCGINNITY, DALE

Vancouver

Congreso; World Congress of Herpetology Vancouver 2012; 2012

University of British Columbia

Improved understanding of the neuroendocrine control of spawning is critical for species conservation. In fish and frogs it is the surge release of luteinizing hormone (LH) that causes coordinated egg release in 731 females and sperm release in males, leading to fertilization. Many neurohormones are involved in controlling pituitary LH release in fish and mammals, but only a few have been studied in amphibians. The decapeptide Gonadotropin-Releasing Hormone (GnRH) is critical. Various synthetic GnRH agonists stimulate LH release, and sometimes spawning in frogs. The catecholamine dopamine (DA) is a potent inhibitor of LH release in many teleosts and several mammals, yet little is known about its role in LH release in frogs. Increasing evidence indicates that combined GnRH agonist/DA antagonist treatments effectively stimulate spawning. We have named this the AMPHIPLEX method. It is simple and effective because both sexes are injected at the same time. There is no need to sacrifice males to obtain viable sperm because amplexus is induced. We have successfully induced spawning on a large scale in Lithobates pipiens both in the breeding season and outside of the breeding season after a short ‗hibernation/brumation period‘. This method has been applied to both abundant and endangered species where there is very little information on their physiology. In L. clamitans, L. pretiosa, Ceratophrys ornata, C. cranwelli, C. aurita, and Odontophrynus americanus we obtained successful spawning and high fertility with subsequent tadpole development and metamorphosis. In the case of the hellbender, Cryptobranchus alleganiensis, one female produced hundreds of eggs and milt was easily stripped from the 3 males approximately one week after AMPHIPLEX. Sperm collected from the males was successfully cryopreserved and had similar morphology, concentration and motility to milt cryopreserved from both healthy and declining populations of wild hellbenders in Tennessee. Some eggs were artificially fertilized, started to develop but did not reach metamorphosis. Post-spawning examination indicated an initial poor egg quality (white yolk sac) in this single female, providing an explanation for failed egg development in hellbender. Our current efforts are focused on a new and easy-to-use formulation and improved induction of spawning outside normal breeding seasons in captive animals. Funded by Environment Canada and the University of Ottawa Research Chair program