Hormonal induction of ovulation in the common eastern froglet

Abstract

Hormone therapies to induce gamete-release are fundamental to the application of reproductive technologies. These technologies can provide far-reaching benefits to biodiversity conservation by improving reproductive outcomes and affording conservation practitioners greater control of the genetic management of threatened species. As a highly threatened vertebrate class, amphibians stand to benefit considerably from the application of reproductive technologies, including hormone therapies, gamete storage, and assisted fertilisations. To date, research attention has focussed on developing hormone therapies to induce spermiation in males, with research aiming to develop protocols to induce ovulation in females receiving relatively less attention. The aim of the present study was to quantify the effect of either no-priming, or a single gonadotropin-releasing hormone analogue (GnRHa) priming dose, on the hormonal induction of ovulation in the common eastern froglet, Crinia signifera. Females in the 'No-prime' treatment were administered an ovulatory dose (2 μg/g bw GnRHa) without prior priming, while the 'Prime' treatment received an ovulatory dose (2 μg/g bw GnRHa) preceded by a priming dose (0.4 μg/g bw GnRHa) administered 24 h earlier. Ovulation responses were then quantified (oocyte yield, clutch mass, oocyte mass, yolk volume, and intra-clutch variation in yolk volume) at 12 h and 14 h after the ovulatory dose was administered. During the first stripping attempt, ovulation responses were significantly higher in the Prime treatment, with 86% of females releasing oocytes compared to 0% of females that received an ovulatory dose without priming. After the second stripping attempt the percentage of females to release oocytes increased to 57% in the No-prime treatment and 100% in the Prime treatment. Additionally, females in the Prime treatment released clutches of significantly higher mass and oocyte yield compared to the No-prime treatment. Overall, we describe successful protocols for the hormonal induction of ovulation in C. signifera.