Hormonal induction of ovulation in the common eastern froglet

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 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 were administered either an ovulatory dose (2 μg/g bw GnRHa) alone (hereafter the 'No-prime' treatment), or an ovulatory dose (2 μg/g bw GnRHa), preceded by a priming dose (0.4 μg/g bw GnRHa) administered 24 h earlier (hereafter the 'Prime' treatment). Ovulation responses were then quantified (oocyte yield, clutch mass, oocyte mass, yolk volume, and intra-clutch variation in yolk volume) 12 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 responses in the No Prime treatment increased to 57% of females and the Priming treatment resulted in 100% of females releasing oocytes, with response rates statistically similar between the two treatments. Overall, 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 oocyte-release in C. signifera.