Unveiling the reproductive secrets of egg-laying mammals
Project Summary Globally, there is currently no sustainable breeding program for captive populations of echidnas. This project seeks to ameliorate this by investigating and describing the enigmatic nature of the short-beaked echidnas mode of reproduction, including characterisation of the female oestrous cycle and associated behaviour, endocrinology and physiology. In achieving this, it may be possible to develop reliable methods of breeding the short-beaked echidna in captivity which may ultimately be adapted to the captive propagation of the critically endangered long-beaked echidna. Aims The specific aims of this research are to:
- Investigate the reproductive behaviour of the short-beaked echidna including when they are sexually receptive, when they are in the egg incubation phase, and after hatching during the growth and development of young.
- Thoroughly describe the full reproductive cycle (oestrous cycle, gestation and early lactation) and the hormones that control reproduction in the short-beaked echidna.
- Describe fat deposition in the echidna and determine if the hormone leptin functions as an adipostat in this species.
Methodology
Aim 1: The project has access to 15 female and 7 male breeding echidnas at a purpose-built facility at Currumbin Wildlife Sanctuary (CWS). CWS has an extensive video monitoring system that will allow the collection of data relating to the timing of reproductive events. Male and female echidnas will be introduced to each other at the beginning of the breeding season in early June and monitored daily for signs of mating activity. After observing mating activity on video, the male will be removed and the female will be monitored for approximately 20 days (gestation) for oviposition and egg pouch incubation behaviour.
Aim 2: To characterise the reproductive physiology of gestation and the subsequent return to oestrus, blood samples will be collected every 3-4 days post-mating through to a period of approximately 10 days post hatching to measure progesterone, oestrogen and vitellogenin levels using established ELISA assays. With this data it will be possible to establish (i) the duration of pregnancy (time of mating to egg-laying), and (ii) the duration of egg deposition to hatching (incubation). In years 1 and 2, eggs will be removed from 8 females to monitor return to oestrus to confirm (i) whether a second cycle can occur after loss of the egg or young and, (ii) whether or not new young can be born as a result of sperm storage from the first mating.
Aim 3: Blood samples (2 mL) will be collected monthly from 12 echidnas (9 female and 3 male controls) over a 15 month period. Body weight will also taken during monthly blood collection. Plasma samples will be analysed using radio immuno-assay for leptin. Plasma samples will also be analysed by EIA for progesterone and testosterone. To validate the use of DEXA to measure body fat in short-beaked echidnas, both DEXA and MRI scans will be performed on four echidna cadavers. Following this, six short-beaked echidnas from Currumbin Wildlife Sanctuary (three male and three female) will have DEXA scans every three months for a period of 15 months to measure body fat % and body weight. To determine the distribution of fat MRI scans will be performed on one male and one female short-beaked echidna post- and pre-breeding season.