Assessment of reproductive status in male echidnas

Abstract

This study reports the development and application of techniques to assess the reproductive status of male echidnas. The pattern of testosterone secretion over a 24-h period in five echidnas was documented. Testosterone secretion after injection i.m. of either 1000 IU hCG ( n = 4) or 4 μg GnRH agonist ( n = 6) was determined to establish whether this could be used as a practical index of the prevailing steroidogenic capacity of the testes. hCG (1000 IU) was also used to assess seasonal changes in testosterone secretion in six echidnas over a 13-month period. Seasonal changes in testicular volume were examined by transabdominal ultrasonography. Electroejaculation was attempted to monitor seasonal changes in sperm production, which was also determined by spermatorrhea. There was no apparent diurnal pattern of testosterone secretion in echidnas and circulating concentrations of testosterone remained relatively low (maximum 1.2 ng/mL) and stable over 24 h. Injection of hCG resulted in an increase ( P < 0.01; n = 4) in testosterone concentration with a peak (2.9 ± 0.3 ng/mL) approximately 4 h after injection. GnRH also induced an increase ( P < 0.01; n = 6) in circulating testosterone that was apparent after 1 h (2.6 ± 0.3 ng/mL) and concentrations remained elevated (3.4 ± 0.3 ng/mL) for up to 8 h after injection. Seasonal changes in testosterone secretion determined after injection of hCG, increased ( P = 0.03; n = 6) from late-autumn, peaked in late-winter, and decreased by early-spring. Testicular volume followed a similar seasonal pattern ( P < 0.01; n = 6) with an increase from late-autumn, peak in winter and a decline in mid-spring. There was no seasonal change in live weight. Electroejaculation was attempted throughout two breeding seasons but no semen was obtained. Spermatorrhoea in the echidna was described for the first time and was subsequently used to assess seasonal sperm production. Spermatozoa were found in the urine from June to September. This study has demonstrated that exogenous hormones can be used to obtain an index of the prevailing steroidogenic capacity of the testes in echidnas, which is not apparent with repetitive non-stimulated samples over 24 h. The assessment of testosterone secretion after injection of trophic hormones provides a valuable and practical procedure for the assessment of reproductive status. Testicular ultrasonography and spermatorrhea are useful in assessing reproductive status and in this study were successfully used to determine seasonal reproduction in captive echidnas.