Challenges associated with the development and transfer of assisted breeding technology in marsupials and monotremes: lessons from the koala, wombat and short-beaked echidna

Abstract

This reflective review describes how a research model, which was originally established for the successful AI of the koala (Phascolarctos cinereus), is currently being developed and extended to the wombat (Lasiorhinus latifrons and Vombatus ursinus) and short-beaked echidna (Tachyglossus aculeatus). The research model centres around the establishment of an AI program and involves: (1) semen collection, evaluation and preservation, requiring an understanding of male reproductive physiology and gamete biology; (2) timing of insemination, based on a knowledge of oestrous cycle and gestation physiology and oestrous behaviour; and (3) the appropriate placement of semen, which relies on an accurate description of female reproductive anatomy. Published and unpublished studies of assisted breeding technology (ABT) development in all three species of Australian mammals reported in this review (koala, wombat and short-beaked echidna) clearly demonstrate the importance of recognising species-specific variation in reproductive biology. Even in closely related species, such as the koala and wombat, subtle differences in reproductive physiology can hinder the transfer of ABT across species. Significant progress in marsupial and monotreme ABT will also require adequate access to captive wildlife colonies (zoos, university collections and private partners) in sufficient numbers in order to conduct quality science.

Biobanks, offspring fitness and the influence of developmental plasticity in conservation biology

“…Research progress leading towards the establishment of biobanks for other mammalian species is still at an early stage, possibly because of the technical difficulties associated with effective sperm cryopreservation despite extensive research efforts (see, for example, the difficult problems around cryopreserving marsupial spermatozoa ( Johnston, 2019 ; Johnston and Holt, 2019 ). Some researchers have argued that because sperm cryopreservation is so unlikely to succeed by the use of traditional cooling and freezing methods, it is now time to develop alternative approaches to genetic biobanking based on the use of cloning and stem cell technologies ( Rodger, 2019 ).…”

Recent Progress in Spermatology Contributing to the Knowledge and Conservation of Rare and Endangered Species

“…No significant differences were seen between the slow-frozen-thawed and the ultrarapid-frozenthawed sperm in terms of percentage of viable sperm or sperm with morphological abnormalities (126). Ultrarapid freezing could be particularly promising for marsupials, in which sperm cryopreservation has been very challenging so far (83).…”

“…They exhibit nuclear flattening in the plane of the midpiece, and the neck of the midpiece inserts into the central region of the ventral surface of the sperm head. The koala and wombat have the only marsupial spermatozoa that do not exhibit nuclear flattening, as a result of their spermatozoa's unique, hook-shaped heads (11,83).…”

Pouch bacteria: an understudied and potentially important facet of marsupial reproduction

“…Captive breeding is also beneficial for expanding and maintaining genetic diversity through the application of selective breeding and recent advances in artificial insemination. 10 This is particularly useful for the genetic rescue of increasingly fragmented mammal populations by targeted translocation. 11 Despite these benefits, however, the successful management and breeding of endangered marsupials in captivity presents several challenges.…”