Assisted breeding technology in the saltwater crocodile Crocodylus porosus: a review and look to the future.

This review reports the current status of artificial breeding technology in the Crocodylia and the future requirements for the establishment of AI in the saltwater crocodile. Although there are challenges regarding safe restraint and immobilisation, semen collection of the saltwater crocodile by manual stimulation has proven effective in yielding sufficient volume and sperm concentrations for empirical and molecular analyses of sperm preservation and physiology. Nevertheless, there is still much to learn with respect to fundamental anatomy, physiology and behaviour in both sexes, but particularly in the female. Although lessons can be learned from successful AI in the alligator, the details of this research are not readily accessible. Future research needs to focus on the proximate factors of seasonality and the underlying control of the female's annual reproductive cycle; this will require novel and innovative ways to collect blood samples without causing stress or injury, and ideally a dedicated crocodile research breeding colony. Because the saltwater crocodile is a farmed species, there is likely to be sufficient impetus for the application of assisted breeding technology to drive future productivity in the industry. These developments will also have benefits for the genetic and reproductive management of endangered captive populations.

The Australian saltwater crocodile (Crocodylus porosus) provides evidence that the capacitation of spermatozoa may extend beyond the mammalian lineage.

Although mammalian spermatozoa only acquire functional maturity as they are conveyed through the male (epididymal maturation) and female (capacitation) reproductive tracts, the degree of post-testicular development necessary to achieve fertilization in other vertebrate species remains far less clear. Indeed, despite reports that the epididymis of birds and reptiles is capable of secreting proteins that bind and modify the sperm surface characteristics, it remains unclear whether capacitation is a pre-requisite for fertilization in these species. Using the ancient reptilian Australian saltwater crocodile as a model, this study was undertaken to explore whether reptile sperm do undergo capacitation-like changes following ejaculation. Our studies revealed that crocodile spermatozoa experienced a rapid and sustained, cyclic-AMP mediated increase in progressive motility following incubation under conditions optimized for the induction of capacitation in mammalian species such as the mouse and human. This response was coupled with elevated levels of phosphorylation associated with both protein kinase A and tyrosine kinase substrates, the latter of which were predominantly localized within the sperm flagellum. In findings that also accord with mammalian spermatozoa, we confirmed a homologue of outer dense fibre 2 as one of the principal substrates for tyrosine phosphorylation. Overall, our findings support the concept that crocodile spermatozoa do undergo a process that is homologous to capacitation in preparation for fertilization of an ovum.