Reproductive Technology for Frog Conservation and Genome Banking
Species extinction is unique among major anthropogenic changes because it is irreversible. It is now accepted amongst biologists that amphibians are experiencing a major world-wide extinction crisis. Substantial range contractions, population reductions and extinctions have been reported on different continents, with hot spots of extinction in Central America and Australia. The reasons for these declines, which only became apparent from about 1980, are poorly understood and controversial, although recent evidence implicates a fungal disease (Chytridiomycosis), with Xenopus species as a probable vector for its spread from Africa. The ideal strategy for the long-term protection of biological diversity is the preservation of natural communities in the wild. However, in-situ preservation is not a viable option in the current circumstances where species are disappearing from pristine environments. This leaves alternative ex-situ strategies such as captive breeding and genome banking as the only insurance against extinction. Assisted Reproduction and cryobiology are essential to these approaches. Recent advances in amphibian cryobiology in ours and other laboratories have developed procedures for the non-invasive collection and cryopreservation of sperm in a number of species. Amphibian embryos can be readily generated using in-vitro fertilization with frozen sperm, since fertilization is external in most species. However, successful cryopreservation of amphibian (like fish) oocytes and embryos/larvae remains an elusive goal. This means that, currently, cryopreservation cannot be used as an insurance against extinction in the wild since only sperm can be recovered from frozen storage. Alternatives to direct cryopreservation of whole oocytes and embryos that should be considered in future research include: (i) androgenesis – with the goal of generating androgenotes between sibling species and (ii) the use of inter-species nuclear transfer technologies to regenerate embryos from cryopreserved totipotent embryonic and other stem cells.