Sperm cryopreservation in wild animals

Abstract

Extinction of a species represents the loss of a resource evolved through eons of mutations and natural selection. Reproductive technologies, including artificial insemination, embryo transfer, in vitro fertilization, gamete/embryo micromanipulation, semen sexing, and genome resource banking (GRB) have all been developed with the aim of solving existing problems and preserving genetic material for conservation purposes. Although protocols from domestic or non-threatened related species have been extrapolated to nondomestic and endangered species, usually these reproductive technologies are species-specific and inefficient in many nondomestic species because of insufficient knowledge on their basic reproduction biology and the need for species-specific customization. Since spermatozoa are usually more accessible and come in large numbers compared to oocytes and embryos, they are considered the primary cell type preserved in most emerging GRBs. For this purpose, semen from endangered species is currently cryopreserved to avail long-term storage. Due to the intractability of most exotic species, semen collection without chemical restraint is limited to only a handful of species and individuals. Viable epididymal spermatozoa can be obtained from dead or castrated animals, but this resource is limited. Electroejaculation, artificial vagina, abdominal massage, and/or transrectal, ultrasound-guided, massage of the accessory sex glands of living animals are viable alternative methods of semen collection. The ultimate goal is to adapt and optimize collection and cryopreservation protocols for each species, making it feasible, among other things, to collect gametes in the wild and introduce them into captive or isolated populations to increase genetic diversity. Recent advances in these fields have allowed the establishment of GRBs for many threatened species.