Spermatology of the giant panda (Ailuropoda melanoleuca): Morpho-functional traits, reproductive adaptations, and new insights into sperm cryoresistance.

Abstract

The giant panda serves as a clear example of the critical role zoological institutions play in conservation programs for endangered wildlife. It is the bear species whose reproductive biology is best understood, and for which the greatest advances in reproductive technologies have been achieved. This review describes various procedures for collecting and cryopreserving giant panda sperm and examines how their morpho-functional characteristics appear to be associated with their reproductive biology. The influence of different factors, such as season and age, on sperm parameters is also addressed. Compared with other bear species, giant panda ejaculates display morpho-functional traits characterized by low pleiomorphy, high concentration, and enhanced kinematic variables, consistent with those typically observed in species with a high degree of polyandry. Giant panda sperm show notable resistance to freeze-thaw procedures. While morphometric characteristics have been considered a key factor in the osmotic stress occurring during cryopreservation, other molecular mechanisms may also contribute to cryoresistance. In the present review, we describe preliminary observations on the identification of aquaporin 3 and androgen receptors in giant panda spermatozoa and discuss their putative roles in modulating the sperm response to the freeze-thaw process.