EFFECT OF COOLING AND CRYOPRESERVATION ON SPERM MOTILITY AND MORPHOLOGY OF SEVERAL SPECIES OF MARSUPIAL

The effects of long-term cooling and freezing on sperm motility are de scribed for six marsupial species: the fat-tailed dunnart, koala, brus htail possum, long-footed potoroo, northern brown bandicoot and ring-t ailed possum. The effects of up to eight days of cooling at 4 degrees C on the motility of dunnart spermatozoa and the effect of cryopreserv ation on spermatozoa of the other species were determined, The cryopro tectant used was a Tris-citrate-fructose-egg yolk-glycerol diluent. Th e percentage and rating of sperm motility, and sperm structure, as det ermined by light microscopy, were investigated. Sperm motility in the fat-tailed dunnart was retained for up to six days when cooled to 4 de grees C, suggesting that sperm from this species have some degree of t olerance to cold shock. After this time, however, the percentage of mo tile spermatozoa and their motility rating declined. In all species ex cept the fat-tailed dunnart, reinitiation of motility following cryopr eservation occurred across a range of glycerol concentrations (4-17%). Cryoprotectant containing 6% and/or 8% glycerol resulted in little ch ange of motility rating or of the percentage of live sperm after thawi ng, although there was some decline in the percentage of motile sperm. The unusual structural and motility characteristics of dunnart sperma tozoa may account for the lack of success of sperm cryopreservation in this species.