In vitro fertilization and embryo culture in the grey short-tailed opossum, Monodelphis domestica.

In vitro fertilization and early embryo culture was undertaken in the South American marsupial, the grey short-tailed opossum, Monodelphis domestica. Adult females were induced into oestrus by a system of pairing with an unfamiliar male and mature oocytes were recovered from the ovary 15-18 h after mating and placed in pre-warmed modified MEM medium at 33 degrees C (basal body temperature) or 37 degrees C. Spermatozoa recovered from the cauda epididymides of adult males were preincubated in medium for 2 h during which time paired spermatozoa separated and initiated hyperactivated motility. Oocytes were transferred to 0.4 ml drops of spermatozoa containing 0.5-1.0 x 10(6) spermatozoa ml-1. Only single spermatozoa bound to the zona pellucida, and fertilization occurred within 1-2 h as indicated by a breach in the zona and confirmed by electron microscopy. At 37 degrees C, 95 of 152 (62.5%) oocytes were fertilized and 64 (67%) developed to two-cell stage or beyond. At 33 degrees C, 5 of 28 (18%) oocytes were fertilized. This is the first report of complete in vitro fertilization in a marsupial.