Pregnancy in the lactating pigmy possum, Cercartetus concinnus

Abstract

The reproductive tracts of seven Cercartetus concinnus with pouch young were examined. One female had recently given birth, four were pregnant, and two were in anoestrus. The post-partum female was near oestrus. The ovaries contained corpora lutea and large follicles, and luteal regression was occurring in the uteri. Ovaries of pregnant females contained old corpora lutea and corpora lutea of pregnancy. Blastocysts recovered from the uteri increased in size with age of the pouch young. Corpora lutea of pregnancy out-numbered blastocysts in many females, and blastocysts often out-numbered teats. Ovaries of anoestrous females contained only old corpora lutea. During birth the young pass through a cleft in the connective tissue between the posterior end of the vaginal culs-de-sac and the posterior vaginal sinus. This cleft, the pseudovaginal canal, closes after parturition. The observation that embryos of C. concinnus do not enter diapause contrasts with conclusions previously drawn from circumstantial evidence that the pigmy possum resembled several species of Macropodidae in undergoing embryonic diapause.

Cercartetus concinnus (Diprotodontia: Burramyidae)

“…Although knowledge of reproduction in C. concinnus is incomplete, examination of available data suggests that diapause, sensu stricto, does not actually occur (see also Renfree 1978;Turner and McKay 1989;TyndaleBiscoe 1973;Ward 1990). However, only about 2 days are needed between the weaning of one litter and commencement of suckling of the next; in that short period the mammary section changes from milk to colostrum and the enlarged teats regress to a size small enough to be taken into the mouth of a neonate (Clark 1967;Flannery 1994;Smith 1995).…”

“…This is based on anecdotal observations of captive females that produced a 2nd litter in the absence of a male (see Bowley 1939;Casanova 1958;Hartman 1940). Further investigations of this phenomenon found that the blastocysts continued to grow during lactation (Clark 1967). Although knowledge of reproduction in C. concinnus is incomplete, examination of available data suggests that diapause, sensu stricto, does not actually occur (see also Renfree 1978;Turner and McKay 1989;TyndaleBiscoe 1973;Ward 1990).…”

“…Newborns have a head length of about 2.9 mm (Clark 1967). The young leave the pouch at around 25 days before the eyes open (Bowley 1939;Clark 1967) but remain in a nest (Bowley 1939;Casanova 1958).…”

“…The reproductive rate is high because breeding may occur throughout the year and females can rear 2 or 3 litters in close succession (Clark 1967;New South Wales National Parks and Wildlife Service 2001;Ward 1990). Records of lactating females and juveniles are concentrated in the spring months and few in the winter months (Ward 1990).…”

Cercartetus nanus (Diprotodontia: Burramyidae)

“…However, in C. concinnus continued growth of blastocysts during lactation suggests that diapause does not occur (Clark 1967) or that it is characterized by a slowing growth of blastocysts rather than a total cessation (Tyndale-Biscoe 1973). More recently, Turner and Ward (1995) considered, based on an unpublished thesis by Athey (1993, not seen, cited in Ward 1998), that female C. nanus do not have embryonic diapause but may return to estrus late in lactation and often give birth to the next litter immediately after the previous litter is weaned.…”