Maternal recognition of pregnancy in marsupials.

Pregnancy in kangaroos and wallabies (macropodid marsupials) induces multiple unilateral responses in the reproductive system that override those related to proximity to the single corpus luteum on one ovary or to the follicle on the contralateral ovary. This situation is in contrast to most other non-macropodid marsupials, in which the responses are dependent on the corpus luteum. There is now good evidence that these unilateral responses in macropodids are controlled by the feto-placental unit acting locally to stimulate the endometrium and myometrium. Pregnancy also influences the duration of the oestrous cycle and maternal behaviour. The stimuli responsible for these effects probably include paracrine, endocrine and mechanical stimuli resulting from uterine stretch. Taken together, these unilateral responses demonstrate that there is a refined maternal recognition of pregnancy in at least the macropodid marsupials.