The experiment presented in Investigating Life: The Control of Diapause in the Tammar Wallaby exploited the fact that removal of the young joey from the pouch of its mother (RYP) stimulated the blastocyst in her uterus to break diapause, implant, and continue development. What diapause-breaking signal might be involved in conjunction with RYP? Researchers hypothesized that RYP resulted in cessation of prolactin release stimulated by suckling of the young, and that the absence of those prolactin pulses initiated the breaking of diapause. The test of that hypothesis was to apply RYP to groups of mother wallabies and test whether applications of prolactin could prevent the breaking of diapause. The results showed that injections of prolactin every 24 hr for 8 days following RYP delayed the progesterone rise that indicates the breaking of diapause. Prolactin injections at 48-hr or longer intervals were less effective or ineffective in maintaining diapause. The conclusion was thus reached that prolactin pulses stimulated by suckling are a signal for the maintenance of diapause, and that the removal of that signal results in the breaking of diapause. Another signal, melatonin, could be involved in the breaking of diapause. The prolactin experiments were all done at the time of year when night length was appropriate for the breaking of diapause.
Reproductive success depends on many factors, including ecological, physiological, and socio-behavioral factors. It is therefore not surprising that evolutionary adaptations have exploited many kinds of information to control the timing of reproduction in various species. While these controlling factors are diverse, in vertebrates they all work through the hypothalamic, pituitary, and gonadal regulatory mechanisms. Therefore whatever we can learn about the physiology of reproduction in one vertebrate species may also apply to other species, or at least inform us as to what questions we should ask of other species, including humans. The answers to these questions can help us preserve endangered species, improve domesticated species, solve reproductive problems in humans, and even help control human population growth.