Parturition in Nonhuman Primates

Open Access
Publisher Website
Google Scholar
Abstract
At present the sequence of events at parturition in nonhuman primates is less clear than in some other mammals. In at least the macaque, the best studied of the nonhuman primates, it appears likely that fetal participation in the onset of parturition occurs. Progesterone acts in its classical role of maintaining uterine quiescence; as term approaches its concentration in uterine venous effluent and therefore presumably in the myometrium declines. A prepartum estrogen rise occurs as in sheep, but there is conflicting evidence in macaques whether estrogen administration will either terminate pregnancy or cause a rise in PGF2α levels as it does in sheep. There is some evidence that PGF2α plays a role in normal parturition in the macaque, and that the declining influence of progesterone is at some point overridden by other events precipitating delivery. The "other events" are not well defined except by a hazardous extrapolation from other better-studied species. More information is needed in the macaque on the interrelationship of progesterone, estrogens, prostaglandins and perhaps on other agents not presently recognized as critical. If the purpose of pregnancy and parturition research among nonhuman primates is to improve understanding of the human counterparts, the macaque, at least as evidenced by the patterns of pregnancy hormones, does not appear to be the best animal. By these limited criteria, either the chimpanzee or marmoset is closer to the human. But mechanisms worked out in any animal can be reliably applied to humans only after their direct demonstration in human subjects. Afterthought: Species differences even among mammals otherwise closely related prevail with regard to reproduction processes to an extent not found in other biological systems. While these differences are widely recognized, possible explanations for their prevalence are not often encountered. A thought in closing that appears attractive assigns to them a survival value. If the proliferation of species enhances survival, then so would a factor which promotes speciation. A new species can become established or an existing one can be maintained only if it is protected by some form of isolation so that excessive hybridization and consequent possible loss of adaptive change is prevented. The most common isolating mechanism is that of geographic separation, well known from the examples of Darwin’s finches. But there are others (Ehrlich et al., 1974). Those species differences in the reproductive process which prevent successful reproduction between species can be regarded as highly effective isolating mechanisms (Dobzhansky, 1970). They can, for example, effectively separate two closely related species on the basis of behaviour or preference even though the two species are sympatric and could in a physiologic sense be readily hybridized (Ehrlich et al., 1974). Distantly related species are so obviously separated that mechanisms maintaining their separation are seldom given any thought. However, if, for example, mice could successfully hybridize with elephants, if a male of any species could successfully reproduce with a female of any other species whether a near or distant relative, the distinctive characteristics that permit a species to fill an ecologic niche would disappear, together, perhaps, with the animals themselves. Viewed in this light, the manifold barriers to hybridization implicit in species differences at all stages of reproduction processes are fundamental to speciation and to survival.

This publication has 0 references indexed in Scilit: