Reproduction in the Impala (Aepyceros melampus Lichtenstein), with particular reference to the population in Mkuzi Game Reserve, Zululand

Abstract

This work reviews the literature on reproduction in .African ungulates, with particular emphasis on the impala (Aepyccros melampus) Original research on a population of this species occurring in Mkuzi Game Reserve, Zululand, is reported upon. The most overriding influence on this particular population is the fact that it is seasonally breeding in nature and, unlike other populations that have boon studied in East Africa, the reproductive processes behavioural, anatomical, and physiological - exhibit a regular cyclic pattern. This renders much of the data a good deal easier to analyse and interpret. As a means, primarily of establishing such parameters as the ago at which sexual maturity is achieved, a method of ageing, initially on the basis of tooth eruption and replacement and in older animals, on molariform tooth attrition, was worked out. Results indicate that females arc capable of brooding at about six months of ago, whilst males, albeit potentially capable at about 13 months, probably do not in fact take part until they are at least three or four years old, when they are socially and physically ready to compete for territories. The paired testes mass exhibits a peak during the time of the rut in May; this is preceded by a prolonged period during which it slowly increases, probably due to increased testicular activity brought on by improved nutrition, and is succeeded by a rapid decline in the mass to its lowest point in the cycle in winter. This cycle is closely followed by behaviour associated with territoriality. The ovaries also show increased activity with the improved nutritional plane between October and May, during which tin10 follicular development takes place. Just prior to the rut, the “silent" ovulation occurs, and this is followed by overt oestrous which is synchronised to the extent that nearly 80% of the conceptions are registered in a period of 14 days. Ovulations appear to be in equal proportions from the left and right ovary, as shown by the presence of corpora lutea of pregnancy. The corpus lutuem of pregnancy is persistent, and appears to increase slightly in diameter, of least up to the 4th month of gestation. It also persists for some years after fulfilling its function, as o corpus albicans or pigmented scar; however it is not possible to use this feature as a means of accurately assessing the brooding history of an individual. The gestation period, determined on a population basis, is between 196 and 204 days, the peak of births in 1970 occurring in the second week of December. The regression, the cube root of foetal moss on conception ago, is a straight line, and the relationship between the two parameters is shown by the formula \rt¼= a(t-t 0 ). In 1970, 14,3% of the juvenile (0-12 month old) females wore pregnant, whilst counts of corpora albicantia revealed that 30% of the juveniles in 1969 had boon pregnant. The sex ratio of males to females in the Mkuzi population, which is artificially controlled numerically, was found to be 1: 1,7.