1) General Zoological Data
The impala is a common and fairly widely distributed African ungulate with several subspecies. Commonest in East Africa is Aepyceros melampus rendilis, while A. m. petersi, the black-faced impala, is the most endangered subspecies and distributed further South. Other nominated subspecies are less well known and controversy as to their designation still exists. Impalas are frequently kept as a game animal on ranches in South Africa. The name "Aepyceros melampus" derives from aipos (Greek = high, lofty), keras (horn - because of the long lyre-shaped horns of males), melas (black) and pous (foot). Impala is a Zulu name (Gotch1979).
The precise origin of the impala has remained uncertain. Vrba & Schaller (2000)
suggested that the Aepycerotini split off the caprine taxa approximately 6.5 MYA. Gatesy et al. (1997) attempted to resolve its origin with data from ribosomal DNA studies but were unable to do so. Likewise, Matthee & Davis (2001) were also unable to classify the "enigmatic taxa" impala, suni and klipspringer by their study of nuclear DNA. They suggested a contemporaneous origin in Africa. Another study, of mtDNA, was undertaken in kudu and impala by Nersting & Arctander (2001) that failed to resolve the issue completely as well. They suggested that the more vulnerable black-faced impala may have "hybridized" with the "common" impala (Aepyceros m. melampus). The karyotype of 2n=60 with only acrocentrics may indicate a rather "primitive" antelope (see section on Genetics, below). On the basis of its cerebral and dental structures, Thenius (1969) felt that impala should not be grouped with the gazelles.
Adult female impalas weigh 40-45 kg; males are 60-65 kg. Neonates weigh around 5 kg. Females have four nipples.
General Gestational Data
The gestational length of impala pregnancies as ascertained by several authors has been given in the review of Mentis (1972). It has been recorded as being "6½ -7 months; 150-180 days, 171 days, 180-210 days; 196 days, 194,196,197 and 200 days". The species has been described as being monotocous, but several twins have occurred, and one set of twins was associated with a single corpus luteum, suggesting MZ twinning. The longevity record for a black-faced impala is 17 years and 9 months (Jones, 1993).
Roettcher et al. (1970) studied the skulls of 100 postnatal impalas of known ages and presented data that allows age determination. At age 2½ years, maturity is attained, even though estrus may occur before then. In the same publication, the authors presented the CR-lengths and weights (and some other characteristics) of 30 fetal impala specimens. They then constructed a graph that, with these determinations, should allow one to date the gestational age of the growing fetus, assuming the gestation to be approximately 190 days long.
Details of fetal/maternal barrier
An extensive description of the electron microscopic details of impala placentas from different early stages (fetal CR measurements from 0.8 to 55 cm) of implantation has been published by Kayanja & Epelu-Opio (1976). From this, the authors concluded this to be a typical epithelio-chorial type of placentation with "interlocking of microvilli from trophoblast and maternal epithelium". The trophoblastic epithelium is cuboidal with a microvillous surface. Relatively small numbers of the typical ruminant binucleate cells were present in my preparations. The binucleate cells, thought to produce placental lactogen and perhaps other glycoproteins, are much larger and darker than the cuboidal trophoblast. The microvillous trophoblastic surface abuts the flattened (and occasionally absent) maternal endometrial surface epithelium. The nuclei of the latter are dark and condensed, much different from the loosely-structured trophoblast. The fine structural study disclosed that many epithelial cells were degenerating and that some of this debris was removed by trophoblast. These authors doubted, however, that phagocytosis alone was able to remove all of the debris. Invasion of endometrium or myometrium has not been seen. No pigment of the cylindrical subchorionic trophoblast was present in my sections and there were no degenerative changes in the apices of maternal septa, nor was there hemorrhage. The trophoblast of the membranes between cotyledons is very tall and cylindrical. The villi have very sparse connective tissue and rare Hofbauer cells.
The umbilical cord attaches mesometrially, halfway along the uterine horn (Lee et al., 1977; Mossman, 1987). One umbilical cord measured 17 cm and had no spirals. It contained 4 large blood vessels and an allantoic duct. In addition, numerous mall blood vessels were present.
There are no other noteworthy features.
I am not aware of any studies.
Other remarks - What additional Information is needed?
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