1) General Zoological Data
"Sitatungas of Africa are semiaquatic, spending most of their life in dense beds of Papyrus" (Nowak1999). Cotton (1935) also refers to their aquatic habitat and the fact that the animals are difficult to spot in the deep papyrus stands. Males are darker and larger than lighter brown females, and only the male has (spiraled) horns. The sitatunga is still widely distributed in East Africa but is said to have nearly disappeared from the west of Africa. Many animals are held in zoological gardens. Gotch (1979) indicated that the name sitatunga derives from an old Bantu language; tragos is Greek for male goat, and elaphos is a deer. Several regional subspecies have been nominated but not further delineated genetically.
The evolution of the tribe Tragelaphini has been of interest in general but to students of cytogenetics specifically. Most of their chromosome numbers are low (around 30) and they possess fusions of sex chromosomes with one specific autosome. The nyala is an exception with a much higher chromosome number (55-56). Wallace (1976, 1978) suggested that the nyala split of earliest, to be followed by speciation of the remainder of Tragelaphini. This, he suggested, was followed and enhanced by chromosomal fusions (see section on genetics below). Vrba & Schaller (2000) indicated that the first recognized tragelaphines are to be found in deposits of 6.5 MYA, having split from the bovid ancestors that are first seen 17 MYA. Matthee & Robinson (1999) studied the phylogeny with cytochrome b analysis of this tribe and came to the conclusion that all members should be assigned the genus Tragelaphus. They grouped nyala and sitatunga closely and suggested, from molecular time clock data, that these two species separated 9.5 MYA (!). Additional relevant studies by Matthee & Davis (2001) and Hassanin & Douzery (1999) provide little further evolutionary insight.
(1993) gives the longevity for Eastern sitatungas as 16+ years, that of
Western sitatungas as 21+ years, longer than Mentis (1972) reported. That
author also indicated that these animals do not have a strict seasonal breeding
period. Neonates weigh around 4 kg; Singletons are the rule, although rarely
twins have been observed - twice among 1087 births (Densmore, 1980). Gestation
lasts between 240-250 days and was reviewed by the same author.
2) General Gestational Data
Gestation lasts 240 and 250 days, as indicated above with usually singletons born. Neonates weigh around 4 kg and twins are uncommon.
General Characterization of the Placenta
Details of fetal/maternal barrier
This is a typical multicotyledonary placenta with epitheliochorial contact to the uterus. There is much of the usual yellow-brown pigment accumulated beneath the chorionic plate of the cotyledons. The nature of the pigment has been discussed in various chapters on other ungulates of this web site. While it has been suggested to have a derivation from degenerating blood, it is always iron-stain-negative. I have suggested that it may be melanin deposits.
The villous surface is covered by a single layer of trophoblast among which are numerous binucleate cells. The trophoblast has intimate contact with the endometrial epithelium which is, again, single-layered. The following photographs show this well. The villi have central capillaries and scant stroma and, in my attached placenta shown, they are rather more edematous appearing beneath the chorionic plate than near the maternal aspect. They become more slender at that point.
The origin of binucleate cells that are so characteristic of ruminant placentas has been studied by numerous investigators, primarily in the sheep and cow. They are believed to produce a variety of glycoproteins, especially placental lactogen and Wooding (1982; Wooding et al., 1997) suggested that they arise by fusion of trophoblast with endometrial cells.
Both umbilical cords were 10 cm long, unspiraled and without plaques on their surfaces. They had four large blood vessels and numerous small allantoic vessels. There was a central allantoic duct. The cord of the third placenta, from a stillborn infant that had the placenta still attached measured 11 cm and was also unspiraled.
Trophoblast external to barrier
No trophoblastic invasion of the uterus was found in the one placenta I was able to study and that was attached to the uterus.
No other remarkable features were identified.
The best-studied endocrine aspect of most ungulate species is the production of a variety of hormones by the binucleate trophoblast. Atkinson et al. (1993) identified a novel carbohydrate as originating from these cells and reviewed other publications that identify other glycoprotein hormones in these cells. It would appear that different populations of binucleate cells may exist with different end-products. Generally speaking, however, the cells are seen as producing primarily placental lactogen (Wooding, 1997).
No other endocrine studies of this species are known to me.
I know of no publications on immunological studies of sitatunga immunology.
Other remarks - What additional Information is needed?
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