Dorcas Gazelle

Gazella dorcas

Order: Artiodactyla
Family: Bovidae

1) General Zoological Data

The Dorcas gazelle (dorcas [Greek=gazelle]) is a North African, desert-dwelling gazelle. Several (perhaps as many as nine) subspecies have been described, many of which are severely endangered. Several breeding colonies exist in zoological parks.

There are numerous species of the Gazellini with a wide variety of coat color and differences in size. They are fully discussed by Nowak in 1999. The animals depicted here are "Saharan Dorcas gazelles". Many, but not all, African gazelles possess a characteristic chromosomal translocation (fusion) of an autosome with the X chromosome. Since the autosome is the same in all these gazelle species, it is conjectured that a common ancestor first had this complex karyotype and that it was the founding species of a large number of African gazelle species.

	Adult male "Saharan" Dorcas gazelle at the San Diego Zoo.

	Adult Dorcas gazelles at the San Diego Zoo.

	Group of Dorcas gazelles at the San Diego Zoo.

2) General Gestational Data

The length of gestation has been cited as 164-174 days (Dittrich, 1970; Slaughter, 1971; Puschmann, 1989, Kranz et al., 1984). Newborns weigh between 1 and 1.8 kg, sexual maturity occurs at 1 year and 9 months. Single births are the rule; twins are uncommon (Jope, 1908; Dittrich, 1970; Kranz et al., 1984). We have encountered a conjoined stillborn twin fetas. Thus, some of the twins may be monozygotic. The male fetus that was associated with the first placenta depicted here, weighed 1,650 g. Adults weigh ca. 15 kg, longevity is over 17 years. There is little sexual dimorphism. Many additional reproductive data were summarized by Hayssen et al. (1993), and also by Kranz et al. (1984). Baharav (1983) compared the reproduction of the mountain gazelle (Gazella g. gazella) with that of the Dorcas gazelle. Both delivered young in March; first conception occurred at age 18 months, singletons were the rule. Dittrich (1970) stated that sexual maturity is reached at 27 months and that placentophagy is normal.

3) Implantation

Early stages of implantation have not been described.

4) General Characterization of the Placent

This is a polycotyledonary placenta with four somewhat irregular rows of cotyledons. The placenta depicted comes from a stillborn fetus and had 60 cotyledons, varying in size from 3.5 x 2.5 to 1.0 cm; they were 0.2 cm thick. This placenta weighed 140 g and had a greatest length of 50 cm. Another placenta that I examined weighed 150 g, had 30 cotyledons that varied between 1 and 4 cm in diameters . A well-preserved placenta was delivered in 2003 and weighed 110 g, had 67 cotyledons and a 7 cm umbilical cord. An additional placenta weighed 200 g and had 60 cotyledons and a 9.5 cm long umbilical cord. In November of 2003 a placenta became available from a stillborn, malformed fetus, delivered by Cesarean section because of dystocia. This dam had two previous stillbirths and had never had a normal offspring. This placenta weighed 197 g and had 70 cotyledons. The umbilical cord had 4 vessels and was 7 cm long, but it was not completely represented in the specimen. The placenta is also shown below. No abnormalities were identified in the placenta. In March of 2004 another placenta became available that weighed 131.9 g, had 90 cotyledons and a 3 cm cord attached. It was similar in all other respects to the placentas already described.

	Term placenta of Dorcas gazelle. The left one-half is the maternal surface; the right one-half is the fetal surface.

	New Dorcas gazelle placenta of term infant.

	Additional placenta of malformed term stillborn infant.

The villi are folded and moderately branched. Unfortunately, both placentas examined have had a moderate amount of autolysis, which is reflected in the histologic appearance. No other specimens have been described.

5) Details of fetal/maternal barrier

The villous structure is similar to that of other bovid species. The fetal/maternal relation is epitheliochorial. Occasional binucleate cells interrupt the cuboidal trophoblast of the villous surface. The fetal capillaries protrude frequently into the trophoblastic cover of the villi. A small amount of pigment, typical of the pigment of the “hematophagous organ” can be found in foci of trophoblast beneath the chorionic surface.

	Fetal surface of a term Dorcas gazelle placenta with edematous-appearing villi. This is secondary to some autolysis.

	Surface of a villus with binucleate trophoblastic cell at arrow.

	Implantation site of term Dorcas gazelle placenta. This is near the edge of the cotyledon and show endometrial glands beneath the maternal blood vessels. The connective tissue of the endometrium is seen to interdigitate with the villi.

	Chorionic membrane between cotyledons. Note the prominent trophoblast beneath the vascular chorionic plate.

6) Umbilical cord

The umbilical cord contains 4 large blood vessels and a large allantoic duct. The umbilical cord is inserted in the mid-portion of the placenta; it has no spirals. Numerous smaller vessels are present in the cord, in addition to the principal blood vessels. Some of the smaller vessels surround the allantoic duct. The cord of the placenta here depicted was 6 cm long; the fetus was stillborn at term. The cord of a live-born obtained in 2004 was only 3 cm long. The allantoic duct is lined by urothelium.

Central portion of umbilical cord near the placental surface. This shows the central allantoic duct with blood (Cesarean section-induced), allantoic vessels and musculature of duct.

7) Uteroplacental circulation

This has not been studied.

8) Extraplacental membranes

The allantoic sac has the characteristic vasculature; hippomanes have not been seen. The amnion has a single-layered flat epithelium. Vitelline remnants are not found at term.

9) Trophoblast external to barrier

There is none.

10) Endometrium

True decidual transformation of the endometrium does not occur.

11) Various features

Whether a subplacenta exists is unknown. No well-preserved implanted placentas have been available, nor have they been described in the literature.

12) Endocrinology

I know no endocrine studies.

13) Genetics

Dorcas gazelles have 31 chromosomes in the males, and 30 chromosomes in females. This species, as so many other Antilopinae, has a fusion between an autosome (the autosome is always the same element) and X-chromosome. Hence, the females have one less chromosome, but the DNA/genetic information is otherwise identical. An extensive chromosomal survey of these species was reported by Effron et al. (1976). From that analysis, the suggestion comes that there must have been one ancestor with this typical fusion of chromosomes that gave rise to most African gazellini. Hybrids between Gazella dorcas and Gazella gazella have been reported by Wahrman et al. (1973). Males were sterile, females were subfertile. Ralls et al. (1980) have discussed the inbreeding depression occurring in the highly productive herd in Washington.

Chromosome karyotypes of male and female Dorcas gazelles

Chromosome karyotypes of male (above) and female Dorcas gazelles (from Hsu & Benirschke, 1974).

14) Immunology

There are no studies.

15) Pathological features

Griner (1983) found a myocardial infarct and aortic arteriosclerosis in an aged Dorcas gazelle. Kranz et al. (1984) reported that parasitic infections have been a consistent problem in captivity. Dittrich (1970) found the cause of deaths in captive Dorcas gazelles as follows: septicemia (0.1); pleurisy/hepatitis (1.1); gastroenteritis (1.0).

Haenichen et al. (2002) reported the unusual infection of a pregnant dorcas gazelle with an unusual form of algae, Chlorella, that causes the green granulomatous inflammation known as "Chlorellosis". The infection recurred and the animal was sacrificed. This infection has only rarely been reported in mammals (cattle, sheep, dromedary).

We have seen one gestation that ended with a set of conjoined twins. Therefore, it is possible that the occasional twins that are encountered in this species may be of monozygotic origin.

16) Physiologic data

No studies exist.

17) Other resources

The Zoological Society of San Diego in its CRES division has fibroblast cell lines in the "Frozen Zoo". They can be made available by Dr. Oliver Ryder at (oryder@ucsd.edu).

18) Other remarks - What additional Information is needed?

We need better information on the frequency of binucleate cells, the possible (likely) presence of "areolae" in the intercotyledonary region, and a description of the maternal/fetal interface of an implanted placenta. Endocrine studies are lacking.

Acknowledgement

I appreciate the consistent help of the pathologists at the San Diego Zoo in collecting this material.

References

Baharav, D.: Reproductive strategies in female mountain and Dorcas gazelles (Gazella gazella gazella and Gazella dorcas). J. Zool. 200:445-453, 1983.

Dittrich, L.: Beitrag zur Fortpflanzungsbiologie afrikanischer Antilopen im zoologischen Garten. Zool. Garten 39:16-40, 1970.

Effron, M., Bogart, M.H., Kumamoto, A.T. and Benirschke, K.: Chromosome studies in the mammalian subfamily Antilopinae. Genetica 46:419-444, 1976.

Griner, L.A.: Pathology of Zoo Animals. Zoological Society of San Diego. San Diego, California, 1983.

Haenichen, T., Facher, E., Wanner, G. and Hermanns, W.: Cutaneous chlorellosis in a gazelle (Gazella dorcas). Vet. Pathol. 39:386-389, 2002.

Hayssen, V., van Tienhoven, A. and van Tienhoven, A.: Asdell's Patterns of Mammalian Reproduction: a Compendium of Species-specific Data. Comstock/Cornell University Press, Ithaca, 1993.

Jope, M.: Meine Erfahrungen in der Aufzucht von Dorcasgazellen und Axis-und Schweinshirschen. D. Zool. Garten 49:374-376, 1908.

Kranz, K.R., Xanten, W.A. and Lumpkin, S.: Breeding history of the Dorcas gazelles Gazella dorcas at the National Zoological Park, 1961-1981. Int. Zoo Yearb. 23:195-203, 1984.

Nowak, R.M.: Walker's Mammals of the World. 6th ed. The Johns Hopkins Press, Baltimore, 1999.

Puschmann, W.: Zootierhaltung. Vol. 2, Säugetiere. VEB Deutscher Landwirtschaftsverlag Berlin, 1989.

Ralls, K., Brugger, K. and Glick, A.: Deleterious effects of inbreeding in a herd of captive Dorcas gazelle Gazella dorcas. Int. Zoo Yearb. 20:137-146, 1980

Slaugther, L.: Gestation period of the Dorcas gazelle. J. Mammal. 52:480-481, 1971.

Wahrman, J., Richler, C., Goitein, R., Horowitz, A. and Mendelssohn, H.: Multiple sex chromosome evolution, hybridization and differential X chromosome inactivation in gazelles. In: Jerusalem Chromosome Conference, and Chromosomes Today 42:434-435, 1973.