1) General Zoological Data
There are at least five "good" species of these small antelopes. Guenther's dik-dik and Kirk's dik-dik are the most commonly examined dik-diks from Africa in zoological gardens, and may be difficult to distinguish (Kingswood & Kumamoto, 1997). All dik-diks are eastern African species, except for Kirk's variety which is also represented in the southeast of Africa, in Namibia. They form a dissociated population from the eastern form. Although now grouped with "Madoqinae", the Kirk's dik-dik was once also identified as Rhynchotragus because of their elongated snouts; further taxonomic features have been listed by Kingswood & Kumamoto (1997). [Madoqua is said to be from the Amharic and means: small antelope. Gotch, 1979]. Kirk's dik-dik has perhaps as many as six subspecies, and a seventh in southwest Africa (Haltenorth & Diller, 1980). Some animals are also described from Arabia and are there endangered (Habibi, 1986). A very detailed review of these species was undertaken by Kingswood & Kumamoto (1997). Adults weigh between 4 and 5 kg.
Dik-diks have a long lineage, dating back some 12 MYA. They are part of Neotragini which are included in the detailed study of mtDNA cytochrome b study of Matthee & Robinson (1999). They found this group to be polyphyletic, and only Guenther and Kirk's dik-diks are more closely related.
Sexual maturity is attained at age 6-8 months (Mentis, 1972). Longevity in captivity is over 14 years (Jones, 1993), but much less in the wild. Several breeding colonies exist in zoological gardens.
General Gestational Data
The length of gestation is from 170-174 days (Kellas, 1955), and implantation is generally in the right uterine horn, mesometrially. The sex ratio of captive-born animals was: M169/F134 (Bent & Reason, 1998). The litter size is usually singletons weighing 560-680 g.
General Characterization of the Placenta
Details of fetal/maternal barrier
The villi of this animal's placenta are not so very different from those of other antelopes. Wislocki felt that insufficient material had been collected as yet and from mostly inadequately fixed uteri so as to allow categorization of the structure of the villi. Besides, most authors tend to section their material somewhat differently, adding to the confusion. The trophoblast that covers the villi is cuboidal, single-layered and has occasionally binucleated trophoblastic cells, as is so typical for ruminants. The trophoblast has a fine brush border of microvilli. Some minor pigment granules are found here and there. My specimen did not have the maternal hematomas described by Strahl (1911), nor did the specimen studied by Wislocki (1941).
The umbilical cord measured 8 cm in length and 0.3 cm in thickness. It contained four vessels, two arteries and two veins. In addition, there is the usual allantoic duct and numerous small blood vessels, most numerous adjacent to the duct. There were no spirals. Wislocki's observation of the immature gestation is that the umbilical cord was only 6 cm long, and it was studded with tiny epithelial protrusions (caruncles).
Trophoblast external to barrier
There is no extravillous trophoblast. The villous surface, while apposed to the endometrium, does not invade the uterus at any place.
I know of no studies.
Other remarks - What additional Information is needed?
Bent, N. and Reason, R.: A preliminary study of sex ratios in captive-born ruminants. Int. Zoo Ybk. 36:223-228, 1998.
Gotch, A.F.: Mammals - Their Latin Names Explained. Blandford Press, Poole, Dorset, 1979.
Habibi, K.: Arabian ungulates - their status and future protection. Oryx 20:100-103, 1986.
Haltenorth, T. and Diller, H.: A Field Guide to the Mammals of Africa including Madagascar. Collins Sons, Glasgow, 1980.
Jones, M.L.: Longevity of ungulates in captivity. Int. Ybk. 32:159-169, 1993.
Kellas, L.M.: Observations on the reproductive activities, measurements and growth of the dik-dik (Rhyncotragus kirkii thomasii Neumann). Proc. Zool. Soc. London 124:751-784, 1955.
Kingswood, S.C. and Kumamoto, A.T.: Madoqua kirkii. In, Mammalian Species # 569, pp. 1-10, Amer. Soc. Mammalogists, 1997.
Kumamoto, A.T., Kingswood, S.C. and Hugo, W.: Chromosomal divergence in allopatric populations of Kirk's dik-dik, Madoqua kirki (Artiodactyla, Bovidae). J. Mammal. 75:357-364, 1994.
Kumamoto, A.T. and Kingswood, S.C.: Description of a fourth cytotype for Kirk's dik-dik, Madoqua kirki (Artiodactyla, Bovidae). Cytogenet. Cell Genet. 71:400 (abstr.), 1995.
Maloy, G.M.O., Rugangazi, B.M. and Clemens, E.T.: Physiology of the dik-dik antelope. Mini Review. Comp. Biochem. Physiol. 91A:1-18, 1988.
Matthee, C.A. and Robinson, T.J.: Cytochrome b phylogeny of the family bovidae: Resolution within the alcelaphini, antilopini, neotragini, and tragelaphini. Mol. Phylog. Evol. 12:31-46, 1999.
Mentis, M.T.: A review of some life history features of the large herbivores of Africa. The Lammergeyer 1-89, 1972.
Roosevelt, T. and Heller, E.: Life-histories of African game animals. John Murray, London, 2:421-798, 1915.
O., Kumamoto, A.T., Durrant, B.S., and Benirschke, K.: Chromosomal divergence
and reproductive isolation in dik-diks. In, Speciation and its Consequences.
Chapter 9, pp. 208-225. D. Otte and J.A. Endler, eds. Sinauer Assoc. Sunderland,
Strahl, H.: Zur Kenntnis der Wiederkäuerplacentome. Anat. Anz. 40:259-2264, 1911.
Wislocki, G.B.: The placentation of an antelope (Rhynchotragus kirkii nyikae Heller). Anat. Rec. 81:221-241, 1941.
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