by Peter Kaufmann
1) General Zoological Data
Capybaras ("carpinchos") are the largest rodents and perhaps derivatives of a much larger species still, Phoberomys, that is now extinct (Sanchez-Villagra et al., 2003). Their body weights normally range from 30 to 50 kg. Capybaras belong to the South American suborder of caviomorph rodents. They live in large groups in and along rivers and lakes in the lowlands of Panama, Colombia, Venezuela and Brazil. Family groups of around six animals are usual; they are commonly seen in the Pantanal of Brazil. The Panamanian subspecies is smaller. Often the genus is called Hydrochoerus as well. Its name is derived from the commonly applied reference as "water pig" (Gotch, 1979).
In the past decades, capybaras have raised the scientific interest of placentologists for a certain period, mainly because of the fact that they are members of the interesting suborder of caviomorph rodents. This suborder is characterized by an enormous diversity in body weight, ranging from the small degu (100 to 150 g) to the sheep-shaped capybara (mean weight is 40,000 g). Moreover, these rodents are charaterized by a rather long pregnancy period, by a hormonal control of pregnancy which is similar to that of the human and, in particular, by their striking homogeneity of placental structure, irrespective of the enormous range in weights - from <1 g (degu) to > 100 g (capybara); they are structurally more or less identical. The longevity of capybaras in captivity is up to 12 years (Nowak, 1999).
the 1980s, most experimental research in placentology was performed in two
(a) In the sheep, which is a species that is easy to keep and breed and that is large enough for sophisticated in vivo experiments such as chronic catheterization of placental vessels for studies of placental transport. The main disadvantage of the sheep, however, is the fact that its placenta is cotyledonary in organization and epitheliochorial in its barrier structure and it thus shows only minimal resemblance to that of the human placenta. Therefore, transport data can be transferred to human placentation only with some reservation.
(b) In contrast to the sheep, there is then the small, handy, easy-to-breed guinea pig which is characterized by having a discoidal, hemochorial placenta with a maternal/fetal barrier largely identical to that of the human placenta. The small body size, however, makes short term experiments difficult, and chronic catheterization nearly impossible.
It is therefore easily understandable that the suggestion coming to placentologists about the existence of a sheep-sized "giant guinea pig" raised enormous expectations. A caviomorph rodent with 30 to 50 kg body size, 1,500 g neonatal weight, 150 days pregnancy length, placental vessels similar to water pipes, and all this together with a discoidal, hemochorial placenta would fulfill even the greatest expectations of every experimentator.
When we started our capybara colony in Aachen, our only fear was that reproduction of these animals might be the problem. This, we were told, was the case in most zoos. We started our colony with two males from a German zoo and three females were imported from Venezuela. In order to develop a strategy how to mate these allegedly difficult to breed animals, and in order to prevent damage to our costly females, males and females were kept in neighboring rooms in our animal facility for the first night. They were separated from each other by two 6 cm strong wooden doors because unexpectedly the perfect cooperation between Lufthansa and the zoo in Caracas, the females arrived earlier than the steel armored cages ordered. The next morning we found that both doors, including considerable parts of the animal laboratories, were ruined and all three females were pregnant.
Rapid reproduction, in fact, became a problem. Our breeding colony grew more quickly than expected and than we could afford, food-wise and space-wise. This was particulalrly true considering the delicate care for big, fierce tropical animals in the cold and rainy climate of Germany. Moreover the animal handlers had problems with our growing colony so that it was finally housed in a high-fenced garden with lakes. It quickly became an attraction for school classes and tourists. The real experimental problem, however, was caused by the fact that capybaras are extremely powerful, have not been truly domesticated, and they are furious animals which do not even fear the jaguar in their South-American habitat. Nor did they fear us. They can be enormously patient and playful so long as you pet them. But they turned into beasts and flattened an entire laboratory when we simply wanted to have a drop of blood.
A "laboratory animal" that cannot be immobilized without general anesthesia, that required general anesthesia for every simple test or treatment, that removed every implanted catheter within hours, even when implanted on its back, and that responded with abortion or preterm delivery to every second general anesthesia given certainly does not fulfill the expectations of a placentologist. Meanwhile our beautiful colony has become the pride of a small zoo to which we had donated it. In spite of this scientific disappointment, the few facts which we were able to collect are listed subsequently.
2) General Gestational Data
Length of gestation: 150 - 155 days
Litter size: 1 - 8, mean 5 (Weir, 1974), under laboratory conditions 3
Body weight (non pregnant) : >30 kg, at full term: up to 65 kg
Fetal weight at full term: 1,500 g
Weight of placenta and membranes at full term: about 100 g.
The general placental type is discoidal, labyrinthine, hemomonochorial, chorioallantoic main placenta with a specialized subplacenta and a separate yolk sac placenta.
The allantois is only used for the formation and vascularization of the chorioallantoic placenta (main placenta and subplacenta). Miglino et al. (2004) have presented a remarkable comparative study of the placentas of agouti, capybara, guninea pig, paca and rock cavy that gives superb details of the vascular organization of these organs.
Details of Fetal/Maternal Barrier
The exchange area, the labyrinth, is identical to that of the guinea pig and other caviomorph rodents: it is the labyrinth that is composed of about 100 finger-like lobes. Each lobe measures from 3 to 6 mm in diameter and 15 to 20 mm in length.
lobe represents its own circulatory unit, the fetal arterioles being located
along its outer surface, the fetal veins being located in its center. The
connecting fetal capillaries are arranged in a radial fashion as shown in
the next diagram. The average length of the fetal capillaries is 1.5 to
3 mm, and thus about three times as long as the capillaries in the guinea
The maternal blood flows from an arterial lacuna located in the lobar center centrifugally via a web of trophoblast-lined blood lacunae to the periphery of the lobe, where it is drained by a web of venous lacunae which pass the interlobar trophoblast.The blood flow arrangement represents a perfect counter-current exchange system.
|The fetal/maternal barrier is hemomonochorial as in all caviomorphs and is shown next. The histology of the labyrinth was described in detail by Miglino et al. (2002). Maternal and fetal blood streams are separated by a layer of syncytiotrophoblast which is separated from the fetal endothelium in most places only by a basal lamina. Intervening connective tissue is rare. Cytotrophoblast can be found only in the first weeks of pregnancy.|
The cord is composed of a vitelline and allantoic portion as shown in the first schematic. It is short and similar to other caviomorphs. (See chapters on guinea pig and nutria).
7) Uteroplacental Circulation
As in the guinea pig, the yolk sac placenta replaces the thin, non-placental, part of the blastocystic trophoblast vesicle. Together with the chorioallantoic placenta it forms the fetal membranes. Its endodermally-covered and fetally vascularized folds are in intimate contact with the endometrial surface epithelium. Those features are diagrammed next and details may be obtained from the publication by Miglino et al. (2002).
Trophoblast External to Barrier
All caviomorph rodents are characterized by an unusual degree of trophoblast invasion. Trophoblast cells, uninucleated and multinucleated in type, do not only invade the endometrium and myometrium, but regularly penetrate the uterine wall and spread as a thin, monocellular layer across the peritoneal cavity. In the guinea pig, it has been shown that trophoblast at term replaces large parts of the peritoneal mesothelium (Nanaev et al., 1995). Our few observations in the capybara suggest the same highly invasive behavior to be present in this species. It remains unknown whether or not the endovascular trophoblast invasion along the uteroplacental arteries is as aggressive as it is in the guinea pig. It might be mentioned, however, that in nutria it is identical (see chapter on Nutria) and may be a feature of most if not all South American hystricomorph rodents.
11) Various Features
Capybaras have 66 chromosomes and, like other South American rodents, their X-chromosome is unusually large (+/- 10% of genome) (Hsu & Benirschke, 1974; Wurster et al., 1971). A molecular study of pancreatic ribonuclease genes has shown a duplication in guinea pigs but only a single copy is found in capybara and cuis (Beintema & Neuteboom, 1983). Hybrids have not been reported.
We know of no relevant studies.
15) Pathological Features
16) Physiological Data
18) Other Remarks - What additional
information is needed?
Cueto, G.R., Allekotte, R. And Kravetz, F.O.: Scurvy in capybaras in captivity in Argentine. J. Wild. Dis. 36:97-101, 2000.
Gotch, A.F.: Mammals - Their Latin Names Explained. Blandford Press, Poole, Dorset, 1979.
Griner, L.A.: Pathology of Zoo Animals. Zoological Society of San Diego, San Diego, California, 1983.
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.
Hsu, T.C. and Benirschke, K.: An Atlas of Mammalian Chromosomes. Springer-Verlag, New York. Vol. 8, Folio 378, 1974.
Kaufmann, P. and Davidoff, M.: The guinea-pig placenta. Adv. Anat. Embryol. Cell Biol. 53: 1-91, 1977.
Lopez Barbella, S.: Determination of the estrous cycle of the capybara (Hydrochoerus hydrochaeris). [In Spanish]. Acta Cient. Venz. 33:497-501, 1982 (not available to us).
Miglino, M.A., Carter, A.M., dos Santos,
R.H. and F. Machado, M.R.: Placentation in the capybara (Hydrochaerus
hydrochaerus), agouti (Dasyprocta aguti) and paca (Agouti
paca). Placenta 23:416-428, 2002.
Nowak, R.M.: Walker's Mammals of the World. 6th ed. The Johns Hopkins Press, Baltimore, 1999.
Paula, T.A., Chiarini-Garcia, H. And Franca, L.R.: Seminiferous epithelium cycle and its duration in capybaras (Hydrochoerus hydrochaeris). Tissue Cell. 31:327-334, 1999.
Sanchez-Villagra, M.R., Aguilera, O. and Horovitz, I.: The anatomy of the world's largest extinct rodent. Science 301:1708-1710, 2003.
Weir, B.J.: Reproductive characteristics of hystricomorph rodents. Symp. Zool. Soc. London 34:265-301, 1974.
Wurster, D.H., Snapper, J.R. and Benirschke, K.: Unusually large sex chromosomes: new methods of measuring and description of karyotypes of six rodents (Myomorpha and Hystricomorpha) and one Lagomorpha (Ochotonidae). Cytogenetics 10:153-176, 1971.
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