Genetic Karyotyping Saves Zoo Dik Diks

Guenther's dik dik

Günther’s dik dik

“Can you do a paternity test on a chimpanzee?” “Can you figure out how closely related this group of California condors is?” We here at the Genetics Division of the San Diego Zoo Institute for Conservation Research frequently gets requests like these from other zoos. So when the studbook keeper (a person who keeps the history and pedigree of a single species) for dik diks stopped by last year and asked us how a cytogenetic study that was done here in the early 1990s told the story of reproduction in zoo dik diks and what that meant for their animal management, we were ready to explain.

What is a dik dik? It is a very small antelope (only a royal antelope is smaller). They are very cute animals, gray-brown with an elongated nose, and the males have horns whereas the females do not. These antelope live in pairs and not herds, and there are five known species.

Kirk's dik dik

Kirk’s dik dik

Back in the 1970s and 1980s, many dik diks were imported into zoos in North America. These dik diks all looked similar, and exactly what locations these animals came from and if they were the same species or subspecies was not known. When zookeepers started to notice that there were issues with reproduction, it was decided that it was important to look at their chromosomes.

So a large study was started and 127 animals were karyotyped (a karyotype is a chromosomal map). It was discovered that there were two species in the North American zoo populations: the Günther’s dik dik Madoqua guentheri and the Kirk’s dik dik Madoqua kirkii. The Günther’s dik dik we studied was found to have a Robertsonian translocation (a chromosomal rearrangement where two chromosomes are joined), which meant they had a chromosome number ranging from 48 to 50. The Kirk’s dik dik was more complex. We found four different subspecies, and each had a different-looking karyotype (named cytotypes A–D).

In this male Günther’s dik dik karyotype, you can see the example of a Robertsonian translocation where in any given animal you could have either two #5 chromosomes and two #17s or two joined 5 and 17 chromosomes (5:17) or one of each, as in this example.

Click to enlarge! In this male Günther’s dik dik karyotype, you can see the example of a Robertsonian translocation where in any given animal you could have either two #5 chromosomes and two #17s or two joined 5 and 17 chromosomes (5:17) or one of each, as in this example.

So how does this impact reproduction in zoo dik diks? It was discovered that there were Günther’s dik diks and Kirk’s dik diks that were housed together, and they would have hybrid offspring that were sterile. In addition, when some of the different cytotypes (subspecies, cytotype A and B) were housed together, their male offspring were also sterile. This was why there was a decline in reproduction in the dik dik. To correct this trend, we needed to work with the studbook keeper to make sure all the dik diks were karyotyped and correctly identified and then housed together by species or subspecies.

This female Kirk’s dik dik is Cytotype A.

Click to enlarge! This female Kirk’s dik dik is Cytotype A.

Karyotyping and animal management helped rescue the dik dik, and this karyotyping process is still being done today. We have recently received samples from six Kirk’s dik diks from two zoos in North America and looked at their chromosomes. They were all cytotype A and are now included in the breeding program for dik diks. Have you seen the Kirk’s dik diks at the Zoo and Safari Park? Look for them in the Park’s Nairobi Village or the Zoo’s Elephant Odyssey.

Suellen Charter is a research coordinator for the San Diego Zoo Institute for Conservation Research. Read her previous post, Frozen Zoo: Sharing Our Knowledge.

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