• Ren Larison

Ain't no mountain high enough

Mountain zebras (Equus zebra), endemic to South Africa and Namibia, are one of three extant species of extant zebras and comprise two recognized subspecies, the Cape mountain zebra (E. z. zebra) and Hartmann’s mountain zebra (E. z. hartmannae). Like their sister species, plains and Grevy’s zebras, they are recognizable by their iconic black and white stripes. Mountain zebras fall between the other two species in size and the thickness of their stripes. Mountain zebras can also easily be distinguished by the fact that they possess a dewlap, a fold of skin hanging from the throat.

As their name implies, they prefer mountainous terrain up to about 3000 feet. Once listed as endangered (IUCN Red List - 1996) with a global population of between 2-3000 only 80 of which were Cape mountain zebra, the species has rebounded to a global population of 35,000, 1700 being the Cape subspecies. They are still vulnerable, however, due to habitat fragmentation and the potential threat of increased drought due to climate change. It was drought that caused the catastrophic decline that led to the population nadir in the 1980’s.

Mountain Zebra stallion by Bernard Dupont, [CC BY-SA 2.0], via flickr.com

Today we share the $1K assembly of the mountain zebra. The sample for the assembly was provided by a mountain zebra named Zakota and obtained by Greg Barsh (Hudson Alpha/ Stanford University) and Ren Larison (UCLA) during a visit to the Hearts and Hands Animal Rescue in Ramona, CA, owned by animal lover and zebra whisperer Nancy Nunke. During our visit Nancy had us stroke the fur along the back of a mountain zebra, allowing us to learn an unusual fact about them; the fur between the saddle and rump grows backward, with the nap back to front instead of front to back.

Like the plains zebra, the mountain zebra shows quite a bit of rearrangement in their chromosomes relative to the domestic horse (see whole genome alignment plots below). This rearrangement is also reflected in the large differences in number chromosomes among the three species, with the horse having 32 pairs of chromosomes, the plains zebra 22, and the mountain zebra only 16 – half that of the horse. In spite of these re-arrangements equids are notorious for their ability to hybridize, leading to the fascinating pelage patterns seen in hebras and zorses, as well as potential conservation threats due to hybridization between the rarer zebra species - mountain zebras and Grevy’s zebras - and the vastly more common plains zebra.

Whole-genome alignment between the new chromosome-length genome assembly for the mountain zebra (Equus_zebra_HiC) and that of the domestic horse (EquCab2.0, from Wade et al., Science 2009).


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