Close neighbors and distant relatives: a story of Bactrian camels

Genome sequences of 128 camels across Asia show that extant wild and domestic Bactrian camels are distant relatives despite sharing a habitat in East Asia. The researchers propose that the domestic Bactrian camel originated in Central Asia rather than East Asia.

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The two-humped or Bactrian camel had served as one of the principal means of transport between East and West, especially during the time of the Silk Road over 2,000 years ago. Bactrian was an ancient Iranian region in Central Asia, and the term “Bactrian” was first used by Aristotle to distinguish it from the Arabian camel that has only one hump. Survival of wild Bactrian camels in East Asia had been long suspected, until Nikolay Przewalski, a renowned Russian geographer, described their existence and presented several specimens in the late 19th century. However, an open question remains elusive since the Przewalski’s time1: Are the extant wild Bactrian camels the progenitor of the domestic form? Or are they just domestic species that have wandered into the field?

Compared with their domestic counterpart, the wild species are characterized by the lower, pyramid-shaped humps, the thinner, lithe legs, and the smaller and more slender body.

Dr. Jirimutu from Inner Mongolia Agricultural University is dedicated to the research on the Bactrian camel and the development of camel products, which have led to increasing in people's attention to camels. “Due to the disturbance of human activities and the continuous deterioration of the natural environment, the number of extant wild Bactrian camels has decreased sharply. At present, there are only about hundreds to a few thousands, which are much fewer than the giant pandas”, says Dr. Jirimutu. He has worked on the rare genetic resources since 2002, and provided the first complete mitochondrial2 and whole-genome sequences3 of the wild Bactrian camel. “The most promising finding of our researches, together with others, is that the subspeciation of the extant wild and domestic lineages had begun so early that the former cannot be the direct progenitor of the latter4”, says Dr. Jirimutu.

Dr. Jirimutu and wild Bactrian camels. The wild species only persist in remote desert between Mongolia and China now and are critically endangered by the International Union for Conservation of Nature.

Then where did the domestic Bactrian camel come from? In his new study published in Commun. Biol.5, Dr. Jirimutu led a multinational team to collect DNA samples from 128 camels across Asia, including 105 domestic Bactrian camels ranging from the Mongolian Plateau to the Caspian Sea, as well as the extant wild Bactrian camels and Arabian camels. A bioinformatics team led by Dr. Yixue Li and Dr. Zhen Wang at Shanghai Institutes for Biological Sciences performed whole-genome sequencing of the samples and analyzed the data. With more than 10 million SNPs, the population structure and history of the Bactrian camels can well be resolved. The researchers concluded that the Bactrian camels were initially domesticated in Central Asia, which then moved to East Asia where extant wild Bactrian camels inhabit. “The biggest challenge in interpreting the results is the admixture between Bactrian and Arabian camels, especially in Central Asia”, says Dr. Wang. Admixture will complicate the phylogeny inference, and the researchers have performed careful analysis to demonstrate that it would not change the conclusion of Central Asian origin.

“This is the most likely answer to the long-controversial question in regard to the origin of domestic Bactrian camels”, says Dr. Jirimutu. The researchers have gone as far as they can with the materials in hand, although it is unfortunate that no wild population of Bactrian camels exist in Central Asia now. The earliest skeletal remains of domestic Bactrian camels were found in Iran, and ancient DNA approach to sequence the archaeological specimens may help to decipher the full history of their domestication.


written by Liang Ming, Zhen Wang and Jirimutu 

Reference

  1. Schaller, G. B. in Wildlife of the Tibetan Steppes 151-162 (University of Chicago Press,2000).
  2. Cui, P. et al. A complete mitochondrial genome sequence of the wild two-humped camel (Camelus bactrianus ferus): an evolutionary history of camelidae. BMC Genomics 8:241 (2007).
  3. Jirimutu et al. Genome sequences of wild and domestic bactrian camels. Nature Communications 3, 1202 (2012). doi:10.1038/ncomms2192
  4. Ji, R. et al. Monophyletic origin of domestic bactrian camel (Camelus bactrianus) and its evolutionary relationship with the extant wild camel (Camelus bactrianus ferus). Animal Genetics 40, 377-382 (2009).
  5. Ming, L. et al. Whole-genome sequencing of 128 camels across Asia reveals origin and migration of domestic Bactrian camels. Communications Biology 3, 1 (2020). doi:10.1038/s42003-019-0734-6
Go to the profile of Zhen Wang

Zhen Wang

PhD, Shanghai Institutes for Biological Sciences

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