Mitogenome Sequencing in the Genus Camelus Reveals Evidence for Purifying Selection and Long-term Divergence between Wild and Domestic Bactrian Camels

Abstract

The genus Camelus is an interesting model to study adaptive evolution in the mitochondrial genome, as the three extant Old World camel species inhabit hot and low-altitude as well as cold and high-altitude deserts. We sequenced 24 camel mitogenomes and combined them with three previously published sequences to study the role of natural selection under different environmental pressure, and to advance our understanding of the evolutionary history of the genus Camelus. We confirmed the heterogeneity of divergence across different components of the electron transport system. Lineage-specific analysis of mitochondrial protein evolution revealed a significant effect of purifying selection in the concatenated protein-coding genes in domestic Bactrian camels. The estimated dN/dS < 1 in the concatenated protein-coding genes suggested purifying selection as driving force for shaping mitogenome diversity in camels. Additional analyses of the functional divergence in amino acid changes between species-specific lineages indicated fixed substitutions in various genes, with radical effects on the physicochemical properties of the protein products. The evolutionary time estimates revealed a divergence between domestic and wild Bactrian camels around 1.1 [0.58–1.8] million years ago (mya). This has major implications for the conservation and management of the critically endangered wild species, Camelus ferus.

Old World camels in a modern world – a balancing act between conservation and genetic improvement

“…Reprint permits were granted by AramcoWorld on March 6, 2019. (Ji et al 2009;Silbermayr et al 2010;Jirimutu et al 2012;Mohandesan et al 2017;Yi et al 2017) confirmed that the wild two-humped camel is an original wild form and separate species C. ferus.…”

“…Within Camelini, three species are recognised today based on the International Commission on Zoological Nomenclature (2003) (Gentry et al 2004) and genomic evidence: the domesticated C. dromedarius and C. bactrianus, and the only remaining wild species, the two-humped C. ferus. Whereas one-and two-humped camels diverged 4.4 (1.9-7.2) Mya (Wu et al 2014), the split between the ancestors of wild and domestic Bactrian camels is more recent and was estimated at 1.1 (0.6-1.8) Mya (Ji et al 2009;Mohandesan et al 2017).…”

Whole-genome sequencing of 128 camels across Asia provides insights into origin and migration of domestic Bactrian camels

“…Historically, the wild Bactrian camel was widely distributed throughout Asia, extending from the great bend of the Yellow River westward to central Kazakhstan, but it can only be found in the Mongolian Gobi and the Chinese Taklimakan and Lop Noor deserts today [7]. Fossil and molecular evidence suggested that the ancestor of camels lived in North America and spread to Asia via the Bering land bridge around 11 or 16 million years ago [8,9]. Within the Camelini, the dromedaries and Bactrian camels were then split around 4 or 5 million years ago [9,10].…”

“…Fossil and molecular evidence suggested that the ancestor of camels lived in North America and spread to Asia via the Bering land bridge around 11 or 16 million years ago [8,9]. Within the Camelini, the dromedaries and Bactrian camels were then split around 4 or 5 million years ago [9,10]. The domestication of camels, like many other domestic mammals, has promoted unprecedented progress in cultural and economic development of human societies, representing a great leap forward for human civilization.…”

“…Nevertheless, molecular studies based on mtDNAs discovered dramatic sequence variations between the wild camels and domestic Bactrian camels, and proposed that the extant wild Bactrian camel was a separate lineage and not the direct progenitor of the domestic Bactrian camel [9,13].…”