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.
Highlights
The genus Camelus is an interesting model to study the role of natural selection in the mitogenome as a driving force for adaptive divergence
Our study contributes to the understanding of evolutionary processes in Old World camels, and we provide support for the conservation and management of the critically endangered wild species Camelus ferus
We investigated the evolutionary history of Old World camelids and studied the role of natural selection in shaping mitochondrial diversity
Summary
The genus Camelus is an interesting model to study the role of natural selection in the mitogenome as a driving force for adaptive divergence. The wild two-humped camels (Camelus ferus) once were distributed over eastern and central Asia, adapted to arid and cold plains and hills[4, 6] Today, this critically endangered wild species (IUCN 2014) can only be found in the Chinese Taklimakan and Lop Noor deserts and in the Mongolian Great Gobi Strictly Protected Area “A”, with a population census indicating as few as 2,000 individuals remain[7, 8]. The relatively small mitogenome (16–17 kb) encodes a suite of 13 proteins, which interact with the nuclear DNA to build the oxidative phosphorylation (OXPHOS) pathway These proteins are involved in key processes in the cells, the evolution of mtDNA has long been considered nearly neutral, and many studies have neglected the direct impact of positive and/or negative selection in shaping mitogenome diversity. Positive selection in the mitochondrial genes (e.g., COX, ATPase complexes, CYTB) has been shown to be involved in adaptation to different environmental pressures such as high altitude[31,32,33] or temperature[18, 34,35,36]
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