Monophyletic origin of domestic bactrian camel (Camelus bactrianus) and its evolutionary relationship with the extant wild camel (Camelus bactrianus ferus)

Abstract

The evolutionary relationship between the domestic bactrian camel and the extant wild two-humped camel and the factual origin of the domestic bactrian camel remain elusive. We determined the sequence of mitochondrial cytb gene from 21 camel samples, including 18 domestic camels (three Camelus bactrianus xinjiang, three Camelus bactrianus sunite, three Camelus bactrianus alashan, three Camelus bactrianus red, three Camelus bactrianus brown and three Camelus bactrianus normal) and three wild camels (Camelus bactrianus ferus). Our phylogenetic analyses revealed that the extant wild two-humped camel may not share a common ancestor with the domestic bactrian camel and they are not the same subspecies at least in their maternal origins. Molecular clock analysis based on complete mitochondrial genome sequences indicated that the sub-speciation of the two lineages had begun in the early Pleistocene, about 0.7 million years ago. According to the archaeological dating of the earliest known two-humped camel domestication (5000-6000 years ago), we could conclude that the extant wild camel is a separate lineage but not the direct progenitor of the domestic bactrian camel. Further phylogenetic analysis suggested that the bactrian camel appeared monophyletic in evolutionary origin and that the domestic bactrian camel could originate from a single wild population. The data presented here show how conservation strategies should be implemented to protect the critically endangered wild camel, as it is the last extant form of the wild tribe Camelina.

Figure 1

Majority-rule (20%) neighbour-joining tree of cytb gene sequences inferring the phylogeny of bactrian camels. The topology is rooted with Camelus dromedarius as the outgroup, based on the maximum likelihood method. The nodes were supported in the boostrap value (1000 replications) and posterior probability shown on each node (the number on the right is the bootstrap value and the number on the left is the posterior probability). The scale bar indicates 1% sequence divergence.

Figure 2

The construction of the phylogenetic relationship between Camelus bactrianus and C. bactrianus ferus based on the complete mitochondrial genomic sequences, excluding the control regions. The tree was reconstructed based on the maximum likelihood method. To estimate the divergence time, alpaca (Lama pacos) was taken as an in-group calibration point; all nodes were supported by the bootstrap value (1000 replications) and posterior probability shown on each node (bootstrap value is above the branch and posterior probability is below the branch). The scale bar indicates 100 substitutions.