Species Delimitation in the Genus Moschus (Ruminantia: Moschidae) and Its High-Plateau Origin

Abstract

The authenticity of controversial species is a significant challenge for systematic biologists. Moschidae is a small family of musk deer in the Artiodactyla, composing only one genus, Moschus. Historically, the number of species in the Moschidae family has been debated. Presently, most musk deer species were restricted in the Tibetan Plateau and surrounding/adjacent areas, which implied that the evolution of Moschus might have been punctuated by the uplift of the Tibetan Plateau. In this study, we aimed to determine the evolutionary history and delimit the species in Moschus by exploring the complete mitochondrial genome (mtDNA) and other mitochondrial gene. Our study demonstrated that six species, M. leucogaster, M. fuscus, M. moschiferus, M. berezovskii, M. chrysogaster and M. anhuiensis, were authentic species in the genus Moschus. Phylogenetic analysis and molecular dating showed that the ancestor of the present Moschidae originates from Tibetan Plateau which suggested that the evolution of Moschus was prompted by the most intense orogenic movement of the Tibetan Plateau during the Pliocene age, and alternating glacial-interglacial geological eras.

Fig 1. Geographic distribution of Moschus species and consensus mitochondrial gene tree.

Tree is equivalent to that of Fig 3. All the information about geographic distribution of Moschus species were came from IUCN (http://www.iucnredlist.org/), except a new distribution area of M. berezovskii, which was marked by a star [39].

Fig 2. Phylogram showing the phylogenetic relationship in Moschus.

The species from Moschus were highlight in different colors. The values on nodes indicate Bayesian posterior probabilities and ML support; “-” indicated that the value was less than 70.

Fig 3. Phylogram showing the phylogenetic relationship in Moschidae.

The values on nodes include three parts. The first two values indicate the split time and Bayesian posterior probabilities which were calculated by BEAST 1.7.4. The last values were the Bayesian posterior probabilities calculated by MrBayes 3.1.2.

Fig 4. The species delimitation results based on the complete mt genome in four species of Moschus (M. chrysogaster, M. moschiferus, M. berezovskii and M. anhuiensis).

A: the posterior probability of number of species when θ changed (τ₀ = 1: 100); B: the posterior probability of number of species when τ₀ changed (θ = 1: 2 000). P(4) means that the probability of four species; P(3) means that the probability of three species; P(2) means that the probability of two species; P(1) means that the probability of one species.

Fig 5. Sliding window analyses showing the nucleotide diversity based on alignment of complete mtDNAs of four species in Moschus (M. chrysogaster, M. moschiferus, M. berezovskii and M. anhuiensis).

The black line shows the value of nucleotide diversity (π) in a sliding window analysis of window size 300 bp with step size 10, the value is inserted at its mid-point. Gene boundaries are indicated with an indication of the total number of variable positions per gene; ATP8 with ATP6, ND4L with ND4, and ND5with ND6 are overlapping.

Fig 6. The genetic distance among four species of Moschus based on each gene in mitochondrial genome.

Ma, Mb, Mm, Mc represents M. anhuiensis, M. berezovskii, M. moschiferus and M. chrysogaster, respectively.