Further assessment of the Genus <i>Neodon</i> and the description of a new species from Nepal

Recent molecular systematic studies of arvicoline voles of the genera Neodon, Lasiopodomys, Phaiomys, and Microtus from Central Asia suggest the inclusion of Phaiomys leucurus, Microtus clarkei, and Lasiopodomys fuscus into Neodon and moving Neodon juldaschi into Microtus (Blanfordimys). In addition, three new species of Neodon (N. linzhiensis, N. medogensis, and N. nyalamensis) have recently been described from Tibet. Analyses of concatenated mitochondrial (Cytb, COI) and nuclear (Ghr, Rbp3) genes recovered Neodon as a well-supported monophyletic clade including all the recently described and relocated species. Kimura-2-parameter distance between Neodon from western Nepal compared to N. sikimensis (K2P = 13.1) and N. irene (K2P = 13.4) was equivalent to genetic distances observed between recognized species of this genus. The specimens sampled from western Nepal were recovered sister to N. sikimensis in the concatenated analysis. However, analyses conducted exclusively with mitochondrial loci did not support this relationship. The occlusal patterns of the first lower (m1) and third upper (M3) molars were simpler in specimens from western Nepal in comparison to N. sikimensis from eastern Nepal and India. Twelve craniodental characters and four external field measurements were examined from specimens of N. sikimensis from eastern Nepal and India, N. irene, and Neodon from western Nepal. Neodon from western Nepal were significantly different from N. sikimensis from eastern Nepal and India in ten out of 16 characters measured and from N. irene for all characters except ear height. Specimens from western Nepal were smaller in size than N. sikimensis from Eastern Nepal and India and larger than N. irene. Together the results of the molecular and morphological analyses indicate that Neodon from western Nepal are distinct under the phylogenetic, genetic and morpho species concepts.针对中亚地区川田鼠属（Neodon）、毛足田鼠属（Lasiopodomys）、白背田鼠属（Phaiomys）和田鼠属（Microtus）的田鼠类群的最新分子系统学研究显示，应将白背田鼠（Phaiomys leucurus）、克拉克田鼠（Microtus clarkei）以及棕色毛足田鼠（Lasiopodomys fuscus）归入川田鼠属，同时将朱尔达什川田鼠（Neodon juldaschi）移至田鼠属（Blanfordimys亚属，Microtus (Blanfordimys)）。此外，近期在西藏地区记述了3个川田鼠属新种：林芝川田鼠（N. linzhiensis）、墨脱川田鼠（N. medogensis）以及聂拉木川田鼠（N. nyalamensis）。基于串联线粒体基因（细胞色素b基因Cytb、细胞色素氧化酶亚基I基因COI）与核基因（生长激素受体基因Ghr、视黄醇结合蛋白3基因Rbp3）的分析结果表明，川田鼠属为一支支持度极高的单系群，涵盖了所有新近记述及分类地位调整的物种。尼泊尔西部川田鼠种群与锡金川田鼠（N. sikimensis）、艾琳川田鼠（N. irene）之间的Kimura双参数（K2P）遗传距离分别为13.1和13.4，该数值与该属公认物种间的遗传距离水平相当。在串联基因分析中，尼泊尔西部的采样标本被聚类为锡金川田鼠的姊妹群，但仅基于线粒体基因座的分析并不支持这一亲缘关系。相较于尼泊尔东部及印度的锡金川田鼠，尼泊尔西部标本的下第一臼齿（m1）与上第三臼齿（M3）的咬合面结构更为简单。研究对尼泊尔东部及印度的锡金川田鼠、艾琳川田鼠以及尼泊尔西部川田鼠标本的12项颅齿特征与4项野外外部形态测量指标进行了检测。尼泊尔西部川田鼠在16项检测特征中有10项与尼泊尔东部及印度的锡金川田鼠存在显著差异，且在除耳高外的所有特征上均与艾琳川田鼠存在显著差异。尼泊尔西部标本的体型小于尼泊尔东部及印度的锡金川田鼠，但大于艾琳川田鼠。综合分子与形态学分析结果来看，基于系统发育、遗传学以及形态学物种概念，尼泊尔西部川田鼠种群均为独立的物种类群。