Wang Zhongsong, Zhao Di, Song Wenyu, Dong Wenge
Yunnan Provincial Key Laboratory for Zoonosis Control and Prevention, Institute of Pathogens and Vectors, Dali University, Dali 671000, China.
Biology (Basel). 2025 Jul 28;14(8):948. doi: 10.3390/biology14080948.
The Millard's rat (), a threatened murid endemic to Southeast Asian montane rainforests and the sole member of its monotypic genus, faces escalating endangered risks as a Near Threatened species in China's Biodiversity Red List. This ecologically specialized rodent exhibits diagnostic morphological adaptations-hypertrophied upper molars and cryptic pelage-that underpin niche differentiation in undisturbed tropical/subtropical forests. Despite its evolutionary distinctiveness, the conservation prioritization given to is hindered due to a deficiency of data and unresolved phylogenetic relationships. Here, we integrated morphological analyses with the first complete mitogenome (16,289 bp in size; no structural rearrangements) of to validate its phylogenetic placement within the subfamily Murinae and provide novel insights into genetic diversity erosion. Bayesian and maximum likelihood phylogenies robustly supported as sister to (PP = 1.0; BS = 100%), with an early Pliocene divergence (4.8 Mya, 95% HPD: 3.65-5.47 Mya). Additionally, based on its basal phylogenetic position within Murinae, we propose reclassifying from Rattini to the tribe Micromyini. Codon usage bias analyses revealed pervasive purifying selection (Ka/Ks < 1), constraining mitogenome evolution. Genetic diversity analyses showed low genetic variation (: = 0.0135 ± 0.0023; : = 0.0101 ± 0.0025) in fragmented populations. We propose three new insights into this genetic diversity erosion. (1) Evolutionary constraints: genome-wide evolutionary conservation and shallow evolutionary history (4.8 Mya) limited mutation accumulation. (2) Anthropogenic pressures: deforestation-driven fragmentation of habitats (>20,000 km/year loss since 2000) has reduced effective population size, exacerbating genetic drift. (3) Ecological specialization: long-term adaptation to stable niches favored genomic optimization over adaptive flexibility. These findings necessitate suitable conservation action by enforcing protection of core habitats to prevent deforestation-driven population collapses and advocating IUCN reclassification of from Data Deficient to Near Threatened.
米勒鼠（）是东南亚山地雨林特有的一种受威胁的鼠科动物，也是其单型属的唯一成员，在中国生物多样性红色名录中作为近危物种面临着不断升级的濒危风险。这种生态特化的啮齿动物表现出诊断性的形态适应特征——上颌臼齿肥大和毛色隐秘——这是其在未受干扰的热带/亚热带森林中生态位分化的基础。尽管它具有进化独特性，但由于数据不足和系统发育关系未解决，对它的保护优先级受到阻碍。在这里，我们将形态学分析与米勒鼠的首个完整线粒体基因组（大小为16289 bp；无结构重排）相结合，以验证其在鼠亚科中的系统发育位置，并为遗传多样性侵蚀提供新的见解。贝叶斯和最大似然系统发育强烈支持米勒鼠与[某物种]为姐妹关系（PP = 1.0；BS = 100%），上新世早期分化（约480万年前，95% HPD：365 - 547万年前）。此外，基于其在鼠亚科中的基部系统发育位置，我们建议将米勒鼠从鼠族重新分类到小家鼠族。密码子使用偏好分析揭示了普遍的纯化选择（Ka/Ks < 1），限制了线粒体基因组的进化。遗传多样性分析表明，在碎片化种群中遗传变异较低（[某群体]： = 0.0135 ± 0.0023；[另一群体]： = 0.0101 ± 0.0025）。我们对这种遗传多样性侵蚀提出了三个新的见解。（1）进化限制：全基因组的进化保守性和较浅的进化历史（约480万年前）限制了突变积累。（2）人为压力：森林砍伐导致的栖息地碎片化（自2000年以来每年损失超过20000平方公里）减少了有效种群大小，加剧了遗传漂变。（3）生态特化：长期适应稳定的生态位有利于基因组优化而非适应性灵活性。这些发现需要采取适当的保护行动，通过加强对核心栖息地的保护以防止森林砍伐导致的种群崩溃，并倡导世界自然保护联盟将米勒鼠的分类从数据缺乏重新分类为近危。
