Jiang Jian-Ping, Jia Jia, Zhang Meihua, Gao Ke-Qin
Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu, China.
School of Earth and Space Sciences, Peking University, Beijing, China.
PeerJ. 2018 Mar 28;6:e4517. doi: 10.7717/peerj.4517. eCollection 2018.
The Longdong Stream Salamander , living in a mountain stream environment at Mt. Emei in Sichuan Province, China, represents a rare species that is facultatively neotenic in the family Hynobiidae. Although the species has been known to science for some 40 years since its initial discovery in the late 1970s, anatomical details of its osteology remain poorly understood and developmental information is still lacking for the species. This study (1) provides a detailed osteological account of based on micro-CT scanning and clearing and staining of multiple specimens from the type locality; (2) provides a discussion of intraspecific variation related to life-history differences; and (3) presents a discussion on limb features related to morphological evolution of limb patterns correlative with ecological adaptation to mountain stream environments. Osteological comparisons with congeneric species has led to recognition of several diagnostic features that are unique to , including: vomers widely separated from one another, lacking a midline contact; presence of uncommon perichondral ossification of the ascending process of the palatoquadrate as part of the suspensorium; and presence of a prominent posterodorsal process of the scapular blade, which serves as a ligamentous insertion of the levator muscle of the scapula. In addition, some but not all neotenic individuals retain the palatine as a discrete element, indicative of its delayed absorption after sexual maturity. Postmetamorphic and neotenic individuals are strikingly different in the complexity of hyobranchial structures. Neotenes display a high degree of ossification of hyobranchial elements, tend to increase ossification of both hypobranchial I and ceratobranchial I during aging, and retain fully ossified ceratobranchial III and IV; in contrast, these elements remain entirely cartilaginous or are totally lost by resorption in postmetamorphic individuals. In addition, all postmetamorphic forms display an inverted "T"-shaped basibranchial II, whereas neotenes show transformation from a "fork"-shaped to the "T"-shaped configuration after sexual maturity. displays a mosaic of apomorphic and plesiomorphic states in its limb ossifications: presence of a single centrale element in both the manus and pes is a derived condition in Hynobiidae and other families as well, whereas retention of a postminimus in the pes is obviously plesiomorphic within Urodela. Reduction in number of digits from five to four in the pes and possession of a cornified sheath covering the terminal phalanges are also derived features shared with some but not all mountain stream salamanders that are adapted to a similar type of environment.
陇东溪鲵生活在中国四川省峨眉山的山间溪流环境中，是隐鳃鲵科中一种罕见的兼性幼态延续物种。尽管自20世纪70年代末首次发现该物种以来，科学界对其已了解约40年，但对其骨骼学的解剖细节仍知之甚少，且该物种仍缺乏发育方面的信息。本研究：（1）基于对模式产地多个标本的显微CT扫描、骨骼透明和染色，提供了详细的骨骼学描述；（2）讨论了与生活史差异相关的种内变异；（3）探讨了与肢体模式形态进化相关的肢体特征，这些特征与对山间溪流环境的生态适应有关。与同属物种的骨骼学比较识别出了陇东溪鲵独有的几个鉴别特征，包括：犁骨彼此广泛分离，缺乏中线接触；方骨上升突存在不常见的软骨周骨化，作为悬器的一部分；肩胛骨有一个突出的后背部突起，作为肩胛提肌的韧带附着点。此外，部分（但并非全部）幼态延续个体保留了腭骨作为一个离散元素，这表明其在性成熟后吸收延迟。变态后个体和幼态延续个体在鳃器结构的复杂性上有显著差异。幼态延续个体的鳃器元素高度骨化，在衰老过程中，下咽骨I和角鳃骨I的骨化往往会增加，并且保留完全骨化的角鳃骨III和IV；相反，这些元素在变态后个体中仍完全为软骨或通过吸收完全消失。此外，所有变态后形态的第二基鳃骨呈倒“T”形，而幼态延续个体在性成熟后显示从“叉”形到“T”形的转变。陇东溪鲵在其肢体骨化中呈现出近裔性状和祖征性状的镶嵌：手部和足部都存在单个中央骨元素在隐鳃鲵科和其他科中也是一种衍生状态，而足部保留小后骨在有尾目中显然是祖征。足部趾数从五减少到四以及拥有覆盖指（趾）末端指（趾）骨的角质鞘也是一些（但并非全部）适应类似环境类型的山间溪流蝾螈共有的衍生特征。
