拟平鳅头背部斑纹和下唇结构变异及其分类学意义

Abstract

针对拟平鳅（<em>Liniparhomaloptera disparis</em>） 的两个亚种（<em>L. disparis disparis</em> 和<em>L. disparis qiongzhongensis</em>） 现有形态分类特征的含糊，通过观察标本室保存的15条水系441尾标本，首次提出利用下唇结构类型作为拟平鳅亚种的补充形态鉴别依据，结合头背部斑纹特征，能有效地鉴别拟平鳅各地理种群和亚种，为拟平鳅的分类和鉴定提供参考依据。依据头背部斑纹差异归纳出4种类型，分别为小斑块型（云开山脉以东的7条水系及海南岛万泉河），虫蚀纹型（云开山脉以西的5条水系），混合斑纹型（海南岛的万泉河、南渡江、昌化江共3条水系），大斑块型（海南岛的昌化江）。 依据下唇结构变化情况总结出3种下唇类型，分别是半圆型（云开山脉以西的5条水系），几字型（云开山脉以东的7条水系），马蹄型（海南岛的3条水系）。 依据头背部斑纹特征结合下唇结构特征，对照模式标本的描述，重新定义了拟平鳅原有的两个亚种，将分布于云开山脉以东水系的种群鉴定为指名亚种，拟平鳅<em>L. disparis disparis</em>，其鉴别特征为：头背部斑纹为小斑块型并且下唇类型为几字型； 将海南岛种群鉴定为琼中拟平鳅<em>L. disparis qiongzhongensis</em>，它们都具有独特的马蹄型下唇类结构，且头背部斑纹以混合斑纹型为主。重要的发现是，分布于云开山脉以西的种群与已命名的2个亚种在形态上有明显的差异，其头背部斑纹为独特的虫蚀纹型且下唇类型为半圆型。 这可能是一个新亚种。分子生物学方法也许能证明云开山脉以西的种群在遗传上的独特性以及形成新亚种的可能性。 云开山脉东、西两侧以及海南岛不同水系的拟平鳅的种群分化问题值得进一步探究。;Ambiguity of morphological characteristics made distinguishing the two subspecies of <em>Liniparhomaloptera disparis</em>(Cypriniformes: Homalopteridae) difficult. Further morphological evidence in infralabial shape and head spot pattern of the loach were herein provided for the first time to define the subspecies, based on laboratory observation of 441 specimens from 15 drainage systems, including the three western, northeastern, and eastern major rivers on Hainan Island. We recognized four head patterns of dark spots: small spots, vermiform spots, mixture of small and vermiform spots, and large spots. The small-spotted head pattern occurred in all seven populations east of the Yunkai Mountains, as well as in the only eastern population on Hainan Island. The vermiform-spotted head pattern occurred in all five populations west of the Yunkai Mountains. The mixed head pattern of small and vermiform spots occurred in both the western and northeastern populations on Hainan Island, but the large-spotted head pattern was also found in the western population. Additionally, we recognized three infralabial shapes: semicircular, subtrapezoidal, and horseshoe-like. The semicircular infralabium occurred in all five populations west of the Yunkai Mountains. The subtrapezoidal infralabium occurred in all seven populations east of the Yunkai Mountains. The horseshoe-like infralabium occurred in all three populations on Hainan Island. Therefore, populations east of the Yunkai Mountains had distinctly small-spotted head pattern and subtrapezoidal infralabia in combination, defined as the nominate subspecies <em>L. disparis</em> <em>disparis</em> according to the holotypic locality. Surprisingly; populations on Hainan Island were distinctly differentiated from the nominate mainlanders; all had uniquely the horseshoe-like infralabium, but the eastern population had small-spotted head pattern like the nominate mainlanders, the northeastern population had the mixed-spotted head pattern solely, and the western population had both the mixed-spotted and large-spotted head patterns. Based on the subspecific type locality(Wanquan River), we have redefined all three populations on Hainan Island that had mostly the mized-spotted head pattern and horseshoe-like infralabium in combination as the second subspecies <em>L. disparis</em> <em>qiongzhongensis</em>. Populations west of the Yunkai Mountains had distinctly the vermiform-spotted head pattern and semicircular infralabium in combination. This morphological variation may have resulted from the orogeny of the Yunkai Mountains. The differences in head spot pattern among populations on Hainan Island and the differences in infralabial shape either between mainland and Hainan Island or between east and west of the Yunkai Mountains suggest geographic isolation of rivers may have occurred long ago but at different times. This paper demonstrates the infralabial shape as a taxonomic character for the first time; this character in combination with the previous characters like head spot pattern can be used to identify subspecies or geographic populations effectively. Molecular analyses may prove the mainland populations west of the Yunkai Mountains and the populations on Hainan Island are genetically unique, new subspecies, and their geophylogenetic associations.