Molecular phylogenetics of desmognathine salamanders (Caudata: Plethodontidae): a reevaluation of evolution in ecology, life history, and morphology

Phylogenetic relationships were reconstructed for salamanders of the plethodontid subfamily Desmognathinae to examine evolution of morphology, ecology, and life history. Mitochondrial DNA sequences encoding 12S and 16S ribosomal RNA and the valine transfer RNA provided 259 phylogenetically informative sites from approximately 1,200 nucleotide positions for 21 specimens representing 15 species and subspecies. These data were analyzed in conjunction with 13 morphological and reproductive characters to generate phylogenetic hypotheses. The directly developing terrestrial desmognathines Phaeognathus hubrichti and Desmognathus wrighti represent, respectively, the first and second phylogenetic branching events within the subfamily, and the remaining terrestrial lineage, D. aeneus, also branches near the base of the phylogenetic tree. These results challenge earlier hypotheses that within Desmognathus the small nonmetamorphosing species, D. aeneus and D. wrighti, represent the end of a graded phylogenetic decrease in size and decrease in use of aquatic habitats. In contrast to previous hypotheses, our results suggest that desmognathine evolution includes transformations in the direction of larger body sizes, lengthened larval periods, and greater use of aquatic habitats.

本研究针对无肺螈科（Plethodontidae）狄格螈亚科（Desmognathinae）的蝾螈类群重建系统发育关系，以探究其形态学、生态学与生活史的演化规律。本研究使用了涵盖15个物种及亚种的21份标本，利用编码12S、16S核糖体RNA以及缬氨酸转运RNA的线粒体DNA序列，在约1200个核苷酸位点中筛选得到259个系统发育信息位点。结合13个形态学与繁殖学性状对上述数据开展联合分析，以此构建系统发育假说。直接发育的陆生狄格螈亚科物种哈氏黑螈（Phaeognathus hubrichti）与莱特螈（Desmognathus wrighti），分别对应该亚科内的首次和第二次系统发育分支事件；其余陆生支系D. aeneus同样位于系统发育树的基部区域。该结果挑战了此前的假说：此前学界认为狄格螈属（Desmognathus）内的小型非变态物种D. aeneus与D. wrighti，是体型逐级缩小、水生栖息地利用程度逐步降低的系统发育演化终点。与此前的假说相悖，本研究结果显示狄格螈亚科的演化历程包含体型增大、幼虫期延长以及对水生栖息地依赖程度提升的转变方向。