Data from: Reversal to air-driven sound production revealed by a molecular phylogeny of tongueless frogs, family Pipidae

BACKGROUND: Evolutionary novelties often appear by conferring completely new functions to pre-
existing structures or by innovating the mechanism through which a particular
function is performed. Sound production plays a central role in the behavior of frogs, which use their calls to delimit territories and attract mates. Therefore, frogs have evolved complex vocal structures capable of producing a wide variety of advertising sounds. It is generally acknowledged that most frogs call by moving an air column from the lungs through the glottis with the remarkable exception of the family
Pipidae, whose members share a highly specialized sound production mechanism
independent of air movement. RESULTS: Here, we performed behavioral observations in the poorly known African pipid genus Pseudhymenochirus and demonstrate that sound production in this aquatic frog is air-driven. However, morphological comparisons revealed an indisputable pipid nature of Pseudhymenochirus larynx. To place this paradoxical pattern into an evolutionary framework, we reconstructed robust molecular phylogenies of pipids based on complete mitochondrial genomes and nine nuclear protein-coding genes that coincided in placing Pseudhymenochirus nested among other pipids. CONCLUSIONS: We conclude that although Pseudhymenochirus has evolved a reversal to the ancestral non-pipid condition of air-driven sound production, the mechanism through which it occurs is an evolutionary innovation based on the derived larynx of pipids. This strengthens the idea that evolutionary solutions to functional problems often emerge based on previous structures, and for this reason, innovations largely depend on possibilities and constraints predefined by the particular history of each lineage.

研究背景：进化新性状通常通过两种方式产生：一是赋予原有结构全新功能，二是革新特定功能的执行机制。发声在蛙类行为中占据核心地位，蛙类依靠鸣叫声划定领地并吸引配偶。因此，蛙类演化出了复杂的发声结构，可产生种类丰富的求偶鸣叫声。学界普遍认为，绝大多数蛙类通过将肺内的空气柱经声门排出完成鸣叫，但负子蟾科（Pipidae）是显著例外：该科物种拥有高度特化的发声机制，无需依赖空气流动。
研究结果：本研究针对鲜为人知的非洲拟髯蟾属（Pseudhymenochirus）开展行为观察，证实这种水生蛙类的发声依赖空气驱动。但形态学对比显示，拟髯蟾属的喉部（larynx）具有毋庸置疑的负子蟾科特征。为将这一矛盾现象置于演化框架中解释，我们基于完整线粒体基因组与9个核蛋白编码基因，构建了可信度极高的负子蟾科分子系统发育树，所有分析均一致显示拟髯蟾属嵌入于其他负子蟾类群之中。
研究结论：本研究认为，尽管拟髯蟾属演化出了对祖先类群非负子蟾科空气驱动发声状态的逆转，但其背后的机制却是基于负子蟾科特化喉部的演化创新。这进一步佐证了这一观点：针对功能需求的演化解决方案通常依托已有结构产生，因此演化创新很大程度上取决于各演化支系独特历史所预先设定的可能性与约束条件。