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：进化新特征的产生通常依托两种路径：一是为已有结构赋予全新功能，二是革新特定功能的执行机制。发声行为在蛙类行为体系中居于核心地位，蛙类依靠鸣声划定领地、吸引配偶。因此，蛙类演化出了复杂的发声结构，可产生多样的宣告性鸣声。学界普遍认为，多数蛙类通过将肺内气柱经声门（glottis）排出完成鸣叫；负子蟾科（Pipidae）是显著例外，该科所有类群均拥有完全独立于空气运动的高度特化发声机制。
研究结果：本研究针对鲜为人知的非洲负子蟾科拟膜蟾属（Pseudhymenochirus）开展行为观测，证实该水生蛙类的发声行为依赖空气驱动。但形态学对比结果显示，拟膜蟾属的喉部具备毋庸置疑的负子蟾科特征。为将这一矛盾现象纳入进化框架进行阐释，本研究基于完整线粒体基因组（mitochondrial genomes）与9个核蛋白编码基因（nuclear protein-coding genes），构建了可信度极高的负子蟾科分子系统发育树，所有分析均一致将拟膜蟾属嵌套于其他负子蟾类群之中。
研究结论：本研究认为，尽管拟膜蟾属演化出了向祖先非负子蟾类群空气驱动发声状态的反转，但其发声机制却是基于负子蟾科特化喉部的进化革新。这进一步佐证了如下观点：解决功能问题的进化方案通常依托原有结构演化而来；正因如此，进化革新很大程度上取决于各演化支系特定历史预先设定的可能性与约束条件。