Allometric escape from acoustic constraints in frog calls is rare

Allometric constraint is a product of natural selection, particularly with respect to body size and traits constrained by physical properties thereof, such as metabolism, longevity, and vocal frequency. Parameters describing allometric relationships are conserved across most lineages, indicating that physical constraints dictate scaling patterns in deep time, despite substantial genetic and ecological divergence among organisms. Acoustic allometry (sound frequency ~ body size) is conserved across frogs, in defiance of massive variation in both body size and frequency. Here, we find four major instances of allometric escape, potentially deriving from ecomorphological adaptations to new signal modalities and invasion of biogeographic regions. In these instances of allometric escape, the optima and strength of the scaling relationship are different than expected for most other frog species, representing new adaptive regimes of body size ~ call frequency. Allometric constraints in frogs are highly conserved and have rarely promoted allometric escape despite frequent invasions of new adaptive regimes and dramatic ecomorphological divergence. Our results highlight instances in which natural and sexual selection combined could overcome physical constraints on sound production.异速生长约束（allometric constraint）是自然选择的产物，尤其聚焦于体型以及受其物理属性约束的性状，例如代谢速率、寿命与发声频率。描述异速生长关系（allometric relationships）的参数在绝大多数演化支中均保守存在，这表明尽管不同生物间存在显著的遗传与生态分化，物理约束仍在漫长的深时尺度中主导着生物性状的缩放模式。声学异速生长（acoustic allometry），即声音频率与体型的异速关联，在蛙类中高度保守，即便蛙类的体型与发声频率均存在极大变异，该规律也未被打破。本研究发现了四类主要的异速生长逃逸（allometric escape）实例，其成因可能是对新信号模态的生态形态适应，以及对全新生物地理区域的入侵。在这些异速生长逃逸的案例中，缩放关系的最适参数与强度均异于多数其他蛙类的预期值，代表了体型与鸣唱频率间全新的自适应域。蛙类的异速生长约束整体高度保守，尽管它们频繁入侵新的自适应域并发生显著的生态形态分化，异速生长逃逸现象却极少出现。本研究结果揭示了自然选择与性选择共同克服发声相关物理约束的具体实例。