Reinforced acoustic divergence in two syntopic neotropical treefrogs

Phylogenetic inertia often drives sister species to exhibit similar acoustic signals, compromising species recognition and increasing competition for acoustic space. Consequently, natural selection favours acoustic divergence in sympatry through behavioural plasticity or character displacement. Although well-documented in temperate regions, these phenomena have been less investigated in tropical communities, characterised by more complex interactions and saturated acoustic spaces. Here we examined acoustic divergence in the advertisement calls of two closely related neotropical treefrogs that share similar signals, habitat, and phenology, and that hybridise in nature. Our results revealed differences in call parameters between syntopy and allotopy, each species showing a specific response. While the smaller-sized species, <i>Boana bischoffi</i>, increased dominant frequency in syntopy, <i>Boana prasina</i> prolonged call duration, both increasing acoustic divergence between these sister species. In contrast, morphological and environmental factors had little influence on acoustic parameters, with only body size affecting dominant frequency in <i>B. bischoffi</i>. These findings suggest that vocal adjustment (acoustic plasticity) or character displacement (local adaptation) may enlarge acoustic divergence in advertisement calls, reinforcing reproductive isolation and reducing interspecific competition for acoustic space in sister taxa.

系统发育惯性（phylogenetic inertia）常促使姊妹物种呈现相似的声学信号，进而损害物种识别能力，并加剧声学空间的竞争压力。因此，自然选择倾向于通过行为可塑性（behavioural plasticity）或特征替换（character displacement），在同域分布（sympatry）类群中推动声学特征分化。尽管这类现象在温带地区已有充分记载，但在以复杂种间互作和饱和声学空间为特征的热带群落中，相关研究却较为匮乏。本研究针对两种亲缘关系密切的新热带树蛙展开分析，它们具有相似的鸣唱信号、栖息生境与物候特征，且在自然条件下存在杂交现象，我们对其求偶鸣叫（advertisement calls）的声学分化情况进行了考察。研究结果显示，同域栖息（syntopy）与异域分布（allotopy）种群间的鸣叫参数存在显著差异，且两个物种各自呈现出特异性响应。体型较小的布氏雨滨蛙（*Boana bischoffi*）在同域栖息环境中提升了鸣唱主频（dominant frequency），而普氏雨滨蛙（*Boana prasina*）则延长了鸣唱时长（call duration），二者均扩大了这对姊妹物种间的声学分化程度。相较而言，形态与环境因素对声学参数的影响极小，仅体型大小会对布氏雨滨蛙（*B. bischoffi*）的鸣唱主频产生影响。本研究结果表明，鸣唱调整（声学可塑性，acoustic plasticity）或特征替换（本地适应，local adaptation）或许能够扩大求偶鸣叫的声学分化程度，进而强化姊妹类群间的生殖隔离（reproductive isolation），并降低其在声学空间上的种间竞争压力。