Data from: Sensory drive does not explain reproductive character displacement of male acoustic signals in the Upland Chorus Frog (Pseudacris feriarum)

Biotic and abiotic factors have been proposed to explain patterns of reproductive character displacement, but which factor is most important to character displacement of acoustic signals is not clear. Male vocalizations of the frog Pseudacris feriarum are known to undergo reproductive character displacement in areas of sympatry with P. brimleyi and P. nigrita. Despite evidence for reinforcement as an important mechanism, local adaptation via sensory drive might explain this pattern because Pseudacris breed in different habitat types and mating signals are exposed to a variety of environments. We tested the sensory drive hypothesis by playing synthesized vocalizations representing the spectrum of variation in P. feriarum at 12 different study sites. If sensory drive has occurred, then vocalizations should transmit better in the site of origin or at ecologically similar sites. We found that variation in acoustic signals did not produce better transmission in particular sites, the effect of site was uniform, and acoustic signals often transmitted better in habitats external to their origin. Ecological variation among habitats did not explain signal degradation. Our playback experiments, ecological analyses, and comparisons of different habitat types provide no support for sensory drive as a process promoting reproductive character displacement in this system. Reinforcement is the more likely primary mechanism.

已有研究提出利用生物与非生物因子解释生殖特征置换（reproductive character displacement）的分布格局，但针对声学信号的生殖特征置换而言，何种因子最为关键，目前仍不明确。已知拟蝗蛙属（Pseudacris）的费氏拟蝗蛙（Pseudacris feriarum），其雄性鸣声在与布氏拟蝗蛙（P. brimleyi）和黑拟蝗蛙（P. nigrita）同域分布的区域中会发生生殖特征置换。尽管已有证据表明强化作用（reinforcement）是该过程的重要机制，但通过感官驱动（sensory drive）实现的局部适应或许也能解释这一格局——因为拟蝗蛙属物种的繁殖生境类型多样，且交配信号会暴露于多种环境之中。我们通过在12个不同研究点位播放代表费氏拟蝗蛙鸣声变异范围的合成鸣声，对感官驱动假说开展了检验。若感官驱动确实发生，则鸣声应在其起源点位或生态相似的点位实现更优的传播。研究结果显示，声学信号的变异并未使其在特定点位获得更优的传播效果，不同点位的传播效果并无显著差异，且鸣声往往在其起源生境以外的生境中传播效果更佳。生境间的生态差异也无法解释信号衰减（signal degradation）的情况。我们的回放实验、生态分析以及不同生境类型的比较，均未支持感官驱动作为促进该系统生殖特征置换的过程这一假说。相较而言，强化作用更可能是其核心机制。