Asymmetric frequency shift in advertisement calls of sympatric frogs

Character displacement is commonly observed when
species occur in secondary contact zones and traits related to resource
competition or reproduction diverge in sympatry. However, few studies have
considered the factors determining and delimiting the direction of character
evolution in this context. We studied displacement in advertisement calls in
two species of hylid frogs from allopatric and sympatric populations, both of
which call with similar frequencies but differ substantially in temporal
parameters. We found asymmetrical character displacement in sympatry, as only Scinax
madeira (but not S. fuscomarginatus) repeatedly showed displacement.
Instead of diverging in already existing differences in temporal characters, S.
madeirae showed character displacement for frequency-related characters. We
explored possible reasons for this specific pattern concerning the displaced
characters and tested if socio-functional constraints in specific call
parameters are responsible for the shift of only spectral parameters in that
species. Finally, we argue that the simultaneous action of ecological and
reproductive character displacement, or alternatively, a short-term behavioral
response for the same reason (avoidance of hybridization) could explain the
pattern. The present study identifies a set of new hypotheses that will
stimulate future research on mechanisms of mate recognition and behavioral
responses.

物种在次生接触区域出现时，通常观察到特征位移现象，此时与资源竞争或繁殖相关的特征在共生状态下发生分化。然而，关于决定和界定该环境下特征进化方向的因素的研究寥寥无几。本研究针对来自地理隔离和共生种群的两类树蟾属物种在广告鸣叫声中的位移现象进行了探讨，这两种物种的鸣叫频率相似，但在时间参数上存在显著差异。我们发现共生状态下存在非对称特征位移，仅Scinax madeira（而非S. fuscomarginatus）反复表现出位移现象。S. madeirae并非在已有的时间特征差异上发生分化，而是在与频率相关的特征上表现出特征位移。我们探讨了这种特定模式的可能原因，并测试了特定叫声参数中的社会功能限制是否是导致该物种仅光谱参数发生位移的原因。最终，我们认为生态特征位移和生殖特征位移的同时作用，或者说是由于相同原因（避免杂交）而产生的短期行为反应，可以解释这种模式。本研究提出了一系列新的假设，这将激发未来关于配偶识别机制和行为反应研究的新进展。