Wilczynski W, Rand A S, Ryan M J
Department of Psychology and Institute for Neuroscience, University of Texas at Austin, Tex 78712, USA.
Brain Behav Evol. 2001;58(3):137-51. doi: 10.1159/000047268.
In species within the Physalaemus pustulosus species group, male frogs produce a whine-like advertisement call consisting of a frequency sweep typically descending from 1,000 to 400 Hz (depending on the species). One species, Physalaemus pustulosus, the túngara frog, has evolved a second call syllable, the chuck, which males place after their whine. Most energy in the chuck is above 1,500 Hz and peaks at 2,400 Hz. We investigated whether the evolution of this new call component in P. pustulosus coincided with evolution of auditory tuning. We used multiunit electrophysiological recordings of auditory-evoked activity in the midbrain to characterize auditory tuning in Physalaemus pustulosus, four other Physalaemus species within the P. pustulosus clade, and three additional, closely related Physalaemus species as outgroups. All eight species had similar sensitivity profiles, with a broad area of enhanced sensitivity from 100 to 1,100 Hz, which we presume represents amphibian papilla (AP) tuning, and a second, narrower area of enhanced sensitivity centered above 2,100 Hz, which we presume represents basilar papilla (BP) tuning. For all species, the whine stimulates the AP. The P. pustulosus chuck stimulates the BP. The frequency with greatest AP sensitivity differed significantly among species. Although in all cases the AP peak lay within the frequency sweep of the whine, phylogenetically corrected correlations revealed no significant relationships between AP tuning and any spectral feature of the whine. BP tuning was similar among all species, with mean BP best excitatory frequencies (BEFs) around 2,100-2,200 Hz, with the exception of P. pustulatus, with a mean BP BEF of 2,549 Hz. Physalaemus pustulosus, the only investigated species that produces a call component stimulating the BP, had a BP BEF that was not significantly different from any of the species within its clade except P. pustulatus, or from any of the outgroup species. A phylogenetic reconstruction of ancestral BP tuning confirms that the only point of evolutionary change in BP tuning is in the line of descent leading to P. pustulatus, not in the line leading to P. pustulosus despite this being the species using the BP for communication. The results indicate that BP tuning around 2,200 Hz is a conserved trait in the Physalaemus pustulosus species group and that no evolution of BP tuning accompanied the subsequent evolution of the call component (the chuck) that stimulates it. This supports the sensory exploitation idea, which posits that signals evolve to match preexisting features of receiver systems.
在脓疱姬蛙物种组内的物种中，雄性青蛙会发出一种类似哀鸣声的求偶叫声，通常由频率从1000赫兹降至400赫兹的扫频组成（具体取决于物种）。有一种物种，即泡蟾，演化出了第二种叫声音节，即咯咯声，雄性会在哀鸣声之后发出。咯咯声中的大部分能量高于1500赫兹，在2400赫兹处达到峰值。我们研究了泡蟾这种新叫声成分的演化是否与听觉调谐的演化同时发生。我们使用中脑听觉诱发活动的多单位电生理记录来表征泡蟾、泡蟾分支内的其他四种姬蛙物种以及另外三种亲缘关系密切的姬蛙物种（作为外类群）的听觉调谐。所有八个物种都有相似的敏感性图谱，在100至1100赫兹之间有一个广泛的敏感性增强区域，我们推测这代表两栖类乳突（AP）调谐，还有第二个较窄的敏感性增强区域，以2100赫兹以上为中心，我们推测这代表基底乳突（BP）调谐。对于所有物种来说，哀鸣声刺激AP。泡蟾的咯咯声刺激BP。AP敏感性最高的频率在物种间有显著差异。尽管在所有情况下AP峰值都在哀鸣声的扫频范围内，但经过系统发育校正的相关性显示，AP调谐与哀鸣声的任何频谱特征之间没有显著关系。所有物种的BP调谐都相似，BP最佳兴奋频率（BEF）的平均值在2100 - 2200赫兹左右，但泡蟾除外，其BP BEF平均值为2549赫兹。泡蟾是唯一被研究的发出刺激BP的叫声成分的物种，其BP BEF与它所在分支内除泡蟾外的任何物种以及任何外类群物种相比，没有显著差异。对祖先BP调谐的系统发育重建证实，BP调谐中唯一的进化变化点在导致泡蟾的谱系中，而不是在导致泡蟾的谱系中，尽管泡蟾是利用BP进行通讯的物种。结果表明，2200赫兹左右的BP调谐是脓疱姬蛙物种组中的一个保守特征，并且在刺激它的叫声成分（咯咯声）随后的演化过程中，BP调谐没有发生进化。这支持了感官利用假说，该假说认为信号的演化是为了匹配接收系统预先存在的特征。
