Body size is an important determinant of resource and mate competition in many species. Competition is often mediated by conspicuous vocal displays, which may help to intimidate rivals and attract mates by providing honest cues to signaler size. Fitch proposed that vocal tract resonances (or formants) should provide particularly good, or honest, acoustic cues to signaler size because they are determined by the length of the vocal tract, which in turn, is hypothesized to scale reliably with overall body size. There is some empirical support for this hypothesis, but to date, many of the effects have been either mixed for males compared with females, weaker than expected in one or the other sex, or complicated by sampling issues. In this paper, we undertake a direct test of Fitch's hypothesis in two canid species using large samples that control for age- and sex-related variation. The samples involved radiographic images of 120 Portuguese water dogs Canis lupus familiaris and 121 Russian silver foxes Vulpes vulpes. Direct measurements were made of vocal tract length from X-ray images and compared against independent measures of body size. In adults of both species, and within both sexes, overall vocal tract length was strongly and significantly correlated with body size. Effects were strongest for the oral component of the vocal tract. By contrast, the length of the pharyngeal component was not as consistently related to body size. These outcomes are some of the clearest evidence to date in support of Fitch's hypothesis. At the same time, they highlight the potential for elements of both honest and deceptive body signaling to occur simultaneously via differential acoustic cues provided by the oral versus pharyngeal components of the vocal tract.

中文翻译：

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两种犬科动物声道长度的射线照相分析及其与整体体型的关系

在许多物种中，体型是资源和配偶竞争的重要决定因素。竞争通常是通过显眼的声音表现来介导的，这可能有助于通过提供信号器大小的诚实线索来恐吓竞争对手并吸引配偶。Fitch 提出声道共振（或共振峰）应该为信号者的大小提供特别好的或诚实的声学线索，因为它们是由声道的长度决定的，而声道的长度又被假设为与整体的身体尺寸可靠地缩放。这一假设有一些实证支持，但迄今为止，男性与女性的许多影响要么是混合的，要么是弱于一种或另一种性别的预期，要么是因抽样问题而变得复杂。在本文中，我们对 Fitch' 进行了直接测试 s 假设在两个犬科动物物种中使用控制年龄和性别相关变异的大样本。样本涉及 120 只葡萄牙水犬 Canis lupus associateis 和 121 只俄罗斯银狐 Vulpes vulpes 的射线照相图像。直接测量来自 X 射线图像的声道长度，并与身体大小的独立测量值进行比较。在两个物种的成年人中，以及在两个性别中，整体声道长度与体型强烈且显着相关。对声道的口腔成分的影响最强。相比之下，咽部的长度与体型的相关性并不那么一致。这些结果是迄今为止支持惠誉假设的一些最明确的证据。同时，