Cunningham Patrick, Shankar Mahita, vonHoldt Bridgett, Brzeski Kristin E, Kienle Sarah S
Department of Biology, Baylor University, Waco, TX 76707, USA.
Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA.
R Soc Open Sci. 2024 Oct 2;11(10):241046. doi: 10.1098/rsos.241046. eCollection 2024 Oct.
Facial expressions are critical for non-verbal communication. The genus epitomizes the interplay between behaviour and morphology in the evolution of non-verbal communication. Recent work suggests that the levator anguli oculi medialis (LAOM) muscle is unique to dogs () within the genus and evolved due to domestication. The LAOM raises the inner eyebrows, resulting in the 'puppy dog eyes' expression. Here, we test whether the LAOM is a derived trait in dogs by (i) examining the facial expression muscles of a closely related and ancestral wild species, the coyote () and (ii) comparing our results with other and canid taxa. We discover that coyotes have a well-developed LAOM like dogs, which differs from the modified/absent LAOM in grey wolves. Our findings challenge the hypothesis that the LAOM developed due to domestication. We suggest that the LAOM is a basal trait that was lost in grey wolves. Additionally, we find inter- and intraspecific variations in the size of the muscles of the outer ear, forehead, lips and rostrum, indicating potential adaptations related to sensory perception, communication and individual-level functional variations within canids. Together, this research expands our knowledge of facial expressions, their evolution and their role in communication.
面部表情对于非语言交流至关重要。该属体现了非语言交流进化过程中行为与形态之间的相互作用。最近的研究表明，内眼角提肌（LAOM）在犬属中是犬类特有的，并且是由于驯化而进化而来。内眼角提肌会抬高眉毛内侧，从而产生“狗狗眼”的表情。在此，我们通过以下方式来测试内眼角提肌是否是犬类的一个衍生特征：（i）检查与之密切相关的野生祖先物种郊狼的面部表情肌肉，以及（ii）将我们的结果与其他狐属和犬科类群进行比较。我们发现，郊狼像犬类一样有发育良好的内眼角提肌，这与灰狼中经过改变/缺失的内眼角提肌不同。我们的研究结果对“内眼角提肌是由于驯化而发育形成”这一假设提出了质疑。我们认为内眼角提肌是一个在灰狼中丧失的基础特征。此外，我们发现外耳道、额头、嘴唇和吻部肌肉大小存在种间和种内差异，这表明犬科动物在感官知觉、交流以及个体水平功能差异方面可能存在适应性变化。总之，这项研究扩展了我们对面部表情、其进化以及在交流中所起作用的认识。
