Supplemental material1_BreedStandard.xlsx from Are dark-eyed dogs favoured by humans? Domestication as a potential driver of iris colour difference between dogs and wolves

Comparative studies have shown that the eye morphology of primates has been shaped by a variety of selection pressures (e.g. communication, environmental factors). To comprehensively elucidate the complex links between ocular morphology and its evolutionary drive, attention should be paid to other phylogenetic groups. Here, we address a new question regarding the evolution of eye colour patterns in the oldest domesticated animal, namely, the domestic dog (<i>Canis familiaris</i>). In this study, we conducted an image analysis of dogs and their closest relatives, grey wolves (<i>Canis lupus</i>), to compare the colours of their irises, with the aim of assessing whether eye colours of dogs affect how humans perceived dogs. We found that the irises of dogs were significantly darker than those of wolves. We also found that facial images of dark-eyed dogs were perceived as more friendly and immature, potentially eliciting caregiving responses from humans. Our findings are consistent with our expectation that humans favour dark-eyed dogs over light-eyed ones and provide an updated hypothesis that dogs with dark eyes may have evolved by acquiring a facial trait that sends a non-threatening gaze signal to humans.

已有比较研究表明，灵长类的眼部形态受到多种选择压力（如通讯需求、环境因素）的塑造。为全面阐明眼部形态与其进化驱动力之间的复杂关联，研究应关注其他系统发育类群。本研究针对最古老的家养动物——家犬（*Canis familiaris*）的眼色模式演化，提出了全新的科学问题。本研究对家犬及其近缘类群灰狼（*Canis lupus*）开展图像分析，以比较二者虹膜颜色，旨在探究家犬的眼色是否会影响人类对家犬的认知评价。研究发现，家犬的虹膜颜色显著深于灰狼。本研究同时发现，深色虹膜的家犬面部图像会被人类评价为更友好、更显幼态，进而可能唤起人类的抚育行为。本研究结果与“人类更偏好深色虹膜家犬”的预期相符，同时提出了更新后的演化假说：深色虹膜家犬可能通过演化出一种向人类传递无威胁凝视信号的面部特征而得以存续。