The meat of the matter: a rule of thumb for scavenging dogs?

Animals that scavenge in and around human settlements need to utilise a broad range of resources, and thus generalist scavengers are likely to be better adapted to human-dominated habitats. In India, free-ranging dogs (Canis lupus familiaris) live in close proximity with humans in diverse habitats, from forest fringes to metropolises, and are heavily dependent on humans for their food. It has been argued that the ability to digest carbohydrates was one of the driving forces for dog domestication. Though dogs are better adapted to digest carbohydrates than other canids, pet dogs show a clear preference for animal proteins. Our observations on streets of urban and semi-urban localities show that the free-ranging dogs are scavengers which primarily receive carbohydrate-rich food from humans. Their source for animal protein is typically garbage bins and leftovers, and such resources are rare. Using a series of field-based experiments, we test if the free-ranging dogs have adapted to a generalist scavenging lifestyle by losing preference for animal protein. Our experiments show that the free-ranging dogs, which are descendants of the decidedly carnivorous gray wolf (Canis lupus lupus), have retained a clear preference for meat, which is manifested by their choice of anything that smells of meat, irrespective of the actual nutrient content. The plasticity in their diet probably fosters efficient scavenging in a competitive environment, while a rule of thumb for preferentially acquiring specific nutrients enables them to sequester proteins from the carbohydrate-dominated environment.在人类聚居区及其周边活动的食腐动物需要利用多样化的资源，因此广食性食腐动物更适应以人类为主导的生境。在印度，散养犬（free-ranging dogs，*Canis lupus familiaris*）在从森林边缘到大都市的多样生境中与人类近距离共存，其食物来源高度依赖人类。有观点认为，消化碳水化合物的能力是犬类驯化的核心驱动力之一。尽管相较于其他犬科动物，犬类更适应碳水化合物的消化，但伴侣犬仍表现出对动物蛋白的明确偏好。我们在城市及半城区街道开展的观测显示，散养犬属于食腐动物，其主要从人类处获取富含碳水化合物的食物；而它们获取动物蛋白的渠道通常为垃圾桶与食物残渣，但这类资源十分稀缺。本研究通过一系列野外实验，探究散养犬是否通过丧失对动物蛋白的偏好，以适应广食性食腐的生活方式。我们的实验结果表明，作为严格肉食性灰狼（gray wolf，*Canis lupus lupus*）的后裔，散养犬仍保留了对肉类的明确偏好——这体现为它们会优先选择任何带有肉类气味的食物，而非考量其实际营养成分。它们的饮食可塑性或许有助于其在竞争激烈的环境中高效开展食腐活动，而优先获取特定营养的经验法则，则使其能够在以碳水化合物为主的环境中摄取蛋白质。