Environmental, nutritional and social aspects of insectivory by Gombe chimpanzees

Humans and many living apes eat insects. Insectivory by humans, chimpanzees and orangutans is often sex-biased (with females consuming insects more frequently and for longer durations than males) and associated with tool-use. Extinct hominins may also have preyed upon insects, yet models of the origins of the human diet have typically emphasized meat-eating (carnivory) over other forms of faunivory. Chen, ❧ As one of the two closest living relations to modern humans, chimpanzees (Pan troglodytes) represent useful referential models for the behavior of extinct hominins. The manufacture and use of tools to acquire insects was among the first major discoveries made by Jane Goodall in her studies of the Kasekela chimpanzees of Gombe National Park of Tanzania. However, even after fifty years of research many basic but important questions about insectivory and insect prey choice in this community remain unanswered. Over three field seasons between February 2008 and February 2010 I conducted a study of insectivory by Kasekela chimpanzees. This study included a survey of social insects across the central and northern regions of the park, nutritional assays on insect prey (and some potential insect prey) available to the Kasekela chimpanzees, observation of chimpanzee predators, and a review of the long-term behavior records. I use the results of this study to test four hypotheses regarding insectivory and insect prey choice by Kasekela chimpanzees. ❧ I found that availability, encounter rates, and colony abundance were not important factors in Kasekela chimpanzees’ choice of insect prey. Kasekela chimpanzees favor insect prey of high caloric value and with high fat and protein content, but ignore some insect prey consumed by Pan elsewhere in Africa with the potential for high caloric and nutritional yields. On a gram-for-gram basis the macronutritional content of insects consumed by Kasekela chimpanzees are comparable if not superior to meat. Socially-learned knowledge of prey and associated foraging techniques also influence prey choice. A novel form of tool-assisted insectivory (“ant-fishing”) appeared in Kasekela in 1994 and spread rapidly through the community, becoming a customary behavior by 2010. The pattern of known practitioners in Kasekela, who are almost entirely immigrant females or native individuals born after 1981, is consistent with social transmission from older to younger individuals and among juveniles and adolescents. Though an independent innovation cannot be completely ruled out, the circumstantial evidence suggests that ant-fishing was introduced by an immigrant female from the neighboring Mitumba community. ❧ Insects are a small but important component of the diet for Kasekela chimpanzees. Further research is warranted on the use and re-use of particular termite mounds, hives, or ant colonies, the caloric and nutritional yields for different forms of insectivory, and the specific vitamin and mineral content of insect prey and other foods for this population. Based on the results of this and previous studies, I hypothesize that termites (particularly the genus Macrotermes) and honey-making bees (particularly Apis mellifera) are the most likely insects to have been preyed upon by extinct African hominins.

人类与诸多现生灵长类均会取食昆虫。人类、黑猩猩及红毛猩猩的昆虫食性常存在性别偏向（雌性相较于雄性更频繁、更持久地食用昆虫），且与工具使用行为相关联。

已灭绝的古人类或许也曾以昆虫为食，但有关人类饮食起源的诸多模型，通常更强调肉食（食肉性）而非其他形式的动物食性。

陈（Chen）：❧ 作为与现代人类亲缘关系最近的两种现生物种之一，黑猩猩（Pan troglodytes）是研究已灭绝古人类行为的可靠参照模型。简·古道尔（Jane Goodall）在对坦桑尼亚贡贝国家公园的卡塞克拉黑猩猩群的研究中，首批重大发现之一便是使用工具获取昆虫的行为。然而即便历经五十年的研究，该社群中有关昆虫食性与昆虫猎物选择的诸多基础且关键的问题仍未得到解答。

2008年2月至2010年2月期间，笔者依托三个野外季开展了针对卡塞克拉黑猩猩昆虫食性的研究。本研究涵盖对公园中部与北部区域社会性昆虫的调查、对卡塞克拉黑猩猩可获取的昆虫猎物（及部分潜在昆虫猎物）的营养成分分析、对黑猩猩捕食行为的观测，以及对长期行为记录的梳理。笔者依托本研究的结果，针对卡塞克拉黑猩猩的昆虫食性与昆虫猎物选择验证了四项假说。

研究结果显示，猎物可获得性、遭遇频次以及虫群丰度并非卡塞克拉黑猩猩选择昆虫猎物的关键影响因素。卡塞克拉黑猩猩偏好高热量、高脂肪与高蛋白的昆虫猎物，但会回避非洲其他区域黑猩猩属物种所取食的、具备较高热量与营养产出潜力的部分昆虫猎物。以单位重量计，卡塞克拉黑猩猩所取食昆虫的宏量营养素含量即便未优于肉类，也可与肉类相媲美。通过社会学习获得的猎物认知与相关觅食技术，同样会影响猎物选择。1994年，卡塞克拉黑猩猩社群中出现了一种全新的工具辅助型昆虫食性行为——‘钓蚁’，并在社群内快速传播，至2010年已成为一种常规行为。目前已知的该行为实践者几乎均为外来雌性个体，或是1981年之后出生的本土个体，这一分布模式与‘年长个体向年轻个体、幼崽与青少年个体间的社会传播’假说相符。尽管无法完全排除独立演化出该行为的可能性，但间接证据显示，‘钓蚁’行为是由邻近的米通巴社群的一只外来雌性黑猩猩引入卡塞克拉社群的。

昆虫是卡塞克拉黑猩猩饮食中占比微小但至关重要的组成部分。后续仍需针对以下内容开展研究：特定蚁冢、蜂巢或蚁群的使用与复用情况、不同昆虫食性行为的热量与营养产出，以及该种群昆虫猎物与其他食物的特定维生素与矿物质含量。

结合本研究与既往研究的结果，笔者提出假说：已灭绝的非洲古人类最有可能以白蚁（尤其是大白蚁属（Macrotermes））与酿蜜蜂类（尤其是西方蜜蜂（Apis mellifera））为食。