Mad, bad and dangerous to know: the biochemistry, ecology and evolution of slow loris venom

Only seven types of mammals are known to be venomous, including slow lorises (Nycticebus spp.). Despite the evolutionary significance of this unique adaptation amongst Nycticebus, the structure and function of slow loris venom is only just beginning to be understood. Here we review what is known about the chemical structure of slow loris venom. Research on a handful of captive samples from three of eight slow loris species reveals that the protein within slow loris venom resembles the disulphide-bridged heterodimeric structure of Fel-d1, more commonly known as cat allergen. In a comparison of N. pygmaeus and N. coucang, 212 and 68 compounds were found, respectively. Venom is activated by combining the oil from the brachial arm gland with saliva, and can cause death in small mammals and anaphylactic shock and death in humans. We examine four hypotheses for the function of slow loris venom. The least evidence is found for the hypothesis that loris venom evolved to kill prey. Although the venom's primary function in nature seems to be as a defense against parasites and conspecifics, it may also serve to thwart olfactory-orientated predators. Combined with numerous other serpentine features of slow lorises, including extra vertebra in the spine leading to snake-like movement, serpentine aggressive vocalisations, a long dark dorsal stripe and the venom itself, we propose that venom may have evolved to mimic cobras (Naja sp.). During the Miocene when both slow lorises and cobras migrated throughout Southeast Asia, the evolution of venom may have been an adaptive strategy against predators used by slow lorises as a form of Müllerian mimicry with spectacled cobras.

目前已知仅七种哺乳动物具有毒性，其中包括蜂猴（slow loris，Nycticebus属物种）。尽管蜂猴的这一独特适应性在演化层面具有重要意义，但学界对蜂猴毒液的结构与功能的认知尚处于起步阶段。本文综述了当前学界关于蜂猴毒液化学结构的研究进展。针对8种蜂猴中的3种的少量圈养样本开展的研究显示，蜂猴毒液中的蛋白质与Fel-d1（即常见猫变应原）的二硫键桥接异二聚体结构高度相似。在对倭蜂猴（N. pygmaeus）与间蜂猴（N. coucang）的对比分析中，研究人员分别检出212种和68种化合物。蜂猴毒液需将臂腺分泌的油脂与唾液混合后方可激活，其可致使小型哺乳动物死亡，亦可引发人类过敏性休克乃至死亡。本文探讨了蜂猴毒液功能的四种假说。其中，‘蜂猴毒液演化以捕杀猎物’这一假说的支持证据最为匮乏。尽管蜂猴毒液在自然环境中的核心功能似乎是抵御寄生虫与同种个体，但它也可用于威慑依赖嗅觉的捕食者。结合蜂猴诸多类蛇特征——包括脊柱多出的椎骨所造就的蛇形运动模式、带有蛇类特征的攻击性鸣叫声、深色长背纹以及毒液本身——本文提出，蜂猴毒液的演化或为模拟眼镜蛇（Naja属）的结果。在中新世时期，蜂猴与眼镜蛇均在东南亚区域扩散，蜂猴毒液的演化或为针对捕食者的适应性策略：蜂猴借此与眼镜蛇形成缪氏拟态（Müllerian mimicry）。