Gersick Andrew S, Cheney Dorothy L, Schneider Jennifer M, Seyfarth Robert M, Holekamp Kay E
Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ, U.S.A.
Department of Biology, University of Pennsylvania, Philadelphia, PA, U.S.A.
Anim Behav. 2015 May;103:107-116. doi: 10.1016/j.anbehav.2015.02.003.
Calls that catalyse group defence, as in the mobbing of predators, appear to facilitate cooperation by recruiting receivers to act collectively. However, even when such signals reliably precede cooperative behaviour, the extent to which the calls function as recruitment signals is unclear. Calls might simply arouse listeners' attention, setting off a cascade of independent responses to the threat. By contrast, they might convey information, for example, about signaller identity and the nature of a threat that affects receivers' decisions to participate. We explored this distinction by investigating a possible long-distance recruitment call used by spotted hyaenas. These social carnivores live in fission-fusion clans and individuals disperse widely within their territories. Putative recruitment calls must therefore attract receivers that are distant from the inciting threat and free to opt out of risky collective aggression. Hyaenas compete with lions over food, and neighbouring clans sometimes engage in violent border clashes. These high-stakes contests are decided based on numerical asymmetries, so hyaenas can only protect critical resources if the dispersed clan can converge quickly at conflict sites. We recorded and analysed whoop bouts produced in multiple contexts and found that bouts produced in response to signs of lion-hyaena conflict had shorter inter-whoop intervals than spontaneous 'display' bouts. In subsequent field playback experiments, resting hyaenas were significantly more likely to move in response to 'recruitment' bouts with shortened intervals than to otherwise identical 'display' bouts. Whereas only stimulus type predicted movement, lower-ranked subjects responded most quickly, perhaps because their feeding opportunities depend on arriving early at any kill site. Results demonstrate that hyaenas possess a signal that can reliably recruit allies across long distances, despite moderating effects of individual circumstances on the strength of receivers' responses.
像围攻捕食者时那样激发群体防御的叫声，似乎通过招募接收者采取集体行动来促进合作。然而，即便此类信号确实可靠地先于合作行为出现，这些叫声作为招募信号的作用程度仍不明确。叫声可能仅仅是引起听众的注意，引发对威胁的一系列独立反应。相比之下，它们可能传达信息，比如信号发出者的身份以及影响接收者参与决策的威胁性质。我们通过研究斑点鬣狗可能使用的一种远距离招募叫声来探究这种区别。这些群居食肉动物生活在裂变融合的群体中，个体在其领地内广泛分散。因此，假定的招募叫声必须吸引远离引发威胁且能够自由选择不参与危险集体攻击的接收者。鬣狗与狮子争夺食物，相邻群体有时会发生激烈的边境冲突。这些高风险的争斗基于数量上的不对称来决定胜负，所以只有当分散的群体能够迅速在冲突地点会合时，鬣狗才能保护关键资源。我们记录并分析了在多种情境下发出的呼叫声回合，发现因狮鬣冲突迹象而发出的回合相比自发的“展示”回合，呼叫声之间的间隔更短。在随后的野外回放实验中，休息的鬣狗对间隔缩短的“招募”回合做出反应而移动的可能性显著高于对其他方面相同的“展示”回合。虽然只有刺激类型能预测移动，但地位较低的个体反应最快，这可能是因为它们的进食机会取决于能否尽早到达任何猎物地点。结果表明，尽管个体情况会对接收者反应的强度产生调节作用，但鬣狗拥有一种能够可靠地在远距离招募盟友的信号。
