Code: Evolutionary cycles in a model of nestmate recognition

Nestmate recognition is a wide-spread phenomenon and evolutionary important trait in the social insects. Yet evidence accumulates that the responses to non-nestmates varies more than previously thought. We present a simple frequency-dependent cost-benefit model of nestmate recognition to understand conditions that might or might not favor the evolution of nestmate recognition that is based on cuticular hydrocarbon (CHC) profiles. Costs accounted for are costs for (i) maintaining a functional recognition system and (ii) keeping a CHC profile that may be sub-optimal regarding other functionalities like desiccation control, whereas the benefit of recognition is the prevention of nest raiding by other colonies. Unsurprisingly, the model indicates that recognition systems only evolve if costs are sufficiently low and benefits sufficiently high. In addition, the model suggests that nestmate recognition is more likely to evolve if colony turnover is fast (colony life-expectancy is low). Our model creates evolutionary cycles that are typically longest under parameter combinations that just allow the evolution of recognition systems at all; the system expresses attributes of a rock-paper-scissors game. The model shows that a breakdown of nestmate recognition may occur under changing ecological situations, e.g. as a result of reduced intraspecific competition or increased abiotic stress. We speculate that such effects may be involved in the formation of supercolonies during invasions. Nestmate recognition may have evolved more to prevent interspecific predation or parasitism by antagonists that managed to mimic their host's CHC profile than as a mechanism to prevent exploitation by conspecific colonies.同类识别 (nestmate recognition) 是社会性昆虫中广泛存在的现象，亦是具有演化重要性的性状。然而越来越多的证据表明，针对非同巢个体的反应差异远超此前的认知。本研究构建了基于表皮碳氢化合物 (cuticular hydrocarbon, CHC) 谱的同类识别频率依赖型成本收益模型，旨在探究支撑或抑制同类识别演化的条件。该模型纳入的成本包括：其一，维持功能性识别系统的成本；其二，维持表皮碳氢化合物谱的成本——此类谱在应对干燥调控等其他生理功能时可能并非最优。而同类识别的收益，则是抵御其他蚁群对本巢的劫掠。不出所料，模型结果显示，仅当成本足够低、收益足够高时，识别系统才会发生演化。此外，模型还表明，当蚁群更替速率较快（即蚁群预期寿命较短）时，同类识别更易发生演化。本模型可生成演化循环，这类循环在恰好仅能支撑识别系统演化的参数组合下通常持续时间最长；该系统呈现出剪刀石头布博弈的特征。模型结果显示，在生态环境发生变化时，同类识别机制可能出现瓦解，例如当种内竞争减弱或非生物胁迫加剧时。我们推测，此类效应或与入侵过程中超级群落的形成存在关联。同类识别的演化，或许更多是为了抵御成功模拟宿主表皮碳氢化合物谱的异种天敌带来的捕食或寄生威胁，而非作为防范同种蚁群剥削的机制。