Reproductive behaviour indicates specificity in resource use: phylogenetic examples from temperate and tropical insects

Specificity (= the degree of ecological specialisation) is one of the fundamental concepts of the science of ecology. Ambiguities on how to define and measure specificity have however complicated respective research efforts. Here we propose that, in insects, a behavioural trait –adult oviposition latency in captivity without a favourable host plant – correlates with a species’ specificity in larval host use. In the absence of a suitable host, monophagous insects are expected to wait for a long time before commencing oviposition, with the long waiting time corresponding to careful host location behaviour in nature. Polyphagous insects, in contrast, should be selected for an increased oviposition rate at the expense of the quality of oviposition substrate encountered and will on average have a short latency time. Using experimentally derived data on oviposition latency, we performed a phylogenetically informed analysis based on Bayesian inference to show that this variable correlates with host specificity (larval diet breadth) in a sample of North-European species of geometrid moths. A closely related index – the probability to lay any eggs on an unfavourable substrate – shows an analogous pattern. To provide an example of how these indices can be applied, we compare our sample of geometrid moths from Northern Europe with a sample from equatorial Africa. A comparative analysis based on an original phylogenetic reconstruction found no differences between the two study sites in parameters of oviposition behaviour. We conclude that behavioural tests can provide information about ecological interactions when the latter cannot be directly recorded. Our example study also hints at the possibility that host specificity of herbivores is not necessarily higher in a tropical region compared to a temperate one.

专化性（Specificity，即生态特化程度）是生态学学科的核心概念之一。然而，有关专化性的定义与测量方式的歧义却给相关研究带来了诸多阻碍。本研究提出，在昆虫类群中，一项行为性状——无适宜寄主植物条件下人工饲养时成虫的产卵潜伏期——与物种在幼虫寄主利用方面的专化性存在关联。当缺乏合适寄主时，单食性（monophagous）昆虫通常会在开始产卵前等待更长时间，这种较长的等待时长对应其自然环境下审慎搜寻寄主的行为策略。与之相反，多食性（polyphagous）昆虫会被选择以牺牲产卵基质质量为代价提升产卵速率，平均而言其产卵潜伏期更短。本研究利用产卵潜伏期的实验数据，基于贝叶斯推断（Bayesian inference）开展了纳入系统发育信息的分析，结果表明，在北欧尺蛾类（geometrid moths）物种样本中，该变量与寄主专化性（幼虫食性广度）显著相关。另一项与之密切相关的指标——即在不适宜基质上产卵的概率——也呈现出相似的关联模式。为展示这些指标的应用方式，我们将北欧尺蛾样本与赤道非洲地区的尺蛾样本进行了对比。基于原创性系统发育重建的比较分析发现，两处研究样地的产卵行为参数并无显著差异。我们由此得出结论：当无法直接记录生态相互作用时，行为实验可用于获取相关信息。本研究案例还提示，相较于温带地区，热带地区植食性动物的寄主专化性未必更高。