Data from: Meek mothers with powerful daughters: effects of novel host environments and small trait differences on parasitoid competition

Outcomes of competition may depend both on subtle differences in traits relevant to fitness and on how those traits are expressed in the context of the environment. Environmental effects on traits impacting population dynamics are often overlooked in studies of parasitic wasp (parasitoid) competition. Lineages of the parasitoid Diachasma alloeum (Hymenoptera: Braconidae) differ in relative ovipositor length (a trait affecting the proportion of hosts available for parasitism). Since the size of natal hosts affects the overall body size of many adult parasitoids, outcomes of competition between D. alloeum lineages should be influenced by both their natal host's size and their inherited ovipositor:body size ratios. Previous genetic work showed the unexpected result that the apparently inferior competitor (the lineage with smaller ovipositors in its ancestral environment) has successfully colonized a new host. We present body size measurements and a phenomological model of competition showing that relative ovipositor sizes of the two lineages predict success of the apparently inferior wasp lineage in the new host. We present several variants of the model, including simulations: 1) wherein competitors have either ancestral trait values or trait values acquired in the novel environment; 2) that allow varying rates of constant immigration from the inferior competitor's source population; and 3) with stochastic immigration from both lineages' source populations. We show that ancestral trait differences and changes in environmentally mediated traits interact to affect outcomes of competition. Apparently inferior female parasitoids (‘meek mothers’) attacking a host in a novel environment can produce highly successful daughters if those daughters inherit large ovipositor:body size ratios and grow to a larger size in the new environment. Predictive models of parasitoid competition that consider effects of environmentally mediated trait changes may be particularly important for biocontrol programs wherein parasitoids are introduced into new environments or used to control novel hosts.

竞争的结局不仅取决于与适合度相关的性状间的细微差异，还取决于这些性状在环境背景下的表达形式。在寄生蜂（parasitoid）竞争的相关研究中，对影响种群动态的性状所受的环境影响往往被忽视。寄生性天敌Diachasma alloeum（膜翅目：茧蜂科）的不同谱系，其产卵器相对长度存在差异——该性状会影响可供寄生的宿主比例。由于初生宿主（natal host）的大小会影响多数成虫寄生蜂的整体体型，因此D. alloeum不同谱系间的竞争结局，应当同时受到其初生宿主大小，以及遗传获得的产卵器-体型比的影响。既往遗传学研究得到了一个出人意料的结果：看似处于竞争劣势的谱系（即在祖先环境中产卵器更短的谱系）已成功定殖了一种新宿主。本文提供了体型测量数据与现象学竞争模型，结果表明两个谱系的相对产卵器长度，可以预测看似劣势的蜂类谱系在新宿主中的竞争成功率。本文展示了该模型的多种变体，其中包含三类模拟实验：1）竞争者要么携带祖先性状值，要么携带在新环境中获得的性状值；2）允许劣势竞争者源种群以可变速率持续迁入；3）存在来自两个谱系源种群的随机迁入。研究表明，祖先性状差异与环境介导的性状变化之间存在交互作用，共同影响竞争结局。在新环境中攻击宿主的看似劣势的雌性寄生蜂（‘温顺母蜂’），若其后代继承了较大的产卵器-体型比，且在新环境中生长为更大体型，则可产生极具竞争优势的子代。对于将寄生蜂引入新环境或用于防治新型宿主的生物防治项目而言，考虑环境介导的性状变化影响的寄生蜂竞争预测模型，或许具有尤为重要的意义。