Data from: Sex determination meltdown upon biological control introduction of the parasitoid Cotesia rubecula?

Natural enemies may go through genetic bottlenecks during the process of biological control introductions. Such bottlenecks are expected to be particularly detrimental in parasitoid Hymenoptera that exhibit complementary sex determination (CSD). CSD is associated with a severe form of inbreeding depression because homozygosity at one or multiple sex loci leads to the production of diploid males that are typically unviable or sterile. We observed that diploid males occur at a relatively high rate (8-13% of diploid adults) in a field population of Cotesia rubecula in Minnesota, USA, where this parasitoid was introduced for biological control of the cabbage white Pieris rapae. However, our laboratory crosses suggest two locus CSD in a native Dutch population of C. rubecula, and moderately high diploid males survival (~70%); a scenario expected to produce low proportions of diploid males. We also show that courtship behavior of diploid males is similar to that of haploid males, but females mated to diploid males produce very few daughters that are triploid. We use our laboratory data to estimate sex allele diversity in the field population of C. rubecula and discuss the possibility of a sex determination meltdown from two locus CSD to effective single locus CSD during or after introduction.

在生物防治引种过程中，天敌类群可能遭遇遗传瓶颈（genetic bottleneck）事件。这类瓶颈对于具备互补性性别决定（complementary sex determination, CSD）的膜翅目寄生蜂类群而言，危害尤为显著。互补性性别决定与严重的近交衰退密切相关：当一个或多个性别位点处于纯合状态时，会产生二倍体雄蜂，这类雄蜂通常无法存活或不育。我们在美国明尼苏达州的菜蛾盘绒茧蜂（Cotesia rubecula）野外种群中观测到，二倍体雄蜂的发生比例相对较高，占二倍体成虫的8%~13%；该蜂是为防治菜粉蝶（Pieris rapae）而引种用于生物防治的寄生蜂类群。然而，我们的实验室杂交实验显示，荷兰本土的菜蛾盘绒茧蜂种群存在双位点互补性性别决定系统，且二倍体雄蜂的存活率中等偏高（约70%），这种理论场景下本应仅产生较低比例的二倍体雄蜂。我们还发现，二倍体雄蜂的求偶行为与单倍体雄蜂并无显著差异，但与二倍体雄蜂交配的雌蜂所产后代中，雌性个体数量极少且均为三倍体。我们借助实验室数据估算了该菜蛾盘绒茧蜂野外种群的性别等位基因多样性，并探讨了在引种过程中或引种后，其双位点互补性性别决定系统退化为有效单位点互补性性别决定系统的可能性。