Data from: Effects of inbreeding on a gregarious parasitoid wasp with complementary sex determination

Inbreeding and inbreeding depression are processes in small populations of particular interest for a range of human activities such as animal breeding, species conservation or pest management. In particular, biological control programs should benefit from a thorough understanding of the causes and consequences of inbreeding because natural enemies experience repetitive bottlenecks during importation, laboratory rearing, and introduction. Predicting the effect of inbreeding in Hymenopteran parasitoid wasps, frequently used in biological control programs, is nonetheless a difficult endeavor. In haplodiploid parasitoids, the purge of deleterious alleles via haploid males should reduce genetic load, but if these species also have complementary sex determination (CSD) abnormal diploid males will be produced, which may jeopardize the success of biological control introductions. <i>Mastrus ridens</i> is such a parasitoid wasp with CSD, introduced to control the codling moth, <i>Cydia pomonella</i> (L.). We studied its life history traits in the laboratory under two conditions: inbred (full sib) and outbred (non-sib) crosses, across five generations, in order to examine the consequences of inbreeding in this species. We found that in inbred lines non reproducing females live less, the number of daughters produced was lower, and that sex ratio (proportion of males) and proportion of diploid males were higher. Diploid males were able to produce fertile daughters, but fewer than haploid males. Lineage survival was similar for inbred and outbred lines across the five generations. The most significant decrease in fitness was thus a consequence of the production of diploid males, but this effect was not as extreme as in most other species with CSD, due to the fertility of diploid males. This study highlights the importance of determining the type of sex determination in parasitoid wasps used for biological control, and the importance of maintaining genetic diversity in species with CSD when importation or augmentation is the goal.

近交与近交衰退是小种群中的关键生态学过程，受到动物育种、物种保护及害虫治理等诸多人类活动的广泛关注。具体而言，生物防治项目亟需深入解析近交的成因与后果——因为天敌类群在引种、实验室饲养及田间释放的过程中，往往会经历反复的种群瓶颈效应。尽管膜翅目寄生蜂常被应用于生物防治项目，但预测其近交效应仍颇具挑战。在单倍二倍体寄生蜂中，通过单倍体雄蜂清除有害等位基因的过程本应降低种群遗传负荷；但若这类物种同时具备互补性性别决定（Complementary Sex Determination，CSD）机制，则会产生异常二倍体雄蜂，进而可能危及生物防治释放的成效。*Mastrus ridens*便是一种带有CSD机制的寄生蜂，其被引入用以防治苹果蠹蛾*Cydia pomonella*（L.）。本研究设置全同胞近交与非同胞远交两组实验条件，历经五代繁育，于实验室环境下探究该物种的生活史性状，以考察近交对其产生的影响。研究结果显示，近交系内不产卵的雌蜂寿命更短，子代雌蜂的产出数量更少，且性比（雄虫占比）与二倍体雄蜂的比例均更高。二倍体雄蜂虽可产生可育的子代雌蜂，但其子代数量少于单倍体雄蜂。在五代繁育周期中，近交系与远交系的家系存活率并无显著差异。由此可见，适合度的最显著下降源于二倍体雄蜂的产生；但由于二倍体雄蜂具备育性，该效应并未像多数其他带有CSD机制的物种那般剧烈。本研究强调了两点重要性：其一，明确生物防治所用寄生蜂的性别决定类型至关重要；其二，当以引种或增殖释放为目标时，维持带有CSD机制的物种的遗传多样性极为必要。