Data from: Balancing selection maintains sex determining alleles in multiple-locus complementary sex determination

Hymenopteran species in which sex is determined through a haplo-diploid mechanism known as complementary sex determination (CSD) are vulnerable to a unique form of inbreeding depression. Diploids heterozygous at one or more CSD loci develop into females but diploids homozygous at all loci develop into diploid males, which are generally sterile or inviable. Species with multiple polymorphic CSD loci (ml-CSD) may have lower rates of diploid male production than species with a single CSD locus (sl-CSD), but it is not clear if polymorphism is consistently maintained at all loci. Here we assess the rate of diploid male production in a population of Cotesia rubecula, a two-locus CSD parasitoid wasp species, approximately 20 years after the population was introduced for biological control. We show that diploid male production dropped from 8–13% in 2005 and 2006 to 3–4% by 2015. We also show from experimental crosses that the population maintained polymorphism at both CSD loci in 2015. We use theory and simulations to show that balancing selection on all CSD alleles promotes polymorphism at several loci in ml-CSD populations. Our study supports the hypothesis that ml-CSD populations have lower diploid male production and are more likely to persist than comparable sl-CSD populations.性别决定通过互补性性别决定（complementary sex determination，CSD）这一单倍二倍体机制的膜翅目昆虫，易受到一种独特的近交衰退影响。在一个或多个CSD位点呈杂合状态的二倍体个体将发育为雌性，而所有CSD位点均为纯合的二倍体则会发育为二倍体雄虫，这类雄虫通常不育或无活力。拥有多个多态性CSD位点的物种（multiple polymorphic CSD loci，ml-CSD），其二倍体雄虫产生率可能低于仅拥有单个CSD位点的物种（single CSD locus，sl-CSD），但目前尚不明确多态性是否能在所有位点持续维持。本研究针对菜粉蝶盘绒茧蜂（Cotesia rubecula）——一种双位点CSD寄生蜂物种——在其被引入用于生物防治约20年后的二倍体雄虫产生率进行了评估。研究发现，该种群的二倍体雄虫产生率已从2005年、2006年的8%~13%降至2015年的3%~4%。此外，本研究通过杂交实验证实，2015年该种群在两个CSD位点上仍维持了多态性。本研究结合理论模型与模拟实验证明，对所有CSD等位基因的平衡选择可促进ml-CSD种群中多个位点的多态性维持。本研究支持以下假说：ml-CSD种群的二倍体雄虫产生率更低，且相较于同类sl-CSD种群更易持续存续。