qPCR data for 5x dilution.

Recurrent polyploidization occurred in the evolutionary history of most Eukaryota. However, how neopolyploid detriment (sterility, gigantism, gene dosage imbalances) has been overcome and even been bridged to evolutionary advantage (gene network diversification, mass radiation, range expansion) is largely unknown, particularly for animals. We used the parasitoid wasp Nasonia vitripennis, a rare insect system with heritable polyploidy, to begin addressing this knowledge gap. In Hymenoptera the sexes have different ploidies (haploid males, diploid females) and neopolyploids (diploid males, triploid females) occur for various species. Although such polyploids are usually sterile, those of N. vitripennis are reproductively capable and can even establish stable polyploid lines. To assess the effects of polyploidization, we compared a long-established polyploid line, the Whiting polyploid line (WPL) and a newly generated transformer knockdown line (tKDL) for fitness traits, absolute gene expression, and cell size and number. WPL polyploids have high male fitness and low female fecundity, while tKDL polyploids have poor male mate competition ability and high fertility. WPL has larger cells and cell number reduction, but the tKDL does not differ in this respect. Expression analyses of two housekeeping genes indicated that gene dosage is linked to sex irrespective of ploidy. Our study suggests that polyploid phenotypic variation may explain why some polyploid lineages thrive and others die out; a commonly proposed but difficult-to-test hypothesis. This documentation of diploid males (tKDL) with impaired competitive mating ability; triploid females with high fitness variation; and hymenopteran sexual dosage compensation (despite the lack of sex chromosomes) all challenges general assumptions on hymenopteran biology. We conclude that polyploidization is dependent on the duplicated genome characteristics and that genomes of different lines are unequally suited to survive diploidization. These results demonstrate the utility of N. vitripennis for delineating mechanisms of animal polyploid evolution, analogous to more advanced polyploid plant models.

多数真核生物（Eukaryota）的演化历程中均反复发生多倍化事件。然而，新多倍体所带来的有害效应（不育、体型巨化、基因剂量失衡）是如何被克服，甚至被转化为演化优势（基因网络多样化、大规模辐射、分布范围扩张）的，目前仍未被明确，尤以动物类群为甚。本研究以具有可遗传多倍性的稀有昆虫模型——丽蝇蛹集金小蜂（Nasonia vitripennis）为研究对象，着手填补这一认知空白。在膜翅目（Hymenoptera）昆虫中，不同性别的染色体倍性存在差异：雄性为单倍体，雌性为二倍体；且多个物种均会产生新多倍体个体（二倍体雄性、三倍体雌性）。尽管这类多倍体通常不育，但丽蝇蛹集金小蜂的多倍体个体却具备生殖能力，甚至可建立稳定的多倍体品系。为评估多倍化的效应，本研究选取长期构建的多倍体品系——怀廷多倍体品系（Whiting polyploid line, WPL），以及新构建的Transformer敲低品系（transformer knockdown line, tKDL），对其适合度性状、绝对基因表达量以及细胞大小与数量进行了比较分析。WPL多倍体的雄性适合度较高，但雌性繁殖力较低；而tKDL多倍体的雄性配偶竞争能力较弱，但繁殖力较高。WPL多倍体的细胞体积更大，但细胞数量减少；而tKDL多倍体在这两方面均无显著差异。对两个管家基因（housekeeping genes）的表达分析显示，无论染色体倍性如何，基因剂量均与性别相关联。本研究表明，多倍体的表型变异或许可以解释为何部分多倍体类群能够繁盛，而另一些则走向灭绝——这是一个被广泛提出但难以验证的假说。本研究中记录的具有交配竞争能力受损的二倍体雄性（tKDL品系）、具有高适合度变异的三倍体雌性，以及膜翅目昆虫的性别剂量补偿机制（尽管其缺乏性染色体），均对膜翅目生物学的通用认知提出了挑战。综上，本研究认为多倍化进程取决于重复基因组的特征，且不同品系的基因组在二倍化存活能力上存在差异。这些结果证明，丽蝇蛹集金小蜂可作为阐明动物多倍化演化机制的理想模型，其价值可与更成熟的多倍体植物模型相媲美。