Data from: Sperm production characteristics vary with level of sperm competition in Cataglyphis desert ants

Under polyandry, males are selected to produce more competitive ejaculates. Theoretical models have explored how the mechanism of sperm competition drives males to partition investment within an ejaculate between sperm quantity and quality. The raffle-based competition model predicts that increased level of sperm competition selects for larger numbers of sperm in ejaculates. Sperm competition is also thought to promote the evolution of longer sperm, because longer sperm could be faster. In eusocial Hymenoptera, the mating system imposes unique selective pressures on male ejaculates. Males are short lived; they reach adulthood with a finite amount of spermatozoa, and they mate typically with a single or a few females and die. The actual number of spermatozoa stored in their accessory testes at emergence is thus a reliable measure of total investment into sperm production. In a comparative study of 15 species of Cataglyphis desert ants, we used phylogenetically controlled analyses to investigate relationships between levels of sperm competition, sperm production and sperm length. We measured sperm production by quantifying the number of spermatozoa present in testes, instead of using a proxy measure such as size of testes. Multiple queen mating is the ancestral state in the genus but reduction in mating frequency evolved secondarily and independently in some clades, providing a unique opportunity to examine how reduction from multiple to single mating influences sperm traits. Our results provide phylogenetically robust evidence that species experiencing greater levels of sperm competition produce more sperm. After controlling for male size, investment in sperm production decreases significantly according to the sequence obligatory multiple queen mating > multiple–single queen mating > single–double queen mating. Furthermore, the number of spermatozoa produced per male decreases significantly with reduction in paternity frequency for each species. In contrast, neither sperm length nor male size was significantly associated with the mating system classes or the number of patrilines. Our measures of sperm number provide the first direct evidence that sperm production covaries with the level of sperm competition in a eusocial insect. Given the reversal from multiple to single mating in Cataglyphis, our comparative analysis also shows convincingly that reduction in sperm competition influences sperm traits.在一妻多夫制（polyandry）下，雄性会被自然选择青睐以产生更具竞争力的射精产物。现有理论模型已深入探讨了精子竞争机制如何驱使雄性在单次射精的精子数量与质量之间分配资源投入。基于抽奖式的精子竞争模型预测，精子竞争强度的提升会促使雄性射精产出更多精子。此外，精子竞争被认为会推动更长精子的演化，因为更长的精子游动速度通常更快。 在真社会性膜翅目昆虫中，交配系统会对雄性射精产物施加独特的选择压力。雄性寿命极短：它们在羽化至成虫阶段时仅拥有有限数量的精子，且通常仅与一只或少数几只雌性交配后便死亡。因此，成虫羽化时储存在副睾中的实际精子数量，可作为雄性精子生产总投入的可靠量化指标。在针对15种箭蚁属（Cataglyphis）沙漠蚂蚁的比较研究中，我们采用系统发育校正分析，探究了精子竞争强度、精子生产总量与精子长度之间的关联。我们通过直接计数睾丸内的精子数量来衡量精子生产投入，而非使用睾丸大小等替代指标。 该属蚂蚁的祖先交配系统为多雌交配，但在部分演化支中，交配频率的降低是独立次生演化而来的，这为我们研究从多雌交配到单雌交配的转变如何影响精子性状提供了独特的研究契机。 我们的研究结果提供了具有系统发育稳健性的证据：经历更强精子竞争的物种，其精子生产总量更高。在控制雄性体型这一变量后，精子生产投入随交配系统类型呈显著下降趋势：专性多雌交配组 > 多-单雌交配组 > 单-双雌交配组。此外，对于每个物种而言，雄性单头个体的精子生产总量随父权频率的降低而显著减少。与之相反，精子长度与雄性体型均未与交配系统类别或父系群数量呈现显著关联。 我们的精子数量量化结果首次为真社会性昆虫中精子生产总量与精子竞争强度存在协同变化提供了直接证据。鉴于箭蚁属存在从多雌交配到单雌交配的演化逆转，本比较分析同样确凿地证明了精子竞争强度的降低会对精子性状产生影响。