Among adaptive traits under sexual selection, the length of spermatozoa shows high interspecific variation. In insects, extremes exist for both short and long sperm. The spermatozoa of the endoparasitic wasp Cotesia congregata (Say) are the shortest flagellated sperm described in animals, 6.6 µm in length. By comparison, the sperm of Drosophila bifurca are almost 6000 times longer. Thus, C. congregata has the potential to shed light on the selection pressures that drive variation in sperm length in relation to their production and use. The reproductive organs, sperm counts, controlled oviposition and sex ratios were investigated. The testes showed stratified differentiation stages of spermatogenesis, and sperm counts revealed continuous spermatogenesis in the late pupal stage. The small female spermatheca stored ~1000 sperm, resulting in an extremely high sperm concentration. The number of progeny per brood decreased over time until depletion of eggs. Females produced up to 370 daughters, corresponding to the effective use of 34% of the average sperm stock. Haploid males made up a greater proportion of broods in later parasitisms. Sperm miniaturization may be an adaptation to transfer increased quantities for the entire reproductive life of females in the absence of sperm competition but in the reduced space offered by the spermatheca.

中文翻译：

---

寄生黄蜂Cotesia congregata（膜翅目：Braconidae）极短精子的生殖环境

在性选择下的适应性状中，精子的长度显示出较高的种间变异。在昆虫中，精子的长短都存在极端现象。内寄生蜂黄蜂Cotesia congregata（Say）的精子是动物中描述的最短的鞭毛精子，长度为6.6 µm。相比之下，果蝇的精子长了将近6000倍。因此，C。congregata有可能揭示选择压力，这些选择压力会导致精子长度与其生产和使用有关的变化。研究了生殖器官，精子数量，控制性排卵和性别比。睾丸显示出精子发生的分层分化阶段，而精子计数则显示出p后期的连续精子发生。雌性小精子可储存约1000个精子，导致精子浓度极高。每个卵的后代数量随着时间的推移而减少，直到鸡蛋耗尽。女性育出最多370个女儿，相当于有效使用了平均精子存量的34％。在后来的寄生虫中，单倍体雄性在育雏中所占的比例更大。