Mechanisms of sperm competition revealed by sperm viability assessment using live/dead dual fluorescence

蝶蛹科的雌性豆娘有两个储存精子的器官，一个球形的囊性交基质和一个管状的精囊；雄性有一个特殊的喙，它有一个弯曲的头，用来去除法囊精子，侧面的刺突用来去除精囊精子。然而，就其相对于精囊管的宽度而言，不同物种或种群的侧突不同；较窄的管道在物理上能够接触到精囊精子，而较宽的管道则不能。本研究采用一种基于活/死双荧光的新方法，比较了两种具有不同精子结构的Calopteryx cornelia和Mnais pruinosa的精子储存模式和精子结构，不仅在精子数量（数量）方面，而且在精子质量（活力）方面。Calopteryx cornelia是一种典型的精子清除器。在这个物种中，法囊精子和精囊精子的生存能力相似。另一方面，在M. pruinosa中，精囊比囊小得多，通常不含精子。即使这个物种的精子囊确实含有精子，也有很高的比例是死亡的。虽然M. pruinosa的精囊有这样的萎缩趋势，但雄性的精囊有类似于C. cornelia的长而多刺的侧突。这表明除精子外还有其他功能。侧突可能起着阻止或引导的作用，以操纵喙状头从滑囊中取出精子团。

Female damselflies in the family Calopterygidae have two sperm-storage organs, a spherical bursa copulatrix and a tubular spermatheca; males possess a peculiar aedeagus with a recurved head, with which to remove bursal sperm, and lateral spiny processes to remove spermathecal sperm. The lateral processes, however, differ among species or populations in terms of their width relative to the spermathecal duct; the narrower processes are physically able to access spermathecal sperm, while the wider ones are not. In this study, sperm-storage patterns and aedeagal structures were compared between two calopterygid species with different spermathecal structures, Calopteryx cornelia and Mnais pruinosa, with respect not only to sperm quantity (number) but also to sperm quality (viability), by using a recently developed method based on live/dead dual fluorescence. Calopteryx cornelia is a typical spermathecal sperm remover. In this species, viability was similar between bursal and spermathecal sperm. On the other hand, in M. pruinosa the spermatheca was much smaller than the bursa and often contained no sperm. Even when the spermatheca of this species did contain sperm, a high percentage was dead. While the spermatheca of M. pruinosa has such atrophic tendencies, males, have developed long and spiny lateral processes similar to those of C. cornelia. This suggests functions other than spermathecal sperm removal. The lateral processes possibly function as stoppers or guides for manipulating the aedeagal head to remove the sperm mass from the bursa.