Morphologically divergent sperm in Odonata: phylogenetic patterns and relations with sperm competition

本研究比较了约150种豆娘和蜻蜓（昆虫纲：蜻蜓目）精子的形状和大小。在豆娘身上观察到的所有精子都有一种常见的形式，就像在大多数其他昆虫身上看到的那样；然而，在蜻蜓中观察到的这些是非典型的，鞭毛或束状。从正常精子到鞭毛精子的变化似乎在它们可能的系统发育树上只发生一次。从正常精子到捆绑精子的变化在系统发育上也发生过一次。生殖结构在近缘物种豆娘之间存在显著差异，表明生殖结构受到交配行为选择压力的影响。根据DNA序列对日本Mnais和Trigomphus进行了详细的系统发育分析。每个属的种属被核DNA清楚地分开，但没有被线粒体DNA分开。基于mtDNA和nDNA的不一致的系统发育结论表明，近缘种之间在过去发生过渐进杂交。在这种情况下，避免杂交，即加强生殖隔离，可能对促进物种形成起重要作用。

In this study, the shape and size of sperm were compared among about 150 species of damselflies and dragonflies (Insecta: Odonata). All sperm observed in damselflies had a usual form as seen in most other insects; however, those observed in dragonflies were atypical, aflagellar or bundled. Changes from normal sperm to aflagellar sperm seemed to occur once on their possible phylogenetic tree. Changes from normal sperm to bundled sperm also occurred once phylogenetically. Genital structure conspicuously differed between the closely related species of damselflies, and this suggested that the genital structure is influenced by some selection pressure in mating behavior. Detailed phylogenetic analyses were conducted for Japanese Mnais and Trigomphus species, based on DNA sequences. The species belonging to each genus were clearly separated by the nuclear DNA, but not by mitochondrial DNA. The incongruent phylogenetic conclusions based on mtDNA and nDNA suggests that introgressive hybridization had occurred between the closely related species in the past. In such a situation, avoidance of hybridization, that is reinforcement of reproductive isolation, may play an important role to advance speciation.