Asymmetric male genitalia in calopterygid damselflies : their function and evolutionary patterns

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Males of some calopterygid damselfly species(Odonata) have asymmetric genitalia in which the left lateral-process is protruded more than the right process, but those of other species have symmetric genitalia. The function of the lateral-processes is removal of rival sperm from the female spermathecal ducts, which are Y-shaped and placed at the deep part of the female sperm storage organ. On the molecular phylogeny of the family Calopterygidae based on 16S rRNA, asymmetric male genitalia appeared once(all left-handed) and after that the degree of asymmetry changed depending on the female sperm storage tactics.