Relationship between lateral oviduct morphology and reproductive strategy in earwigs

The earwig (Dermaptera) order contains around 2200 insect species with extremely diverse reproductive strategies. The vast majority of free-living earwigs are oviparous, i.e. the females lay eggs and the embryonic development takes place in an external environment. In contrast, the two known epizoic groups (Arixeniina and Hemimerina) are viviparous, i.e. embryogenesis takes place inside the female, which “gives birth” to the young offspring. There are also examples of another reproductive strategy, i.e. ovoviviparity, when the embryos develop inside eggs retained in the mother's body. The ovoviviparous earwigs are free-living and belong to the family Spongiphoridae. Here I present the results of ultrastructural analysis of lateral oviducts in three earwig species belonging to three different reproductive strategy groups: (1) oviparous Forficula auricularia (Forficulina, Forficulidae), (2) ovoviviparous Chaetospania borneensis (Forficulina, Spongiphoridae) and (3) viviparous Arixenia esau (Arixeniina, Arixeniidae), and show that the lateral oviducts of viviparous species undergo extensive structural and functional modifications, which facilitate gas exchange, nourishment and protection of developing embryos.