Ovoviviparity in the Tropical Earwig Species Spongovostox semiflavus (Dermaptera: Spongiphoridae), With Potential Convergent Elongation of Male Genitalia

Ovoviviparity and viviparity have evolved independently multiple times in animals. Although females exhibit extensive parental care of their eggs, (ovo) viviparity has only been reported in a few species of free-living, nonepizoic earwigs. In contrast, to date, all the studied members of families Arixeniidae and Hemimeridae, which live on mammals, are viviparous. We herein report ovoviviparity in the tropical earwig species, Spongovostox semiflavus (Bormans, 1894) (Forficuloidea: Spongiphoridae: Spongiphorinae). We observed that females of this species retain well-developed embryos within the ovaries and then lay them with complete egg envelopes just before hatching. An average of 9.4 embryos concurrently developed in a female's body. A similar condition has been reported for only one other species Marava arachidis (Yarsin, 1860), in the subfamily Spongiphorinae. Without additional mating, Spo. semiflavus females produced at least three clutches, consisting of an average of nine offspring within a period of 14-27 d. Both Spo. semiflavus and M. arachidis males are characterized by elongated male genitalia that are more than twice as long as their body lengths. Interestingly, elongated male genitalia are also present in the two other spongiphorids for which (ovo) viviparity has been reported. We discuss the causes of the potential convergence of the evolution of the male genital structure and the development of (ovo) viviparity in females.