DOI: 10.3897/asp.83.e159694

Authors: Shodo Mtow, Ryuichiro Machida

Abstract: We examined the morphology of the male and female genitalic regions of Petrobiellus akkesiensis and describe its mating behavior as analyzed using video recordings. Petrobiellus belongs to the monogeneric subfamily Petrobiellinae (Machilidae), an enigmatic group known only from the Far East. Its male genitalic region shows remarkable specialization, leading to the inference that Petrobiellus performs direct spermatophore transfer through genital coupling. Video analysis revealed that, as expected, the male holds the female’s ovipositor using both his penis and styli on the 9th abdominal segment: the penis grasps the basal region of the ovipositor with its hook-like tip and the styli hold the midsection of the ovipositor from above and below; the spermatophore is then discharged onto the dorsal side of the basal region of the ovipositor from the apex of the penis, and the sperm is taken into the ovipositor, thereby completing the direct sperm transfer from male to female. This is the first documented case of direct sperm (spermatophore) transfer via genital coupling in apterygote hexapods. Based on current and previous findings, we compared and characterized the mating behaviors of Archaeognatha and discuss their implications in terms of evolution of mating strategies in Hexapoda. The mating behavior of Petrobiellus represents one of the most derived modes within Machilidae and Archaeognatha, for which we propose the name “direct transfer of spermatophore by genital coupling”.

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