Scientists discover a missing link in the evolution of insect mating

Understanding the evolution of insect mating behavior is essential for explaining how early insects adapted to life on land. A new study examines Petrobiellus akkesiensis, a rare jumping bristletail, and reveals that its highly specialized male genital structures enable direct spermatophore transfer via genital coupling—a mechanism previously undocumented in apterygote insects. This discovery provides an important missing link in the evolution of mating strategies within Archaeognatha.

Mating is a fundamental animal behavior, and insects often show complex reproductive strategies. Studying these behaviors helps clarify how mating evolved and how it shapes species survival.

Apterygote insects—like silverfish, firebrats, and jumping bristletails—are among the earliest insect lineages. Most rely on indirect sperm transfer, where males place spermatophores for females to pick up. Over time, however, their mating strategies have evolved in ways that supported their adaptation to life on land. Understanding these changes is key to tracing the early evolution of insect mating.

A new study by Assistant Professor Shodo Mtow from the Department of Agrobiological Resources, Meijo University, Japan, and Dr. Ryuichiro Machida, University of Tsukuba, Japan, focuses on the mating behavior of the jumping bristletail Petrobiellus akkesiensis. This species belongs to Archaeognatha, an order within the apterygotes. “Petrobiellus is an important group for understanding the evolution of mating behavior; however, due to its rarity, very little biological research has been conducted to date. In this study, a large number of living specimens—both male and female—were collected from the coast of Hokkaido, enabling detailed behavioral observations,” mentioned Dr. Mtow. “The species also has an exceptionally developed penis compared with other Archaeognatha and was therefore suspected of exhibiting a mating behavior similar to copulation,” he added. The study was published in Volume 83 of the Arthropod Systematics & Phylogeny journal on December 10, 2025.

Petrobiellinae species live on rocky coasts, suggesting adaptations to terrestrial life. In this study, researchers examined their genital structures microscopically and analyzed mating behavior through video recordings, comparing P. akkesiensis with other Archaeognatha to assess its evolutionary significance.

The mating behavior is distinct in P. akkesiensis. The male insects usually transfer the sperm in the ovipositor, the egg-laying organ in the female insects. The male insects use the styli, short, unsegmented, leg-like appendages found at the end of the abdomen, along with the penis, to hold the female’s ovipositor. The penis clasps the basal region of the ovipositor with its hook-like tip, while the styli holds the midsection of the ovipositor from above and below. This allows a direct spermatophore transfer via genital coupling. The spermatophore is 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.

Earlier studies identified three main spermatophore-transfer modes in Archaeognatha. This study reveals a previously unknown, derived mating behavior that does not fit those categories.

It is the first documented case of direct spermatophore transfer via genital coupling in apterygote hexapods, offering a key missing link in the evolution of insect mating. The findings also enhance the understanding of coastal insect ecology and how these species respond to environmental change.

“Further focused investigations are needed to accurately identify the ancestral mating modes that led to the mechanism of direct sperm transfer via copulation,” mentioned Dr. Mtow. This study deepens our understanding of insect diversity and evolution, and may ultimately inspire advances in biomimetics and other related scientific fields.

About Meijo University

Meijo University traces its origin back to the establishment of the Nagoya Science and Technology Course in 1926, giving it a proud history of more than 90 years. As one of the largest universities in the Chubu region, Meijo University is a comprehensive learning institution that supports a wide range of academic fields from the humanities to physical sciences. With a network of more than 200,000 graduates and alumni, it strives to contribute not only to local industries but also to international communities in various fields. Meijo University is also known as the birthplace of the carbon nanotube. To foster the human resources of the next generation, the university continues to tackle ongoing challenges by further enhancing its campus and creating new faculties.

Website: https://www.meijo-u.ac.jp/english/

About Assistant Professor Shodo Mtow from Meijo University

Dr. Shodo Mtow is an Assistant Professor at Meijo university Japan. Dr. Mtow completed his doctoral research from the University of Tsukuba. This research interests include entomology, embryology, and comparative morphology, with a particular focus on stoneflies, silverfishes and jumping bristletails as materials. He has published 14 research articles till date. He is a member of The Arthropodan Embryological Society of Japan, The Entomological Society of Japan and The Zoological Society of Japan. He was awarded by The Arthropodan Embryological Society of Japan in 2024 for his research.

Funding information

This work was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI: Grant-in-Aid for JSPS Research Fellow, JP20J00039 to Shodo Mtow and Scientific Research (C), JP19K06821 to Ryuichiro Machida.