Photo by Tai Komoriya

The stag beetle Prosopocoilus hachijoensis is the only flightless species of the genus Prosopocoilus in Japan. Researchers at University of Tsukuba investigated the mechanisms underlying the loss of flight by comparing this beetle with closely related species that are capable of flight. Their analyses revealed that the atrophy of flight muscles was the primary proximate cause and that increased reliance on terrestrial locomotion may have relaxed the evolutionary pressure to maintain flight.

Tsukuba, Japan—Flight is a crucial mode of locomotion in insects that facilitates predator avoidance, foraging, and mating. However, some insect species have lost their ability to fly. Despite its significance, the evolutionary processes driving the loss of flight—particularly the transition toward becoming completely flightless—remain poorly understood.

The research team examined the causes of flight loss in Prosopocoilus hachijoensis, an endemic stag beetle inhabiting Hachijojima Island, by comparing it with flight-capable Prosopocoilus species inhabiting the Izu Islands. Their findings showed that the atrophy of flight muscles directly accounts for the species' inability to fly. They also found that this species exhibits a reduced relative wing size and enhanced walking performance, particularly in females. These results suggest that decreased dependence on flight and increased reliance on ground-based locomotion may have been key evolutionary factors that shaped flight loss. They also observed different morphological growth patterns among island populations, corresponding to both geographical arrangement and the speciation process. These differences suggest that local island environments may have influenced morphological evolution, including traits associated with flight loss.

Overall, this study demonstrates that the loss of flight is not merely a regressive process but an adaptive shift resulting from changes in dispersal strategy within a unique insular environment. These findings provide new insights into how insects transition toward a "flightless lifestyle" and the ecological pressures that shape their locomotion strategies.

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This work was supported by the Sasakawa Scientific Research Grant from The Japan Science Society.

Original Paper

Title of original paper:

Mechanisms of flight loss in Island-endemic stag beetle Prosopocoilus hachijoensis (Coleoptera: Lucanidae): a comparative analysis of flight and walking traits among congeners

Journal:

The Science of Nature

DOI:

10.1007/s00114-026-02081-8

Correspondence

KOMORIYA Tai
Degree Programs in Life and Earth Sciences, Graduate School of Science and Technology

Associate Professor YOKOI Tomoyuki
Institute of Life and Environmental Sciences, University of Tsukuba

Assistant Professor SAGA Tatsuya
Graduate School of Human Development and Environment, Kobe University

IKEMOTO Mito, Ph.D., JSPS Research Fellow
National Institute for Environmental Studies

Related Link

Institute of Life and Environmental Sciences