Exaggerated legs and aggressive behavior in the long-armed fruit fly <i>Drosophila prolongata</i> (Diptera, Drosophilidae)

Sexually exaggerated traits are widespread among insects, and exaggerated parts of the body vary among species. The body parts and exaggeration levels are associated with the style and intensity of fights for access to resources, such as food and mates, as well as territories that contain these resources. Likewise, the characterization of sexually exaggerated traits is associated with whether the traits are used as ornaments. Therefore, to clarify how sexually exaggerated traits have evolved and been maintained, it is necessary to deepen our understanding of the natural history of each species. Several researchers and I have studied the morphology and behavior of Drosophila prolongata (Diptera: Drosophilidae). Males of this species have exaggerated forelegs, which they use for intrasexual aggression as well as courtship for females. However, little is known about the biological characteristics of D. prolongata in the wild. The use of legs in intrasexual competition has rarely been reported in other dipterans. Elucidating the ecological factors that have favored the evolution of exaggerated forelegs in D. prolongata males may help clarify why the legs are not used as weapons as in other flies. In this paper, I discuss the evolutionary mechanisms of sexually exaggerated legs in insects with regard to their feeding habits and oviposition sites. I also introduce inter- and intraspecific variation in morphological and behavioral traits of D. prolongata and outline the relationship between aggressiveness and life-history traits.