Drosophila prolongata, a member of the rhopaloa subgroup of the melanogaster species group, occurs in Southeast Asia. Drosophila prolongata is known to have unique and prominent sexual dimorphism, with extraordinarily thick and elongated forelegs only in males. Mating behavior of D. prolongata is also characteristic: males perform “leg vibration” in their courtship toward females, in which the elongated forelegs play an important role. Comparisons with closely related species suggest that these morphological and behavioral traits have evolved rapidly after the divergence of D. prolongata. In the present study, variation in morphological and behavioral traits was examined among D. prolongata strains derived from single females collected in their natural habitats. Significant variations were detected in the size of various body parts, aggressiveness of interactions between males, and mating behavior. However, no obvious relationship was observed between morphological and behavioral traits. These results suggested that genetic factors contribute to the variation in morphological and behavioral traits in D. prolongata. The strains characterized in this study are useful for studies on the genetic mechanisms underlying the evolution of characteristic traits in D. prolongata.

Induction of alternative mating tactics by surrounding conditions, such as the presence of conspecific males, is observed in many animal species. Satellite behaviour is a remarkable example in which parasitic males exploit the reproductive investment by other males. Despite the abundance of parasitic mating tactics, however, few examples are known in which males alter courtship behaviour as a counter tactic against parasitic rivals. The fruit fly Drosophila prolongata shows prominent sexual dimorphism in the forelegs. When courting females, males of D. prolongata perform 'leg vibration', in which a male vibrates the female's body with his enlarged forelegs. In this study, we found that leg vibration increased female receptivity, but it also raised a risk of interception of the female by rival males. Consequently, in the presence of rivals, males of D. prolongata shifted their courtship behaviour from leg vibration to 'rubbing', which was less vulnerable to interference by rival males. These results demonstrated that the males of D. prolongata adjust their courtship behaviour to circumvent the social context-dependent risk of leg vibration.

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18The development of transgenesis systems in non-model organisms provides a 19 powerful tool for molecular analysis and contributes to the understanding of phenomena

Considerable variations in behavior and physiology exist among sexes and strains of species. The amount and allocation of energy resources can affect the health and survival of individuals. If an individual devotes a large amount of energy to interact with other conspecifics, the resources may become too scarce to maintain their physical condition, which could reduce longevity. In this study, I examined the interactive effects of sex, strain, and the presence of conspecifics on adult longevity using four strains of Drosophila prolongata. This species shows a large intraspecific variation in behavior and morphology among isofemale strains. Under solitary conditions, longevity was significantly different among strains for both sexes. The effects of same-sex conspecifics on adult longevity were also highly variable between the sexes and among strains. When exposed to conspecifics, the longevity of males of a hyper-aggressive strain was more notably decreased than that of females of the same strain or either sex of other less aggressive strains. These results indicate that differences in the balance of costs and benefits of social interactions lead to differences in adult longevity under group conditions between the sexes and among strains within the same species.

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The eye stalks in Diopsidae (Bilberg, 1820) have been widely examined, but the evolutionary origin of this unique trait remains unclear. Thus, further studies of Sphiracephala (Say, 1828), the extant genus forming a basal branch of Diopsinae, are needed. The present study aimed to identify the karyotype of Sphyracephala detrahens (Walker, 1860) with conventional Giemsa staining. Cytogenetic analysis revealed a diploid number of 2n = 10 including two pairs of metacentric chromosomes, a pair of telocentric chromosomes, a pair of dot-like chromosomes, and a pair of sex chromosomes in S. detrahens. The congener Sphyracephala brevicornis (Say, 1817) has been reported to have the same diploid number, 2n = 10, but different chromosome formula. These results demonstrate that chromosome rearrangements often occur in the genus Sphyracephala.

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