Variation in morphological and behavioral traits among isofemale strains of Drosophila prolongata (Diptera: Drosophilidae)

Abstract

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.

Social context-dependent modification of courtship behaviour in Drosophila prolongata

“…What kind of males adopt this parasitic tactic remains to be investigated. Males of D. prolongata compete for food territories [19]. Both in the laboratory and field observations, subordinate males tended to stay the side of the food source, hiding from the dominating male, which occupied the top surface of the food source.…”

“…In many Drosophila species, females do not accept a second mating for several days (reviewed in [30,31]). Although there was variation in the remating tendency among strains of D. prolongata [19], courting males are not likely to have a chance to mate with the intercepted females. Therefore, leg vibration bears a social contextdependent risk of losing invested time and energy in vain.…”

“…Mating behaviour of D. prolongata was shown to be influenced by the genetic background [19]. Therefore, we used multiple strains of known behavioural characteristics to ascertain the robustness of the results.…”

“…However, successful copulations were not always preceded by leg vibration [16,19], suggesting that males of D. prolongata have alternative courtship sequences. As courtship behaviour was observed from above in the previous studies [16,19], some behavioural elements may have been out of view. We re-examined the courtship sequence by closer observations from the side as follows: a male and a female were introduced into a vial (25 mm diameter  100 mm height) containing cornmeal medium.…”

“…The functional relationship between leg vibration and the enlarged forelegs suggests that this courtship behaviour has played an important role in the evolution of foreleg morphology. However, males of D. prolongata do not always perform leg vibration, and the proportion of males performing leg vibration varies between strains [19].…”