Meeting Abstract

P3.53  Jan. 6  Free flight yaw turns of stalk-eyed flies (Cyrtodopsis dalmanni) RIBAK, G*; SWALLOW, J.G; Univ of South Dakota, Vermillion; Univ of South Dakota, Vermillion gribak@usd.edu

The eyes of stalk-eyed flies (Diopsidae) are positioned at the end of rigid peduncles projecting laterally from the head. The length of these eye-stalks is sexually selected in males of some species resulting in an exaggerated increase in eye span of males relative to females. In Cyrtodiopsis dalmanni eye span of males exceeds body length by 20% and the allometric slope of eye span on body length in males is larger 2 fold than the slope of females. We tested whether this sexually selected trait results in a reduction in the flight performance of males. Analysis with body mass as a covariate showed that mass of the entire head or mass of the eyes did not differ between males and females. However the lengthening of the eye-stalks in males doubles the moment of inertia of the head for roll and yaw. The 3D flight trajectories of 76 males and 76 females were tracked at 60 Hz inside a large enclosure. The trajectories contained intervals of straight flight separated by yaw turns (<92° in 90% of the cases). Both sexes decreased flight speed during the turns. Using average turn rate, turn radius, horizontal speed and centripetal acceleration for each one of 857 observed turns, we tested for differences between males and females in the entire data set and in the upper 20% of the observed turning performance. Small but statistically significant differences were found in all the parameters supporting the hypothesis that larger head structures result in a slight performance loss for males. However the small magnitude of the differences observed probably reflects the adaptation of males to compensate for any interference from elongated eye stalks through morphological design. Support to this idea is found in the observation that males have larger wings and larger front legs. NSF IOB 0448060