Free flight maneuvers of stalk-eyed flies: do eye-stalks affect aerial turning behavior?

摘要

The eyes of stalk-eyed flies (Diopsidae) are positioned at the end of rigid peduncles projected laterally from the head. In dimorphic species the eye-stalks of males exceed the eye-stalks of females and can exceed body length. Eye-stalk length is sexually selected in males improving male reproductive success. We tested whether the long eye-stalks have a negative effect on free-flight and aerial turning behavior by analyzing the morphology and free-flight trajectories of male and female Cyrtodiopsis dalmanni. At flight posture the mass-moment-of-inertia for rotation about a vertical axis was 1.49-fold higher in males. Males also showed a 5% increase in wing length compared to females. During free-flight females made larger turns than males (54 ± 31.4 vs. 49 ± 36.2°, t test, P < 0.033) and flew faster while turning (9.4 ± 5.45 vs. 8.4 ± 6.17 cm s?1, ANOVA, P < 0.021). However, turning performance of both sexes overlapped, and turn rate in males even marginally exceeded turn rate in females (733 ± 235.3 vs. 685 ± 282.6 deg s?1, ANCOVA, P < 0.047). We suggest that the increase in eye-span does result in an increase in the mechanical requirements for aerial turning but that male C. dalmanni are capable of compensating for the constraint of longer eye-stalks during the range of turns observed through wingbeat kinematics and increased wing size.