Mating in a viscous universe: the race is to the agile, not to the swift

Abstract

Charles Darwin's theory of natural selection has at its focal point the mating success of organisms. Among male animals, large body size is widely seen as the principal determinant of mating success. However, where mating takes place in a three-dimensional arena such as water, the arboreal habitat or air, small size with its concomitant aerobatic advantages might be advantageous. Despite considerable interest, the relationship between aerobatic ability and mating success has not yet been demonstrated in a single animal species. Here, we test the hypothesis that the known mating success of small male midges is due to their greater aerobatic ability. To do this, male midges collected from leks in the wild were flown and their flight paths in free flight were recorded on high-speed cameras in the laboratory. Four flight parameters that would seem relevant to male mate acquisition in flight, i.e. acceleration, maximum speed, tortuosity and turn-rate, were analysed with respect to body size. We show that, while in terms of maximum speed there was no detectable difference between small and large males, small males outperformed larger ones with respect to acceleration, tortuosity and turn-rate. We conclude that the hypothesis that small males gain their mating advantage through aerobatic superiority is consistent with the observations reported here.

Echolocating bats use future-target information for optimal foraging

“…We approximated the position of pulse emissions by bats using the polynomial function [i.e., polynomial approximation for each time series coordinate datum (X, Y, Z) of the calculated sound source]. The flight speed of P. abramus during natural foraging was 9 m/s at a maximum (average, 5 m/s), which is roughly 10 times greater than that of a prey species of the bats (29). At the study site, we also visually observed that dipteran midges took several seconds to fly across an area of a few tens of centimeters.…”

Bumblebee flight performance in cluttered environments: effects of obstacle orientation, body size and acceleration

“…Mechanistic explanations for the hypothesis that larger animals perform more poorly in cluttered environments often invoke the predicted decrease in mass-specific force production (and thus acceleration) with increased body size (Vogel, 1994). Maximum mass-specific force production does decrease with body size in bees (Buchwald and Dudley, 2010;Dillon and Dudley, 2004) (although perhaps not across insects more broadly; see Marden, 1987), and there is some evidence that accelerations during free flight decrease with body size in midges (Crompton et al, 2003). Limits to acceleration capacity may reduce an animal's ability to rapidly change its speed and/or direction to avoid collisions, and may also impose limits on flight speed through cluttered environments, as increased speed along a curved path requires higher radial acceleration.…”

Fluctuating Asymmetry in Flies, What Does It Mean?

“…The findings I present have wide application to understanding an aspect of sexual selection where FA affects the biomechanics of mating. This largely neglected type of mating system will reward attention, particularly because technology, in the form of high-speed video recording equipment, offers a tool for close observation of acrobatics in the wild [13,38]. The emphasis on the biomechanical consequences of FA in an aerial mating system is not meant to exclude other possible effects such as direct visual mechanisms, which are known to be important in the biology of some insects [39].…”

“…The fertilized female then departs on an egg laying flight. In such an arrangement, sexual selection appears to favor aerobatic ability in the male [13], where access to females may involve competition for a favorable location within the mating swarm [16]. Hence anything that perturbs aerobatic performance tends to reduce mating success and hence male fitness.…”

“…I go further and consider how the study of predators and parasites of the midge provided insights into FA in the functioning of an elusive and fascinating mating system. Chironomids have adopted a swarm based mating system, reviewed by [12], and thus the biomechanics of mating on the wing lies at the centre of their mating behavior [13]. This contrast with ornament based mating systems which have provided the main focus of research on FA.…”