Drosophila幼虫が外部機械的圧力に対抗する力を生成する

To counteract or to retreat presents a fundamental dilemma for biological organisms when facing adverse abiotic environmental conditions. In many cases, the predominant strategy animals adopt is to retreat. However, if counteraction is possible, and how the choice between counteraction and retreat is decided, are not clear. Here, we report that Drosophila larvae can actively counteract external mechanical pressure, inspired by Drosophila larval cleft-squeezing behaviour. We developed a behavioural paradigm to investigate the counteracting force of larvae in response to external pressures. Instead of retreating by crawling backward, a portion of Drosophila larvae could crawl forward and counteract against the external physical pressure. Under externally applied pressing forces of 25mN, 93.9% of forward peristaltic movements increased the counterforce, while 88.2% of backward peristaltic movements decreased it. The activeness in counteraction force was reflected by the longer inter-wave delay, more oscillation work and longer force wave period during consecutive forward peristaltic waves. As the external pressing force was increased from 25mN to 50mN, 75mN and 100mN, counteraction by forward peristalsis was less frequent, while retreat by backward peristalsis was more frequent when pressure is high. A reduction of the external pressure immediately following the counteracting forward peristalsis, which might serve as rewarding signal, could reinforce the counteraction and induce more ensuing forward peristalsis. The rewarding effect of reducing external pressure by forward crawling was much more than that by backward crawling. Our study sheds light on the intricate mechanisms underlying animal proactive responses to adverse abiotic environmental conditions.