Data from: Diversity in morphology and locomotory behavior is associated with niche expansion in the semi-aquatic bugs

Acquisition of new ecological opportunities is a major driver of adaptation and species diversification. However, how groups of organisms expand their habitat range is often unclear. We study the Gerromorpha, a monophyletic group of heteropteran insects that occupy a large variety of water surface-associated niches, from small puddles to open oceans. Due to constraints related to fluid dynamics and exposure to predation, we hypothesize that selection will favor high speed of locomotion in the Gerromorpha that occupy water-air interface niches relative to the ancestral terrestrial life style. Through biomechanical assays and phylogenetic reconstruction, we show that only species that occupy water surface niches can generate high maximum speeds. Basally branching lineages with ancestral mode of locomotion, consisting of tripod gait, achieved increased speed on the water through increasing midleg length, stroke amplitude, and stroke frequency. Derived lineages evolved rowing as a novel mode of locomotion through simultaneous sculling motion almost exclusively of the midlegs. We demonstrate that this change in locomotory behavior significantly reduced the requirement for high stroke frequency and energy expenditure. Furthermore, we show how the evolution of rowing, by reducing stroke frequency, may have eliminated the constraint on body size, which may explain the evolution of larger Gerromorpha. This correlation between the diversity in locomotion behaviors and niche specialization suggests that changes in morphology and behavior may facilitate the invasion and diversification in novel environments.

获取全新生态机遇是生物适应与物种多样化的核心驱动力。然而，生物类群如何拓展其栖息范围的具体机制迄今仍不甚明晰。本研究聚焦黾蝽次目（Gerromorpha）——一类单系群（monophyletic group）的异翅类昆虫（heteropteran insects），其栖息的水面关联生态位（niche）类型多样，涵盖从小型水洼到开阔大洋的各类生境。鉴于流体动力学（fluid dynamics）限制与捕食暴露的双重压力，我们提出假说：相较于祖先陆生生活模式，栖息于水-气界面生态位的黾蝽次目类群将受到自然选择青睐，演化出更高的运动速度。通过生物力学测定（biomechanical assays）与系统发育重建（phylogenetic reconstruction）分析，本研究证实仅栖息于水面生态位的黾蝽类群能够实现极高的最大运动速度。保留祖先三足步态（tripod gait）运动模式的基部分支类群，通过延长中足（midleg）长度、增大划动幅度（stroke amplitude）与提升划动频率（stroke frequency），实现了水面运动速度的提升。而衍生类群（derived lineages）则演化出划行（rowing）这一全新运动模式：几乎完全依赖中足开展同步划动（sculling motion）。我们证实，这种运动行为的改变显著降低了对高划动频率与能量消耗（energy expenditure）的依赖。此外，我们阐明了划行运动通过降低划动频率，如何解除了对体型的演化约束，这或许可以解释大型黾蝽类群的起源。运动行为多样性与生态位特化之间的这种关联表明，形态与行为的演化改变或许能够助力生物侵入新环境并实现物种多样化。