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 [ 1–4 ]. However, how groups of organisms expand their habitat range is often unclear [ 3 ]. 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 [ 5, 6 ]. Due to constraints related to fluid dynamics [ 7–9 ] and exposure to predation [ 5, 10 ], 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分化的核心驱动力[1–4]。然而，生物类群拓展栖息范围的具体机制迄今仍不甚明晰[3]。本研究聚焦于黾蝽亚目（Gerromorpha）——一类单系群异翅目昆虫，其栖息生态位涵盖从小型水坑至开阔大洋的各类水面相关生境[5,6]。鉴于流体动力学带来的约束[7–9]以及暴露于捕食者的风险[5,10]，我们提出假说：相较于祖先的陆生生活模式，栖息于水-气界面生态位的黾蝽类群将受到自然选择的青睐，演化出更高的运动速度。通过生物力学实验与系统发育重建分析，我们证实：仅栖息于水面生态位的黾蝽物种能够实现极高的最大运动速度。保留祖先运动模式（即三足步态）的基部分支类群，通过延长中足长度、提升划动幅度与划动频率，实现了水面运动速度的提升。而衍生类群则演化出一种全新的划行运动模式：几乎仅依靠中足同步完成划水动作。本研究表明，这种运动行为的转变显著降低了对高划动频率与能量消耗的需求。此外，我们还阐明：划行运动模式的演化通过降低划动频率，解除了对体型大小的约束，这或许能够解释大型黾蝽类群的演化历程。运动行为多样性与生态位特化之间的这种关联表明，形态与行为的改变或许能够助力生物入侵全新环境并推动物种分化。