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.