figure 1

(A) Schematic of hydrostatic climbing mechanics. Like a rocket, a larva generates thrust in the direction it points (top), enabling it to generate upwards trajectories by rotating upwards to adopt nose-up postures. Complementarily, it may generate lift like a helicopter (bottom), creating an attack angle between trajectory and posture. (B) Trajectory of individual swim bouts as a function of posture, for control (2912 bouts) and finless larvae (1890 bouts). The unity line corresponds to 0 attack angle. Example postures and corresponding trajectories (inset) are indicated with red circles. (C) Representative epochs of climbing by one control and one finless larva, depicting posture and trajectory at the times of sequential bouts. Relative positions are to scale, but the body schematic is smaller than actual size to better highlight the trajectory. (D) Mean attack angles for control and finless siblings from six clutches (pairwise t-test, t5=4.55, p=0.0061). (E) Cumulative fractions of postures during climbs with trajectories greater than 20°, for control and finless siblings, plotted as mean ± S.D. across clutches. (F) Absolute deviation of posture from horizontal during climbs in (D) for control and finless siblings (t5=5.02, p=0.0040).