Capillary-based static self-assembly in higher organisms

Abstract

Organized structures produced by dynamic self-assembly are often observed in animal groups. Static self-assembly, however, has to date only been observed at the cellular and sub-cellular levels. The aim of this study was to analyse organized structures in immobile whirligig beetle groups on the water surface. We used theoretical and computational approaches to model the meniscus around whirligig beetles and to calculate the surface energy for configurations involving two beetles. Theoretical predictions were then tested using live insects and resin casts. Observations were also made for three and more casts. The meniscus of whirligig beetles had a bipolar shape with two concave parts. For two beetles, predicted configurations based on energy minima corresponded to beetles in contact by their extremities, forming lines and arrows, and agreed well with observations. Experimental results for three and more beetle casts revealed new geometrical arrangements similar to those obtained with colloids at interfaces. This study provides the first example of static self-assembly at the inter-organism level and shows the importance of capillary interactions in such formations. We identify the ecological context in which our findings are of relevance.

Capillary Assembly of Colloids: Interactions on Planar and Curved Interfaces

“…Indeed, particles with scant surface charge (PMMA or poly(methyl methacrylate) microparticles) assemble side-to-side, as shown in Figure 5b [72]. Similar arrangements have been reported for diverse ellipsoidal shaped objects, including mosquito eggs [66] and whirligig beetles [44]. The mechanics of these structures is rich.…”

Switchable self-assembled capillary structures

“…13,15 Such multipolar effects were considered for example to explain the particular natural patterns forming along water-air interfaces with mosquito eggs and whirligig beetles. 16 Based on multipolar capillary interactions, sophisticated self-assembled structures can therefore be envisioned, as already tested by our group. 7,8 In these earlier works, we 3D printed branched objects for producing either positive or negative charges located at the tips of the branches.…”

Additive‐Free Tunable Transport and Assembly of Floating Objects at Water‐Air Interface Using Bubble‐Mediated Capillary Forces

“…This work is inspired by the mechanism of beetles to climb the slippery water meniscus. The motion is triggered by the surface deformation induced by the beetle, and when this deformation interacts with the deformation due to the side wall, minimization of surface area comes into play which results in an uphill motion of the beetle toward the side wall . This mechanism is demonstrated to be capable of organizing spherical particles, anisotropic objects, and bubbles around a fixed pillar, also for fabricating complex self‐assembled structures .…”