Excitation of Faraday-like body waves in vibrated living earthworms

Ivan S Maksymov,Andrey Pototsky

doi:10.1038/s41598-020-65295-4

Ivan S Maksymov, Andrey Pototsky

Open Access

https://doi.org/10.1038/s41598-020-65295-4

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Journal: Scientific Reports	Publication Date: May 22, 2020
Citations: 11	License type: open-access

Affiliation: Swinburne University of Technology

Abstract

Biological cells and many living organisms are mostly made of liquids and therefore, by analogy with liquid drops, they should exhibit a range of fundamental nonlinear phenomena such as the onset of standing surface waves. Here, we test four common species of earthworm to demonstrate that vertical vibration of living worms lying horizontally on a flat solid surface results in the onset of subharmonic Faraday-like body waves, which is possible because earthworms have a hydrostatic skeleton with a flexible skin and a liquid-filled body cavity. Our findings are supported by theoretical analysis based on a model of parametrically excited vibrations in liquid-filled elastic cylinders using material parameters of the worm’s body reported in the literature. The ability to excite nonlinear subharmonic body waves in a living organism could be used to probe, and potentially to control, important biophysical processes such as the propagation of nerve impulses, thereby opening up avenues for addressing biological questions of fundamental impact.

Highlights

Biological cells and many living organisms are mostly made of liquids and by analogy with liquid drops, they should exhibit a range of fundamental nonlinear phenomena such as the onset of standing surface waves
We observe experimentally the subharmonic oscillations of the body of living earthworms lying horizontally on a flat solid surface subjected to vertical vibration
We measure the critical amplitude of the onset of subharmonic response as a function of the vibration frequency f, and we reveal that the obtained dependence exhibits signature characteristics of parametrically excited capillary surface waves in vibrated liquid drops[30,31,32,33]

Summary

Introduction

Biological cells and many living organisms are mostly made of liquids and by analogy with liquid drops, they should exhibit a range of fundamental nonlinear phenomena such as the onset of standing surface waves. Earthworms – tube-shaped, segmented worms that have a world-wide distribution and are commonly found in soil – have become a subject of intensive research focused on their response to vibrations and sound. Some of these studies aim to explain the response of these animals to natural vibrations produced by predators, rain or plants[9]. Earthworms are cheap and using them does not require ethics approval We choose these animals to demonstrate the onset of Faraday-like subharmonic body waves in a living organism subjected to external mechanical vibration. The drop can either adopt a regular star shape[30,31,32,33] or exhibit a more dramatic transformation by spontaneously elongating in horizontal direction to form a worm-like structure of gradually increasing length[34,35,36,37]

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