Oxygenation-Controlled Collective Dynamics in Aquatic Worm Blobs

TL;DR

This study investigates how oxygen levels influence the collective behavior and emergent properties of California blackworm blobs, revealing significant behavioral adaptations and internal stress generation under varying oxygen conditions.

Contribution

It uncovers the relationship between dissolved oxygen levels and collective dynamics, including stress generation and surface area changes, in worm blobs, providing insights into adaptive collective behaviors.

Findings

Tail reaching activity flux is ~75x higher in low DO.

Exposed surface area of blobs is ~1.4x higher in low DO.

Internal stress allows blobs to be lifted off the bottom in high DO.

Abstract

Many types of organisms utilize group aggregation as a method for survival. The freshwater oligochaete, California blackworms Lumbriculus variegatus form tightly entangled structures, or worm "blobs", that have adapted to survive in extremely low levels of dissolved oxygen (DO). Individual blackworms adapt to hypoxic environments through respiration via their mucous body wall and posterior ciliated hindgut, which they wave above them. However, the change in collective behavior at different levels of DO is not known. Using a closed-loop respirometer with flow, we discover that the relative tail reaching activity flux in low DO is $\sim$75x higher than in the high DO condition. Additionally, when flow rate is increased to suspend the worm blobs upward, we find that the average exposed surface area of a blob in low DO is $\sim$1.4x higher than in high DO. Furthermore, we observe emergent properties that arise when a worm blob is exposed to extreme DO levels. Here we show that internal stress is generated when worm blobs are exposed to high DO levels, allowing them to be physically lifted off from the bottom of a conical container using a serrated endpiece. Our results demonstrate how both collective behavior and the emergent generation of internal stress in worm blobs change to accommodate differing levels of oxygen, which could be used to model and simulate swarm robots, self-assembly structures, or soft material entanglements.