Oxygenation-Controlled Collective Dynamics in Aquatic Worm Blobs

Abstract

Many organisms utilize group aggregation as a method for survival. The freshwater oligochaete, Lumbriculus variegatus (California blackworms) 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 ∼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 ∼1.4x higher than in high DO. Furthermore, we observe emergent properties that arise when a worm blob is exposed to extreme DO levels. We demonstrate that internal mechanical 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 mechanical stress in worm blobs change to accommodate differing levels of oxygen. From an engineering perspective, this could be used to model and simulate swarm robots, self-assembly structures, or soft material entanglements.

Amorphous Entangled Active Matter

“…For example, according to Tuazon, et. al, worm blobs show less activity and less structural exposed surface area in high DO (>8 mg/L) as opposed to hypoxic conditions (<2 mg/L) 42 . Furthermore, worm blobs in high DO shows higher internal mechanical stress, which was demonstrated by lifting worm blobs using a 3D serrated endpiece (Fig.…”

“…We purchased, reared, and habituated blackworms as described in Tuazon, et al The experimental setup and data analysis is also the same 42 . For the toppling experiment, blackworms were placed in a 250 mL cell culture flask with 100 mL of filtered water.…”

“…Using stress-strain tests on an entangled chain of smarticles, we discover various properties related to their emergent auxeticity. Finally, we compare a few of these properties to biological experiment using California blackworms (Lumbriculus variegatus), whose collectives demonstrate a non-trivial macroscopic rheological analogue with features and properties from microscopic entanglement 4,32,42 .…”

Amorphous entangled active matter

“…2.2.1 Animals. We purchased, reared, and habituated blackworms as described in Tuazon, et al 42 Using blackworms for experiments does not require approval by an institutional animal care and use committee (IACUC).…”

“…We compare some of these properties to biological experiment using California blackworms (Lumbriculus variegatus), whose collectives demonstrate a non-trivial macroscopic rheological analogue with features and properties from microscopic entanglement. 4,32,42 2 Materials and methods…”