Thermal Stress Disrupts Symbiotic Fluid Dynamics in Bobtail Squid

Abstract: The impact of thermal stress on beneficial symbiosis, in the face of rapid climate change, remains poorly understood. We investigate this using the model system, Euprymna scolopes, the Hawaiian Bobtail Squid, and its bioluminescent symbiont, Vibrio fischeri, which enables the squid to camouflage itself through counter-illumination. Successful colonisation of the squid by V. fischeri must occur hours after hatching and is mediated by fluid flow due to respiration within the squid mantle cavity. To study this process, we develop a mathematical model using the Method of Regularised Stokeslets to simulate the flow and resulting bacterial trajectories within the squid. We explore how thermal stress, mediated by physiological changes in respiration, ciliary dynamics, and internal geometry, affects this early colonisation by analysing the time bacteria spend in regions crucial to the establishment of symbiosis in these simulations. A variance-based sensitivity analysis of physiologically relevant parameters on these metrics demonstrates that changes in the breath cycle significantly impact and reduce the time bacteria spend in the critical zone within the squid, hindering colonisation.