The electric ecology of freshwater with a special focus on the isopod Asellus aquaticus and some freshwater invertebrates of Costa Rica

Abstract

This thesis investigates the role of electric fields in the ecology of freshwater
invertebrates, emphasising the behaviour of the crustacean isopod Asellus
aquaticus in response to electric fields, and exploring the electric ecology of
invertebrates from Costa Rica’s freshwater ecosystem. The present studies provide
insights into the dynamics of electroreception in aquatic invertebrates, a modality
largely overlooked in the field of electroreception.
The first chapter provides a comprehensive overview of electroreception. Emphasis
is placed on exploring electroreception across a broad range of taxa and reviewing
its historical progression and ecological context. Through this lens, advancements
in identifying electroreceptive invertebrates are discussed.
The second chapter investigates the changes in behaviour of Asellus aquaticus to
electric fields of varying strengths and frequencies through a pair of experiments. It
focuses on the response to direct current electric fields – suggested as an indicator
of a food source. Asellus aquaticus was expected to be attracted to the electric field.
Instead, the behaviour exhibited requires a more nuanced view, suggesting the
electrosensory system of Asellus aquaticus functions differently to those previously
described.
The third chapter explores alternating current electric field effects on Asellus
aquaticus. The initial hypothesis was that Asellus aquaticus would interpret the
electric fields (intended as facsimile predator electric fields) and respond
accordingly. However, subjects were unaffected by the presence of these signals.
Instead, direct current and anthropogenic frequency electric fields had the greatest
effect, causing differences in aggregation.
The fourth chapter quantifies the electric fields of free-swimming invertebrates in
the tropics of Costa Rica using two methods. In the process, a novel method for
allowing the subjects to behave freely using agar moulds is detailed, and the
techniques used in other studies are compared.
This thesis constitutes a significant contribution to the field of electric ecology,
paving the way for future electroreception research.

Date of Award	17 Jun 2025
Original language	English
Awarding Institution	University of Bristol
Supervisor	Martin J Genner (Supervisor) & Daniel Robert (Supervisor)