Understanding structure and function relationships in gastropod mucus

Gastropods use adhesive locomotion to successfully traverse a range of substrates by adapting the properties of a thin mucus layer. The mucus is a complex natural material with interesting viscoelastic, rheological properties whose biomimetic potential is hindered by our limited understanding of its native state. This thesis seeks to bridge this gap by developing methods that attempt to capture the native state of mucus, enabling the relationship between gastropod locomotion and the mucus trail to be studied without losing the biological context of the material.
A scientometric literature review revealed a knowledge gap within the foundations of the gastropod mucus field and highlighted the necessity to reassess fundamental assumptions, such as trail thickness and topography, that locomotion models, biomimetic solutions and malacological studies are based on. Furthermore, the citation network highlighted that gastropod mucus is often studied in isolation from the animal, where biological function can only be extrapolated from research undertaken in a purely engineering context.
This thesis utilised a range of non-destructive techniques to study mucus in its native state. This provided a comprehensive overview of the mucus layer from the dried trail to the in-situ deposition of the hydrated mucus trail under the slug. The native hydrated mucus was characterised for the first time. This provided empirical evidence for current theories on the role of mucus in gastropod locomotion, which rely on a consistent mucus layer between gastropods and the substrate.
Contextualising these results within the framework of its native state and animal behaviour uncovered a previously overlooked cost and limiting factor to mucus production, the water cost. This highlighted that mucus should be considered more akin to a composite, especially within the context of energetic costs. Finally, a model for adhesive locomotion, based on the observations in this thesis, was proposed.