Adhesive defence mucus secretions in the red triangle slug (Triboniophorus graeffei) can incapacitate adult frogs

Abstract

Gastropods are known to secrete mucus for a variety of purposes, including locomotion, reproduction, adhesion to surfaces and lubrication. A less commonly known function of mucus secretion in this group involves its use as a defence against predation. Amongst the terrestrial slugs, mucus that serves this particular purpose has been studied for only a handful of species under laboratory conditions, where it is thought to be produced to make individuals unpalatable or difficult to consume. However, the mechanisms of how these defensive secretions operate and their effectiveness in deterring predation in the natural world have not been described in much detail. In this study, we provide evidence of adhesive mucus secretions in the red triangle slug (Triboniophorus graeffei) as an adaptation against predation. Field observations of a large red‐eyed green tree frog (Litoria chloris) trapped in the mucus secretions of a nearby T. graeffei revealed that this mucus serves to incapacitate predators rather than just an overall deterrence. Mechanical stimulation of T. graeffei under laboratory conditions revealed that adhesive secretions were produced from discrete sections of the dorsal surface when disturbed, leading to the production of a highly sticky and elastic mucus that was unlike the thin and slippery mucus used during locomotion. The adhesiveness of the defensive secretions was strengthened and reactivated when in contact with water. This appears to not only be the first description of defensive mucus production in this slug species but one of the first natural observations of slug secretions incapacitating a relatively large vertebrate. The biomechanical properties of this mucus and its ability to maintain and strengthen its hold under wet conditions make it potentially useful in the development of new adhesive materials.

Comparative Animal Mucomics: Inspiration for Functional Materials from Ubiquitous and Understudied Biopolymers

“…Research into animal mucus and the questions being asked are as diverse as the mucus itself, and by understanding key factors contributing to mucin functional diversity, the versatility of mucus could be exploited in highly tunable advanced materials. Examples of secretions actively studied and the properties investigated include tissue-dependent proteomic immunology in oysters, 96 biomechanics and biochemistry of slime in velvet worms, 97 venom transport in marine snails, 98 predator traps in slugs, 99 wet adhesion in tree frogs, 100 particle capturing networks in tunicates, 21 UV protection in corals, 101 bioluminescence 102 and tube construction 103 in marine worms, and fibrous network formation in hagfish slime. 104 Our goal here is to highlight recent advances by the groups who study these animal mucuses, and in doing so, illustrate the wide diversity of approaches used to investigate these fascinating matrixes.…”

Identification and functional characterization of the first molluscan neuromedin U receptor in the slug, Deroceras reticulatum

“…This likely immoderate muscle contraction in the slug induced by the peptide is a similar physiological change observed in the insects above. It is noteworthy that treated specimens secreted copious amounts of milky mucus, which is a well-known defense response for D. reticulatum usually against physical attack [59][60][61][62] . This suggests that the pedal mucus gland could be an additional location for receptors, which active peptides could directly or indirectly target.…”

Advancing Discovery of Snail Mucins Function and Application

“…Certain snail species have specialized uses for mucus. For example, Falsilunatia eltanini (Moon Snail) uses mucus to protect their eggs, and Tikoconus costarricanus (Costa Rican Land Snail), uses mucus for load-bearing activities, such as to hide from the Sun on the bottom of leaves during droughts ( Gould et al, 2019 ; Barrientos, 2020 ). Recent advances in omics (genomic, transcriptomic, proteomic, glycomics) technologies have expanded the exploration of gastropod mucins as a scientific resource with wide ranging applications across chemistry, biology, biotechnology, and medicine.…”