Association between shell morphology of micro-land snails (genus Plectostoma) and their predator’s predatory behaviour

Abstract

Association between shell morphology of micro-land snails (genus Plectostoma) and their predator's predatory behaviourPredator-prey interactions are among the main ecological interactions that shape the diversity of biological form. In many cases, the evolution of the mollusc shell form is presumably driven by predation. However, the adaptive significance of several uncommon, yet striking, shell traits of land snails are still poorly known. These include the distorted coiled "tuba" and the protruded radial ribs that can be found in micro-landsnails of the genus Plectostoma. Here, we experimentally tested whether these shell traits may act as defensive adaptations against predators. First, we identified the predators, namely, Atopos slugs and Pteroptyx beetle larvae, and their predatory strategies towards Plectostoma snails. Then, we characterised and quantified the possible anti-predation behaviour and shell traits of Plectostoma snails both in terms of their properties and efficiencies in defending against the Atopos slug predatory strategies, namely, shell-apertural entry and shell-drilling. The results showed that Atopos slugs would first attack the snail by shell-apertural entry, and, should this fail, shift to the energetically more costly shell-drilling strategy. We found that the shell tuba of Plectostoma snails is an effective defensive trait against shell-apertural entry attack. None of the snail traits, such as resting behaviour, shell thickness, shell tuba shape, shell rib density and intensity can protect the snail from the slug's shell-drilling attack. However, these traits could increase the predation costs to the slug. Further analysis on the shell traits revealed that the lack of effectiveness these anti-predation shell traits may be caused by a functional trade-off between shell traits under selection of two different predatory strategies. Lastly, we discuss our results in the framework of Red Queen predator-prey coevolution and escalation, and propose several key elements for future study.PeerJ PrePrints | https://peerj.com/preprints/86v1/ | v1 received:

Life History Traits of the Perforate Dome Snail, Ventridens Demissus (Binney, 1843) (Gastropoda: Zonitidae), From Seabrook, Texas

“…A shell crushing strength of 4.6 N was measured in V. demissus, at least one order of magnitude less than that observed in Cepaea nemoralis (Jordaens et al 2006) and the genus Cerion (Quensen & Woodruff 1997). In land snails, predation is believed to strongly influence shell thickness and ornamentation (Woodruff 1978;Liew & Schilthuizen 2014). Zonitid snails like V. demissus are frequently preyed on by aperture-entering malacophagous snails, insects, and worms (Barker 2004 and references therein).…”

Zoogeographic patterns on very small spatial scales in rock-dwellingPlectostomasnails from Borneo (Gastropoda: Caenogastropoda: Diplommatinidae)

“…In the laboratory, empty adult Plectostoma shells were extracted from these soil samples by placing the soil in water, removing all floating debris, drying this, and then passing it under a dissecion microscope to pick out the shells (Tweedie, 1961). The shell of each individual was identified to species, and the typical holes produced during predation by Atopos rapax slugs (Schilthuizen et al, 2003b(Schilthuizen et al, , 2006Liew & Schilthuizen, 2014) were recorded. Again, individuals with clearly intermediate morphology were marked as hybrids and separately recorded.…”

“…Each of all these populations is distinct genetically and in shell shape and ornamentation. Genetic analysis revealed that it is an old (several million years) radiation and that the allopatric speciation process involves both genetic drift and local adaptation, primarily in response to predation by Atopos rapax (Rathouissidae), a molluscivorous slug (Liew & Schilthuizen, 2014; Vermeulen & Liew, 2022).…”

Specific damage recognised on land snail shells as a tool for studying predation intensity: differences related to habitat and predator types

“…Various aperture modifications have been found to have an important effect on reducing water loss (Machin, 1967). Denticles and other structures developed in the aperture area are considered to have an anti-predation function (Solem, 1972;Gittenberger, 1995;Liew & Schilthuizen, 2014). While there have been studies focusing on the advantages of overall shell thickness in relation to predation (Yom-Tov, 1970;Quensen & Woodruff, 1997), the importance of a thickened aperture itself has never been analysed in more detail.…”