Testing the adaptive value of gastropod shell morphology to flow: a multidisciplinary approach based on morphometrics, computational fluid dynamics and a flow tank experiment

Abstract

A major question in stream ecology is how invertebrates cope with flow. In aquatic gastropods, typically, larger and more globular shells with larger apertures are found in lotic (flowing water) versus lentic (stagnant water) habitats. This has been hypothetically linked to a larger foot, and thus attachment area, which has been suggested to be an adaptation against risk of dislodgement by current. Empirical evidence for this is scarce. Furthermore, these previous studies did not discuss the unavoidable increase in drag forces experienced by the snails as a consequence of the increased cross sectional area. Here, using Potamopyrgus antipodarum as a study model, we integrated computational fluid dynamics simulations and a flow tank experiment with living snails to test whether 1) globular shell morphs are an adaptation against dislodgement through lift rather than drag forces, and 2) dislocation velocity is positively linked to foot size, and that the latter can be predicted by shell morphology. The drag forces experienced by the shells were always stronger compared to the lift and lateral forces. Drag and lift forces increased with shell height but not with globularity. Rotating the shells out of the flow direction increased the drag forces, but decreased lift. Our hypothesis that the controversial presence of globular shells in lotic environments could be explained by an adaptation against lift rather than drag forces was rejected. The foot size was only predicted by the size of the shell, not by shell shape or aperture size, showing that the assumed aperture/foot area correlation should be used with caution and cannot be generalized for all aquatic gastropod species. Finally, shell morphology and foot size were not related to the dislodgement speed in our flow tank experiment. We conclude that other traits must play a major role in decreasing dislodgement risk in stream gastropods, e.g., specific behaviours or pedal mucus stickiness. Although we did not find globular shells to be adaptations for reducing dislodgement risk, we cannot rule out that they are still flow-related adaptations. For instance, globular shells are more crush-resistant and therefore perhaps adaptive in terms of diminishing damage caused by tumbling after dislodgement or against lotic crush-type predators.Electronic supplementary materialThe online version of this article (10.1186/s40851-018-0119-6) contains supplementary material, which is available to authorized users.

Hydrodynamic role of substrate attachment in shaping the suspension‐feeding current created by the marine gastropod Crepidula fornicata

“…Our CFD simulation results support our PIV flow measurements and also offer a mechanistic understanding of our observations. CFD simulations have been previously used to compute bivalve inhalant siphon flows using an axisymmetric setting (Du Clos et al, 2017), to investigate the effect of mussel exhalant jets on local mixing using a two-dimensional setting (Nishizaki & Ackerman, 2017), and to test the adaptive value of gastropod shell morphology to flow by conducting three-dimensional flow simulations for a gastropod shell submerged in flowing water (Verhaegen et al, 2019). The present CFD modeling, however, is a first attempt to model a full-scale et al, 1986).…”

Species density and shell morphology of gold ring cowry (Monetaria annulus, Linnaeus, 1758) (Mollusca: Gastropoda: Cypraeidae) in the coastal waters of Ambon Island, Indonesia

“…The shape of the shell of M. annulus was more globular than that of the M. annulus at the other stations. At the geographical conditions with open area waters, the shape of the gastropod shells will be more globular than the shells found in semi-open areas or in protected areas (Trussell 1997;Verhaegen et al 2019). This condition plays a role to reduce the strength of current and ocean waves so that the M. annulus does not easily come off the substrate.…”

Phenotypic Plasticity and the Endless Forms of Freshwater Gastropod Shells

“…In its native range, P. antipodarum shells are larger at more downstream-riverine locations, and shell size increases with depth in lakes (Haase 2003;Vergara et al 2016). The selective advantages of such shell variation are unclear because larger apertures do not convey resistance to dislodgement (Verhaegen et al 2019), and environmental correlations do not inform the causes of shell variation.…”