Correlates of snail shell variation along a unidirectional freshwater gradient in Lithasia geniculata (Haldeman, 1840) (Caenogastropoda: Pleuroceridae) from the Duck River, Tennessee, USA

Abstract

Phenotypic plasticity in snail shells is a well-documented phenomenon, specifically in freshwater species. In riverine taxa, shells respond to the unidirectional gradient of flow and depth as well as to predation by crushing predators. Using populations of Lithasia geniculata from the Duck River, Tennessee, USA, we examined environmental correlates of shell shape change and resistance to crushing along a riverine gradient. Shells were more globose, more robust, and more resistant to crushing forces downstream relative to upstream; these characteristics were correlated with river discharge and presence of molluscivorous fish. Size, however, did not have effects on shape nor crushing strength. These data are consistent with those observed in other snail species, and expand on our knowledge of potential fitness benefits and causes of plasticity in freshwater snail shells.

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

“…[58, 59]). Therefore, the increase in globularity of the shells in lotic habitats represents maybe an adaptation against habitat specific predators as recently demonstrated for Lithasia geniculata [12]. We conclude that in aquatic gastropods the relationships of shell morphology and habitat are more complex than assumed.…”

Phenotypic Plasticity and the Endless Forms of Freshwater Gastropod Shells

“…However, the evidence presented in these studies is limited to correlations with environmental factors or examination of allozyme variation unrelated to shell traits, and none provide unequivocal evidence of phenotypic plasticity. Other studies have documented shell variation in Lithasia geniculata, Elimia spp., and Pleurocera acuta that is correlated with environmental factors or stream position, but have not proposed a cause for this variation (Minton et al 2007(Minton et al , 2018Dillon and Robinson 2011;Ross et al 2014;Cazenave and Zanatta 2016).…”