Large Differences Over Small Distances: Plasticity in the Shells of Elimia potosiensis (Gastropoda: Pleuroceridae)

Abstract

Phenotypic plasticity in freshwater mollusks is a well-known phenomenon, occurring in both bivalves and gastropods. Most work on freshwater snail plasticity has focused either on presence/absence of a single factor, or has looked at responses to environmental gradients over large geographical scales. Using the pleurocerid snail Elimia potosiensis from a spring and creek in Arkansas, we show a plastic environmental response at a scale thousands of times smaller than was previously known. Shells of E. potosiensis exhibit plasticity consist with that seen in other pleurocerids over the course of hundreds of meters. Possible explanations for this small-scale plasticity are offered.

Riverscape genetic variation, migration patterns, and morphological variation of the threatened Round Rocksnail, Leptoxis ampla

“…Moreover, hypotheses that predict diversity patterns across riverine landscapes have been mostly developed with data on freshwater insects and fish (reviewed by Davis et al, ; Hughes et al, ). These hypotheses include the River Continuum Concept that predicts lower species diversity in headwaters compared to main stem populations (Vannote et al, ), the Mighty Headwaters Hypothesis that postulates headwater or tributary populations will harbour greater genetic uniqueness than main stem river segments (Finn, Bonada, Múrria, & Hughes, ), and the Stream Hierarchy Model that states populations will demonstrate a pattern of isolation by distance along a stream network path (Meffe & Vrijenhoek, ). Many riverine species also demonstrate a pattern of increased genetic diversity in downstream river reaches (i.e.…”

“…Recently, Minton, McGregor, Hayes, Paight, and Inoue () used inter‐simple sequence repeats to examine population structure in Elimia potosiensis , but resolution across its range was limited. Research is needed to inform management decisions (Allendorf, ; McMahon, Teeling, & Höglund, ) and assess whether predictions of genetic diversity patterns across riverine landscapes (Finn et al, ; Meffe & Vrijenhoek, ; Paz‐Vinas et al, ; Vannote et al, ) are applicable to low‐dispersing, nonarthropod, invertebrates.…”

“…Fine‐scale population genetics, coupled with morphological analyses, could also recover a better understanding of intraspecific shell shape variation displayed by many pleurocerid species. A common theme of many studies examining conchological variation within pleurocerid species is the hypothesis that shell shape variation is only, or primarily, the result of ecophenotypic plasticity (Dillon, ; Dillon, Jacquemin, & Pryon, ; Dunithan, Jacquemin, & Pyron, ; Minton, Lewis, Netherland, & Hayes, ; Minton, Norwood, & Hayes, , but see Whelan, Johnson, & Harris, ). This hypothesis states that intraspecific shell variation is not heritable and is instead the result of stream size (Dillon, ), or possibly other environmental factors.…”

What can aquatic gastropods tell us about phenotypic plasticity? A review and meta-analysis

“…However, populations and species often differ in their degree of shell plasticity (for example, Appleton and Palmer, 1988;Palmer, 1990;Trussell, 1996;Edgell and Neufeld, 2008;Bourdeau, 2012). Environmental factors other than predator cues can also modify or limit the plasticity of gastropod shell form (for example, water motion (Hollander et al, 2006;Minton et al, 2007Minton et al, , 2011Dillon et al, 2013), temperature (Melatunan et al, 2013) and calcium availability ). In the case of water temperature, thinner shells are predicted to develop in relatively cold water because the amount of calcium carbonate needed to saturate cold water is larger than that in warm water and dissolution rates increase with decreasing water temperature.…”

Genetic structuring in the Pyramid Elimia, Elimia potosiensis (Gastropoda, Pleuroceridae), with implications for pleurocerid conservation

“…While E. potosiensis does possess shell variation that may have an environmental component (Minton et al 2011), no additional data supports recognition of any separate morphological entities. Jones and Branson performed detailed examinations of internal anatomy and radula structure of all four nominal E. potosiensis taxa, noting that, without their shells, internal structures of the morphotypes "...can not be separated" (Jones and Branson 1964: 60), and that the shell variations seen among the forms could be found throughout the species' range.…”