Cryptic phenotypic plasticity in populations of the North American freshwater gastropod, Pleurocera semicarinata

Abstract

Background: Phenotypic plasticity is termed 'cryptic' when it becomes so extreme as to prompt an (erroneous) hypothesis of speciation. Populations of pleurocerid snails nominally identified as Pleurocera ('Goniobasis' or 'Elimia') livescens are common elements of the macrobenthos in rivers and on lakeshores from Vermont through northern Ohio and northern Indiana to Wisconsin, USA. Small streams in southern Ohio, southern Indiana, and Kentucky are inhabited by Pleurocera semicarinata, and larger rivers by Lithasia obovata. The three nominal species differ only in qualitative aspects of shell morphology -P. semicarinata demonstrating a slender shell with a small body whorl, L. obovata a robust shell with a large body whorl, and P. livescens intermediate.

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

“…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.…”

“…headwater tributaries vs. main stem). Despite the prevalence of studies claiming that shell shape differences among pleurocerid populations are the result of ecophenotypic plasticity (Dillon, 2011(Dillon, , 2014Dillon et al, 2013;Dunithan et al, 2011;Minton et al, 2011Minton et al, , 2008, no study has examined shell shape in conjunction with high-resolution, population genomic data.…”

Phenotypic Plasticity and the Endless Forms of Freshwater Gastropod Shells

“…3D, E). Many studies have invoked phenotypic plasticity as a cause of shell variation in Pleuroceridae (e.g., Minton et al 2008;Dillon 2011Dillon , 2014Minton et al 2011;Dunithan et al 2012;Dillon et al 2013). 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.…”

“…Most other groups have not been studied well enough to determine the extent of phenotypic plasticity and whether this cause of shell variation is rare or merely poorly documented. Yet, phenotypic plasticity is often stated, or implied, to be common throughout freshwater gastropods (e.g., Urabe 2000; Glaubrecht and Köhler 2004;Minton et al 2008Minton et al , 2011Dillon 2011Dillon , 2014Dunithan et al 2012;Dillon et al 2013;Clewing et al 2015). Such statements appear to stem from untested assumptions and confusion about the types of studies that can confirm phenotypic plasticity.…”

The Heritability of Shell Morphometrics in the Freshwater Pulmonate Gastropod Physa

“…Evidence of direct effects of current and flow upon shell morphology in the pulmonate snail Lymnaea (or Radix ) has been offered by Lam and Calow [ 16 ], effects of water chemistry have been demonstrated by Rundle et al [ 17 ], and predator effects have been documented by Bronmark et al [ 18 , 19 ]. Evidence of ecophenotypic responses in shell morphology to predator pressure have also been documented in populations of the pulmonate planorbid Helisoma [ 20 , 21 ] and in the prosobranch pleurocerids [ 22 – 24 ]. Rearing morphologically diverse populations in a constant environment (“common garden experiments”) suggest a significant ecophenotypic component to shell height in the pulmonate limpet Ferrissia [ 25 ].…”