subtitle for learnabout section of A SNAIL'S ODYSSEY
  Life on the high shore
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Salinity tolerance

  This section on life on the high shore is divided into topics of salinity tolerance, considered here, and DESICCATION, THERMAL TOLERANCE, WAVES & CURRENTS, and VISION & OTHER SENSORY INPUTS, considered elsewhere.
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Research study 1

histogram showing salinity tolerances of littorinid snails Littorina subrotundata from open-shore and salt-marsh sitesIn Barkley Sound, British Columbia 2 littorinid species Littorina subrotundata and L. sitkana inhabit both open-shore and salt-marsh habitats (see map). Surface-water salinities in the open-shore habitats range annually from 26-31‰, while those in the salt-marsh habitats range from 7-20‰, the variability owing to differences in river/stream inputs.  Tests of physiological responses to salinity and desiccation stress at the Bamfield Marine Sciences Centre show, as map showing study sites used in salinity-tolerance investigation of littorinid snails Littorina subrotundata and L. sitkanapredicted, that individuals from salt-marsh populations are significantly more tolerant to low salinities and significantly less resistant to drying than open-shore individuals (data for both species are similar; only L. rotundata shown here).

What is especially interesting is that the differences are present in both species and persist over a long period of laboratory acclimation.  To assess whether the differences have a genetic basis the researchers use a neutral polymorphic marker to estimate the level of gene flow between the populations. The results show a significant isolation by distance in both species, indicating that the open-shore and salt-marsh ecotypes of both species are true “physiological races”.  The authors interpret their results as an evolution of convergent phenotypes in similar habitats in the 2 species.  Sokolova & Boulding 2004 Mar Biol 145: 133.

NOTE  the researchers also assay responses to high salinities but data for these experiments and the data for desiccation stress are not shown here

NOTE the genomic DNA marker used is an intron of the aminopeptidase N gene

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