File:American malacological bulletin (1987) (17968804570).jpg

Title: American malacological bulletin
Identifier: americanmal4519861987amer (find matches)
Year: 1983 (1980s)
Authors: American Malacological Union
Subjects: Mollusks; Mollusks
Publisher: (Hattiesburg, Miss. ?) : (American Malacological Union)
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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McMAHON AND WHITEHEAD: SHELL VARIATION IN ANCYLUS 117
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0.2 0.3 0.4 0.5 0.6 mm AL / 30 DAYS Fig. 8. Interpopulation variation of estimated mean shell aperture length:shell height ratios (AL/SH) in relation to growth rate in Irish Ancylus fluviatilis. The y axis is mean shell AL/SH ratio estimated for a 4.5 mm AL standard individual from least squares linear regression equations relating AL/SH to AL for each population collected. The x axis is annual population growth rate in mm AL per 30 days. The open circles are estimated mean AL/SH ratios for each population for which collection sites are indicated by the adjacent numbers (see Tables 1 and 2). Vertical bars are standard errors of the means. There was no significant correlation (P > 0.05) between estimated AL/SH ratios and growth rate due to an allometric reduction of AL in relation to AW in faster growing populations (see Results for details and Table 4 for regression parameters). of reproductively isolated populations (Russell-Hunter ef a/., 1967, 1981; Nickerson, 1972). In contrast, a direct relation- ship was found between water Ca + 2 concentrations and shell CaC03 content in three populations of the North American pond limpet, Laevapex fuscus (C. B. Adams) (McMahon, 1975), indicating that as environmental calcium availability increased so did the amount deposited in the shell. Indeed, such major differences in the patterns of shell CaC03 content between closely related species occurs more often than not in freshwater molluscs (Burky et al., 1979; Mackie and Flippance, 1983; McMahon, 1983). Differences in the pat- tern of shell CaC03 content with ambient Ca + 2 concentra- tion are even reported between populations of the same species from different geographical areas. Burky et al. (1979) report an inverse relationship between shell CaC03 and en- vironmental Ca + 2 concentration in populations of Sphaerium striatinum from the states of Ohio and New York while Mackie and Flippance (1983) report no correlation between shell CaC03 and Ca + 2 concentration for populations of the same species collected in southern Ontario, Canada. Such large variations in the patterns of interpopulation variation of shell CaC03 content in relation to environmental Ca + 2 within and between closely related species strongly suggest that abiotic and biotic environmental factors other than Ca + 2 concentra- tion are acting to induce non-genetic, interpopulation phenotypic plasticity in the shell CaC03 content of freshwater molluscs. McMahon (1983) has suggested that interpopulation differences in shell CaC03 content may be more related to differences in growth rates than to differences in abiotic fac- tors, giving rise to an apparently random (non-adaptive) distribution of interpopulation variation in shell mineral con- tent. In this model faster growing individuals more rapidly ex- pand the mantle edge, and therefore, deposit CaC03 at the shell edge at a higher rate than slower growing individuals. If deposition of new CaC03 by the underlying mantle to

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