Hunter R Douglas, Lull Wendy W
Department of Biological Sciences, Oakland University, 48063, Rochester, MI, USA.
Oecologia. 1977 Sep;29(3):205-218. doi: 10.1007/BF00345695.
A study of three species of freshwater pulmonate snails, Physa gyrina (11 populations), Physa integra (17 populations), and Helisoma anceps (18 populations) was carried out from 1973 to 1976, primarily in Michigan.The ratio of whole animal calcium content to tissue dry weight (Ca: tissue ratio) changes with age, but these changes are largely restricted to early growth and do not significantly affect individuals over 40 mg total dry weight, regardless of species.Parasitization by larval trematodes was found to have no significant effect on the Ca: tissue ratio in the populations examined regardless of species.Ca: tissue ratio of P. gyrina did not vary greatly between populations and showed a narrow range over a wide range of environmental calcium concentrations. Shell mass in P. gyrina is therefore either physiologically regulated in all populations (at a species specific 'constant' level) or interpopulation variation is minimized by moderately high levels of gene flow between populations.There was no relationship between Ca: tissue ratio and environmental calcium for either P. integra or H. anceps over a wide range of snail and environmental calcium values. In both of the foregoing species, shell calcium content varied greatly between populations. This variation did not conform to any apparent geographic cline.In 7 of the population sites studied, P. integra and H. anceps coexist, and when these sites are listed from highest to lowest Ca: tissue ratios, the rank orders for the two species are nearly identical. This suggests that there is some environmental factor (possibly trophic conditions) at these localities that influences shell mass.In 8 other species of pulmonates briefly examined, differences in Ca: tissue ratio between populations of the same species were often as great as or greater than differences between species.While the patterns of shell mass and environmental calcium for these species are not unlike those previously reported, the proposed causal factors for these patterns are clearly distinct from those suggested for other freshwater pulmonates.
1973年至1976年期间，主要在密歇根州对三种淡水肺螺进行了研究，分别是旋螺（11个种群）、全缘旋螺（17个种群）和钝口螺（18个种群）。全动物钙含量与组织干重的比值（钙：组织比值）随年龄变化，但这些变化主要局限于早期生长阶段，对于总干重超过40毫克的个体，无论物种如何，都不会产生显著影响。研究发现，幼虫吸虫寄生对所检查种群的钙：组织比值没有显著影响，无论物种如何。旋螺的钙：组织比值在不同种群之间变化不大，在广泛的环境钙浓度范围内显示出较窄的范围。因此，旋螺的壳质量要么在所有种群中都受到生理调节（在物种特定的“恒定 ”水平），要么通过种群之间适度高水平的基因流动使种群间的变异最小化。在广泛的蜗牛和环境钙值范围内，全缘旋螺或钝口螺的钙：组织比值与环境钙之间均无关系。在上述两个物种中，壳钙含量在不同种群之间差异很大。这种变异不符合任何明显的地理渐变群。在所研究的7个种群地点中，全缘旋螺和钝口螺共存，当这些地点按钙：组织比值从高到低列出时，两个物种的排名顺序几乎相同。这表明在这些地方存在一些环境因素（可能是营养条件）影响壳质量。在简要检查的其他8种肺螺中，同一物种不同种群之间的钙：组织比值差异通常与不同物种之间的差异一样大或更大。虽然这些物种的壳质量和环境钙模式与先前报道的并无不同，但这些模式的推测因果因素显然与其他淡水肺螺所提出的因素不同。
