Holomuzki Joseph R, Biggs Barry J F
Ohio State University, Department of Evolution, Ecology, and Organismal Biology, 1680 University Drive, Mansfield, Ohio 44906, USA.
Ecology. 2006 Apr;87(4):1038-47. doi: 10.1890/0012-9658(2006)87[1038:hvapti]2.0.co;2.
Studies documenting phenotypic variation among populations show that ecological performance in one activity is sometimes traded off against another. Identifying environment-specific costs and benefits associated with performance trade-offs is fundamental to knowing how conflicting selection pressures shape phenotype-environment matching in populations. We studied phenotypic variation in shell armature (spininess) of the New Zealand mudsnail, Potamopyrgus antipodarum (Gray), and explored how this variability relates to performance trade-offs between flow resistance and predator deterrence. Smooth- and spiny-shell morphotypes exist in populations in New Zealand streams and lakes, but the patterns and correlates of spatial variation of these phenotypes, and the possible hydrodynamical constraints and antipredatory benefits associated with spiny shell armature, are unknown. Samples from 11 rivers and nine lakes on the South Island showed that, on average, nearly 70% of snails in streams were smooth-shelled, whereas >80% of snails in lakes were spiny, suggesting dissimilar selective pressures between habitats. A laboratory flume experiment revealed that spines collected seston (i.e., suspended algae) at current speeds <40 cm/s, making spiny morphs more prone to flow-induced dislodgment than smooth morphs. However, a fish feeding experiment showed that one benefit of spines on shells was a decrease in predation risk from the common bully (Gobiomorphus cotidianus), a widespread predator of mudsnails in both streams and lakes. All snails egested by bullies were dead, further suggesting that these fishes may exert strong lethal effects on mudsnail populations in nature. Spine expression in lakes also appeared to be temperature related. We conclude that functional trade-offs between risk of flow-induced dislodgment and risk of fish predation affect shell armature frequencies of Potamopyrgus in freshwater habitats.
记录种群间表型变异的研究表明，一种活动中的生态表现有时会与另一种活动相互权衡。识别与表现权衡相关的特定环境成本和收益，对于了解相互冲突的选择压力如何塑造种群中的表型-环境匹配至关重要。我们研究了新西兰泥螺（Potamopyrgus antipodarum，Gray）壳饰（棘刺程度）的表型变异，并探讨了这种变异性如何与流动阻力和捕食者威慑之间的表现权衡相关。新西兰溪流和湖泊中的种群存在光滑壳和多刺壳形态类型，但这些表型的空间变异模式及其相关性，以及与多刺壳饰相关的可能流体动力学限制和反捕食益处尚不清楚。从南岛的11条河流和9个湖泊采集的样本表明，平均而言，溪流中近70%的蜗牛是光滑壳的，而湖泊中>80%的蜗牛是多刺的，这表明不同栖息地之间存在不同的选择压力。一项实验室水槽实验表明，在流速<40厘米/秒时，棘刺会收集悬浮物（即悬浮藻类），这使得多刺形态比光滑形态更容易因水流而被冲走。然而，一项鱼类摄食实验表明，壳上有棘刺的一个好处是降低了被常见的细纹鳟（Gobiomorphus cotidianus）捕食的风险，细纹鳟是溪流和湖泊中泥螺广泛存在的捕食者。所有被细纹鳟吐出的蜗牛都死了，这进一步表明这些鱼类可能对自然界中的泥螺种群产生强烈的致死影响。湖泊中棘刺的表达似乎也与温度有关。我们得出结论，水流导致的冲走风险和鱼类捕食风险之间的功能权衡影响了淡水栖息地中Potamopyrgus的壳饰频率。
