BACKGROUND Ecological speciation is a prominent mechanism of diversification but in many evolutionary radiations, particularly in invertebrates, it remains unclear whether supposedly critical ecological traits drove or facilitated diversification. As a result, we lack accurate knowledge on the drivers of diversification for most evolutionary radiations along the tree of life. Freshwater mollusks present an enigmatic example: Putatively adaptive radiations are being described in various families, typically from long-lived lakes, whereas other taxa represent celebrated model systems in the study of ecophenotypic plasticity. Here we examine determinants of shell-shape variation in three nominal species of an ongoing ampullariid radiation in the Malawi Basin (Lanistes nyassanus, L. solidus and Lanistes sp. (ovum-like)) with a common garden experiment and semi-landmark morphometrics. RESULTS We found significant differences in survival and fecundity among these species in contrasting habitats. Morphological differences observed in the wild persisted in our experiments for L. nyassanus versus L. solidus and L. sp. (ovum-like), but differences between L. solidus and L. sp. (ovum-like) disappeared and re-emerged in the F1 and F2 generations, respectively. These results indicate that plasticity occurred, but that it is not solely responsible for the observed differences. Our experiments provide the first unambiguous evidence for genetic divergence in shell morphology in an ongoing freshwater gastropod radiation in association with marked fitness differences among species under controlled habitat conditions. CONCLUSIONS Our results indicate that differences in shell morphology among Lanistes species occupying different habitats have an adaptive value. These results also facilitate an accurate reinterpretation of morphological variation in fossil Lanistes radiations, and thus macroevolutionary dynamics. Finally, our work testifies that the shells of freshwater gastropods may retain signatures of adaptation at low taxonomic levels, beyond representing an evolutionary novelty responsible for much of the diversity and disparity in mollusks altogether.

中文翻译：

---

马拉维湖正在进行的腹足动物辐射中壳形态的适应性发散。

背景技术生态物种形成是多样化的重要机制，但是在许多进化辐射中，尤其是在无脊椎动物中，尚不清楚所谓的关键生态特征是驱动还是促进了多样化。结果，我们缺乏关于生命树上大多数进化辐射的多样化驱动因素的准确知识。淡水软体动物是一个令人难以置信的例子：在各个家庭中，通常是从长寿的湖泊中描述了公认的适应性辐射，而在生态表型可塑性研究中，其他分类单元代表了著名的模型系统。在这里，我们研究了马拉维盆地（Lanistes nyassanus，L.solidus和Lanistes sp。（卵形）），并具有常见的花园实验和半地标形态计量学。结果我们发现，在相反的栖息地中，这些物种的生存和繁殖力存在显着差异。在野外观察到的形态学差异在我们的尼亚萨木霉与固相线虫和L. sp。的实验中仍然存在。（卵形），但固结线虫和L. sp。之间的差异。（卵样）消失并分别在F1和F2代中重新出现。这些结果表明发生了可塑性，但它并不是造成观察到的差异的唯一原因。我们的实验提供了第一个明确的证据，表明正在进行的淡水腹足类动物辐射中壳形态的遗传差异与受控栖息地条件下物种之间的明显适应性差异有关。结论我们的结果表明，在占据不同生境的Lanistes物种之间，壳形态的差异具有适应性价值。这些结果也有助于准确地重新解释化石Lanistes辐射中的形态变化，从而重新解释宏观进化动力学。最后，我们的工作证明淡水腹足动物的壳可能在低的生物分类学水平上保留了适应性特征，不仅仅代表了进化的新颖性，而这些新颖性完全负责了软体动物的多样性和差异。