Data from: Mosaic evolution in the middle Miocene planktonic foraminifera Fohsella lineage

Recent studies have shown that modes of evolution, namely directional trend, random walk, and stasis, vary across morphologic traits and over the geographic range of a taxon. If so, is it possible that our interpretation of evolutionary modes is actually driven by our selection of traits in a study? In an attempt to answer this question, we have restudied the middle Miocene planktonic foraminifera Fohsella lineage, an iconic example of gradual morphologic evolution. In contrast to previous studies that have focused on the gross morphology as embodied by the edge view of tests, we analyze here multiple phenotypic traits chosen because their biologic and ecologic significance is well understood in living populations. We find that traits in the lineage did not evolve in concert. The timing and geographic pattern of changes in shape, coiling direction, size, and ecology were different. The evolution of this lineage is a mosaic combination of different evolutionary modes for different traits. We suggest that overemphasis on the evolution of some single trait, such as the edge-view outline, from narrow geographic ranges, has significantly underestimated the dynamic evolutionary history of this group.

近期研究表明，演化模式（evolutionary modes）——即定向趋势、随机游走与停滞——在不同形态性状之间，以及分类群（taxon）的地理分布范围内存在差异。若果真如此，那么我们对演化模式的解读，是否实则受研究中所选取性状的影响？为解答这一问题，我们重新研究了中中新世（middle Miocene）浮游有孔虫（planktonic foraminifera）Fohsella演化支，该类群曾是渐变形态演化的经典范例。与此前聚焦于壳体（test）侧视所呈现的整体形态的研究不同，本研究分析了多个表型性状（phenotypic traits）：选取这些性状的原因在于，其在现生种群中的生物学与生态学意义已得到充分阐明。本研究发现，该演化支的性状并非协同演化。形态、旋向（coiling direction）、体型以及生态特征的变化时机与地理分布模式均存在差异。该演化支的演化实为不同性状对应不同演化模式的镶嵌组合。我们认为，此前研究过度依赖狭窄地理范围内的单一性状（如侧视轮廓）的演化分析，极大低估了该类群的动态演化历史。