Data from: Test flattening in the larger foraminifer Heterostegina depressa: predicting bathymetry from axial sections

Previous attempts to quantify the test flattening trend in Heterostegina depressa with water depth have been rather unsuccessful. Due to its broad depth distribution, H. depressa is a perfect model species to calibrate test flattening as a bathymetric signal for fossil assemblages. This might enable us to better reconstruct palaeoenvironments of fossil larger foraminiferal communities or even provide clues on the degree of transport in allochthonous deposits. In this study we used growth-independent functions to describe the change of test thickness throughout ontogeny. Four growth-invariant characters, deriving from these functions, clearly quantify a transition of individuals with thicker to thinner central parts along the water depth gradient. This is probably controlled by light intensity because the photosymbionts of H. depressa (diatoms) are most effective at low irradiation levels. Thus, shallower specimens grow thicker to reduce light penetration, whereas specimens living deeper than the light optimum increase their surface by flattening to obtain a better light exposure.此前针对凹陷异盖虫（Heterostegina depressa）壳体随水深变化的扁平化趋势开展定量研究的尝试均未获得理想结果。由于该物种具有广泛的水深分布范围，其是将壳体扁平化校准为化石组合水深信号的理想模式物种。这将有助于我们更精准地重建大型有孔虫化石群落的古环境，甚至可为异地沉积中的生物搬运程度提供研判线索。本研究采用生长无关函数，描述了凹陷异盖虫在整个个体发育过程中的壳体厚度变化规律。基于上述函数提取的四个生长不变特征，清晰定量揭示了随水深梯度变化，个体壳体中心由厚变薄的演化趋势。该趋势大概率受光照强度调控：凹陷异盖虫的光合共生体为硅藻（diatoms），其在低辐照水平下光合效率最佳。因此，生活于浅水区的个体壳体增厚以减少光线穿透，而生活在光照最优深度以下的个体则通过壳体扁平化增大表面积，以获得更充足的光照。