Data from: The temporal window of ecological adaptation in postglacial lakes: a comparison of head morphology, trophic position and habitat use in Norwegian threespine stickleback populations

Background: Studying how trophic traits and niche use are related in natural populations is important in order to understand adaptation and specialization. Here, we describe trophic trait diversity in twenty-five Norwegian freshwater threespine stickleback populations and their putative marine ancestor, and relate trait differences to postglacial lake age. By studying lakes of different ages, depths and distance to the sea we examine key environmental variables that may predict adaptation in trophic position and habitat use. We measured trophic traits including geometric landmarks that integrated variation in head shape as well as gillraker length and number. Trophic position (Tpos) and niche use (α) were estimated from stable isotopes (δ13C, δ15N). A comparison of head shape was also made with two North American benthic-limnetic species pairs. Results: We found that head shape differed between marine and freshwater sticklebacks, with marine sticklebacks having more upturned mouths, smaller eyes, larger opercula and deeper heads. Size-adjusted gillraker lengths were larger in marine than in freshwater stickleback. Norwegian sticklebacks were compared on the same head shape axis as the one differentiating the benthic-limnetic North American threespine stickleback species pairs. Here, Norwegian freshwater sticklebacks with a more "limnetic head shape" had more and longer gillrakers than sticklebacks with "benthic head shape". The "limnetic morph" was positively associated with deeper lakes. Populations differed in α (mean ± sd: 0.76 ± 0.29) and Tpos (3.47 ± 0.27), where α increased with gillraker length. Larger fish had a higher Tpos than smaller fish. Compared to the ecologically divergent stickleback species pairs and solitary lake populations in North America, Norwegian freshwater sticklebacks had similar range in Tpos and α values, but much less trait divergences. Conclusions: Our results showed trait divergences between threespine stickleback in marine and freshwater environments. Freshwater populations diverged in trophic ecology and trophic traits, but trophic ecology was not related to the elapsed time in freshwater. Norwegian sticklebacks used the same niches as the ecologically divergent North American stickleback species pairs. However, as trophic trait divergences were smaller, and not strongly associated with the ecological niche, ecological adaptations along the benthic-limnetic axis were less developed in Norwegian sticklebacks.

研究背景：探究自然种群中营养性状（trophic traits）与生态位利用（niche use）的关联，对于理解适应性演化与生态特化过程至关重要。本研究描述了25个挪威淡水三棘刺鱼（threespine stickleback）种群及其推定的海洋祖先的营养性状多样性，并分析了性状差异与冰后湖（postglacial lake）湖龄的相关性。我们选取了湖龄、水深及距海距离各不相同的湖泊，以此考察可能预测营养位与生境利用适应性的关键环境变量。本研究测定了多项营养性状，包括整合头部形态变异的几何地标（geometric landmarks）数据，以及鳃耙（gillraker）的长度与数量。通过稳定同位素（stable isotopes，δ¹³C、δ¹⁵N）估算了营养位（trophic position, Tpos）与生态位利用指数（α）。此外，我们还将头部形态与北美两对底栖-浮游生境（benthic-limnetic）的三棘刺鱼物种对进行了比较。

研究结果：我们发现海洋与淡水三棘刺鱼的头部形态存在显著分化：海洋种群的口裂更向上倾斜，眼径更小，鳃盖更大，头部更深。经体型校正后的鳃耙长度，海洋种群显著大于淡水种群。我们将挪威三棘刺鱼的头部形态轴与区分北美底栖-浮游物种对的形态轴进行了对比，结果显示，具有更"浮游生境头部形态"的挪威淡水三棘刺鱼，其鳃耙数量更多、长度更长，而具有"底栖生境头部形态"的种群则呈现相反特征。"浮游形态型（morph）"与湖泊水深呈显著正相关。不同种群的生态位利用指数α（平均值±标准差：0.76±0.29）与营养位Tpos（3.47±0.27）均存在差异，其中α随鳃耙长度增加而升高；个体体型越大，其营养位越高。与北美生态分化显著的三棘刺鱼物种对及孤立湖泊种群相比，挪威淡水三棘刺鱼的Tpos与α值范围相似，但性状分化程度显著更低。

研究结论：本研究结果表明，海洋与淡水环境中的三棘刺鱼存在显著性状分化。淡水种群在营养生态与营养性状上存在分化，但营养生态与种群在淡水环境中经历的时长并无关联。挪威三棘刺鱼所利用的生态位与北美生态分化显著的三棘刺鱼物种对一致。然而，由于其营养性状分化程度更低，且未与生态位形成强关联，挪威三棘刺鱼在底栖-浮游生境轴上的生态适应性演化程度相对较弱。