Data from: Evolution of codfishes (Teleostei: Gadinae) in geographical and ecological space: evidence that physiological limits drove diversification of subarctic fishes

Aim: To develop a holistic biogeographical history of codfishes in the subfamily Gadinae based on historical relationships, ecological niche, and evolution of physiological tolerances. Two alternative diversification scenarios were tested in two co-distributed, Northern Hemisphere clades: (1) clade ancestors were temperate, and environmental niche has been conserved over evolutionary time, implying that speciation was driven by vicariance associated with ice sheet formation; and (2) clade ancestors were Arctic, and species convergently adapted to temperate environmental conditions, implying that speciation was driven by repeated adaption to temperate environments. Location: Northern Hemisphere Arctic and subarctic oceans. Methods: Fifty-five new sequences of four genes from 23 tissue samples were combined with 10 GenBank sequences to generate a time-calibrated phylogenetic hypothesis. Combining the phylogeny with information on species' ecological niche tolerances inferred from correlational models, I reconstructed ancestral environmental tolerances of each of the focal clades. These results were combined with Bayesian area-based biogeographical analysis and regional palaeoclimatic history to develop a holistic biogeographical history of Gadinae. Results: Of 18 environmental variables describing species' tolerances to salinity, temperature, sea ice concentration, and mixed layer depth, only mean, maximum and minimum sea bottom temperature, and mean and minimum sea surface temperature showed phylogenetic signal across Gadinae. Both ecological niche and geographical distributions of gadine fishes are largely conservative, but two clades contain both Pacific and Atlantic species. Focal clade divergence time estimates suggest a Pliocene origin for both, with further Pleistocene divergence. Main conclusions: Reconstructed ancestral environmental tolerances of crown cods and tomcods support a temperate origin of both groups. The timing of diversification of these two clades and the intolerance of temperate species to sea ice suggest that cyclical Arctic ice formation drove divergence. Future sea ice reduction may have dramatic consequences for distributions and persistence of commercially important species when currently allopatric temperate species come into secondary contact.

研究目的：基于演化亲缘关系、生态位（ecological niche）及生理耐受特性的演化历程，构建鳕亚科（Gadinae）鱼类完整的生物地理学历史。本研究在两个共分布于北半球的支系中检验了两种不同的多样化情景：（1）支系祖先为温带类群，其环境生态位在演化过程中保持保守，这意味着物种形成由与冰盖形成相关的地理隔离事件驱动；（2）支系祖先为北极类群，物种趋同适应温带环境条件，这意味着物种形成由反复适应温带环境的过程驱动。研究区域：北半球北极与亚北极海域。研究方法：从23份组织样本中获取的4个基因的55条新序列，与10条基因银行（GenBank）序列合并，以构建时间校准的系统发育假说。将系统发育结果与基于相关模型推断的物种生态位耐受信息相结合，重构了各目标支系的祖先环境耐受特性。随后将上述结果与基于贝叶斯的区域生物地理学分析及区域古气候历史相结合，最终构建出鳕亚科完整的生物地理学历史。研究结果：在描述物种对盐度、温度、海冰浓度及混合层深度耐受特性的18项环境变量中，仅平均、最高和最低海底温度，以及平均与最低海表温度在鳕亚科类群中呈现出系统发育信号（phylogenetic signal）。鳕亚科鱼类的生态位与地理分布整体上较为保守，但有两个支系同时包含太平洋与大西洋物种。目标支系的分化时间估算结果显示，两个支系均起源于上新世（Pliocene），并在更新世（Pleistocene）发生进一步分化。主要结论：重构的冠群鳕鱼与汤姆鳕（tomcods）的祖先环境耐受特性，支持这两个类群均起源于温带环境。这两个支系的多样化时间，以及温带物种对海冰的不耐受性，表明周期性北极冰盖形成驱动了物种分化。未来海冰减少可能会产生重大影响：当前异域分布的温带物种将发生二次接触，这将对具有商业价值的物种的分布与存续造成显著后果。