Data from: The significance of past interdrainage connectivity for studies of diversity, distribution and movement of freshwater-limited taxa within a catchment

Aim: Historical connectivity between drainages may represent an underappreciated contributor to the biodiversity within a catchment. First, we tested whether an isolated population of freshwater-limited galaxiids represents a contribution by past interdrainage connectivity to this system’s biodiversity, rather than reflecting intracatchment dispersal or speciation. Second, we sought to distinguish between possible geomorphic processes that could have allowed any past connectivity. Location: The Clutha and adjacent Southland region drainages on the South Island of New Zealand. Methods: We estimated the phylogeographical relationships among 466 cytochrome b sequences from ‘roundhead’ Galaxias populations throughout the Southland region and the Clutha drainage, using three different methods. Subsequently, possible geomorphic mechanisms of interdrainage connectivity were examined concurrently with genetic population divergence time estimates obtained by coalescent analysis. Results: All samples obtained in the lower Clutha system were genetically attributable to G. gollumoides and reflected at least a third, independent colonization event from Southland involving this species, rather than intradrainage dispersal or speciation by pre-existing Clutha populations. Geomorphological inferences and divergence time estimates of less than 7 ka are consistent with headwater connections across low divides between the lower Clutha and the Catlins region of Southland, rather than anastomosing of main channels during low sea stands. Main conclusions: The observation of at least three interdrainage connectivity events influencing the diversity and distribution of G. gollumoides lineages within the Clutha system highlights the potential significance of these processes as contributors to the magnitude and distribution of biodiversity within catchments.研究目标：流域间的历史连通性或为流域内生物多样性的一项被低估的贡献来源。其一，我们验证：淡水限生的南乳鱼（galaxiids）孤立种群是否源于过往跨流域连通对本系统生物多样性的贡献，而非流域内扩散或物种形成的结果；其二，我们旨在区分可能促成此类过往连通性的各类地貌过程。 研究区域：新西兰南岛的克鲁萨（Clutha）流域及邻近的南地（Southland）区域水系。 研究方法：我们采用三种不同方法，对南地区域及克鲁萨流域内的‘圆头’南乳鱼（roundhead Galaxias）种群的466条细胞色素b（cytochrome b）序列开展系统地理学关系推断。随后，结合溯祖分析得到的遗传种群分化时间估计值，对跨流域连通性的潜在地貌机制进行同步探究。 研究结果：克鲁萨下游水系的所有采样样本，在遗传上均隶属于戈氏南乳鱼（G. gollumoides），且至少存在三次独立的、源自南地的该物种拓殖事件，而非克鲁萨原有种群的流域内扩散或物种形成。地貌学推断与小于7千年的分化时间估计值，均支持克鲁萨下游与南地卡林斯（Catlins）区域之间存在河源跨分水岭连通的可能性，而非低海平面时期主河道的网状交织。 主要结论：克鲁萨流域内戈氏南乳鱼（G. gollumoides）谱系的多样性与分布格局，至少受到三次跨流域连通事件的影响。该发现凸显了此类过程对流域内生物多样性的规模与分布格局的潜在重要意义。