Data from: Phylogeography of the Australian freshwater turtle Chelodina expansa reveals complex relationships among inland and coastal bioregions

We examined range-wide mitochondrial phylogeographic structure in the riverine freshwater turtle Chelodina expansa to determine if this species exhibits deep genetic divergence between coastal and inland hydrological provinces as seen in co-distributed freshwater taxa. We sequenced two mitochondrial loci, genealogical relationships were assessed using a network approach, and relationships among biogeographic regions were tested using analyses of molecular variance. Population history was evaluated using neutrality tests, indices of demographic expansion, and mismatch analyses. Twenty one haplotypes were recovered across two mitochondrial haplogroups separated by ca 4% nucleotide divergence. The haplogroups have discrete geographic boundaries but only partially support a hypothesis of deep divergence between coastal and inland bioregions. The first haplogroup comprises populations from the inland Murray-Darling Basin and from coastal catchments south of the Mary River in southeast Queensland. The second haplogroup comprises populations from coastal catchments north of the Mary River. Cryptic phylogeographic barriers separating adjacent coastal populations are congruent with those demonstrated for other freshwater taxa and may result from the combined influences of the Conondale Range and alluvial deposits at the mouth of the Mary River. Our study demonstrates that freshwater taxa commonly display genetic differentiation within a biogeographic region where no boundaries have been recognised, highlighting the need to uncover cryptic microbiogeographic regions to aid conservation of freshwater biota.

本研究针对淡水河龟宽甲长颈龟（Chelodina expansa）的全分布区线粒体系统地理结构（mitochondrial phylogeographic structure）展开分析，旨在验证该物种是否如同同分布淡水类群一般，在沿海与内陆水文区系间存在深度遗传分化。本研究对两个线粒体基因座（mitochondrial loci）进行测序，采用网络分析法（network approach）评估其系统发育关系，并通过分子方差分析（analyses of molecular variance）检验不同生物地理区域间的遗传分化关系。同时，本研究借助中性检验（neutrality tests）、种群扩张指数（indices of demographic expansion）及错配分析（mismatch analyses），对该物种的种群历史进行了评估。本研究共获得21个单倍型（haplotype），这些单倍型隶属于两个线粒体单倍群（haplogroup），二者间的核苷酸分歧度约为4%。两个单倍群具有明确的地理分布边界，但仅部分支持沿海与内陆生物地理区之间存在深度遗传分化的假说。第一个单倍群包含来自内陆墨累-达令盆地（Murray-Darling Basin）以及昆士兰州东南部玛丽河（Mary River）以南沿海流域的种群。第二个单倍群则包含来自玛丽河以北沿海流域的种群。分隔相邻沿海种群的隐秘系统地理屏障（cryptic phylogeographic barriers），与其他淡水类群中已证实的屏障相吻合，其成因或为康登德尔山脉（Conondale Range）与玛丽河河口冲积沉积（alluvial deposits）的共同作用。本研究表明，淡水类群通常会在尚未被识别出地理边界的生物地理区域内发生遗传分化，这凸显了开展隐秘微观生物地理区系（microbiogeographic regions）研究的必要性，以助力淡水生物群落（freshwater biota）的保护工作。