Data from: Australian spiny mountain crayfish and their temnocephalan ectosymbionts: an ancient association on the edge of coextinction?

Australian spiny mountain crayfish (Euastacus, Parastacidae) and their ecotosymbiotic temnocephalan flatworms (Temnocephalida, Platyhelminthes) may have co-occurred and interacted through deep time, during a period of major environmental change. Therefore, reconstructing the history of their association is of evolutionary, ecological and conservation significance. Here, time-calibrated Bayesian phylogenies of Euastacus species and their temnocephalans (Temnohaswellia and Temnosewellia) indicate near-synchronous diversifications from the Cretaceous. Statistically significant cophylogeny correlations between associated clades suggest linked evolutionary histories. However, there is a stronger signal of codivergence and greater host specificity in Temnosewellia, which co-occurs with Euastacus across its range. Phylogeography and analyses of evolutionary distinctiveness suggest that regional differences in the impact of climate warming and drying had major effects both on crayfish and associated temnocephalans. In particular, Euastacus and Temnosewellia show strong latitudinal gradients in evolutionary distinctiveness and, conversely, in geographic range size, with the most distinctive, northern lineages facing the greatest risk of extinction. Therefore, environmental change has, in some cases, strengthened ecological and evolutionary associations, leaving host-specific temnocephalans vulnerable to coextinction with endangered hosts. Consequently, the extinction of all Euastacus species currently endangered (75%) predicts coextinction of approximately 60% of the studied temnocephalans, with greatest loss of the most evolutionarily distinctive lineages.

澳洲刺状山地螯虾（Australian spiny mountain crayfish，Euastacus属，副螯虾科Parastacidae）与其生态共生的头槽目扁形虫（Temnocephalida，扁形动物门Platyhelminthes）可能在漫长的地质时间尺度中伴随重大环境变化事件共存并产生相互作用。因此，重建二者的共生演化历史，具有进化生物学、生态学与保护生物学层面的重要意义。本研究通过时间校准的贝叶斯系统发育分析发现，Euastacus物种与其共生的扁形虫（Temnohaswellia属与Temnosewellia属）的类群几乎在白垩纪同期发生物种分化。关联类群间存在统计学显著的共系统发育相关性，表明二者的演化历史存在联动性。然而，在分布范围与Euastacus完全重叠的Temnosewellia属类群中，共分化信号更强，宿主特异性也更高。系统发生地理学分析与演化独特性评估结果显示，气候变暖与干旱带来的区域差异影响，对螯虾及其共生扁形虫均产生了显著作用。具体而言，Euastacus与Temnosewellia的演化独特性均呈现明显的纬度梯度，反之二者的地理分布范围则呈现相反的梯度格局：演化独特性最高的北部类群面临着最高的灭绝风险。因此，环境变化在部分情境下强化了二者的生态与演化关联，使得宿主特异性的扁形虫面临与濒危宿主共同灭绝的风险。据此预测，当前所有濒危的Euastacus物种（占比75%）若全部灭绝，将导致本次研究涉及的扁形虫类群中约60%一同灭绝，其中损失最为惨重的将是演化独特性最高的类群。