Data from: Two for the price of one: eDNA metabarcoding reveals temporal and spatial variability of mussel and fish co-distributions in Michigan riverine systems

Freshwater mussels (family Unionidae) are among the world’s most endangered taxa, with almost 75% of North American taxa classified as a species of concern, threatened, or endangered. Despite the critical importance of comprehensive distributional data for the conservation of unionids and fishes, these data are often lacking because of the labor and resources associated with traditional survey methods. During their larval stage, unionid mussels use various fish species as obligate hosts, making native fish species vital to unionid persistence and an understanding of host distribution similarly important. Here, we utilized an eDNA metabarcoding approach to evaluate patterns of co-distribution of unionid mussels and fishes along ~362 km of the densely sampled Grand River network as well as the outlets of 19 tributaries along the eastern shore of Lake Michigan, USA. We detected a total of 21 mussel and 40 fish taxa, with distinctive composition of both mussel and fish assemblages across tributaries and differences in fish taxa between sampling periods. Notably, we detected more mussel taxa within the Grand River watershed than at the outlets of all 20 rivers combined. Within the Grand River network, two fish taxa (Pylodictus olivaris and Cyprinella) were found more frequently in areas of high mussel diversity, and three fish taxa more frequently in areas of low mussel diversity (Umbra, Leuciscidae, and Etheostoma). There was little difference between eDNA detections of mussels from samples collected in June versus August, but we detected significantly more fish taxa in August compared to June. Taken together, our findings demonstrate the value of eDNA metabarcoding for evaluating co-distribution of ecologically connected taxa. The use of eDNA as a tool for determining distributions of mussels and their obligate hosts may facilitate conservation efforts for these imperiled taxa.

淡水蚌类（蚌科Unionidae）是全球范围内受威胁最严重的生物分类群之一，北美地区近75%的蚌类分类群被列为受关注物种、易危物种或濒危物种。尽管全面的分布数据对蚌类与鱼类的保护至关重要，但由于传统调查方法需要耗费大量人力与资源，这类数据往往较为匮乏。淡水蚌类在幼体阶段需以多种鱼类作为专性宿主，这使得本土鱼类对蚌类的存续至关重要，因此了解宿主的分布同样意义重大。本研究采用环境DNA元条形码（eDNA metabarcoding）技术，对美国密歇根湖东岸沿岸的格兰德河密集采样河段（总长约362千米）及其19条支流的河口区域进行了蚌类与鱼类的协同分布模式评估。本研究共检测到21种蚌类与40种鱼类分类群，不同支流间的蚌类与鱼类群落组成均存在显著差异，且不同采样时段的鱼类分类群组成也有所不同。值得注意的是，我们在格兰德河网络内检测到的蚌类分类群数量，多于全部20条河流河口的检测总和。在格兰德河网络内，两种鱼类分类群（Pylodictus olivaris与Cyprinella）在蚌类多样性较高的区域出现频率更高；另有三种鱼类分类群（Umbra、Leuciscidae和Etheostoma）则在蚌类多样性较低的区域出现频率更高。6月与8月采集的样本中，蚌类的eDNA检测结果差异不大，但8月检测到的鱼类分类群数量显著多于6月。综合来看，本研究结果证实了环境DNA元条形码技术在评估生态关联类群协同分布模式中的应用价值。利用环境DNA技术确定蚌类及其专性宿主的分布情况，或将助力这类濒危类群的保护工作。