Combining morphological and genomic evidence to resolve species diversity and study speciation processes of the Pallenopsis patagonica (Pycnogonida) species complex

Background: Pallenopsis patagonica (Hoek, 1881) is a morphologically and genetically variable sea spider species whose taxonomic classification is challenging. Currently, it is considered as a species complex including several genetic lineages, many of which have not been formally described as species. Members of this species complex occur on the Patagonian and Antarctic continental shelves as well as around sub-Antarctic islands. These habitats have been strongly influenced by historical large-scale glaciations and previous studies suggested that communities were limited to very few refugia during glacial maxima. Therefore, allopatric speciation in these independent refugia is regarded as a common mechanism leading to high biodiversity of marine benthic taxa in the high-latitude Southern Hemisphere. However, other mechanisms such as ecological speciation have rarely been considered or tested. Therefore, we conducted an integrative morphological and genetic study on the P. patagonica species complex to i) resolve species diversity using a target hybrid enrichment approach to obtain multiple genomic markers, ii) find morphological characters and analyze morphometric measurements to distinguish species, and iii) investigate the speciation processes that led to multiple lineages within the species complex. Results: Phylogenomic results support most of the previously reported lineages within the P. patagonica species complex and morphological data show that several lineages are distinct species with diagnostic characters. Two lineages are proposed as new species, P. aulaeturcarum sp. nov. Dömel & Melzer, 2019 and P. obstaculumsuperavit sp. nov. Dömel, 2019, respectively. However, not all lineages could be distinguished morphologically and thus likely represent cryptic species that can only be identified with genetic tools. Further, morphometric data of 135 measurements showed a high amount of variability within and between species without clear support of adaptive divergence in sympatry. Conclusions: We generated an unprecedented molecular data set for members of the P. patagonica sea spider species complex with a target hybrid enrichment approach, which we combined with extensive morphological and morphometric analyses to investigate the taxonomy, phylogeny and biogeography of this group. The extensive data set enabled us to delineate species boundaries, on the basis of which we formally described two new species. No consistent evidence for positive selection was found, rendering speciation in allopatric glacial refugia as the most likely model of speciation

Combining NCBI and BOLD databases for OTU assignment in metabarcoding and metagenomic datasets: The BOLD_NCBI _Merger

Metabarcoding and metagenomic approaches are becoming routine techniquesfor use in biodiversity assessment and in ecological studies. The assignment of taxonomic information to millions of sequences obtained via high-throughput sequencing is challenging, as many DNA reference libraries are lacking information on certain taxonomic groups and can contain erroneous sequences. Combining different reference databases is therefore a promising approach for maximising taxonomic coverage and reliability of results. The "BOLD_NCBI_Merger" bash script is introduced, which combines sequence data obtained from the National Centre for Biotechnology Information (NCBI) GenBank and the Barcode of Life Database (BOLD) and prepares it for taxonomic assignment with the software MEGAN

Supplementary material 1 from: Macher J, Macher T, Leese F (2017) Combining NCBI and BOLD databases for OTU assignment in metabarcoding and metagenomic datasets: The BOLD_NCBI _Merger. Metabarcoding and Metagenomics 1: e22262. https://doi.org/10.3897/mbmg.1.22262

Metabarcoding and metagenomic approaches are becoming routine techniquesfor use in biodiversity assessment and in ecological studies. The assignment of taxonomic information to millions of sequences obtained via high-throughput sequencing is challenging, as many DNA reference libraries are lacking information on certain taxonomic groups and can contain erroneous sequences. Combining different reference databases is therefore a promising approach for maximising taxonomic coverage and reliability of results. The "BOLD_NCBI_Merger" bash script is introduced, which combines sequence data obtained from the National Centre for Biotechnology Information (NCBI) GenBank and the Barcode of Life Database (BOLD) and prepares it for taxonomic assignment with the software MEGAN

TaxonTableTools - A comprehensive, platform-independent graphical user interface software to explore and visualise DNA metabarcoding data

DNA-based identification methods, such as DNA metabarcoding, are increasingly used as biodiversity assessment tools in research and environmental management. Although powerful analysis software exists to process raw data, the translation of sequence read data into biological information and downstream analyses may be difficult for end users with limited expertise in bioinformatics. Thus, the need for easy-to-use, graphical user interface (GUI) software to analyze and visualize DNA metabarcoding data is growing. Here we present TaxonTableTools (TTT), a new platform-independent GUI that aims to fill this gap by providing simple, reproducible analysis and visualization workflows. The input format of TTT is a so-called "TaXon table". This data format can easily be generated within TTT from two common file formats that can be obtained using various published DNA metabarcoding pipelines: a read table and a taxonomy table. TTT offers a wide range of processing, filtering and analysis modules. The user can analyze and visualize basic statistics, such as read proportion per taxon, as well as more sophisticated visualizations such as interactive Krona charts for taxonomic data exploration, or complex parallel category diagrams to assess species distribution patterns. Venn diagrams can be calculated to compare taxon overlap among replicates, samples, or analysis methods. Various ecological analyses can be produced directly, including alpha or beta diversity estimates, rarefaction analyses, and principal coordinate or non-metric multidimensional scaling plots. The taxonomy of a data set can be validated via the Global Biodiversity Information Facility (GBIF) API to check for synonyms and spelling mistakes. Furthermore, geographical distribution data can be automatically downloaded from GBIF. Additionally, TTT offers a conversion tool for DNA metabarcoding data into formats required for traditional, taxonomy-based analyses performed by regulatory bioassessment programs. Beyond that, TTT is able to produce fully interactive html-based graphics that can be analyzed in any web browser. The software comes with a manual and tutorial, is free and publicly available through GitHub (https://github.com/TillMacher/TaxonTableTools) or the Python package index (https://pypi.org/project/taxontabletools/)

Evaluating five primer pairs for environmental DNA metabarcoding of Central European fish species based on mock communities

Environmental DNA (eDNA) metabarcoding has become a powerful tool for examining fish communities. The demand for methodological standardization and the implementation of eDNA-based assessments into the regulatory monitoring (e.g., Water Framework Directive) are imminent. To ensure methodical accuracy and to meet regulatory standards, various sampling, laboratory and bioinformatic workflows have been established. However, a crucial prerequisite for a comprehensive fish monitoring is the choice of suitable primer pairs to accurately depict the present fish fauna. Various fish-specific primer pairs targeting different genetic marker regions were published over the past decade. However, a dedicated study to evaluate performance of frequently applied fish primer pairs to assess Central European fish species has not yet been conducted. Therefore, we created an artificial community composed of DNA from 45 Central European fish species and examined the discriminatory power and reproducibility of five fish primer pairs. Our study highlights the effect of the primer choice and bioinformatic filtering on the outcome of eDNA metabarcoding results. From the five primer pairs evaluated in our study the tele02 (12S gene) primer pair proved to be best choice for eDNA metabarcoding of Central European freshwater fish. Here, the MiFish-U (12S) and SeaDNA-mid (COI) primer pairs also displayed good discriminatory power and reproducibility. However, more general primer pairs (i.e., targeting vertebrates) were found to be less reliable and generated high numbers of false-positive and false-negative detections. Our study illustrates how careful selection of primer pairs and bioinformatic pipelines can make eDNA metabarcoding a more reliable tool for fish monitoring

Evaluating five primer pairs for environmental DNA metabarcoding of Central European fish species based on mock communities

Environmental DNA (eDNA) metabarcoding has become a powerful tool for examining fish communities. Prior to the introduction of eDNA-based assessments into regulatory monitoring contexts (e.g., EU Water Framework Directive), there is a demand for methodological standardization. To ensure methodical accuracy and to meet regulatory standards, various sampling, laboratory and bioinformatic workflows have been established. However, a crucial prerequisite for comprehensive fish monitoring is the choice of suitable primer pairs to accurately identify the fishes present in a given water body. Various fish-specific primer pairs targeting different genetic marker regions were published over the past decade. However, a dedicated study to evaluate the performance of frequently applied fish primer pairs to assess Central European fish species has not yet been conducted. Therefore, we created an artificial 'mock' community composed of DNA from 45 Central European fish species and examined the detection ability and reproducibility of five primer pairs. Our study highlights the effect of primer choice and bioinformatic filtering on the outcome of eDNA metabarcoding results. From the five primer pairs evaluated in our study the tele02 (12S gene) primer pair was the best choice for eDNA metabarcoding of Central European freshwater fish. Also, the MiFish-U (12S) and SeaDNA-mid (COI) primer pairs displayed good detection ability and reproducibility. However, less specific primer pairs (i.e., targeting vertebrates) were found to be less reliable and generated high numbers of false-positive and false-negative detections. Our study illustrates how the careful selection of primer pairs and bioinformatic pipelines can make eDNA metabarcoding a more reliable tool for fish monitoring

It's raining species: Rainwash eDNA metabarcoding as a minimally invasive method to assess tree canopy invertebrate diversity

Abstract Forest canopies are highly diverse ecosystems, but despite several decades of intense research, there remain substantial gaps in our knowledge of their biodiversity and ecological interactions. One fundamental challenge in canopy research is the limited accessibility of the ecosystem. Consequently, previous studies have relied on the application of either highly invasive methods such as chemical knockdown, or on time‐consuming and expensive setups such as canopy walkways or cranes. Therefore, time‐ and cost‐efficient, ideally minimally invasive yet comprehensive applications are required to help close this knowledge gap. High‐throughput metabarcoding of environmental DNA (eDNA) collected from water, soil, or air provides a minimally invasive method for biodiversity assessment, yet its potential for canopy biodiversity monitoring has not been explored. Herein, we conducted metabarcoding of eDNA washed off the canopy via rainwater to explore its potential for biodiversity monitoring and ecological research. We placed four 1 m2 rain samplers beneath the canopies of four different trees (beech, oak, larch, and pine) prior to a major rain event, filtered eDNA from the collected rainwater, and performed cytochrome c oxidase subunit I (COI) gene metabarcoding to profile the invertebrate community. Additionally, we collected and identified all specimens present in the rainwater to assess if eDNA only came from specimens physically present in the rainwater. We detected 50 invertebrate species by eDNA metabarcoding, of which 43 were not physically present in the water sample, thus likely representing true canopy biodiversity signals. Furthermore, we observed distinct species occurrence patterns corresponding to the four trees, suggesting that ecological patterns such as host specificity can potentially be assessed using the method. In conclusion, our study provides a proof of principle that rainwash eDNA metabarcoding offers a minimally invasive and comprehensive method for biodiversity monitoring in tree canopies

New insights into Danube’s macroinvertebrate communities from DNA metabarcoding as part of the Joint Danube Survey 4 (JDS4)

The Joint Danube Survey (JDS) is a multinational effort in monitoring Danube’s water quality, including its major tributaries. The Danube river stretches over a distance of 2,800 km and flows through or borders 10 different countries to which it is of utter importance as a source of potable water and hydrodynamic power. The JDS is conducted every 6 years and provides a unique opportunity to collect comprehensive data on both abiotic parameters and organisms and to raise awareness of the importance of water as a natural resource. As part of JDS and as a biological quality element in many monitoring programs worldwide, macroinvertebrates are monitored as indicators for various environmental conditions. However, due to their diverse taxonomic composition, associated difficulties with their morphology-based identification as well as their sheer abundance, macroinvertebrates are often analysed with a low taxonomic resolution (i.e., above species level). As an alternative, DNA metabarcoding offers a promising approach to capture this species diversity more accurately.Here, we used DNA metabarcoding to investigate the macrozoobenthic diversity of 46 sites from the latest JDS sampling campaign in 2019. To analyse macroinvertebrate diversity, bulk samples were taken by kick-net sampling and analysed using two different approaches, analysing the bulk sample fixative and analysing homogenised organisms from complete bulk samples. DNA metabarcoding of the sample fixative revealed 1,146 Operational Taxonomic Units (OTUs) and 231 species compared to 833 OTUs and 333 species from homogenised sample analysis. While more dipterans, in particular Chironomidae, were detected in fixative (136 species) than homogenised bulk (90 species) analyses, the latter picked up more Trichoptera (19 vs. 2), Amphipoda (10 vs. 4) and Bivalvia species (13 vs. 5). Even though these results of a DNA-based assessment deliver new insights into species richness and composition of Danube’s macroinvertebrate communities from the Danube source to its delta already, it is evident that the majority of OTUs was not assigned to species. While filling this lack of reference sequences poses a major challenge, the JDS consortium also offers a unique opportunity to complement reference databases in a multinational effort towards a more comprehensive Danube assessment and monitoring

Beyond fish eDNA metabarcoding: Field replicates disproportionately improve the detection of stream-associated vertebrate species

Fast, reliable, and comprehensive biodiversity monitoring data are needed for environmental decision making and management. Recent work on fish environmental DNA (eDNA) metabarcoding shows that aquatic diversity can be captured fast, reliably, and non-invasively at moderate costs. Because freshwater ecosystems act as sinks in the landscape, they also collect traces of terrestrial species via surface runoff or when specimens come into direct contact with water (e.g., for drinking purposes). Thus, fish eDNA metabarcoding data can provide information on fish but also on other, even terrestrial vertebrate species that live in riparian habitats. This data become available and may offer a much more comprehensive approach for assessing vertebrate diversity at no additional costs. Studies on how the sampling strategy affects species detection especially of stream-associated communities, however, are scarce. We therefore performed an analysis on the effects of biological replication on both fish as well as (semi-)terrestrial species detection. Along a 2-km stretch of the river Mulde (Germany), we collected 18 1L water samples and analyzed the relation of detected species richness and quantity of biological replicates taken. We detected 58 vertebrate species, of which 25 were fish and lamprey, 18 mammals, and 15 birds, which account for 50%, 24% and 7% of all native species to the German federal state of Saxony-Anhalt. However, while increasing the number of biological replicates resulted in only 25 % more detected fish and lamprey species, mammal and bird species richness increased disproportionately by 69 % and 84 %, respectively. Contrary, PCR replicates showed little stochasticity. We thus emphasize to increase the number of biological replicates when the aim is to improve general species detections. This holds especially true, when the focus is on rare aquatic taxa or on (semi-)terrestrial species, the so-called ‘bycatch’. As a clear advantage, this information can be obtained without any additional sampling or laboratory effort when the sampling strategy regarding biological replication is chosen carefully. With the consideration of frequent eDNA metabarcoding as part of national biomonitoring programs, the additional information provided by the bycatch can be used to further investigate the state of the environment and its biodiversity on a much broader scale