DNA from lake sediments reveals long-term ecosystem changes after a biological invasion

Species distribution modeling combined with environmental DNA analysis to explore distribution of invasive alien mosquitofish (Gambusia affinis) in China

China has become one of the most serious countries suffering from biological invasions in the world. In the context of global climate change, invasive alien species (IAS) are likely to invade a wider area, posing greater ecological and economic threats in China. Western mosquitofish (Gambusia affinis), which is known as one of the 100 most invasive alien species, has distributed widely in southern China and is gradually spreading to the north, causing serious ecological damage and economic losses. However, its distribution in China is still unclear. Hence, there is an urgent need for a more convenient way to detect and monitor the distribution of G. affinis to put forward specific management. Therefore, we detected the distribution of G. affinis in China under current and future climate change by combing Maxent modeling prediction and eDNA verification, which is a more time-saving and reliable method to estimate the distribution of species. The Maxent modeling showed that G. affinis has a broad habitat suitability in China (especially in southern China) and would continue to spread in the future with ongoing climate change. However, eDNA monitoring showed that occurrences can already be detected in regions that Maxent still categorized as unsuitable. Besides temperature, precipitation and human influence were the most important environmental factors affecting the distribution of G. affinis in China. In addition, by environmental DNA analysis, we verified the presence of G. affinis predicted by Maxent in the Qinling Mountains where the presence of G. affinis had not been previously recorded.

Molecular analyses of carangid fish diets reveal inter-predation, dietary overlap, and the importance of early life stages in trophic ecology

Carangid fishes are commercially important in fisheries and aquaculture. They are distributed worldwide in both tropical and subtropical marine ecosystems. Their role in food webs is often unclear since their diet cannot be easily identified by traditional gut content analysis. They are suspected to prey on pelagic and benthic species, with clupeiform fishes being important dietary items for some species, though it is unknown whether carangids share food resources or show trophic segregation. Here, we used metabarcoding to overcome traditional challenges of taxonomic approaches to analyze the diet of seven carangid species caught as bycatch in the Brazilian southwest Atlantic sardine fishery. Stomach contents were processed from the following species: Caranx crysos, Caranx latus, Chloroscombrus chrysurus, Hemicaranx amblyrhynchus, Oligoplites saliens, Selene setapinnis, and Trachinotus carolinus. Identified diets were dominated by teleost fishes. The C. latus diet was the most distinct among the seven species, preferentially consuming Engraulis anchoita, but H. amblyrhynchus, O. saliens, and S. setapinnis also showed a trend of predominantly consuming small pelagic fishes. Finally, we found evidence of inter-predation in carangids, especially strong between S. setapinnis and C. crysos, suggesting that consumption of early life stages may result in indirect competition through reduced recruitment in these fishes. These findings provide unprecedented insights into the biodiversity in marine ecosystems, especially the poorly known diet of carangid fishes.

What determines plant species diversity along the Modern Silk Road in the east?

As primary producers, plants provide food, oxygen, and other resources for global ecosystems, and should therefore be given priority in biodiversity protection. Most biodiversity research focuses on biodiversity hotspots, while biodiversity coldspots, such as deserts, are largely ignored. We propose that the factors shaping plant species diversity differ between biodiversity hot spots and cold spots, especially for desert ecosystems. To test this hypothesis, we investigated plant species diversity along the Modern Silk Road in the Northwest China desert, an area characterized by low precipitation, scarce vegetation, a limited number of species, and variable human activities. Surface soil was sampled from 144 plots, environmental DNA (eDNA) was extracted from soil samples, and seed plant species were identified using DNA metabarcoding technology. A total of 671 seed plant species were detected, which was more diverse than indicated by plot survey data. Plant species diversity gradually decreased from east to west along the Silk Road. In this area, temperature determines plant species diversity more than precipitation. Additionally, human activity has altered plant species diversity by introducing crops and invasive plants and eliminating environmentally adapted indigenous plants. Our results demonstrate the potential of eDNA metabarcoding technology for plant species diversity surveying. Desert plants have adapted to dry environments by relying on underground water or utilizing occasional rainfall as ephemerals, which are often not visible during surface surveys because of their short aboveground life cycle but can be detected with eDNA metabarcoding technology. Groundwater maintenance and human activity control are recommended for plant species diversity conservation and desertification control.

MetaDamage tool: Examining post-mortem damage in sedaDNA on a metagenomic scale

The use of metagenomic datasets to support ancient sedimentary DNA (sedaDNA) for paleoecological reconstruction has been demonstrated to be a powerful tool to understand multi-organism responses to climatic shifts and events. Authentication remains integral to the ancient DNA discipline, and this extends to sedaDNA analysis. Furthermore, distinguishing authentic sedaDNA from contamination or modern material also allows for a better understanding of broader questions in sedaDNA research, such as formation processes, source and catchment, and post-depositional processes. Existing tools for the detection of damage signals are designed for single-taxon input, require a priori organism specification, and require a significant number of input sequences to establish a signal. It is therefore often difficult to identify an established cytosine deamination rate consistent with ancient DNA across a sediment sample. In this study, we present MetaDamage, a tool that examines cytosine deamination on a metagenomic (all organisms) scale for multiple previously undetermined taxa and can produce a damage profile based on a few hundred reads. We outline the development and testing of the MetaDamage tool using both authentic sedaDNA sequences and simulated data to demonstrate the resolution in which MetaDamage can identify deamination levels consistent with the presence of ancient DNA. The MetaDamage tool offers a method for the initial assessment of the presence of sedaDNA and a better understanding of key questions of preservation for paleoecological reconstruction.

Emerging biological archives can reveal ecological and climatic change in Antarctica

Anthropogenic climate change is causing observable changes in Antarctica and the Southern Ocean including increased air and ocean temperatures, glacial melt leading to sea-level rise and a reduction in salinity, and changes to freshwater water availability on land. These changes impact local Antarctic ecosystems and the Earth's climate system. The Antarctic has experienced significant past environmental change, including cycles of glaciation over the Quaternary Period (the past ~2.6 million years). Understanding Antarctica's paleoecosystems, and the corresponding paleoenvironments and climates that have shaped them, provides insight into present day ecosystem change, and importantly, helps constrain model projections of future change. Biological archives such as extant moss beds and peat profiles, biological proxies in lake and marine sediments, vertebrate animal colonies, and extant terrestrial and benthic marine invertebrates, complement other Antarctic paleoclimate archives by recording the nature and rate of past ecological change, the paleoenvironmental drivers of that change, and constrain current ecosystem and climate models. These archives provide invaluable information about terrestrial ice-free areas, a key location for Antarctic biodiversity, and the continental margin which is important for understanding ice sheet dynamics. Recent significant advances in analytical techniques (e.g., genomics, biogeochemical analyses) have led to new applications and greater power in elucidating the environmental records contained within biological archives. Paleoecological and paleoclimate discoveries derived from biological archives, and integration with existing data from other paleoclimate data sources, will significantly expand our understanding of past, present, and future ecological change, alongside climate change, in a unique, globally significant region.

On the Use of Spores of Coprophilous Fungi Preserved in Sediments to Indicate Past Herbivore Presence

Fungal spores that grew on the faeces of herbivores in the past can be extracted from sediments and used to identify the presence of herbivores in former ecosystems. This review: (i) examines the factors that should be considered when interpreting these fungal spores, (ii) assesses the degree to which they can be used to estimate past herbivore populations and biomass density change, and (iii) identifies gaps in our current understanding that limit, or confound, the information that can be extracted from the fungal spore record. We focus on the life cycles of coprophilous fungi and highlight the importance of understanding spore dispersal mechanisms to ensure robust palaeoecological interpretation. We then discuss how variation in methodological approaches across studies and modifications can influence comparability between studies. The key recommendations that emerge relate to: (i) improving our understanding of the relationship between spores of coprophilous fungi (SCF) and herbivores through the study of the coprophilous fungi succession; (ii) refining our understanding of how climate and environment parameters effect fungal spore abundance, with particular reference to estimating past herbivore biomass density; and (iii) enhancing sedimentary DNA (SedaDNA) analysis to identify SCF that do not allow preservation in a way that allows visual identification. To further this field of study and provide more robust insights into herbivores in the past, we suggest that additional research is required to help to reduce bias during the preparation process, that concertation metrics are used for the quantification of SCF, and that multiple cores should be taken in each site and multiproxy analysis should be utilised.

Two Millennia of Complexity and Variability in a Perialpine Socioecological System (Savoie, France): The Contribution of Palynology and sedaDNA Analysis

Over the last two millennia, European Alpine ecosystems have experienced major changes in response to the important, yet fluctuating, impact of human activities. This study aims to reconstruct the environmental history of the last 1800 years on the western edge of the Alps by analyzing sediments from Lake Aiguebelette, a large lake located in the perialpine area. We have combined analyses of pollen and other palynomorphs, such as coprophilous fungal spores, together with sedimentary DNA (from plants and mammals) in order to reconstruct both vegetation and land-use histories. A sedimentological and geochemical analysis was also conducted in order to gain an understanding of changes in erosion dynamics in response to landscape modifications that were influenced by climate and human activities. This work highlights alternating phases of anthropization and agricultural abandonment allowing forest recovery. While pollen reflects the major phases of regional deforestation and afforestation related to the dynamic of farming activities, plant DNA provides precise information on the plants cultivated in fields, orchards and vegetable gardens over the past centuries. The combination of mammal DNA and coprophilous fungal spores completes this work by documenting the history of pastoral practices.

Century-Long Homogenization of Algal Communities Is Accelerated by Nutrient Enrichment and Climate Warming in Lakes and Reservoirs of the North Temperate Zone

Anthropogenic pressures can threaten lake and reservoir ecosystems, leading to harmful algal blooms that have become globally widespread. However, patterns of phytoplankton diversity change and community assembly over long-term scales remain unknown. Here, we explore biodiversity patterns in eukaryotic algal (EA) and cyanobacterial (CYA) communities over a century by sequencing DNA preserved in the sediment cores of seven lakes and reservoirs in the North Temperate Zone. Comparisons within lakes revealed temporal algal community homogenization in mesotrophic lakes, eutrophic lakes, and reservoirs over the last century but no systematic losses of α-diversity. Temporal homogenization of EA and CYA communities continued into the modern day probably due to time-lags related to historical legacies, even if lakes go through a eutrophication phase followed by a reoligotrophication phase. Further, algal community assembly in lakes and reservoirs was mediated by both deterministic and stochastic processes, while homogeneous selection played a relatively important role in recent decades due to intensified anthropogenic activities and climate warming. Overall, these results expand our understanding of global change effects on algal community diversity and succession in lakes and reservoirs that exhibit different successional trajectories while also providing a baseline framework to assess their potential responses to future environmental change.

Shifts in DNA yield and biological community composition in stored sediment: implications for paleogenomic studies

Lake sediments hold a wealth of information from past environments that is highly valuable for paleolimnological reconstructions. These studies increasingly apply modern molecular tools targeting sedimentary DNA (sedDNA). However, sediment core sampling can be logistically difficult, making immediate subsampling for sedDNA challenging. Sediment cores are often refrigerated (4 °C) for weeks or months before subsampling. We investigated the impact of storage time on changes in DNA (purified or as cell lysate) concentrations and shifts in biological communities following storage of lake surface sediment at 4 °C for up to 24 weeks. Sediment samples (~ 0.22 g, in triplicate per time point) were spiked with purified DNA (100 or 200 ng) or lysate from a brackish water cyanobacterium that produces the cyanotoxin nodularin or non-spiked. Samples were analysed every 1–4 weeks over a 24-week period. Droplet digital PCR showed no significant decrease in the target gene (nodularin synthetase – subunit F; ndaF) over the 24-week period for samples spiked with purified DNA, while copy number decreased by more than half in cell lysate-spiked samples. There was significant change over time in bacteria and eukaryotic community composition assessed using metabarcoding. Amongst bacteria, the cyanobacterial signal became negligible after 5 weeks while Proteobacteria increased. In the eukaryotic community, Cercozoa became dominant after 6 weeks. These data demonstrate that DNA yields and community composition data shift significantly when sediments are stored chilled for more than 5 weeks. This highlights the need for rapid subsampling and appropriate storage of sediment core samples for paleogenomic studies.

Do Invasive Mammal Eradications from Islands Support Climate Change Adaptation and Mitigation?

Climate change represents a planetary emergency that is exacerbating the loss of native biodiversity. In response, efforts promoting climate change adaptation strategies that improve ecosystem resilience and/or mitigate climate impacts are paramount. Invasive Alien Species are a key threat to islands globally, where strategies such as preventing establishment (biosecurity), and eradication, especially invasive mammals, have proven effective for reducing native biodiversity loss and can also advance ecosystem resilience and create refugia for native species at risk from climate change. Furthermore, there is growing evidence that successful eradications may also contribute to mitigating climate change. Given the cross-sector potential for eradications to reduce climate impacts alongside native biodiversity conservation, we sought to understand when conservation managers and funders explicitly sought to use or fund the eradication of invasive mammals from islands to achieve positive climate outcomes. To provide context, we first summarized available literature of the synergistic relationship between invasive species and climate change, including case studies where invasive mammal eradications served to meet climate adaptation or mitigation solutions. Second, we conducted a systematic review of the literature and eradication-related conference proceedings to identify when these synergistic effects of climate and invasive species were explicitly addressed through eradication practices. Third, we reviewed projects from four large funding entities known to support climate change solutions and/or native biodiversity conservation efforts and identified when eradications were funded in a climate change context. The combined results of our case study summary paired with systematic reviews found that, although eradicating invasive mammals from islands is an effective climate adaptation strategy, island eradications are poorly represented within the climate change adaptation and mitigation funding framework. We believe this is a lost opportunity and encourage eradication practitioners and funders of climate change adaptation to leverage this extremely effective nature-based tool into positive conservation and climate resilience solutions.

Integrating multi-taxon palaeogenomes and sedimentary ancient DNA to study past ecosystem dynamics

Ancient DNA (aDNA) has played a major role in our understanding of the past. Important advances in the sequencing and analysis of aDNA from a range of organisms have enabled a detailed understanding of processes such as past demography, introgression, domestication, adaptation and speciation. However, to date and with the notable exception of microbiomes and sediments, most aDNA studies have focused on single taxa or taxonomic groups, making the study of changes at the community level challenging. This is rather surprising because current sequencing and analytical approaches allow us to obtain and analyse aDNA from multiple source materials. When combined, these data can enable the simultaneous study of multiple taxa through space and time, and could thus provide a more comprehensive understanding of ecosystem-wide changes. It is therefore timely to develop an integrative approach to aDNA studies by combining data from multiple taxa and substrates. In this review, we discuss the various applications, associated challenges and future prospects of such an approach.

Lake microbial communities are not resistant or resilient to repeated large-scale natural pulse disturbances

Opportunities to study community level responses to extreme natural pulse disturbances in unaltered ecosystems are rare. Lake sediment records that span thousands of years can contain well resolved sediment pulses, triggered by earthquakes. These paleo-records provide a means to study repeated pulse disturbance and processes of resistance (insensitivity to disturbance) and ecological resilience (capacity to regain structure, function and process). In this study, sedimentary DNA was extracted from a sediment core from Lake Paringa (New Zealand) that is situated in a near natural catchment. Metabarcoding and inferred functions were used to assess the lake microbial community over the past 1,100 years - a period that included four major earthquakes. Microbial community composition and function differed significantly between highly perturbed (postseismic, c. 50 yrs) phases directly after the earthquakes and more stable (interseismic, c. 250 yr) phases, indicating a lack of community resistance. Although community structure differed significantly in successive postseismic phases, function did not, suggesting potential functional redundancy. Significant differences in composition and function in successive interseismic phases demonstrates communities are not resilient to large-scale natural pulse disturbances. The clear difference in structure and function, and high number of indicator taxa (responsible for driving differences in communities between phases) in the fourth interseismic phase likely represents a regime shift, possibly due to the two-fold increase in sediment and terrestrial biospheric organic carbon fluxes recorded following the fourth earthquake. Large pulse disturbances that enhance sediment inputs into lake systems may produce an underappreciated mechanism that destabilises lake ecosystem processes.

Seagrass (Halophila stipulacea) invasion enhances carbon sequestration in the Mediterranean Sea

The introduction and establishment of exotic species often result in significant changes in recipient communities and their associated ecosystem services. However, usually the magnitude and direction of the changes are difficult to quantify because there is no pre-introduction data. Specifically, little is known about the effect of marine exotic macrophytes on organic carbon sequestration and storage. Here, we combine dating sediment cores (²¹⁰ Pb) with sediment eDNA fingerprinting to reconstruct the chronology of pre- and post-arrival of the Red Sea seagrass Halophila stipulacea spreading into the Eastern Mediterranean native seagrass meadows. We then compare sediment organic carbon storage and burial rates before and after the arrival of H. stipulacea and between exotic (H. stipulacea) and native (C. nodosa and P. oceanica) meadows since the time of arrival following a Before-After-Control-Impact (BACI) approach. This analysis revealed that H. stipulacea arrived at the areas of study in Limassol (Cyprus) and West Crete (Greece) in the 1930s and 1970s, respectively. Average sediment organic carbon after the arrival of H. stipulacea to the sites increased in the exotic meadows twofold, from 8.4 ± 2.5 g C_org  m^-2  year^-1 to 14.7 ± 3.6 g C_org  m^-2  year^-1 , and, since then, burial rates in the exotic seagrass meadows were higher than in native ones of Cymodocea nodosa and Posidonia oceanica. Carbon isotopic data indicated a 50% increase of the seagrass contribution to the total sediment C_org pool since the arrival of H. stipulacea. Our results demonstrate that the invasion of H. stipulacea may play an important role in maintaining the blue carbon sink capacity in the future warmer Mediterranean Sea, by developing new carbon sinks in bare sediments and colonizing areas previously occupied by the colder thermal affinity P. oceanica.

Towards the Optimization of eDNA/eRNA Sampling Technologies for Marine Biosecurity Surveillance

The field of eDNA is growing exponentially in response to the need for detecting rare and invasive species for management and conservation decisions. Developing technologies and standard protocols within the biosecurity sector must address myriad challenges associated with marine environments, including salinity, temperature, advective and deposition processes, hydrochemistry and pH, and contaminating agents. These approaches must also provide a robust framework that meets the need for biosecurity management decisions regarding threats to human health, environmental resources, and economic interests, especially in areas with limited clean-laboratory resources and experienced personnel. This contribution aims to facilitate dialogue and innovation within this sector by reviewing current approaches for sample collection, post-sampling capture and concentration of eDNA, preservation, and extraction, all through a biosecurity monitoring lens.

Sedimentary Ancient DNA (sedaDNA) Reveals Fungal Diversity and Environmental Drivers of Community Changes throughout the Holocene in the Present Boreal Lake Lielais Svētiņu (Eastern Latvia)

Fungi are ecologically important in several ecosystem processes, yet their community composition, ecophysiological roles, and responses to changing environmental factors in historical sediments are rarely studied. Here we explored ancient fungal DNA from lake Lielais Svētiņu sediment throughout the Holocene (10.5 kyr) using the ITS metabarcoding approach. Our data revealed diverse fungal taxa and smooth community changes during most of the Holocene with rapid changes occurring in the last few millennia. More precisely, plankton parasitic fungi became more diverse from the Late Holocene (2–4 kyr) which could be related to a shift towards a cooler climate. The Latest Holocene (~2 kyr) showed a distinct increase in the richness of plankton parasites, mycorrhizal, and plant pathogenic fungi which can be associated with an increased transfer rate of plant material into the lake and blooms of planktonic organisms influenced by increased, yet moderate, human impact. Thus, major community shifts in plankton parasites and mycorrhizal fungi could be utilized as potential paleo-variables that accompany host-substrate dynamics. Our work demonstrates that fungal aDNA with predicted ecophysiology and host specificity can be employed to reconstruct both aquatic and surrounding terrestrial ecosystems and to estimate the influence of environmental change.

Lake Sedimentary DNA Research on Past Terrestrial and Aquatic Biodiversity: Overview and Recommendations

The use of lake sedimentary DNA to track the long-term changes in both terrestrial and aquatic biota is a rapidly advancing field in paleoecological research. Although largely applied nowadays, knowledge gaps remain in this field and there is therefore still research to be conducted to ensure the reliability of the sedimentary DNA signal. Building on the most recent literature and seven original case studies, we synthesize the state-of-the-art analytical procedures for effective sampling, extraction, amplification, quantification and/or generation of DNA inventories from sedimentary ancient DNA (sedaDNA) via high-throughput sequencing technologies. We provide recommendations based on current knowledge and best practises.

Sedimentary DNA record of eukaryotic algal and cyanobacterial communities in a shallow Lake driven by human activities and climate change

Global freshwater lakes are changing due to human activities and climate change. Unfortunately, sufficient long-term monitoring is lacking for most lakes. However, lake sedimentary archives can extend the instrumental record and reveal historical environmental trends. In particular, sedimentary DNA analysis of lacustrine sediment cores can aid the reconstruction of past trends in eukaryotic algal and cyanobacterial communities, as was conducted in this study for Lake Chaohu in China. The results presented here indicate that the construction of the Chaohu Dam in 1963 is associated with decreased richness of eukaryotic algal and cyanobacterial communities. Several groups, including the eukaryotic algal taxa, Chlorophyceae, and cyanobacterial groups like Dolichospermum, Microcystis, Planktothricoides, Cyanobium, Pseudanabaena, and Synechococcus, increased in abundance following inferred historical nutrient enrichment. Nutrient concentrations and hydrologic conditions were further implicated as the dominant controls on communities based on Random Forest and generalized additive modeling statistical analyses. In particular, significant increases in lake hydraulic residence times after the construction of the Chaohu Dam were significantly associated with altered biological community structures. Further, phosphorus enrichment was positively associated with increased richness and diversity of these communities following the 1980s. In addition, effects from increased atmospheric temperatures on eukaryotic algal and cyanobacterial communities were apparent. Here, high-throughput sequencing analysis of sedimentary DNA allowed the inference of long-term biodiversity dynamics of Lake Chaohu. These results underscore the important impacts of anthropogenic activities and climate change on aquatic ecosystems at the decadal scale.

Status and prospects of marine NIS detection and monitoring through (e)DNA metabarcoding

In coastal ecosystems, non-indigenous species (NIS) are recognized as a major threat to biodiversity, ecosystem functioning and socio-economic activities. Here we present a systematic review on the use of metabarcoding for NIS surveillance in marine and coastal ecosystems, through the analysis of 42 publications. Metabarcoding has been mainly applied to environmental DNA (eDNA) from water samples, but also to DNA extracted from bulk organismal samples. DNA extraction kits have been widely used and the 18S rRNA and the COI genes the most employed markers, but less than half of the studies targeted more than one marker loci. The Illumina MiSeq platform has been used in >50% of the publications. Current weaknesses include potential occurrence of false negatives due to the primer-biased or faulty DNA amplification and the incompleteness of reference libraries. This is particularly concerning in the case of NIS surveillance, where proficiency in species level detection is critical. Until these weaknesses are resolved, ideally NIS metabarcoding should be supported by complementary approaches, such as morphological analysis or more targeted molecular approaches (e.g. qPCR, ddPCR). Even so, metabarcoding has already proved to be a highly sensitive tool to detect small organisms or undifferentiated life stages across a wide taxonomic range. In addition, it also seems to be very effective in ballast water management and to improve the spatial and temporal sampling frequency of NIS surveillance in marine and coastal ecosystems. Although specific protocols may be required for species-specific NIS detection, for general monitoring it would be vital to settle on a standard protocol able to generate comparable results among surveillance campaigns and regions of the globe, seeking the best approach for detecting the broadest range of species, while minimizing the chances of a false positive or negative detection.

Warming favors subtropical lake cyanobacterial biomass increasing

Subtropical lakes are increasingly subject to cyanobacterial blooms resulting from climate change and anthropogenic activities, but the lack of long-term historical data limits understanding of how climate changes have affected cyanobacterial growth in deep subtropical lakes. Using high-resolution DNA data derived from a sediment core from a deep lake in southwestern China, together with analysis of other sedimentary hydroclimatic proxies, we investigated cyanobacterial biomass and microbial biodiversity in relation to climate changes during the last millennium. Our results show that both cyanobacterial abundance and microbial biodiversity were higher during warmer periods, including the Medieval Warm Period (930-1350 CE) and the Current Warm Period (1900 CE-present), but lower during cold periods, including the Little Ice Age (1400-1850 CE). The significant increases in cyanobacterial abundance and microbial biodiversity during warmer intervals are probably because warm climate not only favors cyanobacterial growth but also concentrates lake water nutrients through water budgets between evaporation and precipitation. Furthermore, because rising temperatures result in greater vertical stratification in deep lakes, cyanobacteria may have exploited these stratified conditions and accumulated in dense surface blooms. We anticipate that under anthropogenic warming conditions, cyanobacterial biomass may continue to increase in subtropical deep lakes.

Leveraging eDNA to expand the study of hybrid zones

Hybrid zones are important windows into ecological and evolutionary processes. Our understanding of the significance and prevalence of hybridization in nature has expanded with the generation and analysis of genome‐spanning data sets. That said, most hybridization research still has restricted temporal and spatial resolution, which limits our ability to draw broad conclusions about evolutionary and conservation related outcomes. Here, we argue that rapidly advancing environmental DNA (eDNA) methodology could be adopted for studies of hybrid zones to increase temporal sampling (contemporary and historical), refine and geographically expand sampling density, and collect data for taxa that are difficult to directly sample. Genomic data in the environment offer the potential for near real‐time biological tracking of hybrid zones, and eDNA provides broad, but as yet untapped, potential to address eco‐evolutionary questions.

Persistence of environmental DNA in cultivated soils: implication of this memory effect for reconstructing the dynamics of land use and cover changes

eDNA refers to DNA extracted from an environmental sample with the goal of identifying the occurrence of past or current biological communities in aquatic and terrestrial environments. However, there is currently a lack of knowledge regarding the soil memory effect and its potential impact on lake sediment eDNA records. To investigate this issue, two contrasted sites located in cultivated environments in France were studied. In the first site, soil samples were collected (n = 30) in plots for which the crop rotation history was documented since 1975. In the second site, samples were collected (n = 40) to compare the abundance of currently observed taxa versus detected taxa in cropland and other land uses. The results showed that the last cultivated crop was detected in 100% of the samples as the most abundant. In addition, weeds were the most abundant taxa identified in both sites. Overall, these results illustrate the potential of eDNA analyses for identifying the recent (< 10 years) land cover history of soils and outline the detection of different taxa in cultivated plots. The capacity of detection of plant species grown on soils delivering sediments to lacustrine systems is promising to improve our understanding of sediment transfer processes over short timescales.

Human access impacts biodiversity of microscopic animals in sandy beaches

Whereas most work to understand impacts of humans on biodiversity on coastal areas has focused on large, conspicuous organisms, we highlight effects of tourist access on the diversity of microscopic marine animals (meiofauna). We used a DNA metabarcoding approach with an iterative and phylogeny-based approach for the taxonomic assignment of meiofauna and relate diversity patterns to the numbers of tourists accessing sandy beaches on an otherwise un-impacted island National Park. Tourist frequentation, independently of differences in sediment granulometry, beach length, and other potential confounding factors, affected meiofaunal diversity in the shallow “swash” zone right at the mean water mark; the impacts declined with water depth (up to 2 m). The indicated negative effect on meiofauna may have a consequence on all the biota including the higher trophic levels. Thus, we claim that it is important to consider restricting access to beaches in touristic areas, in order to preserve biodiversity.

Martínez et al. use DNA metabarcoding and a phylogeny-based approach to demonstrate the effects of tourist access on meiofauna diversity of beaches in Asinara National Park. Their results show that tourist frequentation decreases meiofaunal diversity at the shallow “swash” zone, and can be used to inform tourist access and management of beaches.

From metabarcoding to metaphylogeography: separating the wheat from the chaff

Metabarcoding is by now a well-established method for biodiversity assessment in terrestrial, freshwater, and marine environments. Metabarcoding data sets are usually used for α- and β-diversity estimates, that is, interspecies (or inter-MOTU [molecular operational taxonomic unit]) patterns. However, the use of hypervariable metabarcoding markers may provide an enormous amount of intraspecies (intra-MOTU) information-mostly untapped so far. The use of cytochrome oxidase (COI) amplicons is gaining momentum in metabarcoding studies targeting eukaryote richness. COI has been for a long time the marker of choice in population genetics and phylogeographic studies. Therefore, COI metabarcoding data sets may be used to study intraspecies patterns and phylogeographic features for hundreds of species simultaneously, opening a new field that we suggest to name metaphylogeography. The main challenge for the implementation of this approach is the separation of erroneous sequences from true intra-MOTU variation. Here, we develop a cleaning protocol based on changes in entropy of the different codon positions of the COI sequence, together with co-occurrence patterns of sequences. Using a data set of community DNA from several benthic littoral communities in the Mediterranean and Atlantic seas, we first tested by simulation on a subset of sequences a two-step cleaning approach consisting of a denoising step followed by a minimal abundance filtering. The procedure was then applied to the whole data set. We obtained a total of 563 MOTUs that were usable for phylogeographic inference. We used semiquantitative rank data instead of read abundances to perform AMOVAs and haplotype networks. Genetic variability was mainly concentrated within samples, but with an important between seas component as well. There were intergroup differences in the amount of variability between and within communities in each sea. For two species, the results could be compared with traditional Sanger sequence data available for the same zones, giving similar patterns. Our study shows that metabarcoding data can be used to infer intra- and interpopulation genetic variability of many species at a time, providing a new method with great potential for basic biogeography, connectivity and dispersal studies, and for the more applied fields of conservation genetics, invasion genetics, and design of protected areas.

Quaternary DNA: A Multidisciplinary Research Field

The purpose of this Milankovitch review is to explain the significance of Quaternary DNA studies and the importance of the recent methodological advances that have enabled the study of late Quaternary remains in more detail, and the testing of new assumptions in evolutionary biology and phylogeography to reconstruct the past. The topic is wide, and this review is not intended to be an exhaustive account of all the aDNA work performed in the last three decades on late-Quaternary remains. Instead, it is a selection of relevant studies aimed at illustrating how aDNA has been used to reconstruct not only environments of the past, but also the history of many species including our own.

New insights on lake sediment DNA from the catchment: importance of taphonomic and analytical issues on the record quality

Over the last decade, an increasing number of studies have used lake sediment DNA to trace past landscape changes, agricultural activities or human presence. However, the processes responsible for lake sediment formation and sediment properties might affect DNA records via taphonomic and analytical processes. It is crucial to understand these processes to ensure reliable interpretations for “palaeo” studies. Here, we combined plant and mammal DNA metabarcoding analyses with sedimentological and geochemical analyses from three lake-catchment systems that are characterised by different erosion dynamics. The new insights derived from this approach elucidate and assess issues relating to DNA sources and transfer processes. The sources of eroded materials strongly affect the “catchment-DNA” concentration in the sediments. For instance, erosion of upper organic and organo-mineral soil horizons provides a higher amount of plant DNA in lake sediments than deep horizons, bare soils or glacial flours. Moreover, high erosion rates, along with a well-developed hydrographic network, are proposed as factors positively affecting the representation of the catchment flora. The development of open and agricultural landscapes, which favour the erosion, could thus bias the reconstructed landscape trajectory but help the record of these human activities. Regarding domestic animals, pastoral practices and animal behaviour might affect their DNA record because they control the type of source of DNA (“point” vs. “diffuse”).

Detection of introduced and resident marine species using environmental DNA metabarcoding of sediment and water

Environmental DNA (eDNA) surveys are increasingly being used for biodiversity monitoring, principally because they are sensitive and can provide high resolution community composition data. Despite considerable progress in recent years, eDNA studies examining how different environmental sample types can affect species detectability remain rare. Comparisons of environmental samples are especially important for providing best practice guidance on early detection and subsequent mitigation of non-indigenous species. Here we used eDNA metabarcoding of COI (cytochrome c oxidase subunit I) and 18S (nuclear small subunit ribosomal DNA) genes to compare community composition between sediment and water samples in artificial coastal sites across the United Kingdom. We first detected markedly different communities and a consistently greater number of distinct operational taxonomic units in sediment compared to water. We then compared our eDNA datasets with previously published rapid assessment biodiversity surveys and found excellent concordance among the different survey techniques. Finally, our eDNA surveys detected many non-indigenous species, including several newly introduced species, highlighting the utility of eDNA metabarcoding for both early detection and temporal / spatial monitoring of non-indigenous species. We conclude that careful consideration on environmental sample type is needed when conducting eDNA surveys, especially for studies assessing community change.

Environmental DNA provides information on sediment sources: A study in catchments affected by Fukushima radioactive fallout

An excessive supply of sediment is observed in numerous rivers across the world where it leads to deleterious impacts. Information on the sources delivering this material to waterbodies is required to design effective management measures, and sediment tracing or fingerprinting techniques are increasingly used to quantify the amount of sediment derived from different sources. However, the current methods used to identify the land use contributions to sediment have a limited discrimination power. Here, we investigated the potential of environmental DNA (eDNA) to provide more detailed information on the plant species found in sediment source areas as a next generation fingerprint. To this end, flood sediment deposits (n = 12) were collected in 2017 in two catchments impacted by the Fukushima radioactive fallout along differing river sections draining forests, cropland or a mix of both land uses. Conventional fingerprints (i.e. fallout radionuclides and organic matter properties) were also measured in these samples. The conventional fingerprint model results showed that most sediment samples contained a dominant proportion of subsoil material. Nevertheless, the eDNA information effectively discriminated the three above-mentioned groups of sediment, with the dominance of tree, shrub and fern species in sediment sampled in rivers draining forests versus a majority of grass, algae and cultivated plant species in sediment collected in rivers draining cropland. Based on these encouraging results, future research should examine the potential of eDNA in mixed land use catchments where the contribution of topsoil to sediment dominates and where the cultivation of land has not been abandoned in order to better characterize the memory effect of eDNA in soils and sediment.