When are environmental DNA early detections of invasive species actionable?

Environmental DNA (eDNA) sampling provides sensitive early detection capabilities for recently introduced taxa. However, natural resource managers struggle with how to integrate eDNA results into an early detection rapid response program because positive eDNA detections are not always indicative of an eventual infestation. We used a structured decision making (SDM) framework to evaluate appropriate response actions to hypothetical eDNA early detections of an introduced aquatic plant in Sebago Lake (Maine, USA). The results were juxtaposed to a recent study that used a similar SDM approach to evaluate response actions to hypothetical eDNA early detections of introduced mussels in Jordanelle Reservoir (Utah, USA). We found that eDNA early detections were not actionable in Sebago Lake because the plant's invasion potential was spatially constrained and the current management activities provided acceptable levels of mitigation. In Jordanelle Reservoir, eDNA detections were actionable due to high invasion potential and analyses supported management actions to contain the invasion. The divergent outcomes of the two case studies are related to the unique attributes of the habitats and species, highlighting the utility of the SDM approach when considering an eDNA monitoring program. We use these two case studies to present a general SDM framework and a set of heuristics that can be efficiently applied to eDNA early detection rapid response scenarios and other instances associated with indeterminant eDNA detections, especially when there is an imperative to make decisions as quickly as possible.

A framework to integrate innovations in invasion science for proactive management.

Invasive alien species (IAS) are a rising threat to biodiversity, national security, and regional economies, with impacts in the hundreds of billions of U.S. dollars annually. Proactive or predictive approaches guided by scientific knowledge are essential to keeping pace with growing impacts of invasions under climate change. Although the rapid development of diverse technologies and approaches has produced tools with the potential to greatly accelerate invasion research and management, innovation has far outpaced implementation and coordination. Technological and methodological syntheses are urgently needed to close the growing implementation gap and facilitate interdisciplinary collaboration and synergy among evolving disciplines. A broad review is necessary to demonstrate the utility and relevance of work in diverse fields to generate actionable science for the ongoing invasion crisis. Here, we review such advances in relevant fields including remote sensing, epidemiology, big data analytics, environmental DNA (eDNA) sampling, genomics, and others, and present a generalized framework for distilling existing and emerging data into products for proactive IAS research and management. This integrated workflow provides a pathway for scientists and practitioners in diverse disciplines to contribute to applied invasion biology in a coordinated, synergistic, and scalable manner.

Trends in nonindigenous aquatic species richness in the United States reveal shifting spatial and temporal patterns of species introductions.

Understanding the spatial and temporal dynamics underlying the introduction and spread of nonindigenous aquatic species (NAS) can provide important insights into the historical drivers of biological invasions and aid in forecasting future patterns of nonindigenous species arrival and spread. Increasingly, public databases of species observation records are being used to quantify changes in NAS distributions across space and time, and are becoming an important resource for researchers, managers, and policy-makers. Here we use publicly available data to describe trends in NAS introduction and spread across the conterminous United States over more than two centuries of observation records. Available data on first records of NAS reveal significant shifts in dominance of particular introduction patterns over time, both in terms of recipient regions and likely sources. These spatiotemporal trends at the continental scale may be subject to biases associated with regional variation in sampling effort, reporting, and data curation. We therefore also examined two additional metrics, the number of individual records and the spatial coverage of those records, which are likely to be more closely associated with sampling effort. Our results suggest that broad-scale patterns may mask considerable variation across regions, time periods, and even entities contributing to NAS sampling. In some cases, observed temporal shifts in species discovery may be influenced by dramatic fluctuations in the number and spatial extent of individual observations, reflecting the possibility that shifts in sampling effort may obscure underlying rates of NAS introduction.

Escape from the Ponto-Caspian: evolution and biogeography of an endemic goby species flock (Benthophilinae: Gobiidae: Teleostei).

Endemic Ponto-Caspian gobies include a flock of 24 "neogobiin" species (containing the nominal genera and subgenera Apollonia, Babka, Neogobius, Mesogobius, Ponticola, and Proterorhinus; Teleostei: Gobiidae), of which a large proportion (5 species; 21%) recently escaped to invade other freshwater Eurasian systems and the North American Great Lakes. We provide its first comprehensive phylogenetic and biogeographic analysis based on 4709 bp sequences from two mitochondrial and two nuclear genes with maximum parsimony, likelihood, and Bayesian approaches. We additionally compare its relationships with the tadpole gobies (Benthophilus and Caspiosoma), which comprise a related endemic Ponto-Caspian gobiid group; along with a variety of postulated relatives and outgroups. Results of all phylogenetic approaches are highly congruent and provide very strong support for recognizing the subfamily Benthophilinae; which encompasses both the "neogobiins" and tadpole gobies, and genetically diverges from other Gobiidae subfamilies-including (non-monophyletic) Gobiinae and Gobinellinae. Benthophilinae contains three tribes: Neogobiini (Neogobius, which is synonymized here with Apollonia; containing the type species N. fluviatilis, along with N. melanostomus and N. caspius), Ponticolini (containing the genera Mesogobius, Proterorhinus, Babka, and Ponticola-elevating the latter two from subgenera and removing them from the formerly paraphyletic Neogobius), and Benthophilini (tadpole gobies). Within Ponticolini, Proterorhinus and Mesogobius comprise the sister clade of the Ponticola and Babka clade. Further work is needed to clarify the interrelationships of the tadpole gobies. Invasiveness is widespread in freshwater and euryhaline taxa of Neogobius, Proterorhinus, Babka, and Ponticola; but not in marine species, Mesogobius, or tadpole gobies.

Microsatellite loci for Ponto-Caspian gobies: markers for assessing exotic invasions.

We developed and tested eight polymorphic microsatellite loci for Ponto-Caspian 'neogobiin' gobies, many of which are invasive in Eurasia and North America, whose study will aid understanding of the population genetics underlying their success. We tested samples from one to two locations from 12 taxa in the recently revised genera Babka, Benthophilus, Mesogobius, Neogobius = Apollonia, Ponticola and Proterorhinus; including the bighead, Caspian, knout, monkey, racer, round, tadpole and tubenose gobies; and taxa from introduced vs. native populations, those diverging between fresh and marine waters, and those differentiated between the Black and Caspian Seas. Populations conformed to Hardy-Weinberg equilibrium expectations, averaging five to 15 alleles per locus and 0.11 to 0.67 mean heterozygosity. Allelic variation significantly differentiated among all taxa and populations.

Genetic diversity of invasive species in the Great Lakes versus their Eurasian source populations: insights for risk analysis.

Combining DNA variation data and risk assessment procedures offers important diagnostic and monitoring tools for evaluating the relative success of exotic species invasions. Risk assessment may allow us to understand how the numbers of founding individuals, genetic variants, population sources, and introduction events affect successful establishment and spread. This is particularly important in habitats that are "hotbeds" for invasive species--such as the North American Great Lakes. This study compares genetic variability and its application to risk assessment within and among three Eurasian groups and five species that successfully invaded the Great Lakes during the mid 1980s through early 1990s; including zebra and quagga mussels, round and tubenose gobies, and the ruffe. DNA sequences are compared from exotic and native populations in order to evaluate the role of genetic diversity in invasions. Close relatives are also examined, since they often invade in concert and several are saline tolerant and are likely to spread to North American estuaries. Results show that very high genetic diversity characterizes the invasions of all five species, indicating that they were founded by very large numbers of propagules and underwent no founder effects. Genetic evidence points to multiple invasion sources for both dreissenid and goby species, which appears related to especially rapid spread and widespread colonization success in a variety of habitats. In contrast, results show that the ruffe population in the Great Lakes originated from a single founding population source from the Elbe River drainage. Both the Great Lakes and the Elbe River populations of ruffe have similar genetic diversity levels--showing no founder effect, as in the other invasive species. In conclusion, high genetic variability, large numbers of founders, and multiple founding sources likely significantly contribute to the risk of an exotic species introduction's success and persistence.