Global Invader Research Articles

Cutting a Gordian knot of tubeworms with DNA data: the story of the Hydroides operculata-complex (Annelida, Serpulidae)

Hydroides operculata (Treadwell, 1929) was originally very briefly described from a single specimen as Eupomatus operculata, collected in the Gulf of Aden, Somalia. Later the species was reported from the Mediterranean as a potential Lessepsian migrant. The taxa Hydroides inornata Pillai (1960) from Sri Lanka, as well as H. basispinosa and H. gradata described by Straughan (1967) from Australia, were synonymised with H. operculata based only on their similar opercular morphology, making the latter species’ distribution to include South and East Africa, India, Pakistan, Sri Lanka, Hong Kong, tropical Australia, and the eastern Mediterranean. Here we examined the taxonomic status of H. operculata using standard molecular techniques to determine whether this species is a global invader, a complex of regionally distributed morphologically similar species, or a combination of both. The study revealed three well supported clades suggesting a natural phylogeographic pattern. Thus, we argue that the taxa H. inornata (India and Hong Kong) and H. basispinosa (Australia) should be re-instated to full species, but that the Australian H. gradata should be synonymised with H. basispinosa.

Elevated seasonal temperatures eliminate thermal barriers of reproduction of a dominant invasive species: A community state change for northern communities?

AbstractAimCouple field and modelling studies to evaluate the effects of rising water temperature on reproduction of a dominant marine species and how temperature induced changes in a species' phenology may affect fouling communities that occur along a temperature gradient.LocationNorth western Atlantic.MethodsWe examined the interaction between maximum and seasonal elevations in seawater temperature and reproductive phenology of a global invader to forecast the effect of climate warming on traits associated with the spread and establishment (i.e., growth and reproduction) of an invasive species. We then coupled these data with a study of early succession along a temperature gradient to forecast invasion success in species assemblages across a range of latitudes.ResultsElevated seasonal temperature will lead to greater asexual reproduction and to multi‐annual sexual reproduction in areas that currently have bi‐annual or annual reproduction. The output from our model combined with our field studies of early succession in communities suggest that in colder environments, communities may be more affected by climate‐induced shifts in reproductive phenology as they have more free space at the beginning of the growing season and fewer competitively superior species.Main conclusionsPredicted elevated water temperature will eliminate the thermal barriers that limit reproductive success of a cosmopolitan invasive species. Increased reproduction combined with limited biological resistance in regions with cooler water temperatures may lead to a community state change.

Heat and hypoxia give a global invader, Gambusia holbrooki, the edge over a threatened endemic fish on Australian floodplains

Deciphering the mechanisms by which climate change interacts with invasive species to affect biodiversity is a major challenge of global change biology. We conducted experiments to determine whether the global invader, Gambusia holbrooki, was more resistant to high water temperature (heat) and low dissolved oxygen (hypoxia) than a threatened native fish, Nannoperca australis. Metabolic experiments conducted at 25 and 29 °C showed that G. holbrooki had at least four times the capacity for metabolic depression during hypoxia than N. australis. An increase in environmental temperature from 25 to 29 °C had no significant impact on the critical oxygen tension, P crit, of G. holbrooki, but significantly and strongly increased P crit of N. australis. Gambusia holbrooki also had a lower Q 10 of standard metabolic rate than N. australis. Our results indicate that G. holbrooki have physiological traits conferring greater resistance to hypoxia than N. australis, and as temperature increases, the resistance of N. australis to hypoxia was more eroded than that of G. holbrooki. Intensive monitoring of the temperature and dissolved oxygen dynamics of wetlands showed that contemporary heat waves are already causing conditions that might give G. holbrooki the edge over N. australis on Australian floodplains. Our study adds weight to recent anecdotal reports of drought and heat waves causing localised extinction of N. australis, but the proliferation of G. holbrooki.

Reconstructing the introduction history of an invasive fish predator in South Africa

The Largemouth Bass (Micropterus salmoides) is a global invader with demonstrated ecological impacts on native fish communities. Introductions of fishes in freshwater ecosystems are often characterized as complex processes, yet an understanding of the nature of the introduction can inform management and conservation actions. Early in the twentieth century, two introductions of Largemouth Bass were made into South Africa for the establishment of a recreational fishery, and subsequent translocations have expanded their distribution to include much of southern Africa. In this study we quantified neutral genetic variation, modeled potential introduction scenarios, and identified potential source regions from within the native range. We documented limited levels of genetic diversity in nuclear microsatellite genotypes across populations (mean allelic richness = 1.80 and mean observed heterozygosity = 0.16) and observed low levels of genetic differentiation among four of the five focal populations (mean pairwise fixation index = 0.09), with a fifth population displaying greater levels of genetic divergence (mean pairwise fixation index = 0.27). A total of three cytochrome b haplotypes were recovered from South Africa samples and the single most common haplotype (93% of individuals) was identical to a haplotype from a population of Largemouth Bass in Maryland, USA. Using limited available stocking data along with outputs from Principal Component Analysis and approximate Bayesian evaluation of competing introduction scenarios we confirm the presence of multiple introductions. Despite evidence for multiple introductions, Largemouth Bass in South African water bodies harbor extremely low neutral genetic diversity, suggesting that even a very limited number of propagules can experience a high likelihood of success in invading nonnative waters.

Cooperation induces other cooperation: Fruiting bodies promote the evolution of macrocysts in Dictyostelium discoideum

Biological studies of the evolution of cooperation are challenging because this process is vulnerable to cheating. Many mechanisms, including kin discrimination, spatial structure, or by-products of self-interested behaviors, can explain this evolution. Here we propose that the evolution of cooperation can be induced by other cooperation. To test this idea, we used a model organism Dictyostelium discoideum because it exhibits two cooperative dormant phases, the fruiting body and the macrocyst. In both phases, the same chemoattractant, cyclic AMP (cAMP), is used to collect cells. This common feature led us to hypothesize that the evolution of macrocyst formation would be induced by coexistence with fruiting bodies. Before forming a mathematical model, we confirmed that macrocysts coexisted with fruiting bodies, at least under laboratory conditions. Next, we analyzed our evolutionary game theory-based model to investigate whether coexistence with fruiting bodies would stabilize macrocyst formation. The model suggests that macrocyst formation represents an evolutionarily stable strategy and a global invader strategy under this coexistence, but is unstable if the model ignores the fruiting body formation. This result indicates that the evolution of macrocyst formation and maintenance is attributable to coexistence with fruiting bodies. Therefore, macrocyst evolution can be considered as an example of evolution of cooperation induced by other cooperation.

Canopy hydrometeorological dynamics across a chronosequence of a globally invasive species, Ailanthus altissima (Mill., tree of heaven)

Many mechanisms aid invasive plants’ competitive interactions. Yet, the extent to which invasive plants alter canopy hydrometeorological mechanisms determining the quantity and distribution of rainwater resources to soils have never been assessed. We examine these mechanisms for a global invader, Ailanthus altissima, across an invasion chronosequence (stands aged 20, 30, 40 years) for 99 storms, each with ∼200 net rainfall observations. With age woody area index, ratio of wet canopy evaporation and rainfall rates, and stem drainage coefficient increased; while leaf area index, canopy water storage, and gap fraction declined. This corresponded to increased stemflow and decreased throughfall across annual, seasonal, and interstorm scales. Promotion of stemflow may be advantageous to the invasive species as it increases water supply to roots and may help distribute allelopathic chemicals through the soil. Further research is needed on relationships between canopy hydrometeorological changes during invasion and redistribution of water to soils.

Understanding and forecasting dispersal of non-indigenous marine decapods (Crustacea: Decapoda) in East European and North Asian waters

A survey of publications and collections databases reveals a pattern of non-indigenous decapods distribution in the 13 seas around Russia and adjacent countries. No alien species were reported from Russian territorial waters and exclusive economic zone in the Japan, Okhotsk, west Bering and most of the Siberian shelf Seas. From the seas and their basins in East Europe, 13 alien species have been recorded, with seven of these yet to become established. Established or commonly occurring species can be categorized as: ‘global invaders’ (Chinese mitten crab,Eriocheir sinensisin the White, Baltic, Black, Azov and Caspian Seas; and Harris mud crab,Rhithropanopeus harrisiiin all mentioned seas, except the White Sea); ‘regional aliens’ (Palaemon adspersusandP. elegansin the Caspian Sea and the latter species in the Baltic); and ‘Arctic invaders’ (Kamchatka king crabParalithodes camtschaticusand snow crabChionoecetes opilio).Eriocheir sinensisis the most widely occurring alien decapod species, but there are no indications of an established population in East Europe. For this and other mentioned crab species, invasion history, distribution and important biological data are reviewed. In the seas where few or no native crab species have been present, Harris mud crab (in the Azov and Caspian Seas), Kamchatka crab (in the Barents Sea) and snow crab (in the Barents and Kara Seas) have shown rapid establishment (within two decades) of an invasive population throughout an entire basis or its significant part.

Unexpected survival of sharptooth catfish Clarias gariepinus (Burchell 1822) during acute rotenone toxicity trials will complicate management of invasions

The sharptooth catfish Clarias gariepinus is an emerging global invader for which control strategies might include the use of piscicides such as rotenone. Experimental exposure demonstrated that C. gariepinus was less susceptible to rotenone than most other fish species, with unexpected survival observed at rotenone concentrations of 87.5 and 100 µg L−1. C. gariepinus were also observed exhibiting avoidance behaviour to rotenone treated water and were found to be capable of recovering from rotenone exposure. As such, effective eradication might not be attainable even at a dose exceeding 100 µg L−1 with exposures of longer than 24 h. This exposure scenario may pose an unacceptable risk to non-target fauna and highlights the difficulty associated with managing current and future invasions.

Genetic evidence for a worldwide chaotic dispersion pattern of the arbovirus vector, Aedes albopictus.

BackgroundInvasive species represent a global concern for their rapid spread and the possibility of infectious disease transmission. This is the case of the global invader Aedes albopictus, the Asian tiger mosquito. This species is a vector of medically important arboviruses, notably chikungunya (CHIKV), dengue (DENV) and Zika (ZIKV). The reconstruction of the complex colonization pattern of this mosquito has great potential for mitigating its spread and, consequently, disease risks.Methodology/Principal findingsClassical population genetics analyses and Approximate Bayesian Computation (ABC) approaches were combined to disentangle the demographic history of Aedes albopictus populations from representative countries in the Southeast Asian native range and in the recent and more recently colonized areas. In Southeast Asia, the low differentiation and the high co-ancestry values identified among China, Thailand and Japan indicate that, in the native range, these populations maintain high genetic connectivity, revealing their ancestral common origin. China appears to be the oldest population. Outside Southeast Asia, the invasion process in La Réunion, America and the Mediterranean Basin is primarily supported by a chaotic propagule distribution, which cooperates in maintaining a relatively high genetic diversity within the adventive populations.Conclusions/SignificanceFrom our data, it appears that independent and also trans-continental introductions of Ae. albopictus may have facilitated the rapid establishment of adventive populations through admixture of unrelated genomes. As a consequence, a great amount of intra-population variability has been detected, and it is likely that this variability may extend to the genetic mechanisms controlling vector competence. Thus, in the context of the invasion process of this mosquito, it is possible that both population ancestry and admixture contribute to create the conditions for the efficient transmission of arboviruses and for outbreak establishment.

A global invader or a complex of regionally distributed species? Clarifying the status of an invasive calcareous tubeworm Hydroides dianthus (Verrill, 1873) (Polychaeta: Serpulidae) using DNA barcoding

Clarifying taxonomic status is essential to understanding invasion source and the spread of invasive species. Here we used barcoding gene cytochrome c oxidase subunit I to explore the issue in a common fouling invasive species Hydroides dianthus. The species was originally described from off New England, USA, reported along the east coast of North America down to Florida and the Caribbean region, introduced to China, Europe, Japan and West Africa via anthropogenic transport and is now collected in Brazil for the first time. Unlike most congeners, H. dianthus has tolerance for a wide temperature range, being distributed from temperate to subtropical waters. Our results based on 112 specimens collected from 17 localities worldwide confirmed that H. dianthus sensu stricto is indeed a global invader. Observed higher haplotypes diversity in the Mediterranean seems to contradict the currently accepted native range of H. dianthus sensu stricto in the USA. The study also revealed the existence of a potential cryptic species H. cf. dianthus with a genetic distance of 5.6%. The cryptic lineage found in Texas was evidently introduced to the Black Sea only recently. Given that both lineages within H. dianthus are invasive, a greater emphasis on adequate monitoring and management of the routes responsible for introductions of this species is needed.

De Novo Assembly of the Liver Transcriptome of the European Starling, Sturnus vulgaris.

The European starling, Sturnus vulgaris, is a prolific and worldwide invasive species that also has served as an important model for avian ecological and invasion research. Although the genome sequence recently has become available, no transcriptome data have been published for this species. Here, we have sequenced and assembled the S. vulgaris liver transcriptome, which will provide a foundational resource for further annotation and validation of the draft genome. Moreover, it will be important for ecological and evolutionary studies investigating the genetic factors underlying rapid evolution and invasion success in this global invader.

Local co-occurrence of several highly invasive ants in their native range: are they all ecologically dominant species?

An important goal of invasion ecology is to understand the colonization, establishment, and spread of exotic species. To accomplish this, it is essential to examine the ecology of introduced species in native populations. We examined organization patterns, spatial structure, and competitive abilities of ground-dwelling ants in different habitats of a protected area in east-central Argentina, where several highly invasive ant species naturally coexist, to determine whether all they are ecologically dominant in their native range as in their introduced range. We sampled ant communities at Otamendi Nature Reserve and found 49 ant species co-occurred with moderate separation among habitats, including five species that are global invaders; but only Solenopsis richteri (the most numerically dominant) and Linepithema humile (the best mass recruiter) were ecologically co-dominant along with another three non-invasive species in locally rich assemblages. Their co-occurrence was apparently facilitated by both niche and competitive differences. However, we found no evidence for discovery-dominance trade-offs, and ant diversity and spatial segregation suggested that competition only plays a secondary role in structuring assemblages in arboreal habitats. Despite L. humile and S. richteri were ecologically co-dominant, their hegemony was lower in the reserve than in their introduced range likely due to biotic resistance. The other invasive ants (Wasmannia auropunctata, Brachymyrmex patagonicus, and Nylanderia fulva) were not dominant. It is possible that their establishment, persistence, and high prevalence in anthropic habitats in native and introduced populations to be attributed to their better physiologic adaptations to disturbed habitats rather than to their superior competitive abilities.

Major drivers of invasion risks throughout the world

AbstractIn this paper, we investigate how climate, land use, habitat characteristics, and socioeconomic activities contribute to predict the current potential distributions of the “100 among the world's worst invasive alien species”. We calculated the predictive power of each of the 41 variables for the 95 species including a large number of plants, vertebrates and invertebrates. We then calibrated the species distribution models with a set of appropriate variables for each invasive alien species to predict the potential distribution of these species and identify the major regions of origin of the invasive alien species. We found that climate variables were primarily predictors of the distribution of the global invaders studied. In addition, the habitat characteristics were also important predictors following by the socioeconomic variables such as the nearest distance to airports, seaports and human population density. We show that the potential areas at the highest risk of invasions from these species are located in Western Europe, Eastern United States, Central America, the eastern coast of Australia, and some Indonesian islands. We argue that these potential hotspots of invasions should be monitored in priority to prevent new invasions from these species. This study provides evidence of the importance of considering both habitat characteristics, socioeconomic and climate change factors for the current and future predictions of biological invasions.

Plant species loss and community nestedness after leguminous tree Acacia pycnantha invasion in a Mediterranean ecosystem

Invasions of ecosystems by alien species are one of the major threats to biodiversity. Among alien plant species, members of the family Fabaceae s.l. represent some of the most dangerous and well known global invaders. In Mediterranean ecosystems, many Australian acacias have been found to establish and rapidly spread, often determining severe impacts on understorey vegetation. In the present work, we report a case study of an Acacia pycnantha invasion in a typical Mediterranean matorral (Elba Island, central Mediterranean Sea, Italy). We conducted a survey of understorey plant communities across an invasion gradient from non-invaded to transitional and invaded areas, aiming to quantify the impacts on the understorey assemblage and to investigate the ecological processes involved in the changes in species composition. The understorey plant community was highly affected starting from the intermediate stage of invasion. Species richness, diversity and total cover were all lower in invaded than in non-invaded plots, with a transition generally in the middle. In addition, plant community composition severely changed along the invasion gradient. The species set we recorded showed a nested structure, with the composition of species in the invaded plots representing a subset of the others. According to our findings, A. pycnantha exerted detrimental impacts on the native vegetation, mainly causing a severe species loss in the understorey assemblage and the impoverishment of the invaded ecosystems.

Invasive house geckos are more willing to use artificial lights than are native geckos

There is increasing concern about the ecological effects of light pollution, as artificial lighting spreads with urban expansion. While artificial lighting can negatively affect some species, others use it in novel ways. In tropical and subtropical regions, artificial lighting has created a novel niche: the ‘night light’ niche. Geckos living as human commensals (house geckos) are apparently well adapted to occupy this niche. In an urban area in north-eastern Australia, we found that the invasive Asian house gecko Hemidactylus frenatus (Gekkonidae) occupies a broader range of light environments in the field than does the native gecko Gehyra dubia (Gekkonidae). Experimental removal of the invasive species from a building indicated that it did not behaviourally influence the light environments chosen by the native species in the short term; they continued to use darker areas even after the invasive species was removed. In Y-maze experiments, neither species showed a significant preference for light or dark areas; however, preliminary data suggest the invasive species was more willing to explore the Y-maze than the native species. The willingness of H. frenatus to forage closer to lights, where insect abundance is typically higher, might account for its success as a global invader of human environments, even in areas where other gecko species are established.

Global Invader Impact Network (GIIN): toward standardized evaluation of the ecological impacts of invasive plants

Terrestrial invasive plants are a global problem and are becoming ubiquitous components of most ecosystems. They are implicated in altering disturbance regimes, reducing biodiversity, and changing ecosystem function, sometimes in profound and irreversible ways. However, the ecological impacts of most invasive plants have not been studied experimentally, and most research to date focuses on few types of impacts, which can vary greatly among studies. Thus, our knowledge of existing ecological impacts ascribed to invasive plants is surprisingly limited in both breadth and depth. Our aim was to propose a standard methodology for quantifying baseline ecological impact that, in theory, is scalable to any terrestrial plant invader (e.g., annual grasses to trees) and any invaded system (e.g., grassland to forest). The Global Invader Impact Network (GIIN) is a coordinated distributed experiment composed of an observational and manipulative methodology. The protocol consists of a series of plots located in (1) an invaded area; (2) an adjacent removal treatment within the invaded area; and (3) a spatially separate uninvaded area thought to be similar to pre-invasion conditions of the invaded area. A standardized and inexpensive suite of community, soil, and ecosystem metrics are collected allowing broad comparisons among measurements, populations, and species. The method allows for one-time comparisons and for long-term monitoring enabling one to derive information about change due to invasion over time. Invader removal plots will also allow for quantification of legacy effects and their return rates, which will be monitored for several years. GIIN uses a nested hierarchical scale approach encompassing multiple sites, regions, and continents. Currently, GIIN has network members in six countries, with new members encouraged. To date, study species include representatives of annual and perennial grasses; annual and perennial forbs; shrubs; and trees. The goal of the GIIN framework is to create a standard yet flexible platform for understanding the ecological impacts of invasive plants, allowing both individual and synthetic analyses across a range of taxa and ecosystems. If broadly adopted, this standard approach will offer unique insight into the ecological impacts of invasive plants at local, regional, and global scales.

Recent discovery of small naturalised populations of Melaleuca quinquenervia (Cav.) S.T. Blake in South Africa

The discovery of a naturalised population of Melaleuca quinquenervia in South Africa in 2009 prompted an evaluation of the species’ distribution across South Africa. We found records at seven localities in two of the nine provinces of South Africa, with naturalised populations at two sites — ~300 plants were discovered over 0.3ha in a confined-seep on a mountain slope, while at an old arboretum 12 large, planted trees and 9 naturalised trees were found. An additional herbarium record from Mozambique suggests that this global invader is present at other sites within the sub-region, and so while the extirpation of populations in South Africa is recommended and looks feasible, further work is required to determine the status and evaluate whether eradication from the sub-region as a whole is possible.

Crayfish as global invaders: Distribution, impact on ecosystem services, and management options

Crayfish as global invaders: Distribution, impact on ecosystem services, and management options

Putative Predators of Carcinus Maenas in Eastern Australia

Following the arrival of non-native species into suitable environments, interactions with native biota can influence non-native species proliferation and spread. The European shore crab, Carcinus maenas, is a global invader for which top-down control by predators has been implicated in limiting range expansion in its North American range. Little is known, however, about predators of this non-native species within its Australian distribution. We conducted quarterly trapping over 2 years in ten Australian estuaries to assess relationships between the abundance of C. maenas and native predators. Feeding assays between C. maenas and putative predators, identified from negative associations in occurrence, assessed the ability of putative predators to recognise C. maenas as prey. Six taxa were negatively correlated with C. maenas’ abundance and capable of eating the non-native crab. These were the blue swimmer crab (Portunus pelagicus), octopods (Octopus spp.), leatherjackets (Monocanthidae), yellowfin bream (Acanthopagrus australis), toadfish (Tetraodontidae) and the eastern fiddler ray (Trygonorrhina fasciata). Octopus spp. were rare in and blue swimmer crabs absent from mangroves; the habitat in which C. maenas was most abundant. A tethering experiment confirmed that Octopus spp. eat C. maenas in the field, with greater rates of mortality of the crab close to than away from the Octopus spp. lairs. Overall, our study indicates that a diverse assemblage of predators may prey upon C. maenas in southeastern Australia. Further studies assessing relative rates of predation by these predators on C. maenas are needed to assess whether they are exerting significant top-down control.

Population characteristics of bighead and silver carp on the northwestern front of their North American invasion

Invasive species are considered the second largest threat to native biodiversity, and ecosystem function and services. One pair of global invaders, bighead, Hypophthalmichthys nobilis, and silver carp, H. molitrix, (collectively referred to as Asian carps) have been introduced throughout the world, and are invading three prairie stream tributaries to the Missouri River in the United States. There is a paucity of knowledge and understanding about Asian carp population characteristics and biology in North America. As such, we documented spatial and temporal trends in population dynamics (i.e., density, size structure, age, growth and condition) of Asian carps in three tributaries to the Missouri River in South Dakota: Big Sioux, James and Vermillion from 2009 to 2012. Finally, native planktivore (i.e., gizzard shad, Dorosoma cepedianum, bigmouth buffalo, Ictiobus cyprinellus, and emerald shiner, Notropis atherinoides) characteristics were examined using condition (Fulton’s K). Overall, 469 silver carp and eight bighead carp were collected using boat electrofishing and mean catch-per-unit-effort of silver carp increased annually. The three rivers’ populations were similar in length frequencies. Silver carp growth was faster initially than later ages and overall was slower than Middle Mississippi River populations. Recruitment of silver carp was erratic with the 2010 year class dominating 91% of catches. Silver carp condition was also similar across rivers, seasons, and years. South Dakota silver carp populations were predicted from a length-weight regression to be lighter than the Gavins Point reach population of the Missouri River, and heavier than both the middle Mississippi and the Illinois River populations. Additionally, mean catch-per-unit-effort for bigmouth buffalo and emerald shiner decreased over the study period. Continued monitoring and research on this newly invading population of Asian carps will provide additional invaluable insight into complex invasive species, assist with understanding Asian carps population dynamics during and after an invasion, and expose the potential negative impacts Asian carps may be having on prairie stream ecosystems.