Invasion Success Research Articles

Soil bacterial community could be affected by Amaranthus retroflexus L.

Invasive plants can disrupt the growth performance of native plants by releasing allelochemicals affecting on litter decomposition. Furthermore, these invaders can establish a plant-soil feedback loop with soil microorganisms, which promotes their continued successful invasion primarily through decomposition process. Consequently, it is of the utmost importance to conduct research that analyzes the impacts of invasive plants' allelopathy on their interaction with soil microorganisms. This study aims to investigate the effects of Amaranthus retroflexus L., an invasive Amaranthaceae plant's allelopathy, on its interaction with soil bacterial communities, compared to the native plant A. tricolor L., and also the impacts of the allelopathy of Amaranthus retroflexus on soil enzyme activities. The research was conducted via an indoor planting experiment in which a gradient of Amaranthus retroflexus leaf litter was added. In particular, Amaranthus retroflexus leaf litter resulted in an increase in pH, electrical conductivity, total nitrogen, and neutral protease activity in soil under certain treatments. The amount of Amaranthus retroflexus leaf litter and the form of incubation condition may be the primary determinants of the composition of bacterial communities in soil and the number of functional gene pathways of soil bacteria involved in the decomposition process (especially the decomposition of carbon-containing substances), rather than the alpha diversity of soil bacteria. Consequently, Amaranthus retroflexus may predominantly modify the composition of bacterial communities in soil and the number of functional gene pathways of soil bacteria involved in the decomposition process, rather than the alpha diversity of soil bacteria, to facilitate its subsequent invasion.

Chromosome-level genome assembly reveals adaptive evolution of the invasive Amazon sailfin catfish (Pterygoplichthys pardalis)

Catfish represents a diverse lineage with variable number of chromosomes and complex relationships with humans. Although certain species pose significant invasive threats to native fish populations, comprehensive genomic investigations into the evolutionary adaptations that contribute to their invasion success are lacking. To address this gap, our study presents a high-quality genome assembly of the Amazon sailfin catfish (Pterygoplichthys pardalis), a member of the armored catfish family, along with a comprehensive comparative genomic analysis. By utilizing conserved genomic regions across different catfish species, we reconstructed the 29 ancestral chromosomes of catfish, including two microchromosomes (28 and 29) that show different fusion and breakage patterns across species. Our analysis shows that the Amazon sailfin catfish genome is notably larger (1.58 Gb) with more than 40,000 coding genes. The genome expansion was linked to early repetitive sequence expansions and recent gene duplications. Several expanded genes are associated with immune functions, including antigen recognition domains like the Ig-v-set domain and the tandem expansion of the CD300 gene family. We also identified specific insertions in CNEs (conserved non-coding elements) near genes involved in cellular processes and neural development. Additionally, rapidly evolving and positively selected genes in the Amazon sailfin catfish genome were found to be associated with collagen formation. Moreover, we identified multiple positively selected codons in hoxb9, which may lead to functional alterations. These findings provide insights into molecular adaptations in an invasive catfish that may underlie its widespread invasion success.

The Role of Phenylpropanoids and the Plant Microbiome in Defences of Ash Trees Against Invasive Emerald Ash Borer.

Plants have coevolved with herbivorous insects for millions of years, resulting in variation in resistance both within and between species. Using a manipulative experiment combined with untargeted metabolomics, microbiome sequencing and transcriptomics approaches, we investigated the roles of plant metabolites and the microbiome in defence mechanisms in native resistant Manchurian ash (Fraxinus mandshurica) trees and non-native susceptible velvet ash (Fraxinus velutina) trees against the highly invasive emerald ash borer (EAB, Agrilus planipennis). Comparative transcriptomics and metabolomics analyses show that the phenylpropanoid pathway, which is enriched in differentially expressed genes and differentially abundant metabolites, may serve as a potential regulator of resistance. Additionally, the microbiome is distinctly shifted in two ash species. Indicator taxa analysis reveals that the distinct genera are dominant in the galleries of two ash species, for example, Pseudomonas in velvet, and Hafnia-Obesumbacterium in Manchurian. The strong correlation between indicator taxa and metabolites suggests that the chemical compounds might impact the microbial community in phloem directly or indirectly, or vice versa. This study significantly enhances our understanding of the variation in resistance between ash species and its contribution to the invasion success of EAB, providing valuable insights for the development of pest management strategies.

Inter-sexual phenotypic divergence is correlated with habitat structure in an invasive lizard

Abstract The success of invasive species is largely dependent on their ability to adapt to new environmental contexts. In dioecious species, adaptive responses can differ between males and females because of variation in the influence of sexual selection and/or the potential for inter-sexual niche differentiation. In invasive species, these effects may be augmented by ecological release, under which the constraints imposed by inter-specific competition on intra-specific niche divergence are shed. Differences in invaded environments, or between invaded and native environments, could therefore lead to different degrees of sexual dimorphism, which could influence intra-specific competition and invasive success. In this study, we investigate the potential for sexual divergence in adaptive change in invasive populations of the Green Anole, Anolis carolinensis, in the Ogasawara Islands, an oceanic archipelago in Japan. We find that limb length is correlated with variation in habitat structure across the islands in male lizards, but not in female lizards. We suggest that the resulting variation in sexual dimorphism is driven by exploitation of the available niche space, with male habitat use diverging further from that of females where local conditions allow. These findings represent evidence that community-level patterns observed among other anole species are mirrored by local, intra-specific patterns in this population, and add to growing evidence of the importance of ecological drivers of sexual dimorphism.

Intraspecific diversity poorly predicts invasibility and invasiveness in communities: a meta‐analysis of experimental invasions

Identifying the biotic factors underlying invasion success into existing communities is critical to understand the dynamics of biological invasions; and while some studies suggest that intraspecific diversity may play an important role, there has not been a systematic evaluation of the evidence. We performed a meta‐analysis on 37 experimental studies and 109 effect sizes to test two hypotheses: 1) higher intraspecific diversity in a resident population decreases the likelihood of it being successfully invaded by other species, and 2) higher intraspecific diversity in an invading population increases its ability to invade another species or community. We found heterogeneous effects among studies and that overall resident genetic diversity has a very small, non‐significant negative effect on invasion success, while invader genetic diversity has a small, non‐significant positive effect. The minimal impact of intraspecific diversity is somewhat unexpected, given the well‐understood mechanisms analogous to those offered for interspecific diversity. These include sampling effects and complementarity, in which diversity is expected to maximize resource use and increase density, thereby reducing niche availability and subsequent invasibility. We recommend that future research focus on a wider diversity of organisms, include longer term experiments, and measure genetic dissimilarity to better understand the role of intraspecific diversity.

Microbiota dynamics in lionfish (Pterois): insights into invasion and establishment in the Mediterranean Sea.

Lionfishes (Pterois spp.), originally native to the Indo-Pacific and Red Sea, have become one of the most invasive marine species globally, including the recent establishment in the Mediterranean Sea. This study investigates the microbiota of lionfish to explore its potential role in their invasion success and establishment. Using high-throughput sequencing and microbiota analyses, we characterized the species-specific core microbiome and identified habitat-specific markers across different regions (Red Sea, Mediterranean Sea, Caribbean, and aquarium populations) and organs. Focusing on the Mediterranean invasion, we tracked lionfish distribution and population dynamics along the Israeli coastline from 2017 to 2023, monitoring size, seasonal trends, and depth preferences. Our findings reveal that lionfish initially established themselves in deeper waters before expanding to shallower habitats, with a gradual increase in population size and body length over time. From a microbial aspect, we compared the microbiota of lionfish organs and identified a similar pattern (Photobacterium), to Earlier Lessepsian migrants fish species. This study provides novel insights into the interactions between microbiota and host ecology, shedding light on the mechanisms that may support the successful invasion. This study contributes to the understanding of lionfish invasion dynamics in the Mediterranean. It highlights the microbiota as an integral component for studying the ecological and biological mechanisms underpinning invasive species' success and establishment of lionfish.

Keystone root bacteria in Ambrosia artemisiifolia promote invasive growth by increasing the colonization rate of Funneliformis mosseae.

Keystone root bacteria in Ambrosia artemisiifolia promote invasive growth by increasing the colonization rate of Funneliformis mosseae.

Hypothesis Description: Darwin’s Naturalisation Hypothesis

In this contribution of the Hypothesis Description series, we provide an overview of one of the longest-standing hypotheses in invasion science: Darwin's naturalisation hypothesis. We present a brief summary of past definitions and propose the revised definition “high phylogenetic distance between non-native species and the recipient community increases invasion success”. This formulation follows the basic form ‘subject – relationship – object’, enabling clarity for future research and computational applications in invasion biology. We also provide formalised definitions for previous formulations of the hypothesis and identify both related and opposite hypotheses to Darwin’s naturalisation hypothesis.

Below- and above-ground mutualisms impact two alien brooms in South Africa differently

Mutualisms are important determinants of the invasion success of alien plants. If alien plants are specialized in their mutualistic requirements, or need different types of mutualistic partners (e.g., pollinators and seed dispersers), invasion success may be hampered. Many studies only consider one type of mutualistic relationship when examining the interaction ecology of alien plants, but most plants interact with multiple types of mutualists. In this study, we explored the interactions between two alien legumes, the brooms Genista monspessulana and Spartium junceum, and their associated below-ground (nitrogen-fixing rhizobia) and above-ground (pollinators) mutualists in South Africa. We conducted pollinator observations, breeding system experiments and collected root nodules to identify rhizobia via 16S rDNA sequencing. Both plants species were entirely dependent on pollinators for seed production. Genista monspessulana was pollinated largely by Apis mellifera capensis and was not pollen limited, while the larger flowers of S. junceum were only pollinated by the larger Xylocopa bees and was pollen limited. Genista monspessulana was nodulated by four distinct Bradyrhizobium (Alpha-proteobacteria) strains, while S. junceum was nodulated by one Paraburkholderia (Beta-proteobacteria) and two Bradyrhizobium strains. Low pollination rates in S. junceum suggest that its reproduction and natural spread in South Africa may be slow. The wider distribution of S. junceum, compared to G. monspessulana, thus likely reflects differences in historic propagule pressure between the two species. The role of rhizobia in limiting plant performance is less clear and the connection between nodulation rate and plant fitness requires further study.

Arbuscular Mycorrhizal Fungi Boost Development of an Invasive Brassicaceae.

Invasive plant growth is affected by interactions with arbuscular mycorrhizal fungi (AMF). AMF are mutualists of most land plants but suppress the growth of many plants within the Brassicaceae, a large plant family including many invasive species. Alliaria petiolata (garlic mustard) is a nonnative, nonmycorrhizal Brassicaceae distributed throughout North America in forest understories where native species rely on AMF. If AMF suppress growth of garlic mustard, it may be possible to inoculate AMF to manage invasions. Here, we show that in contrast to expectation, garlic mustard growth nearly doubled in response to AMF inoculation under both laboratory and field conditions. This effect was negatively linked to investments in glucosinolates, a class of defensive compounds. In contrast to typical symbiosis, AMF did not produce arbuscules where nutrient exchange occurs in roots, but AMF inoculation increased plant and soil nitrogen availability. Our findings reveal an adjacent pathway by which AMF promote invasive plant growth without classic symbiotic exchanges. Prior assumptions that garlic mustard suppresses AMF are inadequate to explain invasion success since it benefits from interactions with AMF. This study is the first to demonstrate extensive growth promotion following AMF inoculation in mustard plants, with important implications for invasion biology and agriculture.

Predicting invasiveness of freshwater fishes imported into North America: regional differences in models and outcomes

Biological invasions driven by international trade heighten the urgency for development of invasion risk models, as the traits and parameters that consistently predict successful invasion remain unresolved. For four regions of North America that include parts of the United States and Canada (Sacramento-San Joaquin River Basins, Lower Colorado River Basin, Great Lakes Region, Mid-Atlantic Region), we construct and compare classification tree models to reveal robust predictors for the establishment and ecological impact stages of freshwater fish invasion. We subsequently apply the models to identify invasive fish species in trade and conduct pathway analyses to determine which trades (aquarium, biological supply, live bait, live food, water garden) and source continents pose the greatest risk to each region. Model results differed by invasion stage and region. Across regions, establishment models shared climate-related predictors including climate match and temperature tolerance. Three of the four impact models contained prior establishment success. The greatest number of species (548) were predicted to establish in the Sacramento-San Joaquin while the fewest (5) were predicted to establish in the Mid-Atlantic. Forty species were predicted to establish in multiple regions, five of which were also predicted to have high impact. The aquarium trade and Asia supplied the most species predicted to establish. Taken together, the results highlight region-specific models, indicating no universal model predicts invasion. Climate-related and prior establishment variables were most useful to risk assessments. The regional models, and identified high-risk pathways and potential invaders, could be applied to prevent future fish invasions in North America.

Positive Linkage in Bacterial Microbiota at the Plant-Insect Interface Benefits an Invasive Bark Beetle.

Symbiotic microbes facilitate rapid adaptation of invasive insects on novel plants via multifaceted function provisions, but little was known on the importance of cross linkages in symbiotic microbiota to insect invasiveness. Novel host pine Pinus tabuliformis is inherently unsuitable for invasive red turpentine beetle (RTB) in China; however, Novosphingobium and Erwinia/Serratia in gallery microbiota (at the interface between RTB larvae and pine phloem) have been discovered to help beetles via biodegrading pine detrimental compounds naringenin and pinitol, respectively. Here, we further revealed significant positive linkage of the two functions, with higher activity level conferring more growth benefit to RTB larvae. Abundance of Erwinia/Serratia was remarkably increased in response to pinitol, while naringenin-biodegrading Novosphingobium was unable to utilize this main phloem carbohydrate directly. High-activity bacterial microbiota produced nutritive metabolites (sucrose and hexadecanoic acid) from pinitol consumption that facilitated growth of both Novosphingobium and beetle larvae. Functional proteins of several bacterial taxa were enriched in high-activity microbiota that appeared to form a metabolic network collectively to regulate the nutrient production. Our results indicate that positive interaction between Erwinia/Serratia and Novosphingobium is critical for RTB invasion success, while Bacilli bacteria might restrict this linkage, providing new insights into symbiotic microbial interactions for insect herbivores.

Dandelion (Taraxacum officinale) has successfully adapted to grow in suburban environments

Dandelion (Taraxacum officinale (L.) Weber ex F.H. Wigg) is a perennial herbaceous plant that, although not native to its current habitat of Australia, North America and South America, has become invasive, posing economic challenges by outcompeting indigenous flora and agricultural crops. The precise factors enabling its dominance remain unclear. We hypothesized that morphological adaptations may play a role in contributing significantly to the dandelion's invasive success. This study focuses on two main drivers: 1. Phenotypic changes in the fruit head peduncle, and 2. Phenotypic plasticity facilitating adaptation to diverse environments. While dandelion fruits are efficiently dispersed by wind, the precise mechanisms are not fully understood. Our research revealed that during fruit head formation, the fruit head peduncle elongates and grows vertically, potentially aiding in fruit dispersal. Morphological variations across habitats, including natural environments, suburban lawns, and playgrounds, contribute to dandelion's success. In suburban lawns of Philadelphia, dandelions exhibit adaptations such as small leaves, short floral peduncle angled at 30 degrees or lower, growing parallel to the lawn grass to evade mowing, while in playgrounds, they develop shorter structures to withstand trampling pressure. Dandelions thriving in the undisturbed fringes of lawns and playgrounds have large floral peduncle and leaves revealing the true extent of their growth potential when allowed to flourish in their natural state. These findings highlight dandelion's adaptability and resilience, attributed to phenotypic plasticity, which enables them to thrive across diverse ecological landscapes.

Cross‐continental variation of herbivore resistance in a global plant invader

While successful plant invasions often occur in novel environments, invasive species usually occupy broad niches within their native and introduced ranges. A better understanding of the process of invasion therefore requires a wide sampling of ranges, and a good knowledge of introduction history. We tested for differentiation in herbivore resistance among 128 introduced (European, North American) and native (Chinese, Japanese) populations of the invasive Japanese knotweed Reynoutria japonica in two common gardens in the native range: one in Shanghai and the other in Yunnan. In both common gardens, we found that herbivore resistance of plants from introduced populations differed from that from native populations in China but not from native populations in Japan, the putative source of introduction. Compared to native Chinese populations, plants from native Japanese populations and introduced European and North American populations had thicker leaves in both common gardens, and a lower C:N ratio but higher flavonoids content in the Shanghai garden. Variation in herbivore resistance was more strongly associated with climate of collecting sites for populations from the native range than for those from introduced ranges. Our results support the hypothesis that introduction of particularly resistant plants from Japan may have played a key role in driving biogeographic variation in herbivore resistance. Our study highlights the importance of understanding introduction history to interpret the biogeographic divergence of global plant invaders.

Photogrammetric assessment of quagga mussel growth shows no winter cessation in lake Geneva

The quagga mussel (Dreissena rostriformis bugensis) is an invasive alien species present in many aquatic ecosystems. Although this species is known for its ecological and economic impacts, there are still significant gaps in our knowledge of its ecophysiology. This is particularly true when its growth rate under natural conditions is considered. Using a photogrammetry-based approach, we assessed bivalve growth in Lake Geneva during different seasons and for a variety of habitats. Based on the recorded changes in maximum shell length analysed during the period of this study (winter and spring 2023–2024), we measured average growth rates ranging from 0.142 ± 0.099 mm day−1 for individuals smaller than 10 mm to 0.089 ± 0.071 mm day−1 for larger individuals. The size class-dependent growth rate was analysed on the basis of the time of year, the type of environment (depth, substrate) or, again, the temperature. Our results reveal that the growth rate, obtained in situ and without manipulation, primarily depends on size and is independent of temperature or habitat within the studied range. This growth capacity in Lake Geneva is the highest found to date and is likely to explain the invasion success of this species.

Genomic Insights into the Successful Invasion of the Avian Vampire Fly (Philornis downsi ) in the Galápagos Islands.

Invasive species pose significant threats to island ecosystems, often leading to the decline of native species and the disruption of ecological balance. The avian vampire fly (Philornis downsi), introduced to the Galápagos Islands of Ecuador, has emerged as a major threat to the endemic avifauna, parasitizing multiple species of Darwin's finches and other passerines. Yet, the genetic mechanisms of its invasion remain unclear. In this study, we conducted the first whole-genome sequencing analysis of P. downsi populations from the Galápagos Islands and their native range in mainland Ecuador. Our results reveal genomic signatures of a founder effect, with reduced genetic diversity in the Galápagos populations, indicative of a recent population bottleneck. We found a lack of significant genetic differentiation and evidence of ongoing gene flow among island populations. Despite low genetic diversity in island populations, we identified adaptive genetic changes, including regions possibly under positive selection near genes related to neural signaling, muscle development, and metabolic processes, which may have contributed to the fly's invasion success. Additionally, we uncovered genetic changes associated with precipitation-related climate adaptation, highlighting the possible role of environmental factors in shaping genetic variation in P. downsi. Our findings provide crucial insights into the invasion dynamics of P. downsi in Galápagos, emphasizing the importance of genomic research in informing conservation strategies. The identification of key adaptive genomic loci and potential environmental drivers of genetic change will aid in the development of targeted management practices to mitigate the impact of this invasive species on the unique biodiversity of the Galápagos Islands.

New Mutualisms at New Ecosystems: Seed Dispersal Assessment of Invasive Shrubs by Native and Non‐Native Mammals

ABSTRACTBiological invasions are a significant driver of global biodiversity decline in the Anthropocene. The success of plant invasions often depends on mutualistic relationships, such as animal‐mediated seed dispersal. While the role of birds in dispersing invasive plants is well documented, the involvement of mammals in new ecosystems remains largely unclear. In the mountains of Central Argentina, Pyracantha species are among the most prominent invasive plants, and their seed dispersal by birds has been extensively studied. In this study, we assessed the role of mammals within a novel assemblage (comprising native, invasive, and domestic species) in the seed dispersal process of invasive Pyracantha angustifolia and P. crenulata shrubs. Specifically, we identified which mammal species are legitimate seed dispersers, evaluated their impact on seed germination, and determined where they deposit the seeds using a combination of observational and experimental approaches. Through camera traps and faecal analyses, we identified the following mammals consuming Pyracantha fruits: (1) domestic species: cattle and horses; (2) native species: grey fox, common hog‐nosed skunk, and collared peccary; and (3) invasive species: European hare, wild boar, and invasive deer (red or spotted deer). We included two additional native mammals (i.e., collared peccaries and brown brocket deers) to perform germination trials due to their presumably frugivorous behaviour. The germination experiment revealed that seed ingestion by captive horses, grey foxes, collared peccaries, brown brocket deer, red deer and exotic deer enhanced seed germination. Principal Component Analysis indicated no specific association between mammal species and seed deposition sites, suggesting non‐directed dispersal. This research highlights the emergence of new mutualisms in anthropogenic systems that may influence plant community structure through the promotion of plant invasions. Understanding these novel mutualisms is crucial for predicting community rearrangements and improving management actions against plant invasions.

Strength of Enemy Release From Parasitoids Is Context Dependent in the Invasive African Fig Fly, Zaprionus indianus.

Understanding the mechanisms underlying the success of biological invasions is essential to employ effective prediction and management strategies. Escape from natural enemies in invaded regions (enemy release hypothesis, ERH) and increased competitive ability are hallmarks of invasive species; however, these two processes are rarely studied within the same context. Here, we examined the effect of enemy release on the competition outcomes of a successful invasive insect pest in North America, the African fig fly (Zaprionus indianus). Parasitoid wasps such as Leptopilina heterotoma that parasitize drosophilid larvae may seek out established species with known host suitability over a novel species, so we hypothesized Z. indianus may have low susceptibility to parasitoids, giving them a competitive advantage over co-occurring drosophilids. We tested this hypothesis by comparing the adult emergence rates from Z. indianus larvae reared alone or in competition with Drosophila hydei or D. simulans larvae in the presence and absence of parasitoid wasps under low and high larval densities. At low larval densities, Z. indianus emerged at equal rates to D. hydei but outcompeted D. simulans, and these outcomes were not affected by parasitoids. However, at high densities, the addition of parasitoids shifted competition outcomes in favor of Z. indianus, suggesting enemy release provides a competitive advantage under some circumstances. These results indicate that the strength of enemy release in Z. indianus is widely dependent on contextual factors such as density and competitor species. This study emphasizes how a community approach to testing the ERH is vital as the overall interpretation of the presence and strength of enemy release differed between intraspecific and interspecific experiments. Further investigation of how these results apply to field environments could offer insight into how Z. indianus alters ecosystems and how productive biological control may limit the spread of Z. indianus.

Low Requirement on the Nest Site Selection Influencing the Invasion Success of House Geckos

ABSTRACTThe selection of nesting sites is fundamental for the reproductive success of oviparous species. However, there are gaps regarding how animals select their reproductive sites, especially among species that do not build their nests; that is, they use natural cavities for oviposition, as is the case with many lizards. Herein, we evaluated how the physical structure and microclimatic conditions of tree hollows influence the selection of oviposition sites in a widely distributed exotic lizard, Hemidactylus mabouia (Squamata, Gekkonidae). We hypothesized that the choice of oviposition sites by females would consider: (a) structural properties of the sites related to the vulnerability of eggs to predation; and/or (b) microclimatic conditions of the sites associated with the stability of the egg incubation process. Over the course of a year, we monitored the use of 53 tree cavities on a weekly basis, recording a total of 69 H. mabouia nests. The width of the opening of the sites, their height in relation to the ground level, and the temperature variation in the hollows did not influence the choice of oviposition sites. However, cavities with less variation in humidity were used more frequently. Our findings contribute to the understanding of selection criteria for oviposition sites in species that use tree cavities as nests in general. Furthermore, we discuss the implications of the generalist habits of H. mabouia in the context of biological invasion, suggesting that the low requirements for the selection of reproductive sites may constitute a determining factor for the successful invasion of exotic lizards.

Competition on a neutral playing field: invaders still win and size still matters… sometimes.

Exotic invasive plant species commonly outcompete native species. However, a great deal of the evidence for this comes from experiments conducted on an uneven playing field-in substrates containing soil biota from the non-native ranges of the exotics, which should give them a competitive advantage. In competition experiments with nine pairs of non-native invasive versus native species in neutral substrates composed of sterilized soil, we found that the competitive effect of invasive species on natives was approximately five times greater than the reverse, and gram-per-gram competitive effects of invasives on natives were almost two times that of the natives on invasives. The effect of plant size on competitive outcomes was complex. The size of invasive species correlated with their effects on natives but not with their tolerance to competition from natives. The size of natives was not correlated with either aspect of competitive ability. This is important since the tolerance of invaders to competition from natives is thought to be essential for successful invasion. Our results also suggest that assumptions about size-based evidence for the evolution of competitive ability in non-native ranges is reasonable, and that even without the advantage gained from escaping soil biota, invaders still win.