Fecundity as a basis for risk assessment of nonindigenous freshwater molluscs

Toward invasive mussel genetic biocontrol: Approaches, challenges, and perspectives

Invasive freshwater mussels, such as the zebra (Dreissena polymorpha), quagga (Dreissena rostriformis bugensis), and golden (Limnoperna fortunei) mussel have spread outside their native ranges throughout many regions of the North American, South American, and European continents in recent decades, damaging infrastructure and the environment. This review describes ongoing efforts by multiple groups to develop genetic biocontrol methods for invasive mussels. First, we provide an overview of genetic biocontrol strategies that have been applied in other invasive or pest species. Next, we summarize physical and chemical methods that are currently in use for invasive mussel control. We then describe the multidisciplinary approaches our groups are employing to develop genetic biocontrol tools for invasive mussels. Finally, we discuss the challenges and limitations of applying genetic biocontrol tools to invasive mussels. Collectively, we aim to openly share information and combine expertise to develop practical tools to enable the management of invasive freshwater mussels.

Invasion potential of the aquarium pet snail Planorbella trivolvis in India: impact of certain abiotic and biotic factors

Planorbella trivolvis (ramshorn snail) is one of India's most extensively sold exotic aquarium pet snails. The unintentional or deliberate release of P. trivolvis may result in the colonisation and establishment as an invasive snail in freshwater ecosystems. However, the successful invasion of P. trivolvis will depend on several abiotic and biotic factors of the concerned freshwater ecosystem. We have assessed the possibility of overcoming the opposing factors in P. trivolvis invasion through laboratory-based experiments and examined the effects of household-derived pollutants on egg hatchability, adult survivability and fecundity, and temperature (15 to 35 °C) on growth, sexual maturity, and reproduction. Additionally, we have evaluated the potential of native predators as biotic resistance to invasion by prey-choice experiment. The results indicated that egg hatchability, adult survivability, and fecundity were reduced with increasing pollutant concentration. However, the same traits did not differ from a native freshwater snail, Indoplanorbis exustus. The fecundity of P. trivolvis increased with increasing body size, but no considerable differences at different temperature levels suggest a wide range of adaptation to temperature. Faster growth and the requirement of comparatively few days to attain sexual maturity were observed in the higher temperatures. The native predators, Glossiphonia weberi and Diplonychus rusticus, avoided P. trivolvis as prey over the alternative prey snails in most instances, suggesting the masking of biotic resistance against the colonisation. Our observations indicate that the chance dispersal of P. trivolvis from household or commercial aquaria may lead to a possible invasion of freshwater ecosystems under suitable conditions.

Sex-Biased Survival, Behavior Response, and Recovery Performance of Pomacea canaliculata Snails to Drought Stress and Rewatering Condition

As the frequency of droughts increases with climate change, the tolerance of aquatic organisms to abiotic stressors will become critical determinants of survival. Pomacea canaliculata has become a widely distributed agricultural and environmental pest in southern China. To evaluate their tolerance and adaptation under the drought condition, the survival, feeding, behavior, and antioxidant system changes in female and male P. canaliculata were investigated during drought stress and rewatering process through an indoor simulation experiment. The results showed that female snails laid eggs before burrowing into the soil to ensure offspring reproduction. Female P. canaliculata had higher survival rates than males under drought stress, and their recovery ability of activity after rewatering was also superior to those of males. The antioxidant system of P. canaliculata showed obvious activation with gender differences after rewatering. Overall, the survival rate of female P. canaliculata was higher after drought stress, and the resilience ability of female snails after rewatering was stronger, including in their behavior, feeding, and antioxidant system recovery. The P. canaliculata tolerance to drought and the ability to recover quickly after drought may contribute to their long-term survival and facilitate continuous invasion.

Dose-dependent inhibitory effects of glyphosate on invasive Pomacea canaliculata reproductive and developmental growth under oxidative deposition

Glyphosate (GLY) is the most widely used herbicide worldwide, and its effects on animals and plants have attracted increasing attention. In this study, we explored the following: (1) the effects of multigenerational chronic exposure to GLY and H₂O_2, alone or in combination, on the egg hatching rate and individual morphology of Pomacea canaliculata; and (2) the effects of short-term chronic exposure to GLY and H₂O₂, alone or in combination, on the reproductive system of P. canaliculata. The results showed that H₂O₂ and GLY exposure had distinct inhibitory effects on the hatching rate and individual growth indices with a substantial dose effect, and the F1 generation had the lowest resistance. In addition, with the prolongation of exposure time, the ovarian tissue was damaged, and the fecundity decreased; however, the snails could still lay eggs. In conclusion, these results suggest that P. canaliculata can tolerate low concentrations of pollution and in addition to drug dosage, the control should focus on two time points, the juvenile and early stage of spawning.

Contrasting energy pathways suggest differing susceptibility of pelagic fishes to an invasive ecosystem engineer in a large lake system

Species invasions can lead to ecological regime shifts by altering food web structure and changing nutrient cycling. Stable isotopes are a powerful tool to understand the potential and realized impacts of invasive species on food webs, especially when used in tandem with other dietary tracers. An invasion by one of the most notorious freshwater invaders in North America, the quagga mussel (Dreissena bugensis), is imminent in Lake Champlain, United States. An invasion by this filter feeder has the potential to drastically alter energy pathways and destabilize pelagic fisheries via bottom-up impacts. However, the extent and magnitude of these impacts depend on the current food web structure of the mid-trophic pelagic food web, which was previously not well described. We used Bayesian stable isotope mixing models informed by stomach content analysis to identify which energy pathways are currently most important to mid-trophic level fishes. We determined that in the Main Lake basin, the spring phytoplankton bloom and deep chlorophyll layer – the resources most vulnerable to quagga mussels – provide a disproportionate amount of support to the pelagic food web via zooplankton and the migrating macroinvertebrate Mysis. The food web in the Northeast Arm of Lake Champlain is supported by epilimnetic phytoplankton, which is more protected from the filtration effects of quagga mussels than the deep chlorophyll layer. However, the Northeast Arm will likely not provide a high-quality foraging refuge to coldwater pelagic fish due to unfavorable oxythermal conditions. The mid-trophic food web of Lake Champlain—and consequently piscivores who rely on these prey—may be vulnerable to the impending quagga mussel invasion if migratory Mysis are not able to shift their diet to benthic resources.

Integrating invasive species risk assessment into environmental DNA metabarcoding reference libraries

Environmental DNA (eDNA) metabarcoding has shown promise as a tool for estimating biodiversity and early detection of invasive species. In aquatic systems, advantages of this method include the ability to concurrently monitor biodiversity and detect incipient invasions simply through the collection and analysis of water samples. However, depending on the molecular markers chosen for a given study, reference libraries containing target sequences from present species may limit the usefulness of eDNA metabarcoding. To explore the extent of this issue and how it may be resolved to aid biodiversity and invasive species early detection goals, we focus on fishes in the well-studied Laurentian Great Lakes region. First, we provide a synthesis of species currently known from the region and of non-indigenous species identified as threats by international, national, regional, and introduction pathway-specific fish risk assessments. With these species lists, we then evaluate 23 primer pairs commonly used in fish eDNA metabarcoding with available databases of sequence coverage and species specificity. Finally, we identify established and potentially invasive non-indigenous fish that should be prioritized for genetic sequencing to ensure robust eDNA metabarcoding for the region. Our results should increase confidence in using eDNA metabarcoding for fisheries conservation and management in the Great Lakes region and help prioritize reference sequencing efforts. The ultimate utility of eDNA metabarcoding approaches will come when conservation management of existing fish communities is integrated with early detection efforts for invasive species surveillance to assess total fish biodiversity.

What we know and don't know about the invasive zebra (Dreissena polymorpha) and quagga (Dreissena rostriformis bugensis) mussels

We summarized existing knowledge on Dreissena polymorpha (the zebra mussel) and D. r. bugensis (the quagga mussel), including data on their taxonomy, systematics, evolution, life cycle, reproduction, feeding, growth and longevity, population dynamics, interspecific competition, habitat requirements, and distribution within and among waterbodies. We analyzed the history of spread of both species and the major pathways and vectors of their spread in Europe and North America. Special consideration was given to their ecological and economic impacts and their natural enemies, like waterfowl, fishes, and parasites, as well as the prevention of their introduction, early detection, control, and containment. We also outlined the most salient ecosystem services provided by zebra and quagga mussels, including water purification, nutrient recycling, culling the effects of eutrophication, biomonitoring, and their role as a food resource for fish and waterfowl. Finally, we identified major knowledge gaps and key studies needed to better understand the biology, ecology, and impacts of these aggressive freshwater invaders. Our review indicates that much crucial information on the quagga mussel is still missing, including key life history parameters, like spawning cues, fecundity, and longevity, particularly for the profundal zone of deep lakes.

Comparative genomics suggests local adaptations in the invasive small hive beetle

Invasive species are a major driver of ecological and environmental changes that affect human health, food security, and natural biodiversity. The success and impact of biological invasions depend on adaptations to novel abiotic and biotic selective pressures. However, the molecular mechanisms underlying adaptations in invasive parasitic species are inadequately understood. Small hive beetles, Aethina tumida, are parasites of bee nests. Originally endemic to sub-Saharan Africa, they are now found nearly globally. Here, we investigated the molecular bases of the adaptations to novel environments underlying their invasion routes. Genomes of historic and recent adults A. tumida from both the endemic and introduced ranges were compared. Analysis of gene-environment association identified 3049 candidate loci located in 874 genes. Functional annotation showed a significant bias toward genes linked to growth and reproduction. One of the genes from the apoptosis pathway encodes an "ecdysone-related protein," which is a crucial regulator in controlling body size in response to environmental cues for holometabolous insects during cell death and renewal. Genes whose proteins regulate organ size, ovary activation, and oviposition were also detected. Functions of these enriched pathways parallel behavioral differences between introduced and native A. tumida populations, which may reflect patterns of local adaptation. The results considerably improve our understanding of the underlying mechanisms and ecological factors driving adaptations of invasive species. Deep functional investigation of these identified loci will help clarify the mechanisms of local adaptation in A. tumida.

Invasive species trait-based risk assessment for non-native freshwater fishes in a tropical city basin in Southeast Asia

Biological invasions have created detrimental impacts in freshwater ecosystems. As non-native freshwater species include economically beneficial, but also harmful, species, trait-based risk assessments can be used to identify and prevent the import of potentially invasive species. Freshwater fishes are one of the most evaluated freshwater taxa to date. However, such assessments have mostly been done in sub-temperate to temperate regions, with a general lack of such research in the tropics. In view of this knowledge gap, this study aims to determine if a different set of traits are associated with successful establishment of non-native fishes within the tropics. In tropical Southeast Asia, Singapore represents a suitable model site to perform an invasive species trait-based risk assessment for the tropical region given its susceptibility to the introduction and establishment of non-native freshwater fishes and lack of stringent fish import regulation. A quantitative trait-based risk assessment was performed using random forest to determine the relative importance of species attributes associated with the successful establishment of introduced freshwater fishes in Singapore. Species having a match in climate, prior invasion success, lower absolute fecundity, higher trophic level, and involvement in the aquarium trade were found to have higher establishment likelihood (as opposed to native distributional range and maximum size being among the commonly identified predictors in subtropical/temperate trait-based risk assessments). To minimize invasive risk, incoming freshwater fishes could be screened in future for such traits, allowing lists of prohibited or regulated species to be updated. The findings could also potentially benefit the development of invasive species action plans and inform management decisions in the Southeast Asian region. Considering a geographical bias in terms of having relatively less documentation of biological invasions in the tropics, particularly Asia, this study highlights the need to perform more of such risk assessments in other parts of the tropics.

Spatiotemporal patterns of non-native terrestrial gastropods in the contiguous United States

The contiguous United States (CONUS) harbor a significant non-native species diversity. However, spatiotemporal trends of some groups such as terrestrial gastropods (i.e., land snails and slugs) have not been comprehensively considered, and therefore management has been hindered. Here, our aims were to 1.) compile a dataset of all non-native terrestrial gastropod species with CONUS occurrence records, 2.) assess overarching spatiotemporal patterns associated with these records, 3.) describe the continental origin of each species, and 4.) compare climatic associations of each species in their indigenous and introduced CONUS ranges. We compiled a georeferenced dataset of 10,097 records for 22 families, 48 genera, and 69 species, with > 70% of records sourced from the citizen science database iNaturalist. The species Cornu aspersum Müller, 1774 was most prevalent with 3,672 records. The majority (> 92%) of records exhibit an indigenous Western European and Mediterranean distribution, with overlap in broad-scale climatic associations between indigenous and CONUS ranges. Records are most dense in urban metropolitan areas, with the highest proportion of records and species richness in the state of California. We show increased prevalence of non-native species through time, largely associated with urbanized areas with high human population density. Moreover, we show strong evidence for a role for analogous climates in dictating geographic fate and pervasiveness between indigenous and CONUS ranges for non-native species.

Gastropods alien to South Africa cause severe environmental harm in their global alien ranges across habitats

Alien gastropods have caused extensive harm to biodiversity and socioeconomic systems like agriculture and horticulture worldwide. For conservation and management purposes, information on impacts needs to be easily interpretable and comparable, and the factors that determine impacts understood. This study aimed to assess gastropods alien to South Africa to compare impact severity between species and understand how they vary between habitats and mechanisms. Furthermore, we explore the relationship between environmental and socioeconomic impacts, and both impact measures with life-history traits. We used the Environmental Impact Classification for Alien Taxa (EICAT) and Socio-Economic Impact Classification for Alien Taxa (SEICAT) to assess impacts of 34 gastropods alien to South Africa including evidence of impact from their entire alien range. We tested for correlations between environmental and socioeconomic impacts per species, and with fecundity and native latitude range using Kendall's tau tests. Kruskal-Wallis tests were used to compare impact magnitude among mechanisms and habitats, respectively. This study presents the first application of EICAT and SEICAT for invertebrates. There was no correlation between environmental impacts and socioeconomic impacts. Habitats did not differ regarding the severity of impacts recorded, but impacts via disease transmission were lower than other mechanisms. Neither fecundity nor native range latitude was correlated with impact magnitude. Despite gastropods being agricultural and horticultural pests globally, resilience of socioeconomic systems makes high impacts uncommon. Environmental systems may be vulnerable to gastropod impacts across habitats, having experienced multiple local extinctions of wetland island snail fauna. South Africa stands out as the only continental country that follows this trend. The knowledge gained on severity and nature of gastropod impacts is useful in risk assessment, which can aid conservation management. To make impact assessments more realistic, we suggest alternative ways of reporting impacts classified under EICAT and SEICAT.

Biosynthesis in the Albumen Gland-Capsule Gland Complex Limits Reproductive Effort in the Invasive Apple Snail Pomacea canaliculata

High fecundity often contributes to successful invasives. In molluscs, this may be facilitated by the albumen gland-capsule gland complex, which in gastropods secretes the egg perivitelline fluid that nourishes and protects embryos. The biochemistry of the albumen gland-capsule gland complex and its relationship with fecundity remain largely unknown. We addressed these issues in Pomacea canaliculata (Lamarck, 1822), a highly invasive gastropod whose fecundity and reproductive effort exceed those of ecologically similar gastropods. We evaluated the dynamics of its major secretion compounds (calcium, polysaccharides, and total proteins) as well as the gene expression and stored levels of perivitellins during key moments of the reproductive cycle, that is, before and after first copulation and at low, medium, and high reproductive output. Copulation and first oviposition do not trigger the onset of albumen gland-capsule gland complex biosynthesis. On the contrary, soon after an intermediate reproductive effort, genes encoding perivitellins overexpressed. A high reproductive effort caused a decrease in all albumen gland-capsule gland complex secretion components. Right after a high reproductive output, the albumen gland-capsule gland complex restored the main secretion components, and calcium recovered baseline reserves; but proteins and polysaccharides did not. These metabolic changes in the albumen gland-capsule gland complex after multiple ovipositions were reflected in a reduction in egg mass but did not compromise egg quality. At the end of the cycle, egg dry weight almost doubled the initial albumen gland-capsule gland complex weight. Results indicate that albumen gland-capsule gland complex biosynthesis limits a constantly high reproductive output. Therefore, lowering fecundity by targeting biosynthesis could effectively reduce the rate of this species' spread.

A habitat-based framework to predict the effects of agricultural drain maintenance on imperiled fishes

One third of the total global land viable for agricultural production has artificial drainage systems. These drainage systems can provide important habitat for fishes and, in some cases, imperiled fish species vulnerable to impact by drainage maintenance activities. A framework to provide quantitative assessments of the effects of maintenance activities on imperiled fish species is needed. In this study, a six-step habitat-based framework was developed to predict suitable habitat for two at-risk species in an agricultural drain: the Endangered Pugnose Shiner (Notropis anogenus) and the Special Concern Blackstripe Topminnow (Fundulus notatus). Using the framework, spatial models were developed to assess the effects of proposed drain maintenance on the overall amount of suitable habitat, habitat patch size, and connectivity of habitat patches. Maintenance had a significant impact on habitat connectivity, but did not significantly reduce the habitat size of isolated patches. The amount of suitable habitat available after maintenance fell below the minimum area for population viability (MAPV) for the Pugnose Shiner, but not the Blackstripe Topminnow. Future impact assessments of drain maintenance should incorporate population viability analysis, coupled with habitat patch analysis (patch size and connectivity), to quantitatively test consequences of proposed alteration to the viability of spatially structured populations.

A temperature-dependent physiologically based model for the invasive apple snail Pomacea canaliculata

In order to set priorities in management of costly and ecosystem-damaging species, policymakers and managers need accurate predictions not only about where a specific invader may establish but also about its potential abundance at different geographical scales. This is because density or biomass per unit area of an invasive species is a key predictor of the magnitude of environmental and economic impact in the invaded habitat. Here, we present a physiologically based demographic model describing and explaining the population dynamics of a widespread freshwater invader, the golden apple snail Pomacea canaliculata, which is causing severe environmental and economic impacts in invaded wetlands and rice fields in Southeastern Asia and has also been introduced to North America and Europe. The model is based on bio-demographic functions for mortality, development and fecundity rates that are driven by water temperature for the aquatic stages (juveniles and adults) and by air temperature for the aerial egg masses. Our model has been validated against data on the current distribution in South America and Japan, and produced consistent and realistic patterns of reproduction, growth, maturation and mortality under different scenarios in accordance to what is known from real P. canaliculata populations in different regions and climates. The model further shows that P. canaliculata will use two different reproductive strategies (semelparity and iteroparity) within the potential area of establishment, a plasticity that may explain the high invasiveness of this species across a wide range of habitats with different climates. Our results also suggest that densities, and thus the magnitude of environmental and agricultural damage, will be largely different in locations with distinct climatic regimes within the potential area of establishment. We suggest that physiologically based demographic modelling of invasive species will become a valuable tool for invasive species managers.

Promise and challenges of risk assessment as an approach for preventing the arrival of harmful alien species

Background: Harmful alien species impose a growing environmental, economic and human well-being burden around the globe. A promising way to reduce the arrival of new species that may become harmful is to utilise pre-border risk assessment (RA) tools that relate the traits of introduced species to whether those species have become established and harmful. These tools can be applied to species proposed for intentional introduction so that informed decisions can be made about whether each species poses an acceptable risk and should be allowed for import. Objectives: A range of approaches to RA tool development have emerged, each relying on different assumptions about the relationships between traits and species impacts, and each requiring different levels and types of data. We set out to compare the qualities of each approach and make recommendations for their application in South Africa, a high biodiversity developing country that already has many invasive species. Method: We reviewed five approaches to pre-border RA and assessed the benefits and drawbacks of each. We focused on how pre-border RA could be applied in South Africa. Results: Recent legislation presents a framework for RA to evaluate species introductions to South Africa, but we find that this framework assumes an approach to RA that is relatively slow and costly and that does not leverage recent advances in RA tool development. Conclusion: There is potential for proven RA approaches to be applied in South Africa that would be less costly and that could more rapidly assess the suite of species currently being introduced.

Life table estimates of the invasive snail Physa acuta Draparnaud, 1805, occurring in India

The life table characteristics of the invasive snail Physa acuta were assessed in the laboratory using the individuals occurring in a newly colonised area in Burdwan, West Bengal, India. Using the changes in the shell length and the body weight of the snails as surrogate, the population growth of the snails was estimated along with longevity and the fecundity schedule. The cohort of P. acuta lived for a maximum of 22 weeks with a life expectancy (ex) of 7.27 weeks and the age-specific survivorship being 0.825. Increment of the shell length of the snails complied with the von Bertalanffy growth equation, lt = 11.75(1 − exp−0.17(t−0.06)), and the observed and the expected data of the length at time t (lt) did not vary significantly (z score = 0.230; P = 0.818; n=20 pairs). Following attainment of sexual maturity between 28 and 42 days, oviposition continued till 20 weeks time, with 0.1-10 eggs laid by each individual. The eggs present per capsule remained between 01 and 11, whilst the net reproductive rate (R0), intrinsic rate of increase (rm) and the finite rate of increase (λ) were 116.07, 0.1 and 1.11, respectively. The observations are similar to those made earlier on the same species but from African and South American continents. The results of the present observation are pioneer in providing the initial studies about the life history of the invasive snail P. acuta in Indian context. Using the present information as a basis, further studies including long-term population monitoring should be initiated to understand the effects of the invasive snail P. acuta in the freshwater ecosystem of West Bengal, India.

Importance of Macrophyte Quality in Determining Life-History Traits of the Apple Snails Pomacea canaliculata: Implications for Bottom-Up Management of an Invasive Herbivorous Pest in Constructed Wetlands

Pomacea canaliculata (Ampullariidae) has extensively invaded most Asian constructed wetlands and its massive herbivory of macrophytes has become a major cause of ecosystem dysfunctioning of these restored habitats. We conducted non-choice laboratory feeding experiments of P. canaliculata using five common macrophyte species in constructed wetlands including Ipomoea aquatica, Commelina communis, Nymphoides coreana, Acorus calamus and Phragmites australis. Effects of macrophytes on snail feeding, growth and fecundity responses were evaluated. Results indicated that P. canaliculata reared on Ipomoea had the highest feeding and growth rates with highest reproductive output, but all individuals fed with Phragmites showed lowest feeding rates and little growth with poorest reproductive output. Plant N and P contents were important for enhancing palatability, supporting growth and offspring quantity of P. canaliculata, whilst toughness, cellulose and phenolics had critically deterrent effects on various life-history traits. Although snail offspring quality was generally consistent regardless of maternal feeding conditions, the reduced growth and offspring quantity of the poorly-fed snails in constructed wetlands dominated by the less-palatable macrophytes could limit the invasive success of P. canaliculata. Effective bottom-up control of P. canaliculata in constructed wetlands should involve selective planting strategy using macrophytes with low nutrient and high toughness, cellulose and phenolic contents.

Competitive replacement of invasive congeners may relax impact on native species: interactions among zebra, quagga, and native unionid mussels

Determining when and where the ecological impacts of invasive species will be most detrimental and whether the effects of multiple invaders will be superadditive, or subadditive, is critical for developing global management priorities to protect native species in advance of future invasions. Over the past century, the decline of freshwater bivalves of the family Unionidae has been greatly accelerated by the invasion of Dreissena. The purpose of this study was to evaluate the current infestation rates of unionids by zebra (Dreissena polymorpha) and quagga (D. rostriformis bugensis) mussels in the lower Great Lakes region 25 years after they nearly extirpated native unionids. In 2011-2012, we collected infestation data for over 4000 unionids from 26 species at 198 nearshore sites in lakes Erie, Ontario, and St. Clair, the Detroit River, and inland Michigan lakes and compared those results to studies from the early 1990 s. We found that the frequency of unionid infestation by Dreissena recently declined, and the number of dreissenids attached to unionids in the lower Great Lakes has fallen almost ten-fold since the early 1990s. We also found that the rate of infestation depends on the dominant Dreissena species in the lake: zebra mussels infested unionids much more often and in greater numbers. Consequently, the proportion of infested unionids, as well as the number and weight of attached dreissenids were lower in waterbodies dominated by quagga mussels. This is the first large-scale systematic study that revealed how minor differences between two taxonomically and functionally related invaders may have large consequences for native communities they invade.

Potential fecundity of a highly invasive gall maker, Dryocosmus kuriphilus (Hymenoptera: Cynipidae)

Fecundity is a key factor in modulating population growth rate, and is of particular significance when considering the invasiveness of introduced species. In insects, fecundity is affected by body size, age, and nutrition. We investigated the potential fecundity of the invasive Asian chestnut gall wasp Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae), an introduced parthenogenetic gall former of Asian origin and a global pest of chestnut (Castanea spp.), to better understand its invasiveness. We compared ovarian, egg, and body metrics of adult wasps of different age. We evaluated insect weight, body length, mesosomal and metasomal lengths and widths, hind femur length, number of eggs, and size of eggs in wasps from four age cohorts. Adult weight and metasomal width were positively correlated with number of eggs. Egg load decreased with wasp age, and egg size initially increased before decreasing. Our findings suggest that adult D. kuriphilus, previously reported as proovigenic, may be resorping eggs in the absence of suitable hosts, and reallocating nutritive resources for body maintenance and egg quality to increase fitness, implicating a plasticity in its reproductive strategy. D. kuriphilus may be able to vary its potential fecundity in response to nutrition and host availability, thus increasing its invasiveness.

Count your eggs before they invade: identifying and quantifying egg clutches of two invasive apple snail species (Pomacea)

Winning the war against invasive species requires early detection of invasions. Compared to terrestrial invaders, aquatic species often thrive undetected under water and do not garner notice until too late for early action. However, fortunately for managers, apple snails (Family Ampullariidae, Genus Pomacea) provide their own conspicuous sign of invasion in the form of vibrantly colored egg clutches. Managers can potentially use egg clutches laid in the riparian zone as a means of early detection and species identification. To facilitate such efforts, we quantified differences in characteristics (length, width, depth, mass, egg number) of field-laid clutches for the two most common invasive species of apple snail, P. canaliculata and P. maculata, in native and non-native populations. Pomacea canaliculata native and non-native populations differed noticeably only in width. Native P. maculata clutches possessed significantly greater width, mass and eggs numbers compared with native P. canaliculata. Non-native P. maculata clutches significantly exceeded all other populations in all measured characteristics. Consequently, these traits may successfully distinguish between species. Fecundity data also allowed us to develop models that accurately estimated the number of eggs per clutch for each species based on clutch dimensions. We tested one, two and three dimensional models of clutches, including rendering a clutch as either a complete ellipsoid or an ellipsoid intersected by a cylinder to represent the oviposition site. Model comparisons found the product of length and depth, with a different function for each population, best predicted egg number for both species. Comparisons of egg number to clutch volume and mass implied non-native P. canaliculata may be food limited, while non-native P. maculata appeared to produce such enormous clutches by having access to greater nutrients than the native population. With these new tools, researchers and managers can quickly identify, quantify and begin eradication of new non-native apple snail populations.

Predation effects of Melanoides tuberculatus Müller 1774) on periphytic biofilm colonization: an experimental approach

The present study evaluated the predation effects of the gastropod Melanoides tuberculatus on the taxa richness and density of the periphyton community. A laboratory experiment was conducted with two treatments: control (without M. tuberculatus) and with M. tuberculatus, each treatment being replicated four times. For periphyton colonization, glass slides were placed in 3.5 L of water from the environment of the gastropods. The analysis of species richness and density of the periphyton community on these artificial substrates showed significant differences (p <0.05) between treatments. In the treatment with M. tuberculatus, taxa richness and density were lower, with a predominance of Chantrasia macrospora in the last days of the experiment. It follows that predation by M. tuberculatus destabilizes the course of periphyton colonization, suggesting the possibility of disruption of natural food chains, however, more studies are needed in this perspectives.

Risk-based probabilistic approach to assess the impact of false mussel invasions on farmed hard clams

The purpose of this article is to provide a risk-based predictive model to assess the impact of false mussel Mytilopsis sallei invasions on hard clam Meretrix lusoria farms in the southwestern region of Taiwan. The actual spread of invasive false mussel was predicted by using analytical models based on advection-diffusion and gravity models. The proportion of hard clam colonized and infestation by false mussel were used to characterize risk estimates. A mortality model was parameterized to assess hard clam mortality risk characterized by false mussel density and infestation intensity. The published data were reanalyzed to parameterize a predictive threshold model described by a cumulative Weibull distribution function that can be used to estimate the exceeding thresholds of proportion of hard clam colonized and infestation. Results indicated that the infestation thresholds were 2-17 ind clam(-1) for adult hard clams, whereas 4 ind clam(-1) for nursery hard clams. The average colonization thresholds were estimated to be 81-89% for cultivated and nursery hard clam farms, respectively. Our results indicated that false mussel density and infestation, which caused 50% hard clam mortality, were estimated to be 2,812 ind m(-2) and 31 ind clam(-1), respectively. This study further indicated that hard clam farms that are close to the coastal area have at least 50% probability for 43% mortality caused by infestation. This study highlighted that a probabilistic risk-based framework characterized by probability distributions and risk curves is an effective representation of scientific assessments for farmed hard clam in response to the nonnative false mussel invasion.

When can efforts to control nuisance and invasive species backfire?

Population control through harvest has the potential to reduce the abundance of nuisance and invasive species. However, demographic structure and density-dependent processes can confound removal efforts and lead to undesirable consequences, such as overcompensation (an increase in abundance in response to harvest) and instability (population cycling or chaos). Recent empirical studies have demonstrated the potential for increased mortality (such as that caused by harvest) to lead to overcompensation and instability in plant, insect, and fish populations. We developed a general population model with juvenile and adult stages to help determine the conditions under which control harvest efforts can produce unintended outcomes. Analytical and simulation analyses of the model demonstrated that the potential for overcompensation as a result of harvest was significant for species with high fecundity, even when annual stage-specific survivorship values were fairly low. Population instability as a result of harvest occurred less frequently and was only possible with harvest strategies that targeted adults when both fecundity and adult survivorship were high. We considered these results in conjunction with current literature on nuisance and invasive species to propose general guidelines for assessing the risks associated with control harvest based on life history characteristics of target populations. Our results suggest that species with high per capita fecundity (over discrete breeding periods), short juvenile stages, and fairly constant survivorship rates are most likely to respond undesirably to harvest. It is difficult to determine the extent to which overcompensation and instability could occur during real-world removal efforts, and more empirical removal studies should be undertaken to evaluate population-level responses to control harvests. Nevertheless, our results identify key issues that have been seldom acknowledged and are potentially generic across taxa.

Pandora's Box Contained Bait: The Global Problem of Introduced Earthworms

Introduced exotic earthworms now occur in every biogeographic region in all but the driest or coldest habitat types on Earth. The global distribution of a few species (e.g., Pontoscolex corethrurus) was noted by early naturalists, but now approximately 120 such peregrine species are recognized to be widespread from regional to global scales, mainly via human activities. Species adapted to human transport and to colonization of disturbed habitats are most widespread and are the principal invasive species. We identify a number of endogenous and exogenous factors that may contribute to the successful establishment and spread of peregrine species. Quantification of these factors may help to determine why certain species become invasive while others do not. Recent advances in theory and modeling of biological invasions and in molecular techniques should prove fruitful in improving our understanding of invasive earthworms, as well as in predicting their impacts on ecosystems.