Feeding and growth of native, invasive and non-invasive alien apple snails (Ampullariidae) in the United States: Invasives eat more and grow more

Increasing Antimicrobial Resistance and Potential Human Bacterial Pathogens in an Invasive Land Snail Driven by Urbanization

Our understanding of the role urbanization has in augmenting invasive species that carry human bacterial pathogens and antimicrobial resistance (AMR) remains poorly understood. Here, we investigated the gut bacterial communities, antibiotic resistance genes (ARGs) and potential antibiotic-resistant pathogens in giant African snails (Achatina fulica) collected across an urbanization gradient in Xiamen, China (n = 108). There was a lack of correlation between the microbial profiles of giant African snails and the soils of their habitats, and the resistome and human-associated bacteria were significantly higher than those of native snails as well as soils. We observed high diversity (601 ARG subtypes) and abundance (1.5 copies per 16S rRNA gene) of giant African snail gut resistome. Moreover, giant African snails in more urban areas had greater diversity and abundance of high-risk ARGs and potential human bacterial pathogens (e.g., ESKAPE pathogens). We highlight that urbanization significantly impacted the gut microbiomes and resistomes of these invasive snails, indicating that they harbor greater biological contaminants such as ARGs and potential human bacterial pathogens than native snails and soils. This study advances our understanding of the effect of urbanization on human bacterial pathogens and AMR in a problematic invasive snail and should help combat risks associated with invasive species under the One Health framework.

Invasive snails alter multiple ecosystem functions in subtropical wetlands

Invasive species that compromise ecosystem functioning through direct and indirect (or cascading) pathways are a rising global threat. Apple snails (Pomacea spp.) are semi-aquatic freshwater invaders that have exerted devastating ecological and economic impacts on agricultural wetlands and are emerging as a major threat to the structures and functions of natural wetlands. In this research, we conducted a field mesocosm experiment in subtropical wetlands in Florida, USA to investigate how P. maculata alter a suite of wetland vegetation, water, and soil processes and how these effects vary across wetlands under two different management intensities. Overall, we found that invasive snails substantially decreased aboveground biomass and vegetation cover and exhibited preferential feeding on wetland plant species. In addition, snails increased water nutrients (e.g., total carbon, nitrogen, phosphorous and dissolved solids), but showed minimal impacts on soil pools and processes. While most effects of invasive P. maculata were similar across wetland types, certain responses (e.g., algal biomass) were divergent. Our study provides holistic evidence on multiple direct and indirect consequences of invasive apple snails along the wetland plant-water-soil continuum. By altering plant assemblages and nutrient cycling (e.g., via consumption, egestion, and excretion), P. maculata invasion could hamper vital wetland services, which is concerning for these globally vulnerable ecosystems. Differential snail effects across management intensities further suggest the need for tailored actions to mitigate apple snail impacts and conserve wetland ecosystems.

Surface crawling and pedal surface collecting in aquatic gastropods: A case of scientific amnesia

Aquatic gastropods, both freshwater and marine, often crawl along the water surface with the sole of the foot facing upward. Differential regulation of the activity of cilia on the sole turns the gliding mechanism into pedal surface collecting, by which food particles floating on the water are collected on the sole. Over the last 300 years, surface crawling and pedal surface collecting have been studied in numerous species, but the accumulated knowledge has fallen victim to scientific amnesia. Today, pedal surface collecting usually is considered a unique behaviour that evolved in the family Ampullariidae (Caenogastropoda), which includes the genus Pomacea with some of the globally worst invasive pests. Consequently it may appear feasible to tackle invasive Pomacea species specifically by delivering molluscicides via the water surface. Based on a review of our forgotten literature, I here argue that such an approach would have potentially devastating, unintended effects on native gastropod faunas.

Comparison of gut microbiome in the Chinese mud snail (Cipangopaludina chinensis) and the invasive golden apple snail (Pomacea canaliculata)

Background

Gut microbiota play a critical role in nutrition absorption and environmental adaptation and can affect the biological characteristics of host animals. The invasive golden apple snail (Pomacea canaliculata) and native Chinese mud snail (Cipangopaludina chinensis) are two sympatric freshwater snails with similar ecological niche in southern China. However, gut microbiota comparison of interspecies remains unclear. Comparing the difference of gut microbiota between the invasive snail P. canaliculata and native snail C. chinensis could provide new insight into the invasion mechanism of P.canaliculata at the microbial level.

Methods

Gut samples from 20 golden apple snails and 20 Chinese mud snails from wild freshwater habitats were collected and isolated. The 16S rRNA gene V3-V4 region of the gut microbiota was analyzed using high throughput Illumina sequencing.

Results

The gut microbiota dominantly composed of Proteobacteria, Bacteroidetes, Firmicutes and Epsilonbacteraeota at phylum level in golden apple snail. Only Proteobacteria was the dominant phylum in Chinese mud snail. Alpha diversity analysis (Shannon and Simpson indices) showed there were no significant differences in gut microbial diversity, but relative abundances of the two groups differed significantly (P < 0.05). Beta diversity analysis (Bray Curtis and weighted UniFrac distance) showed marked differences in the gut microbiota structure (P < 0.05). Unique or high abundance microbial taxa were more abundant in the invasive snail compared to the native form. Functional prediction analysis indicated that the relative abundances of functions differed significantly regarding cofactor prosthetic group electron carrier and vitamin biosynthesis, amino acid biosynthesis, and nucleoside and nucleotide biosynthesis (P < 0.05). These results suggest an enhanced potential to adapt to new habitats in the invasive snail.

Context-dependent differences in the functional responses of conspecific native and non-native crayfishes

Invasive species are proliferating globally and cause a range of impacts, necessitating risk assessment and prioritization prior to management action. Experimentally derived estimates of per capita effects (e.g. functional responses) have been advocated as predictors of field impacts of potential invaders. However, risk assessments based on estimates from single populations can be misleading if per capita effects vary greatly across space and time. Here, we present a large-scale, multi-population comparison of per capita effects of the American spinycheek crayfish, Faxonius (formerly Orconectes) limosus—a species with an extensive invasion history in eastern North America and Europe. Functional responses were measured on individuals from six geographically disparate populations of F. limosus in its native and invaded ranges on two continents. These revealed inter-population differences in both the maximum feeding rate and functional response type that could not be explained by the biogeographic origin of the population nor by time since the invasion. We propose that other differences in source communities (including the presence of competitors) impose selective pressures for phenotypic traits that result in dissimilar per capita effects. We also compared functional responses of the congeners F. limosus and F. virilis in the presence and absence of potential competitors to examine indirect competitive effects on feeding behaviour. The maximum feeding rate of F. limosus, but not F. virilis, was suppressed in the presence of heterospecific and conspecific competitors, demonstrating how the per capita effects of these species can differ across biotic contexts. In the competitor-presence experiments, individuals from the invasive population of F. limosus consistently had a higher maximum feeding rate than those of the native F. virilis, regardless of treatment. Our results caution against invasion risk assessments that use information from only one (or a few) populations or that do not consider the biotic context of target habitats. We conclude that comparative functional responses offer a rapid assessment tool for invader ecological impacts under context dependencies when multiple populations are analyzed.

Dealing with a hyper-successful neighbor: effects of the invasive apple snail Pomacea canaliculata on exotic and native snails in South America

Pomacea canaliculata is a successful invader and also a competitor and predator of other snails and may play a key role in structuring freshwater snail communities both in its native and invaded range. In the present study we evaluated the contact and distant effects of P. canaliculata in its native range on exotic (Melanoides tuberculata and Physa acuta) and native snails (Heleobia parchappii, Biomphalaria peregrina, and Chilina parchappii). Habitat use was affected in P. acuta, H. parchappii, and B. peregrina by contact effects of P. canaliculata, whereas survival was only affected in P. acuta through combined contact and distant effects. Fecundity was reduced in P. acuta and B. peregrina by combined contact and distant effects; evidence of egg mass predation was also observed in both species. Melanoides tuberculata was not affected at all by P. canaliculata. The snail species with higher withdrawal responses to contacts with P. canaliculata were those that suffered less mortality by corporal contact, whereas snails with high crawling away responses suffered from higher mortality. The effects of P. canaliculata seem to be highly negative to small nonoperculate snails that lay gelatinous egg masses, whereas large operculate ovoviviparous snails are not affected in their survival and reproduction. This apple snail may exert biotic resistance against P. acuta but could favor the establishment of M. tuberculata and other functionally similar species in new habitats in South America.

Not in the Least Concern: anthropogenic influences on a South-east Asian apple snail Pila scutata (Ampullariidae)

South-east Asian apple snails, Pila spp., have been declining since the introduction of globally invasive, confamilial South American Pomacea spp., yet Pila ecology remains poorly studied, with most occurrence records unconfirmed. Pila scutata, a previously widespread species, presumed native to the Malay peninsula and assessed as Least Concern in the IUCN Red List, was formerly harvested for food, and may have experienced anthropogenic translocations. We surveyed the Malay peninsula (specifically Peninsular Malaysia and Singapore) to investigate the current distribution and genetic diversity of P. scutata. Six populations were found in Singapore, but only one in Peninsular Malaysia. Mitochondrial COI and 16S sequencing revealed that the Malaysian population shared a single haplotype of both genes with the Singapore populations (500 km distant). This low genetic diversity could stem from a recent anthropogenic introduction, which brings into question the true native range of P. scutata and, coupled with poorly resolved taxonomy of the genus, necessitates a reassessment of its IUCN Red List status. Introduced populations pose a dilemma, and the lack of genetic diversity is of concern in light of Pila decline throughout South-east Asia. Our results highlight that conservation management of P. scutata and its congeners must therefore be better informed by greater taxonomic resolution and more comprehensive investigations of their ecology, both in native and introduced ranges.

Cadmium bioaccumulation and antioxidant enzyme activity in hepatopancreas, kidney, and stomach of invasive apple snail Pomacea canaliculata

The acute toxicity of Cd was tested, and metal bioaccumulation in tissue was determined for the alien invasive species Pomacea canaliculata and its native competitor Sinotaia quadrata under experimental conditions. The invasive species was more tolerant to Cd toxicity than native species, for which the LC₅₀ values were 4.26, 2.24, and 1.98 mg/L at exposure times of 48, 72, and 96 h, respectively, approximately three times higher than those of the native snails. The viscera accumulated the highest Cd concentration, followed by the foot and shell in both species. Metal concentrations in the above three tissues of P. canaliculata were much higher than those of S. quadrata, irrespective of Cd dose and exposure time. For P. canaliculata, the highest concentration of metal was further observed in the hepatopancreas (0.64-3.98 mg/g) followed by the kidney (0.067-3.78 mg/g), with lowest levels in the stomach (0.062-1.53 mg/g). Among the five antioxidant enzymes, the most responsive enzymes were CAT, ALP, and GST in the hepatopancreas; CAT, POD, and GST in the kidney; and POD in the stomach of exposed animals. These results, demonstrating a high Cd tolerance, may partly explain the ability of P. canaliculata to displace S. quadrata in Cd-contaminated habitat. The Cd was accumulated mainly in the hepatopancreas and kidney of invasive species, which changed the activity of antioxidant enzymes allowing the animals to cope with the toxicity. Graphical abstract Cadmium bioaccumulation and antioxidant enzyme activity in the invasive Pomacea canaliculata.

System productivity alters predator sorting of a size-structured mixed prey community

Predator-prey interactions are often size-structured and focused on smaller vulnerable size classes. Predators are also predicted to sort prey communities according to relative vulnerabilities. Increased system productivity and juvenile growth may benefit some species more than others, making relative vulnerability non-static and growth-mediated. We hypothesized that increased system productivity would weaken juvenile-stage predation generally, and potentially shift the community sorting effects of a predator. Using replicated wetland mesocosms we quantified the effects of a generalist size-specific crayfish predator (Procambarus fallax) on juveniles of two species of apple snails (Pomacea spp.) under two levels of system productivity (low vs. high). After 6 weeks of exposure, we quantified predator and productivity effects on snail survival, biomass, and composition of the assemblage. Crayfish depressed the final density and biomass of snails, and sorted the assemblage, selectively favoring survival of the native P. paludosa over the intrinsically more vulnerable invasive P. maculata. Both snails grew faster at higher productivity, but growth differentially increased survival of the invasive snail in the presence of crayfish and weakened the sorting effect. The native P. paludosa hatches at a larger less vulnerable size than the invasive P. maculata, but higher productivity reduced the relative advantage of P. paludosa. Our results are inconsistent with predictions about the sorting effects of predators across productivity gradients because the more resistant prey dominated at low productivity. Our findings highlight that the relative vulnerabilities of prey to a common predator are not always fixed, but can be growth-mediated.

Complete mitochondrial genome of the apple snail Pomacea diffusa (Gastropoda, Ampullariidae) with phylogenetic consideration

We present the complete mitochondrial genome of Pomacea diffusa in this study. The results show that the mitochondrial genome is 16,640 bp in length, which is comprised of 13 protein-coding genes, two rRNA genes, and 21 tRNA genes. The nucleotide compositions of the light strand are 39.62% of A, 30.13% of T, 16.02% of C, and 14.24% of G. Except eight tRNA (Glu, Gly, Trp, Cys, Tyr, Met, Thr, Val) on the light strand, the rest are encoded on the heavy strand. All the protein-coding genes start with ATC initiation codon, and two types of inferred termination codons are TAA and TAG. There are 26 intergenic spacers and two gene overlaps. The phylogenetic analysis shows that P. diffusa clusters with P. canaliculata and P. maculata with high bootstrap support, which is consistent with the morphological and molecular evidence.

Introgressive replacement of natives by invading Arion pest slugs

Hybridization with invasive species is one of the major threats to the phenotypic and genetic persistence of native organisms worldwide. Arion vulgaris (syn. lusitanicus) is a major agricultural pest slug that successfully invaded many European countries in recent decades, but its impact on closely related native species remains unclear. Here, we hypothesized that the regional decline of native A. rufus is connected with the spread of invasive A. vulgaris, and tested whether this can be linked to hybridization between the two species by analyzing 625 Arion sp. along altitudinal transects in three regions in Switzerland. In each region, we observed clear evidence of different degrees of genetic admixture, suggesting recurrent hybridization beyond the first generation. We found spatial differences in admixture patterns that might reflect distinct invasion histories among the regions. Our analyses provide a landscape level perspective for the genetic interactions between invasive and native animals during the invasion. We predict that without specific management action, A. vulgaris will further expand its range, which might lead to local extinction of A. rufus and other native slugs in the near future. Similar processes are likely occurring in other regions currently invaded by A. vulgaris.

Ecology of the non-native snail Sinotaia cf quadrata (Caenogastropoda: Viviparidae). A study in a lowland stream of South America with different water qualities

Sinotaia quadrata is a snail native from Asia recorded for the first time in South America in 2009 in central Argentina. In 2015, this species was also found in a lowland stream with different water qualities. Our aims were to contribute to the knowledge of its population ecology and to compare the individuals from the two locations anatomically. Snails were searched at 6 sites, where physicochemical and hydraulic parameters were measured. Biological samples were also taken at two sites (S3 and S4) to study the population traits of S. cf quadrata (density, size structure, fecundity and sex ratio) and to assess the water quality through macroinvertebrates' biological indices (richness, diversity and IBPamp). Physicochemical and biological parameters allowed us classifying sites as "moderately polluted" (S3) and "heavily polluted" (S4). At S4, the population showed a lower density, larger individuals, higher fecundity and a scarce representation of young snails. The differences observed in the radula and mantle border of snails from the two geographical regions might be attributed to environmental differences. We conclude that this species is tolerant to a wide range of environmental variables which, along with its high fecundity and morphological plasticity, could allow this species to colonize neighbor streams.

Counteracting effects of a non-native prey on the demography of a native predator culminate in positive population growth

Identifying impacts of non-native species on native populations is central to conservation and ecology. While effects of non-native predators on native prey populations have recently received much attention, impacts of introduced prey on native predator populations are less understood. Non-native prey can influence predator behavior and demography through direct and indirect pathways, yet quantitative assessments of the relative impacts of multiple, potentially counteracting, effects on native predator population growth remain scarce. Using ≈20 years of range-wide monitoring data, we tested for effects of a recently introduced, rapidly spreading non-native prey species (Pomacea maculata) on the behavior and demography of the endangered Snail Kite (Rostrhamus sociabilis). Previous studies found that food-handling difficulties caused by the large size of P. maculata (relative to the native P. paludosa) can lead to energetic deficiencies in juvenile kites, suggesting the potential for evolutionary traps to occur. However, high densities of P. maculata populations could facilitate kites by providing supplemental food resources. Contrary to prior hypotheses, we found that juvenile apparent survival increased ≈50% in wetlands invaded by non-native snails. Breeding rates and number of young fledged/successful nests were also positively associated with non-native snail presence, suggesting direct trophic benefits to kites. We found no direct effects of the invasive snail on adult survival or daily nest survival rates. Kite movements and breeding distribution closely tracked the spread of non-native snail populations. Since 2005, kites have been heavily concentrated in northern regions where non-native snails have established. This geographic shift has had hidden costs, as use of northern regions is associated with lower adult survival. Despite negative impacts to this key vital rate, matrix population modeling indicated that the multifarious effects of the non-native snail invasion on kites culminated in increased population growth rates, likely lowering short-term extinction risks. Results suggest that considering only particular components of behavior or demography may be inadequate to infer the population-dynamic importance of non-native prey on native predators, including their role in creating potential evolutionary traps. Our findings provide information pertinent to Everglades restoration, highlighting potential management trade-offs for non-native species that may aid imperiled species recovery yet disrupt other native communities.

Assessing the Value of Novel Habitats to Snail Kites through Foraging Behavior and Nest Survival

Novel ecosystems arise for a variety of reasons, most notably from the introduction of nonnative species. Understanding the interactions between traditional habitats, novel habitats, and species of conservation interest is important when planning successful conservation strategies. In the United States, the snail kite Rostrhamus sociabilis plumbeus is a federally endangered species whose population in Florida has undergone declines within the past decade. While studying the foraging behavior of breeding snail kites on Lake Tohopekaliga (Lake Toho), we discovered the unexpected use of disturbed ephemeral wetlands adjacent to the lake. These wetlands represent a novel habitat for snail kites; they would not have been viable foraging areas prior to the introduction of the exotic island apple snail Pomacea maculata. By examining the differences between snail kite behavior in traditional and novel habitats, we were able to identify some characteristics of novel habitats that may be important in determining their value to snail kites. The novel wetland areas were highly attractive to snail kites, likely because of the high snail capture rates. The survival of snail kite nests occurring within the novel areas appeared to be similar to that of nests occurring in more traditional, nearby areas on Lake Toho. However, whether or not snail kites used novel habitats as nesting areas appeared to be dependent upon water depth and availability of nesting substrate within these areas. The snail kites' dynamic use of the novel habitat demonstrates both the value of a novel ecosystem and the importance of traditional habitats to a species of conservation concern.

The development of Angiostrongylus vasorum (Baillet, 1866) in the freshwater snail Pomacea canaliculata (Lamarck, 1822)

Angiostrongylus vasorum is a parasitic nematode that infects the heart and pulmonary artery and its branches of domestic and wild canids. The parasite can use several species of terrestrial and aquatic molluscs as intermediate hosts, although susceptibility varies. Pomacea canaliculata is a mollusc found in lakes, swamps and rivers in South America. In this study, we evaluated the susceptibility, parasite growth, oviposition and larval development of 282 P. canaliculata infected with 500 A. vasorum first-instar larvae (L1). From day 5 post-infection (pi) to day 30 pi, seven specimens per day were sacrificed to recover the larval instars. We compared 50 egg masses from infected and uninfected molluscs to determine the number of eggs per clutch, the hatching rate and the growth of the molluscs. The percentage of recovered larvae ranged from 39.17% to 67.5%. First-stage larvae (L1) were found until day 19 pi, second-stage larvae (L2) were found from days 11 to 25 pi, and third-stage larvae (L3) were recovered only after day 19 pi. Infected snails exhibited the most eggs during spawning, although the rate of hatching and shell size were lower in the infected snails compared with controls. This is the first report of an experimental infection of P. canaliculata with A. vasorum, and the results confirm the non-specificity of the nematode in relation to the intermediate host and indicate the importance of epidemiological surveys of this parasite and mollusc.

Comparative Functional Responses Predict the Invasiveness and Ecological Impacts of Alien Herbivorous Snails

Understanding determinants of the invasiveness and ecological impacts of alien species is amongst the most sought-after and urgent research questions in ecology. Several studies have shown the value of comparing the functional responses (FRs) of alien and native predators towards native prey, however, the technique is under-explored with herbivorous alien species and as a predictor of invasiveness as distinct from ecological impact. Here, in China, we conducted a mesocosm experiment to compare the FRs among three herbivorous snail species: the golden apple snail, Pomacea canaliculata, a highly invasive and high impact alien listed in “100 of the World's Worst Invasive Alien Species”; Planorbarius corneus, a non-invasive, low impact alien; and the Chinese native snail, Bellamya aeruginosa, when feeding on four locally occurring plant species. Further, by using a numerical response equation, we modelled the population dynamics of the snail consumers. For standard FR parameters, we found that the invasive and damaging alien snail had the highest “attack rates” a, shortest “handling times” h and also the highest estimated maximum feeding rates, 1/hT, whereas the native species had the lowest attack rates, longest handling times and lowest maximum feeding rates. The non-invasive, low impact alien species had consistently intermediate FR parameters. The invasive alien species had higher population growth potential than the native snail species, whilst that of the non-invasive alien species was intermediate. Thus, while the comparative FR approach has been proposed as a reliable method for predicting the ecological impacts of invasive predators, our results further suggest that comparative FRs could extend to predict the invasiveness and ecological impacts of alien herbivores and should be explored in other taxa and trophic groups to determine the general utility of the approach.

Effect of cardiac glycosides from Nerium indicum on feeding rate, digestive enzymes activity and ultrastructural alterations of hepatopancreas in Pomacea canaliculata

Cardiac glycosides from Nerium indicum showed potent molluscicide activity against Pomacea canaliculata (GAS), but the toxicological mechanism is still far less understood. Effects of sublethal treatments of cardiac glycosides on feeding rate, digestive enzymes and ultrastructural alterations of the hepatopancreas in GAS were evaluated in this study. Exposure of GAS to sublethal concentrations of cardiac glycosides resulted in a significant reduction of feeding rate of GAS. The amylase, cellulose and protease activity were increase significantly at the end of 24 h followed by significant inhibition after 48 h of exposure while lipase activity was not affected significantly at the end of 24 h followed by a significant inhibition after 48 h of exposure during experimental period. The main ultrastructural alterations of hepatopancreas observed in snails under cardiac glycosides treatment comprised disruption of nuclear membrane, increased vesiculation and dilatation of endoplasmic reticulum, and vacuolization and swelling of mitochondrial compared to the untreated GAS. These results, for the first time, provide systematic evidences showing that cardiac glycosides seriously impairs the hepatopancreas tissues of GAS, resulting in inhibition of digestive enzymes activity and feeding rate and cause GAS death in the end.

Advancing impact prediction and hypothesis testing in invasion ecology using a comparative functional response approach

Invasion ecology urgently requires predictive methodologies that can forecast the ecological impacts of existing, emerging and potential invasive species. We argue that many ecologically damaging invaders are characterised by their more efficient use of resources. Consequently, comparison of the classical ‘functional response’ (relationship between resource use and availability) between invasive and trophically analogous native species may allow prediction of invader ecological impact. We review the utility of species trait comparisons and the history and context of the use of functional responses in invasion ecology, then present our framework for the use of comparative functional responses. We show that functional response analyses, by describing the resource use of species over a range of resource availabilities, avoids many pitfalls of ‘snapshot’ assessments of resource use. Our framework demonstrates how comparisons of invader and native functional responses, within and between Type II and III functional responses, allow testing of the likely population-level outcomes of invasions for affected species. Furthermore, we describe how recent studies support the predictive capacity of this method; for example, the invasive ‘bloody red shrimp’ Hemimysis anomala shows higher Type II functional responses than native mysids and this corroborates, and could have predicted, actual invader impacts in the field. The comparative functional response method can also be used to examine differences in the impact of two or more invaders, two or more populations of the same invader, and the abiotic (e.g. temperature) and biotic (e.g. parasitism) context-dependencies of invader impacts. Our framework may also address the previous lack of rigour in testing major hypotheses in invasion ecology, such as the ‘enemy release’ and ‘biotic resistance’ hypotheses, as our approach explicitly considers demographic consequences for impacted resources, such as native and invasive prey species. We also identify potential challenges in the application of comparative functional responses in invasion ecology. These include incorporation of numerical responses, multiple predator effects and trait-mediated indirect interactions, replacement versus non-replacement study designs and the inclusion of functional responses in risk assessment frameworks. In future, the generation of sufficient case studies for a meta-analysis could test the overall hypothesis that comparative functional responses can indeed predict invasive species impacts.

Balancing of specific nutrients and subsequent growth and body composition in the slug Arion lusitanicus

Feeding generalists typically occupy broad ecological niches and so are potentially pre-adapted to a range of novel food objects. In northern Europe, the slug Arion lusitanicus has spread rapidly as an invasive species and a serious horticultural and agricultural pest. We used nutritional geometry to analyze nutrient balancing capabilities and consequences for performance in A. lusitanicus when provided with one of three nutritionally fixed diets or when given dietary choice. The slugs over-ingested high amounts of the most abundant nutrient in order to get more of the limited nutrient. However, they regulated protein intake more tightly than carbohydrate intake resulting in a very high food intake when fed a protein-poor diet. Growth and body composition were highly affected by the nutrient balance of their diet. When given the choice to feed from two nutritionally different diets, the slugs selected an intake balance of protein and carbohydrate with sufficient precision to maximize growth. Nutrient utilization efficiency increased with increasing deficiency of the specific nutrient in the diet. Ingested carbohydrate was more efficiently stored as lipid in slugs fed more carbohydrate-poor diets, and ingested nitrogen was more efficiently incorporated into slug bodies in slugs fed more protein-poor diets. Our experiments suggest that the evolved behavioral and physiological regulatory capacities of A. lusitanicus may explain some of the success that this slug experiences as an invasive species. We furthermore propose that invasive species might be more dependent on high protein availability in the environment than non-invasive species.