Stable resource polymorphism along the benthic littoral-pelagic axis in an invasive crayfish

Although intraspecific variability is now widely recognized as affecting evolutionary and ecological processes, our knowledge on the importance of intraspecific variability within invasive species is still limited. This is despite the fact that understanding the linkage between within-population morphological divergences and the use of different trophic or spatial resources (i.e., resource polymorphism) can help to better predict their ecological impacts on recipient ecosystems. Here, we quantified the extent of resource polymorphism within populations of a worldwide invasive crayfish species, Procambarus clarkii, in 16 lake populations by comparing their trophic (estimated using stable isotope analyses) and morphological characteristics between individuals from the littoral and pelagic habitats. Our results first demonstrated that crayfish occured in both littoral and pelagic habitats of seven lakes and that the use of pelagic habitat was associated with increased abundance of littoral crayfish. We then found morphological (i.e., body and chelae shapes) and trophic divergence (i.e., reliance on littoral carbon) among individuals from littoral and pelagic habitats, highlighting the existence of resource polymorphism in invasive populations. There was no genetic differentiation between individuals from the two habitats, implying that this resource polymorphism was stable (i.e., high gene flow between individuals). Finally, we demonstrated that a divergent adaptive process was responsible for the morphological divergence in body and chela shapes between habitats while difference in littoral reliance neutrally evolved under genetic drift. These findings demonstrated that invasive P. clarkii can display strong within-population phenotypic variability in recent populations, and this could lead to contrasting ecological impacts between littoral and pelagic individuals.

Diet characterization and a preliminary investigation into trophic niche placement for an endangered lake sturgeon (Acipenser fulvescens) population in the Saskatchewan River, SK, Canada

All Canadian lake sturgeon (Acipenser fulvescens) populations are listed under the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) due to their complex life history, loss of habitat and negative interactions with anthropomorphic activities. Lake sturgeon diets vary considerably across their range and depend on the local benthic invertebrate fauna, substrata, and competition with congener species. Hence, determining population-specific prey assemblages is a vital contribution to effective conservation efforts. We used carbon and nitrogen stable isotopes to identify lake sturgeon prey preferences for juvenile (<100 cm) and adult (>100 cm) age classes and their trophic niche in the Saskatchewan River, SK, Canada. In this system, lake sturgeon were the top predator within the benthic food web with no direct competition for preferred prey items from congener species. Their diet was dominated by crayfish (49.1± 6.4%) and snails (36.3 ± 5.5%), with no significant differences between age classes. Furthermore, lake sturgeon favoured deep rocky pools throughout the river; a habitat where crayfish and snails are typically found. Therefore, conservation efforts should be directed at preserving these habitats for the residing benthic invertebrate community, and the lake sturgeon’s ability to access them.

Distribution, habitat associations, and conservation status updates for the pilose crayfish Pacifastacus gambelii (Girard, 1852) and Snake River pilose crayfish Pacifastacus connectens (Faxon, 1914) of the western United States

Our study evaluates the distribution, habitat associations, and current conservation status of the Snake River pilose crayfish Pacifastacus connectens (Faxon, 1914) and pilose crayfish Pacifastacus gambelii (Girard, 1852), two little-studied and data-deficient species endemic to the western United States. We first developed a species distribution model (SDM) for the pilose crayfishes based on their historical occurrence records using boosted regression trees and freshwater GIS data layers. We then sampled 163 sites in the summers of 2016 and 2017 within the distribution of these crayfishes, including 50 where these species were observed historically. We next compared our field results to modeled predictions of suitable habitat from the SDM. Our SDM predicted 73 sites (45%) we sampled as suitable for the pilose crayfishes, with a moderate AUC value of 0.824. The pilose crayfishes were generally predicted to occur in larger streams and rivers with less extreme upstream temperature and precipitation seasonality. We found the pilose crayfishes at only 20 (12%) of the 163 total sites we sampled, 14 (20%) of the 73 sites predicted as suitable for them by our SDM, and 12 (24%) of 50 historical sites that we sampled. We found the invasive virile crayfish Faxonius virilis (Hagen, 1870) at 22 sites total and 12 (24%) historical sites for the pilose crayfishes, and we found the “native invader” signal crayfish Pacifastacus leniusculus (Dana, 1852) at 29 sites total and 6 (12%) historical sites for the pilose crayfishes. We subsequently used a single classification tree to identify factors associated with our high rate of false positives for contemporary pilose crayfish distributions relative to our SDM. This classification tree identified the presence of invasive crayfishes, impairment of the benthic community, and sampling method as some of the factors differentiating false positives relative to true positives for the pilose crayfishes. Our study identified the historical distribution and habitat associations for P. connectens and P. gambelii using an SDM and contrasted this prediction to results of contemporary field sampling. We found that the pilose crayfishes have seemingly experienced substantial range declines, attributable to apparent displacement by invasive crayfishes and impairment or change to stream communities and habitat. We recommend increased conservation and management attention to P. connectens and P. gambelii in response to these findings.

Settlement and post-settlement survival rates of the white seabream (Diplodus sargus) in the western Mediterranean Sea

Survival during the settlement window is a limiting variable for recruitment. The survival is believed to be strongly determined by biological interactions and sea conditions, however it has been poorly investigated. We examined the settlement patterns related to relevant biotic and abiotic factors (i.e. Density-dependence, wind stress, wave height and coastal current velocity) potentially determining post-settler survival rates of a coastal necto-benthic fish of wide distribution in the Mediterranean and eastern Atlantic, the white seabream (Diplodus sargus). An observational study of the demography of juveniles of this species was carried out at six coves in Menorca Island (Balearic Islands, western Mediterranean). Three of the coves were located in the northern and wind exposed coast, at the Northeast (NE) side; while the other three were found along the southern and sheltered coast, at the Southwest (SW) side of the island. The settlement period extended from early May to late June and maximum juvenile densities at the sampling sites varied between 5 and 11 ind. m^-1 with maximum values observed in late May simultaneously occurring in the two coasts. Our analysis of juvenile survival, based on the interpretation of the observed patters using an individual based model (IBM), revealed two stages in the size-mortality relationships. An initial density-dependent stage was observed for juveniles up to 20 mm TL, followed by a density independent stage when other factors dominated the survival at sizes > 20 mm TL. No significant environmental effects were observed for the small size class (<20mm TL). Different significant environmental effects affecting NE and SW coves were observed for the medium (20-30mm TL) and large (>30mm TL) size class. In the NE, the wind stress consistently affected the density of fish of 20–30 mm and >30 mm TL with a dome-shape effect with higher densities at intermediate values of wind stress and negative effect at the extremes. The best models applied in the SW coves showed a significant non-linear negative effect on fish density that was also consistent for both groups 20–30 mm and >30 mm TL. Higher densities were observed at low values of wave height in the two groups. Because of these variations, the number of juveniles present at the end of the period was unrelated to their initial density and average survival varied among locations. In consequence, recruitment was (1) primarily limited by denso-dependient procedures at settlement stage, and (2) by sea conditions at post-settlement, where extreme wave conditions depleted juveniles. Accordingly, regional hydrodynamic conditions during the settlement season produced significant impacts on the juvenile densities depending on their size and with contrasted effects in respectto cove orientation. The similar strength in larval supply between coves, in addition to the similar mean phenology for settlers in the north and south of the Island, suggests that all fish may come from the same parental reproductive pool. These factors should be taken into account when assessing relationships between settlers, recruits and adults of white seabream.

Transcriptomic comparison of invasive bigheaded carps (Hypophthalmichthys nobilis and Hypophthalmichthys molitrix) and their hybrids

Bighead carp (Hypophthalmichthys nobilis) and silver carp (Hypophthalmichthys molitrix), collectively called bigheaded carps, are invasive species in the Mississippi River Basin (MRB). Interspecific hybridization between bigheaded carps has been considered rare within their native rivers in China; however, it is prevalent in the MRB. We conducted de novo transcriptome analysis of pure and hybrid bigheaded carps and obtained 40,759 to 51,706 transcripts for pure, F₁ hybrid, and backcross bigheaded carps. The search against protein databases resulted in 20,336–28,133 annotated transcripts (over 50% of the transcriptome) with over 13,000 transcripts mapped to 23 Gene Ontology biological processes and 127 KEGG metabolic pathways. More transcripts were detected in silver carp than in bighead carp; however, comparable numbers of transcripts were annotated. Transcriptomic variation detected between two F₁ hybrids may indicate a potential loss of fitness in hybrids. The neighbor‐joining distance tree constructed using over 2,500 one‐to‐one orthologous sequences suggests transcriptomes could be used to infer the history of introgression and hybridization. Moreover, we detected 24,792 candidate SNPs that can be used to identify different species. The transcriptomes, orthologous sequences, and candidate SNPs obtained in this study should provide further knowledge of interspecific hybridization and introgression.

Crayfish use of trash versus natural cover in incised, sand-bed streams

Historic land use changes and subsequent river channelization created deeply incised, unstable stream channels largely devoid of natural cover throughout the Yazoo River basin, Mississippi, USA. Large trash (e.g., televisions, toilets, car parts) dumped in streams provided shelter for some aquatic fauna. To determine whether trash served as a surrogate for natural cover, I examined crayfish use of both cover types. I sampled crayfishes by kick-seining 2 × 1-m plots in three cover classes: trash, natural cover, and no cover. I captured 415 crayfishes from 136 of the 294 plots. Most crayfishes were in natural cover (253), followed by trash (154), and no-cover (8) plots. Trash use varied by crayfish genus and size. Frequencies of all size classes of Procambarus and of the smallest Cambarus were higher in natural cover than trash. Many of the smallest individuals were found in live root mats. As Cambarus and Orconectes grew, they shifted more toward trash, and the largest Orconectes size class was significantly more abundant than expected in trash. Trash served as "artificial reefs," providing cover for crayfishes and other fauna, but functioned differently than the remaining natural cover. The results confirmed that stream substrate did not provide adequate instream cover for crayfishes in the study area and suggested that high-quality natural cover for large crayfishes was in short supply, at least for some species. Land management that provides for abundant, ongoing input and retention of complex cover, such as trees and live roots, to stream channels should be beneficial for crayfish assemblages.

Global Introductions of Crayfishes: Evaluating the Impact of Species Invasions on Ecosystem Services

Impacts of nonindigenous crayfishes on ecosystem services exemplify the mixture of positive and negative effects of intentionally introduced species. Global introductions for aquaculture and ornamental purposes have begun to homogenize naturally disjunct global distributions of crayfish families. Negative impacts include the loss of provisioning (e.g., reductions in edible native species, reproductive interference or hybridization with native crayfishes), regulatory (e.g., lethal disease spread, increased costs to agriculture and water management), supporting (e.g., large changes in ecological communities), and cultural (e.g., loss of festivals celebrating native crayfish) services. Where quantification of impacts exists (e.g., Procambarus clarkii and Pacifastacus leniusculus in Europe), regulations now prohibit introduction and spread of crayfishes, indicating that losses of ecosystem services have outweighed gains. Recent research advances such as predicting invasiveness, predicting spread, improved detection and control, and bioeconomic analysis to increase cost-effectiveness of management could be employed to reduce future losses of ecosystem services.

A simulation of food-web interactions leading to rainbow smelt Osmerus mordax dominance in Sparkling Lake, Wisconsin

A process-based simulation model was used to examine the nature and intensity of food-web interactions that allow Osmerus mordax to dominate invaded lakes. The model simulates food-web interactions among linked populations of O. mordax, Coregonus artedi and Sander vitreus. Simulations indicated that O. mordax dominate where: (1) adult O. mordax prey on young-of-the-year (YOY) C. artedi, (2) YOY O. mordax negatively affect YOY S. vitreus through competition and (3) adult S. vitreus experience moderate fishing mortality. Osmerus mordax dominated simulations across a broad range of variable values that regulated competition and predation, and displayed threshold responses to increasing angler harvest. Consequently, angler harvest should be carefully managed in lakes susceptible to O. mordax invasions because the alternative could lead to fishery collapse.

Preventing the spread of invasive species: economic benefits of intervention guided by ecological predictions

Preventing the invasion of freshwater aquatic species is the surest way to reduce their impacts, but it is also often expensive. Hence, the most efficient prevention programs will rely on accurate predictions of sites most at risk of becoming invaded and concentrate resources at those sites. Using data from Vilas County, Wisconsin (U.S.A.), collected in the 1970s, we constructed a predictive occurrence model for rusty crayfish (Orconectes rusticus) and applied it to an independent data set of 48 Vilas County lakes to predict which of these were most likely to become invaded between 1975 and 2005. We nested this invasion model within an economic framework to determine whether targeted management, derived from our quantitative predictions of likely invasion sites, would increase the economic value of lakes in the independent data set. Although the optimum expenditure on lake protection was high, protecting lakes at this level would have produced net economic benefits of at least $6 million over the last 30 years. We did not attempt to determine the value of nonmarket benefits of protection; thus, our results are likely to underestimate the total benefits from preventing invasions. Our results demonstrate that although few data are available early in an invasion, these data may be sufficient to support targeted, effective, and economically rational management. In addition, our results show that ecological predictions are becoming sufficiently accurate that their application in management can produce net economic benefits.

Do natural container habitats impede invader dominance? Predator-mediated coexistence of invasive and native container-dwelling mosquitoes

Predator-mediated coexistence of competitors occurs when a species that is superior in competition is also more vulnerable to a shared predator compared to a poorer competitor. The invasive mosquito Aedes albopictus is usually competitively superior to Ochlerotatus triseriatus. Among second instar larvae, A. albopictus show a lesser degree of behavioral modification in response to water-borne cues from predation by the larval midge Corethrella appendiculata than do O. triseriatus, rendering A. albopictus more vulnerable to predation by C. appendiculata than O. triseriatus. The hypothesis that C. appendiculata predation favors coexistence of these competitors predicts that C. appendiculata abundances will be negatively and positively correlated with A. albopictus and O. triseriatus abundances, respectively, and that coexistence will occur where C. appendiculata are common. Actual abundances of O. triseriatus, A. albopictus, and C. appendiculata in three habitats fit this prediction. In natural container habitats like tree holes, C. appendiculata were abundant and competitors co-existed at similar densities. In cemeteries and tires, which occur primarily in non-forested, human-dominated habitats, A. albopictus dominated, with abundances twice those found in tree holes, but C. appendiculata and O. triseriatus were rare or absent. We also tested for whether antipredatory behavioral responses of A. albopictus differed among habitats or populations, or were correlated with local C. appendiculata abundances. We could detect no differences in A. albopictus antipredatory behavioral responses to water-borne cues from predation. Tree hole habitats appear to promote co-existence of O. triseriatus and A. albopictus through interactions with predatory C. appendiculata, and this predator effect appears to limit invasion success of A. albopictus in tree holes. There are many studies on predator-mediated coexistence in natural habitats but to our knowledge this is the first study to suggest differential predator-mediated coexistence between natural and man-made habitats.

Biological Control Through Intraguild Predation: Case Studies in Pest Control, Invasive Species and Range Expansion

Intraguild predation (IGP), the interaction between species that eat each other and compete for shared resources, is ubiquitous in nature. We document its occurrence across a wide range of taxonomic groups and ecosystems with particular reference to non-indigenous species and agricultural pests. The consequences of IGP are complex and difficult to interpret. The purpose of this paper is to provide a modelling framework for the analysis of IGP in a spatial context. We start by considering a spatially homogeneous system and find the conditions for predator and prey to exclude each other, to coexist and for alternative stable states. Management alternatives for the control of invasive or pest species through IGP are presented for the spatially homogeneous system. We extend the model to include movement of predator and prey. In this spatial context, it is possible to switch between alternative stable steady states through local perturbations that give rise to travelling waves of extinction or control. The direction of the travelling wave depends on the details of the nonlinear intraguild interactions, but can be calculated explicitly. This spatial phenomenon suggests means by which invasions succeed or fail, and yields new methods for spatial biological control. Freshwater case studies are used to illustrate the outcomes.