Gammarus Roeseli Research Articles

Successful post-glacial colonization of Europe by single lineage of freshwater amphipod from its Pannonian Plio-Pleistocene diversification hotspot

Gammarus roeselii Gervais, 1835 is a morphospecies with a wide distribution range in Europe. The Balkan Peninsula is known as an area of pre-Pleistocene cryptic diversification within this taxon, resulting in at least 13 Molecular Operational Taxonomic Units (MOTUs). The morphospecies diversified there during Neogene and has probably invaded other parts of the continent very recently, in postglacial or even historical times. Thus, the detailed goals of our study were to (1) identify which lineage(s) colonized Central-Western Europe (CWE), (2) determine their possible geographical origin, (3) verify, whether the colonisation was associated with demographic changes. In total, 663 individuals were sequenced for the cytochrome oxidase I (COI) barcoding fragment and 137 individuals for the internal transcribed spacer II (ITS2). We identified two MOTUs in the study area with contrasting Barcode Index Number and haplotype diversities. The Pannonian Basin (PB) appeared to be a potential ice age refugium for the species, while CWE was colonised by a single lineage (also present in PB), displaying low genetic diversity. Our results suggest that G. roeselii is a relatively recent coloniser in CWE, starting demographic expansion around 10 kya.

Substantial differences in genetic diversity and spatial structuring among (cryptic) amphipod species in a mountainous river basin

AbstractRecent advances in molecular methods foster the documentation of small spatial scale biological diversity over large geographical areas. These advances allow to correctly record α‐diversity, but also enable biomonitoring that describes intraspecific molecular diversity, providing valuable insights into the contemporary history of species. Such information is essential for the accurate monitoring of freshwater communities and provides a promising tool to identify conservation priorities at various spatial scales.Here, we combined morphological species determinations with genetic characterisation via DNA barcoding and species distribution modelling. We aimed to investigate whether closely related amphipod species occupying overlapping ecological niches and occurring in partial sympatry, demonstrate similar spatial patterns of intraspecific genetic diversity and share comparable population histories. Therefore, we characterised the amphipod fauna within the Kinzig catchment (1,058 km2, Hesse, Central Germany) that is a tributary of the Main River and part of the long‐term ecological research network using genetics.Our genetic analysis revealed two more taxonomic entities than previously known. The most common species wasGammarus fossarumclade 11 (or type B), followed byGammarus roeseliiclade C,Gammarus pulexclade D,G. pulexclade B and a very rare previously unknown lineage within theG. fossarum‐species complex, which we refer to asG. fossarumclade RMO. These five taxa differed in their intraspecific genetic diversity, withG. fossarumclade 11 demonstrating the highest diversity and having a prominent small‐scale pattern with endemic haplotypes in headwater regions. Distributions were predicted for the three most abundant molecularly identified species.The upstream reaches maintained high intraspecific α‐ and β‐diversity, pointing towards a more complex population structure ofG. fossarumclade 11. This highlights the importance of considering intraspecific diversity for the conservation of individual species. DNA‐based species distribution models shed light on species‐specific habitat preferences, and showed spatial distribution patterns that supported ecological inference and conservation management. Barcoding specimens prior to modelling can increase robustness and performance of distribution models as juveniles can be incorporated, and cryptic species complexes disentangled.Our integrative study contributes to the further development of science‐informed and holistically considered effective conservation measures. Some poorly dispersing hololimnic species may serve as representatives for our understanding of the natural history of the local communities in headwater regions—and their protection. Intraspecific genetic diversity should be considered in conservation management decisions as it can provide valuable information on past and present population demography, connectivity, and recovery processes of species—information that rarely can be achieved by traditional monitoring approaches.

Extensive variation in the morphological anti-predator defense mechanism of Gammarus roeselii Gervais, 1835 (Crustacea:Amphipoda)

Gammarus roeselii is a common European amphipod, characterized by dorsal spines that defend against fish predation. Despite significant variability in spine length and number, the extent of this variation has never been quantified. Furthermore, widespread freshwater Gammarus taxa, including G. roeselii, are diverse species complexes, comprising numerous narrowly-endemic cryptic or overlooked species. As such, we hypothesized that the morphological variation among Central European populations of G. roeselii reflects the presence of multiple unrecognized species. We measured body and spine length from phenotypically-diverse populations and sequenced a fragment of the mitochondrial gene for the cytochrome c oxidase subunit I to link phenotypes and lineages. Morphological analyses revealed extensive variation and indicated 2 groups: morph A bearing 3 blunt, short spines and morph B with 3 to 4 long, pointy spines. Phylogenetic analyses indicated conspecificity of populations and morphs due to unexpectedly-small genetic divergence and haplotype sharing, thus refuting our hypothesis. All studied populations belong to a widespread Central and Western European clade, which is nestled among the Southeast European lineages of the species complex. We conclude that the anti-predator defense of G. roeselii in Central Europe is extremely variable despite little inter-population genetic differentiation. We presume that this variation is linked to predation intensity, reflecting either phenotypic plasticity or local adaptations of this successful colonizer, and could also shed more light into the complex evolution of spines in the Amphipoda.

Spatial distribution and substrate preferences of the non-indigenous amphipod Gammarus roeselii Gervais, 1835

Gammarus roeselii is one of the successful non-indigenous species recently established in the Ticino River basin (Northern Italy). G. roeselii is not usually considered to be a real threat to native gammarids because no evidence has been reported so far on its effects on biodiversity and habitats. In this study, we assessed the spatial distribution of G. roeselii in the secondary hydrographic system of the southern part of the sub-lacustrine Ticino River basin and examined substrate preferences on the basis of laboratory experiments. We found that G. roeselii is well established in this area, occurring in almost all the seminatural streams, reaching high densities. Furthermore, we found that this species has a preference for two distinct types of substrate: empty shells of the bivalve Corbicula fluminea, which provide a suitable shelter for the introduced amphipod, and aquatic plants, which provide food resources. Conversely, preference for inorganic substrates, such as stones, was lower. In addition, the results indicate that G. roeselii easily inhabits the water column. The high adaptability of G. roeselii, combined with its capacity to exploit different niches and its swimming ability, are ecological characteristics that can favour its colonisation of new areas.

Small-scale phenotypic differentiation along complex stream gradients in a non-native amphipod

BackgroundSelective landscapes in rivers are made up by an array of selective forces that vary from source to downstream regions or between seasons, and local/temporal variation in fitness maxima can result in gradual spatio-temporal variation of phenotypic traits. This study aimed at establishing freshwater amphipods as future model organisms to study adaptive phenotypic diversification (evolutionary divergence and/or adaptive plasticity) along stream gradients.MethodsWe collected Gammarus roeselii from 16 sampling sites in the Rhine catchment during two consecutive seasons (summer and winter). Altogether, we dissected n = 1648 individuals and quantified key parameters related to morphological and life-history diversification, including naturally selected (e.g., gill surface areas) as well as primarily sexually selected traits (e.g., male antennae). Acknowledging the complexity of selective regimes in streams and the interrelated nature of selection factors, we assessed several abiotic (e.g., temperature, flow velocity) and biotic ecological parameters (e.g., conspecific densities, sex ratios) and condensed them into four principal components (PCs).ResultsGeneralized least squares models revealed pronounced phenotypic differentiation in most of the traits investigated herein, and components of the stream gradient (PCs) explained parts of the observed differences. Depending on the trait under investigation, phenotypic differentiation could be ascribed to variation in abiotic conditions, anthropogenic disturbance (influx of thermally polluted water), or population parameters. For example, female fecundity showed altitudinal variation and decreased with increasing conspecific densities, while sexual dimorphism in the length of male antennae—used for mate finding and assessment—increased with increasing population densities and towards female-biased sex ratios.ConclusionsWe provide a comprehensive protocol for comparative analyses of intraspecific variation in life history traits in amphipods. Whether the observed phenotypic differentiation over small geographical distances reflects evolutionary divergence or plasticity (or both) remains to be investigated in future studies. Independent of the mechanisms involved, variation in several traits is likely to have consequences for ecosystem functions. For example, leaf-shredding in G. roeselii strongly depends on body size, which varied in dependence of several ecological parameters.

Microsporidian infections in the species complex Gammarus roeselii (Amphipoda) over its geographical range: evidence for both host\u2013parasite co-diversification and recent host shifts

BackgroundMicrosporidians are obligate endoparasites infecting taxonomically diverse hosts. Both vertical (from mother to eggs) and horizontal (between conspecifics or between species) transmission routes are known. While the former may promote co-speciation and host-specificity, the latter may promote shifts between host species. Among aquatic arthropods, freshwater amphipod crustaceans are hosts for many microsporidian species. However, despite numerous studies, no general pattern emerged about host specificity and co-diversification. In south-eastern Europe, the gammarid Gammarus roeselii is composed of 13 cryptic lineages of Miocene to Pleistocene age but few genotypes of one lineage have spread postglacially throughout north-western Europe. Based on nearly 100 sampling sites covering its entire range, we aim to: (i) explore the microsporidian diversity present in G. roeselii and their phylogenetic relationships, especially in relation to the parasites infecting other Gammaridae; (ii) test if the host phylogeographical history might have impacted host–parasite association (e.g. co-diversifications or recent host shifts from local fauna).MethodsWe used part of the small subunit rRNA gene as source of sequences to identify and determine the phylogenetic position of the microsporidian taxa infecting G. roeselii.ResultsMicrosporidian diversity was high in G. roeselii with 24 detected haplogroups, clustered into 18 species-level taxa. Ten microsporidian species were rare, infecting a few individual hosts in a few populations, and were mostly phylogenetically related to parasites from other amphipods or various crustaceans. Other microsporidians were represented by widespread genera with high prevalence: Nosema, Cucumispora and Dictyocoela. Two contrasting host association patterns could be observed. First, two vertically transmitted microsporidian species, Nosema granulosis and Dictyocoela roeselum, share the pattern of infecting G. roeselii over most of its range and are specific to this host suggesting the co-diversification scenario. This pattern contrasted with that of Dictyocoela muelleri, the three species of Cucumispora, and the rare parasites, present only in the recently colonised region by the host. These patterns suggest recent acquisitions from local host species, after the recent spread of G. roeselii.ConclusionsMicrosporidians infecting G. roeselii revealed two scenarios of host–parasite associations: (i) ancient associations with vertically transmitted parasites that probably co-diversified with their hosts, and (ii) host shifts from local host species, after the postglacial spread of G. roeselii.

Comparison in the response of three European Gammarid species exposed to the growth regulator insecticide fenoxycarb.

Growth regulator insecticides with juvenoid activity can affect the development and reproduction of non-target organisms such as crustaceans. In this perspective, our previous studies revealed deleterious effects of the juvenoid fenoxycarb at 5μgL-1 on the embryogenesis and at 50μgL-1 on the reproductive behavior of the amphipod Gammarus fossarum. In the present study, to determine whether data generated with one amphipod species can be extended to other gammarid species, we tested the effects of a 5μgL-1 fenoxycarb exposure on three European amphipod species: G. fossarum, Gammarus roeseli, and Echinogammarus longisetosus. We exposed individually 60 freshly fertilized females to fenoxycarb throughout the entire oogenesis/embryogenesis cycle (i.e., 19days). In newborn individuals from exposed embryos, we measured both pigmentation and lipid reserve impairments while in exposed females, we observed reproductive behavior. At 5μgL-1 fenoxycarb, reproductive behavior was only altered in G. fossarum. This study demonstrates the variability of the toxic response among the three gammaridae species, underlining the need for acquiring data with a broad phylogenetic representation to better predict toxic effects on freshwater ecosystems.

Differential resource consumption in leaf litter mixtures by native and non-native amphipods

Leaf litter processing is an essential ecosystem function in freshwater systems, since much of the carbon and nutrients moving through freshwater food webs come from the surrounding terrestrial ecosystems. Thus, it is important to understand how the species performing this function differ, especially because many native species are being replaced by non-native species in aquatic ecosystems. We used a field experiment to examine leaf consumption rates of two common shredding macroinvertebrates (the native Gammarus fossarum and the non-native Gammarus roeselii). Leaves from three species, varying in resource quality, were added both in leaf monocultures and as a three-species mixture. Biomass-adjusted daily consumption rates were similar between the two amphipod species, and each consumed nitrogen-rich alder leaves faster than oak or beech leaves. However, because adult G. roeselii are approximately twice the size of G. fossarum, this led to systematic, though nonsignificant, differences in consumption rates at the per-capita or population level. Furthermore, we found nuanced effects of decomposer identity on leaf decomposition in mixtures. Only G. roeselii showed increased consumption of the preferred resource (alder) in the mixture, while G. fossarum consumed all leaves at the same proportional rates as in monocultures. This is an important distinction, as most measures of macroinvertebrate leaf shredding are made in the laboratory with only a single leaf resource available. Our results, based on a field experiment which could control the presence of dominant macroinvertebrates while still providing natural, biologically realistic context, suggest that even functionally similar species may subtly shift ecosystem processes.

No evidence for a genetic impoverishment of the indigenous amphipod Gammarus roeselii (Gervais, 1835) due to the invasion of Dikerogammarus villosus (Sowinsky, 1894) in Lake Constance

The replacement of native species by invasive species is one of the most critical threats to the biodiversity of aquatic systems today. However, little is known about potential effects of species invasions on the genetic diversity of indigenous species in cases where the latter coexist with the invader. Here we present an example of the indigenous amphipod Gammarus roeselii, which has been partly replaced by the invasive Dikerogammarus villosus in Lake Constance (C-Europe) and now mostly exists in small, isolated populations. We compared the genetic diversity, population structure, indicators for bottlenecks and migrations rates of G. roeselii before and after the invasion event from samples collected between 1999 and 2013. We expected a genetic impoverishment in the reduced and segregated populations of G. roeselii. However, no genetic measure on G. roeselii differed temporally or spatially over the investigated period, which indicates that D. villosus has not yet had an impact on G. roeselii at the genetic scale. Hence, even though a decline in population size of G. roeselii was found in Lake Constance, our results on the genetic scale contribute to recent findings that the overall impact of D. villosus on native species is not as strong as often discussed.

Development and validation of a macroinvertebrate-based biomonitoring tool to assess fine sediment impact in small mountain streams

Increased fine sediment deposition is recognised as one of the major causes of biological impairment of rivers and streams influencing all components of aquatic communities. Notably, stream macroinvertebrates are affected showing changes in abundance and community composition. This makes macroinvertebrates an attractive choice for biomonitoring fine sediment stress. However, there are substantial knowledge gaps regarding the quantification of deposited fine sediment and the identification of taxa sensitive to fine sediment deposition, which could serve as indicators.In this study, we developed a stream type-specific index based on the taxon-specific response of macroinvertebrates to deposited fine sediment in small, coarse substrate-dominated mountain streams. We sampled fine sediment at 73 sampling sites in Western Germany (Europe) in spring 2014 and 2015 using a sediment remobilization technique. Macroinvertebrate taxalists originating from WFD monitoring surveys were available for all sites. We applied Threshold Indicator Taxa ANalysis (TITAN) on the fine sediment mass of the sampling sites and the corresponding macroinvertebrate taxalists to identify indicator taxa, which were then used for index development.In total, TITAN identified 95 reliable indicator taxa, of which some taxa tolerated large amounts of fine sediment (e.g., Gammarus roeselii and Tubificidae Gen. sp.), while others were found to be highly sensitive to increased fine sediment mass (e.g., Elodes sp. and Limnius perrisi). The newly developed index was tested on an independent data set and performed well in detecting fine sediment stress (Spearman's r = 0.63). Furthermore, the index was better related to the deposited fine sediment mass as compared to other fine sediment indices and standard metrics used for monitoring purposes under the Water Framework Directive (WFD). The diagnostic index can be a cost-effective biomonitoring tool for stream managers and can be used as a proxy for the impact of deposited fine sediment on the reach scale.

Global warming may lower thermal barriers against invasive species in freshwater ecosystems – A study from Lake Constance

European freshwater ecosystems are increasingly invaded by exotic animal and plant species. Apart from increased connectivity between previously separated watersheds, the increasing temperature of the hydrosystems favors the spread of exotic species. The freshwater fauna of Central Europe is still shaped by the cold-adapted animal assemblages resulting from the last glaciation. It is less diverse, and the species are putatively less performant competitors, compared to the warm-adapted, species-rich fauna of the Ponto-Caspian realm, from which many current aquatic invaders are coming. Our study analyses potential mechanisms explaining the coexistence between one of the most impacting aquatic invaders of the past decades, the ‘killer shrimp’ Dikerogammarus villosus and the previously dominating amphipod Gammarus roeselii in Lake Constance, using laboratory predation experiments and field surveys. Our results indicate two key drivers for coexistence: low winter temperatures and the substrate structure of the alga Chara sp. At temperatures below 6 °C, the predation pressure on G. roeselii was strongly reduced; G. roeselii can therefore disperse throughout the littoral in winter, avoiding predation by D. villosus. Artificial heating of a section of the lake shore, however, resulted in local extinction of G. roeselii by D. villosus. The macroalga Chara sp. completely inhibited predation by D. villosus on G. roeselii. Climate change scenarios indicate that global warming might destroy this thermal refuge during winter until 2085. For the survival of G. roeselii it will then be crucial, which part of the Chara population will maintain epigeic plant parts during winter. The complex interplay between thermal and physical refuges for native species in the context of climate change and changing trophic status of freshwater systems, as disentangled by our study, shows that ecosystem management and restoration strategies need to better consider multiple stressors (and their rather complex mitigation strategies).

Defence is the best offence: invasive prey behaviour is more important than native predator behaviour

Finding universal rules that predict the success of potential invaders is difficult given the breadth of interactions that occur between the invader and the other species in its new range. Among animal species, behavioural traits may play an especially relevant role in mediating these interactions. Whereas the predatory behaviour of invasive predators is especially well documented, less is known about how behaviour may mediate the success of invasive prey species. Here we tested how the behaviour of both an invasive prey species, the amphipod Dikerogammarus villosus, and a common fish predator, the European perch, Perca fluviatilis, affect the outcome of predation events. Invasive D. villosus exhibited significantly greater sheltering and less exploratory behaviour than a naturalized amphipod Gammarus roeseli. This increased sheltering behaviour in the invasive amphipod appears to have a major functional consequence as this species was far less likely than the naturalized amphipod to be predated by the perch. Contrary to our predictions, the behaviour of the individual perch had no influence on consumption of either amphipod species, suggesting that amphipod behaviour was the key determinant of the success of a predation event. Our results highlight the importance of prey behaviour during predation events and emphasize that consideration of antipredator behaviour in potentially invasive prey species may help improve predictions of invasion success.

The complete mitochondrial genome of Gammarus roeselii (Crustacea, Amphipoda): insights into mitogenome plasticity and evolution

This study presents the complete mitochondrial (mt) genome sequence, annotation and analysis of the amphipod Gammarus roeselii, a crustacean species widespread in European continental freshwaters. The circular mt genome has a total length of 16,073 bp and possesses the 37 canonical mt genes of bilaterians. Particularly noticeable is an unusual case of duplication of the full control region (CR). This duplication was confirmed experimentally in G. roeselii individuals caught in the wild, as it was found in all tested individuals from two distinct populations. Furthermore, comparing multiple mt haplotypes from closely related individuals from the western-most part of the distribution range of G. roeselii allowed us to identify single nucleotide polymorphisms and indels that may constitute valuable markers for phylogeographic analyses of G. roeselii. Finally, we performed a phylogenetic analysis that helped understanding the evolutionary dynamics of the CR.

Cryptic species and their utilization of indigenous and non-indigenous intermediate hosts in the acanthocephalan Polymorphus minutus sensu lato (Polymorphidae).

The bird-infecting acanthocephalan Polymorphus minutus has been suggested to comprise different lineages or even cryptic species using different intermediate hosts. To clarify this open question, we investigated Polymorphus cf. minutus cystacanths originating from amphipod intermediate hosts from 27 sites in Germany and France. Parasites and hosts were identified using integrated datasets (COI and/or morphology for hosts and COI + ITS1-5.8S-ITS2 for parasites).Mitochondrial and nuclear data (ITS1) strongly support the existence of three cryptic species in Polymorphus cf. minutus (type 1-3). These three types reveal a high degree of intermediate host specificity, with Polymorphus type 1 only encountered in Gammarus fossarum type B, Polymorphus type 2 in Echinogammarus sp. and Echinogammarus berilloni, and Polymorphus type 3 in Gammarus pulex and Gammarus roeselii. Our results point to a so far neglected cryptic diversity of the genus Polymorphus in Central Europe. Furthermore, Polymorphus type 2 is most likely a non-native parasite in Germany that co-invaded with E. berilloni from the Mediterranean area. Potentially, type 3 originates from South-East Europe and migrated to Germany by G. roeselii, where it might have captured G. pulex as an intermediate host. Therefore, our findings can be seen in the context of ecological globalization in terms of the anthropogenic displacement of intermediate hosts and its impact on the genetic divergence of the parasites.

Male Gammarus roeseli provide smaller ejaculates to females infected with vertically transmitted microsporidian parasites

The effects of parasites on the reproduction of their hosts are widespread, but studies investigating the effect of female parasitic status on sperm allocation in males, a form of postcopulatory mate choice, remain scarce. Because males are often sperm limited, strategic sperm investment, in which females of low reproductive value receive fewer sperm, is predicted to occur to maximize long-term male reproductive success. In this study based on pairs collected in natura, we investigated how Gammarus roeseli (Crustacea: Amphipoda) males allocated sperm when paired with females infected with the vertically transmitted, sex ratio-distorting, microsporidian parasites, Nosema granulosis or Dictyocoela sp. Since infected females had similar fecundity to uninfected ones, and offspring of females infected with N. granulosis showed a higher survival rate, we predicted equivalent or even larger sperm investment from males paired with infected females. Contrary to our predictions, males paired with infected females had a lower sperm count before insemination and provided smaller ejaculates than those paired with uninfected females. This pattern suggests either a strategic sperm investment as a function of the female's parasitic status, or that males in good condition had a higher probability of pairing with uninfected females than those in poor condition.

Potential invasiveness by non-indigenous macrozoobenthos in the secondary hydrographic system of a temperate-climate river catchment

In the context of biological invasions, freshwater aquatic invertebrates represent one of the most successful groups of organisms. At the same time, the secondary hydrographic system of a river catchment acts as a preferential pathway for the dispersion of Non-Indigenous Species (NIS) to nearby ecosystems. The present study investigates the macrozoobenthos assemblage inhabiting 13 representative semi-natural streams of the secondary hydrographic system of the southern course of the River Ticino (Lombardy, Northern Italy). The level of biocontamination of the habitats under study was assessed by the Site-specific BioContamination Index (SBCI), which was paired with a preliminary screening of the NIS that may cause ecological and economic impacts at the sites under study using the recently-developed Aquatic Species Invasiveness Screening Kit (AS-ISK) tool. The SBCI classified one stream as ‘high class’, one as ‘good class’, two as ‘moderate class’, seven as ‘poor class’, and the remaining two as ‘bad class’. Six macrozoobenthic NIS were identified, namely the amphipod Gammarus roeselii, the gastropods Physella acuta, Potamopyrgus antipodarum and Pseudosuccinea columella, the bivalve Corbicula fluminea and the limpet Ferrissia fragilis. Based on the AS-ISK outcomes, the most potentially invasive species were C. fluminea followed by P. columella, both of which were categorised as ‘high risk’. Also, the potential invasiveness of the above species increased after accounting for climate change predictions, as did that for all other species assessed, hence regardless of their corresponding risk level. By combining the results of the SBCI index with those from AS-ISK, a first step is provided towards the identification and refinement of potential management strategies aimed to reduce the impacts of NIS in the RAA, whilst accounting for predicted effects of climate change.

First record of Gammarus roeselii Gervais, 1835 (Amphipoda: Gammaridae) from Kosovo with ecological notes

First record of Gammarus roeselii Gervais, 1835 (Amphipoda: Gammaridae) from Kosovo with ecological notes

A simple centrifugation protocol for metagenomic studies increases mitochondrial DNA yield by two orders of magnitude

Abstract DNA (meta)barcoding is applied to study biodiversity and is available for standardized biodiversity assessments. However, it suffers from PCR bias, which can lead to the loss of specific taxa. PCR‐free techniques such as shotgun metagenomics are therefore thought to be more suited for biodiversity assessments, but are currently limited by incomplete reference libraries. The technique of “mitogenome‐skimming” or “mitogenomics,” in which complete mitochondrial genomes are sequenced, is ideal to bridge the techniques of (meta)barcoding and metagenomics. However, without the enrichment of mitochondria, roughly 99% of all sequencing reads are of non‐mitochondrial origin and mostly useless for common applications, e.g. species identification. Here, we present a simple centrifugation protocol that leads to an average 140‐fold enrichment of mitochondrial DNA. By sequencing six ‘mock’‐communities—comprising the freshwater taxa Corbicula fluminea, Gammarus roeselii and Hydropsyche exocellata each—we recovered whole mitochondrial genomes of these species and the acanthocephalan endoparasite Pomphorhynchus laevis. The enrichment protocol will speed up building reference libraries for whole mitochondrial genomes, as dozens of species can be sequenced on a single MiSeq run. Subsequently, it will also allow biodiversity assessments, using mitogenomics at greatly reduced costs in comparison to mitogenomic approaches without prior enrichment for mitochondria.

Contrasted effects of an anti-cyanobacterial ultrasound device on the non-target freshwater invertebrate species Gammarus roeseli.

The aim of this work was to investigate the effects of an anti-cyanobacterial ultrasound device (supplied by an electrical power of 15W and emitting at 23 and 46kHz) on the widespread freshwater amphipod species Gammarus roeseli. First, laboratory scale experiments in 8-L glass tanks showed that an ultrasound exposure of 2h and 40min was sufficient to produce 50% mortality, along with a 6.5°C water temperature increase. Avoiding excessive heating by using a water-cooling and recirculation system permitted an exposure time of 29h for the same mortality rate. A potential relationship between temperature's rise and amphipod mortality was hence highlighted. Moreover, the use of plastic mesh bag (0.5mm mesh size) as a physical barrier has not shown any lethal effects of ultrasound exposure. Furthermore, the induction of GPx or GST activity as oxidative stress biomarkers was not observed. This could be explained by reduced ultrasound intensity inside the mesh bags. Thus, according to these results, the tested ultrasound system is not expected to be acutely harmful in the field.

Effects of meso- and microhabitat characteristics on the coexistence of two native gammarid species (Crustacea, Gammaridae)

Although the influence of invasive species on the distribution of native species is well-studied, our knowledge on the processes driving the co-occurrence of native gammarid species is limited. We studied the co-occurrence of two common European gammarids, Gammarus fossarum and Gammarus roeselii, along a stream continuum in Mecsek Mountains, SW Hungary. We hypothesized that (1) the large scale distribution is influenced by microhabitat diversity; (2) the distribution of each species is equal among the available microhabitats in the absence of a competitor; (3) microhabitat preference is evident in the case of coexistence; and (4) the mesohabitat structure influences the microhabitat preference. A longitudinal gradient was observed along the stream: The dominance of G. fossarum at upstream sections continuously transitioned into the dominance of G. roeselii through an intermediate section, where both species coexisted. This distribution cannot be completely explained by the microhabitat diversity. In cases of single species occurrences, no microhabitat preference was found in G. fossarum, whereas G. roeselii preferred lithal and biotic microhabitats. The presence of a competitor significantly modified the microdistribution: G. roeselii retreated from lithal microhabitats and G. fossarum almost disappeared from gravel. Moreover, the location of microhabitats within mesohabitats significantly affected the distribution of gammarids. Both species occurred in meso- and microhabitat combination resembling their habitat usually occupied along the stream continuum: G. fossarum was an indicator species for the fast-flowing shallow riffles with the dominance of lithal microhabitat, whereas G. roeselii was abundant in the slow-flowing deeper pools usually characterized by vegetation or organic matter. Our results suggest that, beyond the large scale longitudinal distributional pattern and species-specific life-cycles, the meso- and microhabitat characteristics of a stream can drive stable and long-term coexistence among G. fossarum and G. roeselii.