Genus Gammarus Research Articles

A new species of freshwater Gammarus Fabricius, 1775 (Amphipoda: Gammaridae) from a desert spring in Texas, with a key to the species of the genus Gammarus from North America

A new species of freshwater Gammarus Fabricius, 1775 (Amphipoda: Gammaridae) from a desert spring in Texas, with a key to the species of the genus Gammarus from North America

Two new Gammarus species and a new name (Crustacea: Amphipoda: Gammaridae) from Northwest China.

Two new species of the genus Gammarus are described and illustrated from Northwest China. A new species name Gammarus tianshan nom. nov. is proposed to replace G. montanus Hou et al., 2004. Gammarus simplex sp. nov. from Altay, Xinjiang, is characterized by uropod III with simple setae on both rami and urosomite I only with setae on dorsal margin. Gammarus glaber sp. nov. from Qinghai, is characterized by uropod III with few simple and plumose setae. Detailed morphological description and differences from related species are discussed. A distribution map of the new species and related species is provided.

A review of Gammaridae (Crustacea: Amphipoda): the family extent, its evolutionary history, and taxonomic redefinition of genera

By molecular analysis of a high number of gammarids, including 29 out-group genera, we could assure the monophyly of Gammaridae. To avoid the paraphyly of the family, we propose the omission of Pontogammaridae, Typhlogammaridae, and all Baikalian families. Similarly, the genera Fontogammarus, Sinogammarus, Lagunogammarus, Pephredo, Neogammarus, and Laurogammarus may be cancelled. But, tens of Baikal genera, nested within Gammarus, are so diverse that they must be retained, although rendering Gammarus paraphyletic. Besides we propose the polyphyletic Echinogammarus–Chaetogammarus group to be divided into monophyletic genera Echinogammarus s. str., Homoeogammarus, Parhomoeogammarus, Marinogammarus, Relictogammarus gen. nov., Chaetogammarus, and Trichogammarus gen. nov. These solutions made it possible to complete the first analysis of the family evolution in light of its phylogeny. Perimarine clades are mainly basally split clades, whereas in some ancient lakes extremely rich endemic faunas had developed polyphyletically. The troglobiotic Typhlogammarus group from Dinarides and Caucasus formed a monophylum, whereas the troglobiotic assemblage of Gammarus species is highly polyphyletic. Reduction of the uropod III endopodite, which classically distinguishes between the genera Gammarus and Echinogammarus, appeared to be highly polyphyletic. Protective dorsal pleonal projections occur scattered across the family and beyond, whereas lateral projections were limited to species of ancient lakes, so both structures were polyphyletic. The evolutionary history of Gammaridae was investigated with ten different calibration schemes, which produced incompatible results; however, the most probable scenario is a late rise of the family, which can only explain the absence of Gammaridae species around the Indo-Pacific. © 2015 The Linnean Society of London

Morphological vs. molecular delineation of taxa across montane regions in Europe: the case study ofGammarus balcanicusSchäferna, (Crustacea: Amphipoda)

Mountainous areas are characterized by substantial biodiversity and endemicity due to their complex geological history and habitat fragmentation. Hence, it can be assumed that particularly high species richness can be found in organisms with limited dispersal capabilities that inhabit mountain streams. A number of scientific papers focus on molecular phylogeography or traditional taxonomy of species or species groups inhabiting such habitats. However, there is a lack of studies that integrate morphological and molecular data to identify and delineate cryptic species. For practical reasons, uncovering cryptic diversity is crucial in taxa used in biomonitoring. Distinct species, hard to separate based on morphology only, may have different tolerance ranges towards a variety of factors. Thus, our goal is to combine the two approaches to reveal potential patterns of diversification within a species widely distributed across European mountains: the amphipod crustacean Gammarus balcanicus. The data were obtained from 13 populations spread across the range of the species. Individuals were initially ascribed to G. balcanicus based on conventional fauna key morpho-anatomical diagnostic features and were further analysed for 23 additional features to explore any putative diversification. Morphometric data were analysed with use of the multiple correspondence analysis and anova. Molecular distances were calculated for 551-bp-long COI sequences. Test for isolation by distance was performed for both morphological and molecular data. The morphometric studies showed that some of the analysed features differed significantly between populations, although there was only a weak correlation between the morphological divergence and the between-population geographical distances. Moreover, high morphological diversity was present within sites. A set of 42 COI haplotypes was identified among the 135 individuals sequenced. No haplotype was shared among populations. The molecular p-distances within the nine localities presenting more than one haplotype were either almost null (ca. <0.003 for 7 localities) or relatively low (ca. 0.01–0.02 for 2 localities). In opposite, the molecular p-distances between localities were mostly at a high level (94% of pairwise comparisons being >0.14), similar as between other well-defined species of the genus Gammarus. Surprisingly, G. balcanicus appears to be polyphyletic based on topology of the neighbour-joining tree. The level of genetic distance between localities was not correlated with their geographical proximity. Globally, combining spatial patterns of morphological versus molecular divergence indicates a high level of cryptic diversity within a species conventionally defined based upon fauna key morphological features. In this context, the name G. balcanicus should be applied only to the population from locus typicus, while the other populations represent a number of putative distinct species. We may expect that such phenomenon would apply also to other animal taxa with conserved morphology, which are widespread over different mountain ranges in Europe.

Ten new Gammarus species (Crustacea: Amphipoda: Gammaridae) from Yunnan-Guizhou Plateau, China.

Ten new species of the genus Gammarus are described from Yunnan-Guizhou Plateau, Southwest China, including Gammarus amabilis sp. nov., G. citatus sp. nov., G. echinatus sp. nov., G. egregius sp. nov., G. eliquatus sp. nov., G. hirtellussp. nov., G. margcomosus sp. nov., G. rivalis sp. nov., G. silendus sp. nov. and G. tranquillus sp. nov. Four of them are stygobite and with no eyes. Detailed illustrations and comparisons with related species are presented. A key to all species from Yunnan-Guizhou Plateau are given.

Two new species of freshwater amphipods (Crustacea: Gammaridae) from Central Asia, with comments on the unusual upper lip morphology

This paper describes two new species of the genus Gammarus Fabricius from the freshwaters of Central Asia: G. montaniformissp. nov. (Kazakhstan, Dzungarian Alatau, Borohudzyr River) and G. alius sp. nov. (Kyrgyzstan, Chatyr-Kul Lake). The mor-phology of the mouth parts of the new species G. alius is characterised by a peculiar upper lip with “hooks” on its epistome thatis discussed. The affinity of the new species for their congeners is discussed, emphasizing morphological and biogeographical relationships.

Eocene habitat shift from saline to freshwater promoted Tethyan amphipod diversification.

Current theory predicts that a shift to a new habitat would increase the rate of diversification, while as lineages evolve into multiple species, intensified competition would decrease the rate of diversification. We used Holarctic amphipods of the genus Gammarus to test this hypothesis. We sequenced four genes (5,088 bp) for 289 samples representing 115 Gammarus species. A phylogenetic analysis showed that Gammarus originated from the Tethyan region with a saline ancestry in the Paleocene, and later colonized the freshwater habitat in the Middle Eocene. Ancestral range reconstruction and diversification mode analysis combined with paleogeological and paleoclimatic evidence suggested that the habitat shift from saline to freshwater led to an increased diversification rate. The saline lineage of Gammarus dispersed to both sides of the Atlantic at 55 million years ago (Ma), because of the few barriers between the Tethys and the Atlantic, and diversified throughout its evolutionary history with a constant diversification rate [0.04 species per million years (sp/My)]. The freshwater Gammarus, however, underwent a rapid diversification phase (0.11 sp/My) until the Middle Miocene, and lineages successively diversified across Eurasia via vicariance process likely driven by changes of the Tethys and landmass. In particular, the freshwater Gammarus lacustris and Gammarus balcanicus lineages had a relatively high diversification shift, corresponding to the regression of the Paratethys Sea and the continentalization of Eurasian lands during the Miocene period. Subsequently (14 Ma), the diversification rate of the freshwater Gammarus decreased to 0.05 and again to 0.01 sp/My. The genus Gammarus provides an excellent aquatic case supporting the hypothesis that ecological opportunities promote diversification.

An overview of the Gammarus Fabricius (Gammaridae: Amphipoda) species of Turkey, with an updated checklist

The genus Gammarus Fabricius, 1775 is represented in Turkey by 38 species. Only four of them occur in marine or brackish habitats and the remaining species are pure freshwater species. Some of them adopted to living in extreme habitats, such as wells, cave waters etc. An updated list of Gammarus taxa reported from Turkey is presented in addition to some supplementary records.

Intraspecific or interspecific variation: delimitation of species boundaries within the genus Gammarus (Crustacea, Amphipoda, Gammaridae), with description of four new species

The delineation of Gammarus species is controversial because of extensive intraspecific morphological variation. The current study examined DNA sequences from the mitochondrial cytochrome c oxidase subunit I and the nuclear 28S genes as well as morphological and ecological data to determine the species boundaries of Gammarus species from China. The results of molecular analyses showed that Gammarus sp1, G. sp2, G. sp3, and G. sp4 are monophyletic and deeply divergent from sister groups. Detailed morphological and ecological comparisons with closely related species were consistent with molecular analyses. Gammarus sp1, G. sp2, G. sp3, and G. sp4 were described as four new species: Gammarus illustris sp. nov., Gammarus clarus sp. nov., Gammarus hypolithicus sp. nov., and Gammarus parvioculus sp. nov. We recommend that molecular detected species should be formally named and described for future research.

Distribution of the genus Gammarus (Crustacea, Amphipoda) along the coast of Arctic fjords as an indicator of prevailing environmental conditions

Distribution of the genus Gammarus (Crustacea, Amphipoda) along the coast of Arctic fjords as an indicator of prevailing environmental conditions

High sensitivity of Gammarus sp. juveniles to deltamethrin: Outcomes for risk assessment

Amphipods from the genus Gammarus are among the most frequently used organisms in ecotoxicological testing and in situ bioindication. Because of their importance in risk assessment, it is necessary to understand the potential roles of life stage, population source and inter-specific differences on the sensitivity of these organisms to contaminants. In the present study, the acute toxicity of deltamethrin, a commonly used pyrethroid insecticide, has been tested for Gammarus fossarum and Gammarus pulex (Crustacea, Amphipoda) to document the inter- and intra-specific variability at different developmental stages. Adult G. fossarum were about two-fold more sensitive to deltamethrin than adult G. pulex, 96-h LC50 being 33.2 and 68.0ngL−1, respectively. However, in the same species, significant differences of sensitivity were observed between individuals from different locations. Furthermore, G. fossarum from certain localities were less sensitive to deltamethrin than certain G. pulex. In addition, juveniles of both species were about 14- to 22-fold more sensitive to deltamethrin than adults: 48-h LC50 in G. fossarum and G. pulex juveniles were 4.0 and 5.7ngL−1. Therefore, lethal effects of deltamethrin on Gammarus sp. populations likely depend more on juvenile response rather than on adult response. Since juveniles were also the most abundant population component, the present results show that risk assessment should consider at this developmental stage.

A new species of the genus Gammarus (Crustacea: Amphipoda: Gammaridae) from the low salinity habitats in the northern Gulf of Mexico

A new species of the genus Gammarus (Crustacea: Amphipoda: Gammaridae) from the low salinity habitats in the northern Gulf of Mexico

Probing marine Gammarus (Amphipoda) taxonomy with DNA barcodes

The genus Gammarus (Amphipoda) is one of the most speciose genera of Crustacea, yet much uncertainty remains concerning taxonomy and systematic relationships, particularly for brackish and marine forms. We used DNA barcode sequences from the mitochondrial cytochrome c oxidase I (COI) gene to probe the taxonomy of prominent members of marine and brackish water Gammarus of the North Atlantic, Baltic, Mediterranean and Black Seas. We investigated 16 putative Gammarus spp. at an average number of 9 specimens per species. This constitutes the most taxonomically and geographically comprehensive molecular study of marine Gammarus to date. Average between‐species sequence divergence (26.8%) was much higher than intraspecific distances (0.8%), enabling clear molecular species identification and highlighting several possible misidentifications from previously published studies. Specimens of Gammarus aequicauda and G. insensibilis from the Black Sea were at least 14% distant from their putative conspecifics elsewhere. Placing these findings in a geographic context provides strong indication of cryptic speciation. Further, we detected phylogeographic splits in G. oceanicus and G. duebeni. Our analyses also suggest phylogenetic positioning of G. marinus with members of the genus Echinogammarus, thus confirming its classification as Echinogammarus marinus. We have demonstrated that comprehensive analyses of taxonomically complex groups using DNA barcodes can result in a diversity of complementary data on taxonomy, phylogeography and phylogenetics. The combination of these results, with further morphological and ecological data, will enable significant progress in our understanding of this ecologically important group of crustaceans.

Spiny-headed worms (Acanthocephala) in the basin of the Sea of Okhotsk: taxonomic and ecological diversity

For the first time the inventory of the taxonomic composition of the spiny-headed worms has been carried out in the basin of the Sea of Okhotsk. It has revealed their high biodiversity. We have registered 100 species and forms of 28 genera of 17 families of 8 orders of 3 classes in composition of the phylum Acanthocephales. Spiny-headed worms of hydrotopic species, both sea and freshwater, totally dominate in the basin of the Sea of Okhotsk. Parasitic systems of the background species of the sea spiny-headed worms are basically composed by the dominant species of intertidal and near-shore sea amphipods, and besides of decapods as intermediate hosts. Structure and biotopic belonging of parasitic systems of the freshwater spiny-headed worms species in the region are determined by the freshwater crustaceans belonging to ostracods of genera Cypria and Candona, amphipods of the genus Gammarus and isopods, namely water slaters of the genus Asellus. Broad transmission of the spiny-headed worms within certain ecosystems and over the basin of the Sea of Okhotsk is realized by their definite and parathenic hosts. Short- and long-distance migrant fishes, birds and mammals are most important among them.

Contrasting sensitivities to toxicants of the freshwater amphipods Gammarus pulex and G. fossarum

Amphipods are an important component of freshwater ecosystems. They are very often used in ecotoxicology, particularly the freshwater amphipod Gammarus pulex. However, there is scarce information on the sensitivity to toxicants of other species within the genus Gammarus. The present study aims to: (1) to compare sensitivities to ivermectin and cadmium between two species of freshwater amphipods (G. pulex and G. fossarum); (2) to compare sensitivities to these toxicants between juveniles and adults within each species; and (3) to assess whether the sensitivity to toxicants of these co-generic species is related with the wideness of their natural distribution area. Eight independent short-term bioassays (96 h) were conducted to assess sensitivity for ivermectin and cadmium for juvenile and adult life stages for each species. The LC50 (mortality) and EC50 (mortality plus immobility) were calculated to 48 and 96 h of continuous exposure. Our results showed that G. pulex was less tolerant to ivermectin than G. fossarum, the reverse being true for cadmium. In general, juveniles of both species were less tolerant to cadmium than adults. In the case of ivermectin, only for G. fossarum EC50 values were different between life stages. These results suggest that the risk assessment of toxicants to freshwater amphipods should include bioassays with the most sensitive species and life stage.

Identifying Chinese species of Gammarus (Crustacea: Amphipoda) using DNA barcoding

Abstract Using a standard cytochrome c oxidase I sequence, DNA barcoding has been shown to be effective to distinguish known species and to discover cryptic species. Here we assessed the efficiency of DNA barcoding for the amphipod genus Gammarus from China. The maximum intraspecific divergence for widespread species, Gammarus lacustris, was 3.5%, and mean interspecific divergence reached 21. 9%. We presented a conservative benchmark for determining provisional species using maximum intraspecific divergence of Gammarus lacustris. Thirty-one species possessed distinct barcode clusters. Two species were comprised of highly divergent clades with strong neighbor-joining bootstrap values, and likely indicated the presence of cryptic species. Although DNA barcoding is effective, future identification of species of Gammarus should incorporate DNA barcoding and morphological detection.

A new species of the genus Gammarus (Crustacea: Amphipoda: Gammaridae) from the low salinity habitats in the northern Gulf of Mexico

In the northern Gulf of Mexico, Gammarus mucronatus sensu lato is represented by at least two forms, G. mucronatus sensu stricto and a less common “macromucronate” form, which appears to be restricted to low salinity habitats. These two forms have traditionally been separated using the size or angle of projection of the dorsal mucronations (processes). However, because of variability in the development of the processes, it is unclear whether this and other morphological differences between G. mucronatus sensu stricto and the “macromucronate” form are ecophenotypic or reflect distinct and separate species. Detailed morphological analyses indicate that these two forms represent distinct species; Gammarus lecroyae, new species, is described in detail and a key to the marine and estuarine Gammarus species from the northern Gulf of Mexico is provided.

Genetic studies of Gammarus

In five marine species of the amphipod genus Gammarus (G. duebeni, G. zaddachi, G. salinus, G. oceanicus, and G. locusta) the electrophoretically defined variation at 19 loci in populations from the Baltic Sea and the Kattegat is compared. In four out of the five Gammarus species there is evidence for differentiation among the Baltic and the Kattegat populations. In addition, the phylogenetic relationship of the five Gammarus species and a single species in the genus Chaetogammarus (C. marinus) is described.

Responses to nutrient enrichment, wave action and disturbance in rocky shore communities

A high degree of resistance against nutrient enrichment has previously been demonstrated for macroalgal-dominated rocky shore communities in the presence of moderate to large amounts of macroinvertebrate grazers. To experimentally examine, under controlled conditions, the possible roles for this resistance of two other factors, i.e. disturbance (presence/absence of the macroalgal canopy itself) and wave action, the canopy algae and associated algal and animal assemblages were removed by scraping from approximately one third of the area of eight littoral mesocosms, subjected to two different wave action regimes. After this, excessive nutrients were added to four mesocosms with the factor nutrients fully crossed with the factor wave action with two replicate mesocosm basins of each nutrient/wave treatment combination. Disturbance was added to the design as a within-basin factor thus making up a split-plot experiment. The abundance of grazers was allowed to vary freely and under the influence of the treatments. After 11 summer weeks, there were significant differences in community structure between nutrient enrichment levels for both algal and animal assemblages when examined by multivariate statistical techniques. Univariate analyses confirmed a significantly stimulated colonisation by green algae, mainly Ulva lactuca, in both disturbed (scraped) and undisturbed areas of nutrient-enriched mesocosms. In un-enriched mesocosms, the green algae were absent from undisturbed areas and rare in disturbed areas, where mainly brown Ectocarpus spp. and red algae had settled. Among the macrofauna, the total abundance of grazers was stimulated in nutrient-enriched mesocosms with individuals of the amphipod genus Gammarus and the isopod genus Jaera being especially numerous. With regard to wave action, no significant differences occurred in community structure, although there were indications of significant nutrient × wave effects for both the amount of exported red algae and the amount of accumulated brown algae. The study shows that eutrophication-related community shifts on rocky shores may occur very rapidly, regardless of the level of wave-energetic stress and the abundance of grazers, if the nutrient concentrations are high and the colonisation and growth of opportunistic algae are facilitated by disturbance such as (naturally or anthropogenically driven) canopy gap forming processes.

A molecular phylogeny of the genus Gammarus (Crustacea: Amphipoda) based on mitochondrial and nuclear gene sequences

A phylogeny of the genus Gammarus Fabricius, 1775 was constructed using DNA sequence data from the mitochondrial genes COI and 16S, and the nuclear genes 18S and 28S. Both parsimony and Bayesian analyses were conducted on separate and combined data partitions. The Bayesian phylogeny from the combined analysis was selected as the preferred phylogenetic hypothesis. The hypothesis supports monophyly of the genus Gammarus, paraphyly of the European-North American Gammarus, and monophyly of the Asian Gammarus. The Asian clade was further split into a southeastern group and a northwestern group. The dramatic climate change following the uplift of the Tibetan Plateau was probably the most important factor in triggering the diversification of southeastern and northwestern groups. The genus Sinogammarus is invalid and should be part of the genus Gammarus.