Amphipod Genus Gammarus Research Articles

Revealing Diversity in Gammarus (Amphipoda: Gammaridae) in the Freshwater Ecosystems of Armenia Using DNA Barcoding

Gammarus plays a central role in the detritus cycle and constitutes an important component in food webs. At the same time, taxonomy and morphological identification to species level is highly challenging in this genus. Thus, the freshwater gammarid diversity in the Caucasus biodiversity hotspot remains largely unstudied to date. We use DNA barcoding for the first time in assessing the biodiversity and taxonomy of gammarids within the amphipod genus Gammarus in the limnic ecosystems of Armenia. The results expand the knowledge on possible diversity and evolutionary lineages of Gammarus in the region. DNA barcodes obtained from our Armenian specimens consistently indicate four to six well-defined molecular operational taxonomic units (MOTUs) within three distinct morphospecies clusters. One to three MOTUs correspond to the Gammarus balcanicus species complex, two MOTUs to the G. komareki complex, and one MOTU to the G. lacustris complex. Five BINs out of six were unique and new to BOLD.

Metabolic rate and osmoregulation in desert spring amphipods

Desert springs contain many endemic taxa and are of conservation concern due to anthropogenic activities that are expected to increase environmental salinity. Understanding the nature of osmoregulation is necessary to predict how non-vagile aquatic organisms will respond to changes. In the Chihuahuan Desert, the amphipod genus Gammarus Fabricius, 1775 is composed of two lineages. These lineages have species that currently inhabit springs ranging from 0.4 to 7.8 parts per thousand (ppt). All Gammarus in this region are of conservation concern because each is endemic to a single spring system. We exposed individuals of Gammarus colei Walters, Cannizzaro, and Berg in Walters, Cannizzaro, Trujillo and Berg, 2020 and Gammarus seideli Cannizzaro, Walters and Berg, 2018 species occupying low-salinity springs, to the range of salinities found in the Chihuahuan Desert. We measured metabolic rates as [Formula: see text] to examine the energetic cost of osmoregulation. We also measured the hemolymph osmolality of G. colei and compared that with the isosmotic line to determine the degree of osmoregulation. Neither species increased its metabolic rate across increasing salinities. However, G. colei showed an increase in hemolymph osmolality. Despite the divergence (∼66 million years ago) between the two lineages, it appears their physiological tolerances have converged, suggesting that both lineages may be able to persist when exposed to moderate salinity changes.

Community metabarcoding uncovers vast diversity and a lack of barcode references for aquatic invertebrates in Carpathian spring fens

Recent studies on diversity of stream amphipods proposed that the Western Carpathians have served as an important glacial refugium of freshwater fauna. If this scenario is true, a considerably high molecular diversity can be expected in this biogeographic region also for other taxa. In our project, we aimed to uncover and characterize molecular diversity of benthic macroinvertebrate fauna of spring fens, a well studied and hence convenient model community. Using a DNA metabarcoding approach, we sequenced a fragment of the COI gene of pooled spring fen invertebrate communities from 21 localities in the Western Carpathians. The preliminary analysis of the sequences revealed a substantially higher amount of operational taxonomic units (OTUs), when compared to the number of taxa identified in the same spring fens based on morphological characters. The lack of reference sequences in public databases (Barcoding of Life Database, GenBank) for the majority of the detected OTUs indicates that the Western Carpathian region is not yet sufficiently covered by barcoding efforts, and suggests that there indeed may be a considerable unrecognized diversity of macrozoobenthos. However, most newly uncovered diversity is concentrated in a few taxa such as the dipteran families Tabanidae and Ceratopogonidae, annelid species (complexes) Eiseniella tetraedra and Helobdella stagnalis or the amphipod genus Gammarus. In the future, these findings will be the basis for several levels of research: detailed investigation of seemingly hyperdiverse taxa (phylogeography, phylogeny, reference coverage) and comparison of overall molecular diversity of these communities in the Western Carpathians and neighbouring Bohemian Massif, a region where we expect much lower diversity due to different biogeographic history.

Dictyocoela microsporidia diversity and co-diversification with their host, a gammarid species complex (Crustacea, Amphipoda) with an old history of divergence and high endemic diversity

BackgroundAlthough the processes of co-evolution between parasites and their hosts are well known, evidence of co-speciation remains scarce. Microsporidian intracellular parasites, due to intimate relationships with their hosts and mixed mode of transmission (horizontal but also vertical, from mother to offspring), may represent an interesting biological model for investigating co-speciation. Amphipod crustaceans, especially gammarids, are regular hosts of microsporidian parasites, in particular the Dictyocoela spp., which have so far been found limited to these amphipods and are known to use a vertical mode of transmission. The amphipod genus Gammarus has a diversification history spanning the last 50–60 Mya and an extensive cryptic diversity in most of the nominal species. Here, we investigated the degree of co-diversification between Dictyocoela and Gammarus balcanicus, an amphipod with high degrees of ancient cryptic diversification and lineage endemism, by examining the genetic diversity of these parasites over the entire geographic range of the host. We hypothesised that the strong host diversification and vertical transmission of Dictyocoela would promote co-diversification.ResultsUsing the parasite SSU rDNA as a molecular marker, analyzing 2225 host specimens from 88 sites covering whole host range, we found 31 haplogroups of Dictyocoela, 30 of which were novel, belonging to four Dictyocoela species already known to infect other Gammarus spp. The relationships between Dictyocoela and gammarids is therefore ancient, with the speciation in parasites preceding those of the hosts. Each novel haplogroup was nevertheless specific to G. balcanicus, leaving the possibility for subsequent co-diversification process during host diversification. A Procrustean Approach to Co-phylogeny (PACo) analysis revealed that diversification of Dictyocoela was not random with respect to that of the host. We found high degrees of congruence between the diversification of G. balcanicus and that of Dictyocoela roeselum and D. muelleri. However, we also found some incongruences between host and Dictyocoela phylogenies, e.g. in D. duebenum, probably due to host shifts between different G. balcanicus cryptic lineages.ConclusionThe evolutionary history of Dictyocoela and Gammarus balcanicus represents an example of an overall host-parasite co-diversification, including cases of host shifts.

What happened to the genus Gammarus (Crustacea: Amphipoda) in Central Asia

We examined the phylogenetic relationships in the unusually structured fauna of the amphipod genus Gammarus in Central Asia, trying to explain its causes. Mitochondrial DNA sequence data were used in MP and ML and Bayesian analyses to generate a phylogenetic hypothesis. All of the recently collected Gammarus spp. specimens belong to the G. lacustris aggregate, except scarce marginal populations of G. balcanicus and G. komareki aggregates. Although molecularly closely related, these. G. lacustris agg. populations are morphologically and ecologically equally diverse as are the numerous European Gammarus spp. Only few populations are morphologically close to the morphotype of G. lacustris. There is a more than 2,000 km wide gap between the eastern and western populations-species of G. balcanicus agg. Since Gammarus lacustris can be spread by birds, and its Asian relatives are molecularly significantly diverse, we suppose that it invaded Central Asia several times and from several sources. It most probably differentiated to diverse morphotypes after reaching Asia. The area of the cryophilic and less nomadic G. balcanicus could have been reached and conquered only by waterways. Its area was probably continuous in the past and divided by aridification during the Neogene. The strong historical aridifications probably extirpated the probably higher Gammarus diversity in Central Asia, including G. balcanicus. This opened the area and its habitats for the reiterated invasions of the particularly euryoecious G. lacustris s.l., followed by its morphological and ecological diversification.

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.

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.

Patterns of Reproduction in Different Populations of Five Species of the Amphipod Genus Gammarus

Different features of reproduction (breeding periods, number of generations per year, clutches per generation, clutch sizes, egg sizes) were studied in five species of Gammarus in the Baltic Sea and in the Limfiord, Denmark and in two species at localities along the west coast of the European continent. Breeding periods, numbers of annual generations (one or two), and number of clutches per generation show some geographical variation within each species; this is explained by interspecific relations (reproductive character displacement) in conjunction with local water temperature. Winter breeding forms have fewer and larger eggs than summer breeding forms; this is explained as an evolutionary adaptation to a larger juvenile mortality resulting from a low growth rate at low temperatures. Reproductive effort (total egg volume per clutch) is nearly identical for four of the species within each area, but differs between areas. No explanation for this effect is attempted; it is pointed out that considerations on rand K-selection are futile for understanding such data. This will require much more detailed data on age specific mortality in nature under different environmental conditions than is normally available for invertebrate populations.

Habitat Selection and Life Cycle Characteristics of Five Species of the Amphipod Genus Gammarus in the Baltic

Habitat selection and life cycle characteristics are given for five species of the amphipod genus Gammarus living in the central Baltic Sea. Gammarus oceanicus is nearly omnipresent and coexists with G. locusta, G. salinus, and G. zaddachi. The three latter species show migrations between habitat types in tight correlation with their breeding periods. Gammarus duebeni is mainly found in rockpools. This behaviour results in a complete separation of the breeding species populations. These findings are discussed in relation to minimum requirements for coexistence, i.e. displaced breeding periods and non-overlapping size distributions, and to mating com

Coexistence and Life Cycle Characteristics of Five Species of the Amphipod Genus Gammarus

The life cycle characteristics of five amphipod species of the genus Gammarus: G. oceanicus, G. locusta, G. salinus, G. zaddachi, and G. duebeni from a Danish brackish water area are given, and discussed in relation to coexistence between the species. The five species are distributed according to salinity and with more or less narrow zones of overlap. The species that do overlap in distribution always have diametrically different life cycles so that the three winter breeding forms (G. duebeni, G. salinus, and G. oceanicus) are separated by the two summer breeding forms (G. zaddachi, G. locusta). These findings are discussed in terms of size differences between coexisting species populations and interspecific precopulation.

Habitat Selection and Distribution Patterns of Five Species of the Amphipod Genus Gammarus

The distribution patterns of five brackish water species of the amphipod genus Gammarus from the inner Danish waters and from the central Baltic Sea are compared. In the former area, the species show zonation patterns which correlate with salinity. In the Baltic, with a low, stable salinity, such patterns are absent, and the species show a much higher degree of coexistence, although habitat selection correlated with the degree of exposure, substrate and depth is indicated. Comparisons with the literature show, that while regionally coexisting Gammarus spp. always show some habitat compression, the actual relationships to environmental gradients of the single species have evolved in different directions in different areas. The findings are discussed in terms of the selection forces which have resulted in habitat selection. It is suggested that selection against interspecific precopula-formation leading to sterile matings is an important factor and that displacements of reproductive periods are important

Tolerance differences and interspecific competition in three members of the amphipod genusGammarus

1. In a series of experiments withG. pulex, G. duebeni celticus andG. d. duebeni populations, pure or mixed, their tolerances for several temperature/salinity conditions have been determined. Tested were 100%, 10%, 1% and 0.1% seawater in combination with temperatures of 5, 10 or 15°C. In general all species tolerated the 5°C conditions better than those with higher temperatures, and the middle salinity range (1% forG. pulex, 1% and 10% forG. d. celticus andG. d. duebeni) better than the lower or higher salinities. 2. In nearly all situations tested.G. pulex had a lower survival rate thanG. d. celticus andG. d. duebeni. 3. Notwithstanding the sometimes unfavourable conditions forG. pulex, this species can compete succesfully withG. d. celticus under most of the experimental conditions, but the interspecific relations betweenG. pulex andG. d. duebeni end in the competetive exclusion of the first species. These results support two theories: (1)G. pulex is able to compete succesfully withG. d. celticus and to expel the latter of its niche, and (2)G. d. duebeni is capable to invade freshwater and to establish inland populations. 4. The differences demonstrated betweenG. d. celticus andG. d. duebeni are an argument for a different development and different capabilities of both subspecies. 5. Sterile interspecific matings between these (sub) species are temperature dependent and do not play a major role in the interspecific relations connected with competition.

Tolerance Differences and Interspecific Competition in three Members of the Amphipod Genus Gammarus

In a series of experiments with G. pulex, G, duebeni celticus and G. duebeni duebeni populations, pure or mixed, their tolerances for several temperature/salinity conditions have been determined. Tested were 100%, 10%, 1% and 0.1% seawater in combination with temperatures of 5°, 10° or 15°C. In general all species preferred the 5°C conditions above those with a higher temperature, and the middle salinity range (1% for G. pulex, 1% and 10% for G. d. celticus and G. d. duebeni) above the lower or higher salinities. In nearly all situations tested G. pulex had a lower survival rate than G. d. celticus and G. d. duebeni. Notwithstanding the sometimes unfavourable conditions for G. pulex, this species can compete successfully with G. d. celticus under most of the experimental conditions, but the interspecific relations between G. pulex and G. d. duebeni end in the competitive exclusion of the first species. These results support two theories: (1) G. pulex is able to compete successfully with G. d. celticus and to expel the latter from its niche, and (2) G. d. duebeni is able to invade freshwater and to establish inland populations. The differences demonstrated between G. d. celticus and G. d. duebeni are an argument for a different development and different capabilities of both subspecies. Sterile interspecific matings between G. pulex and both subspecies of G. duebeni are temperature dependent and do not play a major role in the interspecific relations connected with competition.

On the ciliate fauna associated with the marine species of the amphipod genus Gammarus J. G. Fabricius : Fenchel Tom, 1965. Ophelia, 2 (2): 281–303

On the ciliate fauna associated with the marine species of the amphipod genus Gammarus J. G. Fabricius : Fenchel Tom, 1965. Ophelia, 2 (2): 281–303

On the ciliate fauna associated with the marine species of the amphipod genusGammarusJ. G. fabricius

Abstract The present paper describes the ciliate epifauna found on the marine species of the amphipod genus Gammarus in Scandinavian waters. Twentyfive species of ciliates were found which, ecologically, could be placed in the following four groups: Suspension feeders, herbivores, carnivores, and parasites. It is shown that the forming of swarmers in sessile commensals (peritrichs and chonotrichs) is correlated with the moulting of the host. While most of the epizoans found on Ganunarus are specific for the genus, the distribution of the ciliates within the host genus is controlled mainly by environmental factors. especially salinity. The marine and brackish water Gammarus species have no ciliates in common with the fresh-water species G. lacustris. Even G. duebeni, when living in freshwater, has an impoverished marine fauna of ciliates. Brackish water populations of Gammarus species were found to harbour the greatest number of ciliate species. This is in contrast to the general concept that a smaller number of species is found in brackish water than in similar localities in the sea and in fresh-water. This is explained by the fact that Gammarus forms much denser populations and has a much wider distribution in brackish water than in marine environments.