The relationship between range size and niche breadth: a test using five species of Gammarus (Amphipoda)

Data for five closely related species of gammarid crustaceans are used to examine interspecific relationships between the breadth of fundamental tolerance or capacity and geographical range size. Gammarus duebeni is, almost without exception, the most tolerant species and that with the best physiological performance. Although there is some limited variation, the remaining species can be ranked broadly in the sequence G. zaddachi  > G. salinus  >  G. oceanicus > G. locusta . The wide tolerance and high performance of G. duebeni is associated with the occupation of a wider range of environmental 'types' than any other of the species. In terms of geographical range size, the species can be ranked from most to least widespread in the sequence G. oceanicus  > G. duebeni  >  G. zaddachi  >  G. salinus  >  G. locusta . This provides little support for Brown's hypothesis, or the argument that the more widely distributed species within a taxonomic assemblage also tend to have the widest fundamental niches. However, if marine ( G. oceanicus and G. locusta ) and estuarine ( G. duebeni , G. zaddachi , G. salinus) species are considered separately, then in each case the species with the largest geographical range is also the most tolerant/best performer. In this sense, the jack-of-all-trades is the master-of-all, rather than the master-of-none.     

Electrophoretic approach to the biochemical systematics of gammarids

By utilizing the techniques for electrophoretic separation of proteins by vertical starch gels, the biochemical systematics of 10 Gammaridae species obtained from marine, brackish and freshwater habitats was studied. They includedChaetogammarus marinus, Gammarus zaddachi, G. salinus, G. oceanicus, G. tigrinus, G. chevreuxi, G. locusta, G. duebeni duebeni, G. d. celticus, G. pulex pulex, andG. fossarum. For comparison of electrophoretic mobilities selected enzymes (phosphoglucose isomerase, glutamate oxalacetate transaminase, arginine phosphokinase, hexokinase, leucine amino peptidase, mannose 6-phosphate isomerase) were assayed. They were used as diagnostic characters in terms of electrophoretic identities or diversities of most frequent alleles at polymorphic gene loci. These criteria could be applied to estimate intrageneric enzymic variation and degrees of genetic relatedness between the crustacean amphipod species under consideration, thereby complementing traditional morphological classification.     

Congeneric amphipods show differing abilities to maintain metabolic rates with latitude

Metabolic variability across latitudinal populations of gammarid amphipods was examined in the summer by determining whole-animal rates of oxygen uptake (M(o)?) in four species with overlapping distribution patterns in the northeast Atlantic and Arctic oceans. Comparisons were made between an arctic/boreal species, Gammarus setosus, a subarctic/boreal species, Gammarus oceanicus, a boreal/temperate species, Gammarus duebeni duebeni, and a temperate species, Gammarus locusta. Measurements included acclimatized M(o)? in all four species and M(o)? after acclimation to 10°C in two populations of G. oceanicus and G. locusta. In G. oceanicus, acclimatized M(o)? declined with latitude (13° to 5°C) so that metabolic rates were lower in subarctic (79°N) relative to temperate (58°N) populations and similar to the values in G. setosus at 79°N. Consequently, there was no evidence for metabolic rate compensation in the colder-water, high-latitude populations in the summer. Further examination of the specific effects of temperature revealed similarities in M(o)? between populations of G. oceanicus acclimated at 10°C and similarities in thermal sensitivity (Q(10)) and activation energies (E(a)) on exposure to acute temperature change. In sharp contrast, there was no variation in summer acclimatized M(o)? with latitude in either G. d. duebeni between 48° and 70°N or G. locusta between 38° and 53°N. Instead, the two species maintained relatively high metabolic rates across latitudes, which were associated in G. locusta with differences in M(o)? and with Q(10) and E(a) values in amphipods acclimated at 10°C. The ability to compensate metabolic rate with latitude in the summer suggests greater metabolic flexibility, which predicts a greater capacity for survival during climate change of the temperate/boreal over the subarctic and arctic gammarid species.     

Zur Ökophysiologie,Sexualität und Populationsgenetik litoraler Gammaridea — ein Überblick

Comparative investigations on the physiological capacities in the euryhaline amphipodsGammarus locusta, G. oceanicus, G. salinus, G. zaddachi andG. duebeni were reviewed. In order to assess the adaptations of these species to the abiotic conditions of their environment, the following criteria were examined: oxygen consumption in relation to ambient salinity and temperature levels, respiratory responses following osmotic stress, resistance capacities to oxygen deficiency, resistance to aerial exposure and the simultaneous presence of hydrogen sulphide. Covering the range from marine to typically brackish-water inhabitants, the 5 species show adaptive responses in the above-mentioned order. Respiration is less intensely modified by external factors, and oxygen consumption decreases. Accompanied by faster rates of acclimation to new steady states of performance, resistance capacities increase. The significance of the findings obtained is discussed in relation to the environmental requirements of the amphipods considered. Based on breeding experiments, the sex-determining systems reported thus far inGammarus species are outlined. As demonstrated inG. duebeni, a more or less pronounced influence of external factors such as photoperiod may become effective. A preponderance of males was noted when offspring were raised under long-day photoperiods, whereas females prevailed under short-day conditions. In terms of the critical daylength, the light per day was estimated as being between 13 and 14 h (Elbe estuary population). Feminizing microporidians (Octosporea effeminans, Thelohania herediteria), which are transovarially transmitted, can interfere with the system of sex determination and sex differentiation of the host. As reflected in variousG. duebeni populations, they cause a maternally transferred sex-ratio condition by the production of all-female broods, thereby mimicking extrachromosomal inheritance. An increase of the salinity level to 25–30‰ results in a disappearance ofO. effeminans. In both microsporidians, long exposure to low temperatures (≤4°C) produces eggs which are not all parasitized. Furthermore, intersexuality can be induced by changing environmental factors. Microsporidian species have no influence on sex differentiation inG. duebeni celticus, G. salinus, G. locusta andG. pulex. Patterns of relative electrophoretic mobilities of proteins and the distribution of allele frequencies at polymorphic gene loci can be utilized for species diagnosis and for the evaluation of the relationships between different taxa, particularly at and below the species level. As exemplified by studies on several gammarids from marine, brackish and freshwater environments, inter- and infraspecific gene-enzyme variation is described. Electrophoretic investigations on natural populations of the euryhaline amphipodsG. zaddachi, G. salinus, G. tigrinus and others from different geographic areas provided evidence of considerable biochemical genetic variation. InTalitrus saltator- andTalorchestia deshayesii-populations the extent of variability based on micro-and macrogeographic aspects is illustrated. The large-scale genetic divergence is demonstrated by comparison of samples obtained from the Baltic, North, Atlantic and northern Mediterranean Seas.      

The life-cycles of four amphipod species in the Kattegat

Populations of four species of Gammaridae (Crustacea, Amphipoda) were sampled over 15 months in the south-western Kattegat at Sangstrup Klint (Denmark). Chaetogammarus marinus, C. stoerensis and Gammarus oceanicus had annual life-cycles, while G. salinus most likely had two generations per year. Mature C. marinus females were found from March to July, mature C. stoerensis females from March to June, mature G. oceanicus females from December to early June and mature G. salinus females from late November to late July. The theoretical maximum number of clutches were estimated at five for C. marinus , five plus for C. stoerensis , and six for G. oceanicus and both winter and summer reproducing G. salinus . Spring was the period of main recruitment in all populations, with additional recruitment during summer in G. salinus .
The geographical patterns of the reproductive strategies are discussed in relation to environmental factors and interspecific competition.     

Microtubule systems associated with the septate junctions of the gill cells of four gammarid amphipods

The microtubular systems associated with the septate junctions of the gill epithelial cells of four species of gammarid amphipod are described. The four species examined included two relatively stenohaline marine forms, Chaetogammarus marinus and Gammarus locusta; a highly euryhaline species, Gammarus duebeni, and a stenohaline freshwater species, Gammarus pulex. Of these amphipods, G. locusta and C. marinus maintain only a limited osmotic gradient between their haemolymph and the medium and have a poorly developed junctional microtubular system; G. pulex has haemolymph which is some 300 mOsmol hypertonic to freshwater and has a well ordered system of microtubules on both sides of fairly long septate junctions; G. duebeni from brackish water tend to have a somewhat shorter length of septate junctions lined by one or occasionally by a double row of microtubules. The most complex junctional microtubular systems are shown by specimens of the freshwater race of G. duebeni celticus which have been acclimated to seawater. These can take the form of multiple arrays in which some microtubules are linked to the plasma membrane by dense strands. It is suggested that these findings are consistent with the hypothesis that one role of these microtubules is to provide mechanical stability to enable the integrity of the septate junctions to be maintained during osmotic stress.     

An experimental study on the effects of polymorphiasis in common eider ducklings.

Eight common eider (Somateria mollissima) ducklings were experimentally infected from 1 June through 13 June, 1995 with acanthocephalans (Polymorphus minutus) by allowing the birds to feed on Gammarus spp. (Gammarus oceanicus, G. salinus, G. zaddachi, and G. lacustris) containing acanthocephalan cystacanths. Uninfected Gammarus spp. were fed to a control group of seven ducklings. No mortality of ducklings occurred during the experiment. However, the infected ducklings gained weight more slowly than the control birds. After the 2 wk study period, the mean serum concentrations of total protein, albumin, beta-globulin, gamma-globulin, fructosamine and creatine kinase were lower in the infected group than in the controls. The mean (+/-SE) number of acanthocephalans in the intestine of the infected ducklings was 21 (+/-4). The parasites were attached to the mucosa of the posterior small intestine of the infected ducklings with a mixed inflammatory reaction consisting of heterophils and mononuclear lymphocytes surrounding the attachment sites.     

Life cycles of Gammarus oceanicus and G. salinus (Amphipoda) in the Oslofjord, Norway

In the Oslofjord the amphipods Gammarus oceanicus Segerstråle, 1947 and G. salinus Spooner, 1947 were estimated to live for a maximum of 15 months. All specimens which survived during winter died in spring, mainly in May. A G. oceanicus population living on a freshwater influenced shore contained smaller specimens, had a lower proportion of the female population in breeding condition and probably produced fewer broods than a population living on a fully marine shore. The differences are discussed in relation to environmental factors and the distribution of G. salinus. Gammarus oceanicus possibly was breeding from December to May, some females even in June, resulting in an estimated maximum of three broods from December to May. Gammarus salinus showed two breeding periods, the first from December to May, a few of these females even bred in June, while new females bred from June to October, giving estimated maxima of respectively three (December to May) and five broods. Gammarus salinus females entered a reproductive resting stage in September-October. The sex ratio was mostly female dominated. A shift to male dominance was noted in one population and was related to possible infections. Information from the literature on longevity and breeding periods was compiled and compared to the Oslofjord data.     

Distribution and host range of the microsporidian Pleistophora mulleri

ABSTRACT. Microsporidia of the genus Pleistophora are important parasites of fish and crustacea. Pleistophora mulleri has been described previously as a parasite of the gammarid amphipod crustacean Gammarus duebeni celticus in Irish freshwater habitats. Through a survey of European G. duebeni populations, P. mulleri was found to be widely distributed in the western British Isles (Wales, Scotland, and the Isle of Man), and populations of the subspecies Gammarus duebeni duebeni as well as G. d. celticus were infected. Pleistophora infections were also detected in G. d. duebeni sampled from the Bay of Gdansk on Poland's Baltic coast, indicating a wide distribution of Pleistophora in European G. duebeni . Sequencing and phylogenetic analysis of the 16S rRNA , 18S rRNA , and Rpb1 genes of P. mulleri suggest that this species may be synonymous with P. typicalis , a parasite of fish. These findings suggest that amphipod crustaceans may act as intermediate or reservoir hosts for microsporidian parasites of fish.     

Distribution and microhabitats of native and non-native gammarids (Amphipoda, Crustacea) in Brittany, with particular reference to the endangered endemic sub-species Gammarus duebeni celticus

Aim  To assess temporal changes in gammarid distribution in Brittany and microhabitat-use overlap between the endangered endemic Gammarus duebeni celticus Stock & Pinkster, 1970 , the expanding natives G. pulex (Linnaeus, 1758) and Echinogammarus berilloni (Catta, 1878), and the introduced G. tigrinus Sexton, 1939.
Location  Brittany and adjacent regions in western France.
Methods  The spatial and temporal patterns in distribution of gammarids at the scale of Brittany were studied using 351 sites. Longitudinal distributions (from the source to the estuary of the river) and microhabitat-use (substratum type and water velocity) were also considered in selected rivers.
Results  At the regional scale, all species occurred together less often than expected statistically, with significant deviations from expected for G. pulex vs. both G. duebeni celticus and G. tigrinus , and for E. berilloni vs. both G. duebeni celticus and G. tigrinus . However, at the microhabitat scale, E. berilloni occurred significantly more often than expected with the endemic G. duebeni celticus , and this appears to be due to similar substratum and water velocity preferences, although at both the regional and microhabitat scales E. berilloni prefers wider streams than G. duebeni celticus . This study reveals a decline in the endangered G. duebeni celticus since 1970.
Main conclusions  The longitudinal and local distributions of G. duebeni celticus , and the higher-than-expected co-occurrence of the species with G. pulex , suggest that the decline of the endemic species may be due to changes in the environment and/or interference from native G. pulex , which is expanding its range in Brittany. The results are discussed as regards to the consequences for regional biodiversity.     

Invading predatory crustacean Dikerogammarus villosus eliminates both native and exotic species

As the tempo of biological invasions increases, explanations and predictions of their impacts become more crucial. Particularly with regard to biodiversity, we require elucidation of interspecific behavioural interactions among invaders and natives. In freshwaters in The Netherlands, we show that the invasive Ponto-Caspian crustacean amphipod Dikerogammarus villosus is rapidly eliminating Gammarus duebeni, a native European amphipod, and Gammarus tigrinus, until now a spectacularly successful invader from North America. In the laboratory, survival of single (unguarded) female G. duebeni was significantly lower when male D. villosus were free to roam as compared with isolated within microcosms. In addition, survival of paired (guarded) female G. duebeni was significantly lower when male D. villosus as compared with male G. duebeni were present. D. villosus killed and consumed both recently moulted and, unusually, intermoult victims. Survival of G. tigrinus was significantly lower when D. villosus were free to roam as compared with isolated within microcosms and, again, both moulted and intermoult victims were preyed upon. Male D. villosus were significantly more predatory than were females, while female G. tigrinus were significantly more often preyed upon than were males. Predation by D. villosus on both species occurred over a range of water conductivities, an environmental feature previously shown to promote amphipod coexistence. This predatory invader is predicted to reduce further the amphipod diversity in a range of freshwater habitats in Europe and North America.     

Invasion by the amphipod Gammarus pulex alters community composition of native freshwater macroinvertebrates

Assessing the effects of invading species on native community structure is often confounded by environmental factors and weakened by lack of replicated, long-term pre- and post-invasion monitoring. Here, we uncouple the community effects of a freshwater amphipod invader from environmental differences. In Irish rivers, the introduced Gammarus pulex replaces the native Gammarus duebeni celticus . However, the River Lissan in Northern Ireland is dissected by a weir that has slowed the upstream invasion by G. pulex . This allowed us in 2000 to sample three contiguous 150-m reaches that were (1) G. pulex dominated; (2) mixed Gammarus spp.; and (3) G. duebeni celticus only. In 2003, we resampled these reaches and one additional of mixed Gammarus species and one with only G. duebeni celticus further upstream. In temperature, conductivity, and pH, there were statistically significant but no biologically relevant differences among the five reaches of 2003, and between the three reaches surveyed in both years. Although there was evidence of recovery in macroinvertebrate diversity and richness in invaded reaches between years, continued upstream invasion was associated with sustained reductions in these community metrics as compared to un-invaded sites. Community ordination indicated (1) different associations of community composition attributed to the distribution, abundance, and biomass of the invader; and (2) increasing similarity of invaded communities over time. The impact mechanisms of G. pulex on macroinvertebrate community composition may include predation and competition. The consequences of the observed community changes for ecosystem functioning require further investigation.     

Two species of feminizing microsporidian parasite coexist in populations of Gammarus duebeni

The amphipod crustacean Gammarus duebeni hosts two species of vertically transmitted microsporidian parasites, Nosema granulosis and Microsporidium sp. A. Here it is demonstrated that these co-occurring parasite species both cause infected females to produce female-biased broods. A survey of European G. duebeni populations demonstrates that these two parasites co-occur in six of 10 populations. These findings contrast with the theoretical prediction that two vertically transmitted feminizing parasites should not coexist in a panmictic population of susceptible hosts at equilibrium. Possible explanations for the co-occurrence of the two feminizing microsporidia in G. duebeni include the recent invasion of a new parasite, horizontal transmission of one or both parasites and the spread of alleles for resistance to the dominant parasite in host populations.     

An examination of subspecific differences in the merus of the fifth walking leg of the amphipod Gammarus duebeni Lilljeborg

Stock SL Pinkster (1970) erected two subspecies of Gammarus duebeni primarily on the basis of a difference in the relative dimensions of the merus on the fifth walking leg. The diagnostic feature was given as the ratio of merus length/width, with ratio < 2 in G. duebeni duebeni and ratio > 2 in G. duebeni celticus. It is shown here that the ratio varies with the size of the animal, and this particular ratio is therefore not valid as a taxonomic character. Regressions of log merus width on log merus length were made on large samples of G. duebeni assumed to belong to subspecies celticus and duebeni respectively. The regressions were significantly diiferent and were used to predict that the ratio log merus width/log merus length is relatively constant in both subspecies. Diagnostic values for this ratio were 0.71–0.73 in celticus and 0.74–0.77 in duebeni. The ratio was also determined in small samples of G. duebeni from other localities in western Britain. The morphological difference which characterizes celticus and duebeni was not associated with habitat salinity or with previously determined physiological characteristics. It may be an instance of cHnal variation reinforced by geographical isolation. Regressions of merus length against cephalic length suggest that the relative growth rates of the merus may also differ in the two subspecies.     

Comparative studies on the physiological ecology of five euryhaline Gammarus species

Summary Comparative investigations on the physiological capacities of Gammarus locusta (L.), G. oceanicus Segerstråle, G. salinus Spooner, G. zaddachi Sexton and G. duebeni duebeni Liljeborg obtained from German coastal and estuarine areas were carried out under uniform experimental conditions. In order to assess the adaptation of these species to the abiotic conditions of their particular habitats, the following criteria were examined: (a) oxygen consumption as related to temperature, (b) time course of acclimation to a new steady state of metabolic rate following sudden temperature changes, (c) resistance to oxygen deficiency, and (d) resistance to aerial exposure. Considerable interspecific differences were found among the five amphipods studied. G. locusta reveals the highest O₂ uptake rates and longest thermal acclimation periods as well as lowest resistance capacities to oxyten depletion and air exposure. The other species occupy an intermediate position as indicated in the above-cited order, but contrast with G. duebeni which exhibits comparatively high resistance capacities. The significance of the findings obtained is discussed in relation to the environmental requirements of the five crustaceans considered.     

Impact of a Novel, Feminising Microsporidium on its Crustacean Host

We describe the transmission and pathogenic effects of a novel, feminising microsporidium, probably a Nasema species, on its crustacean host Gammarus duebeni. The parasite prevalence in the field was high (46% of females were infected) and the parasite was transovarially transmitted to 91% of embryos of infected females. The impact of the parasite on the host was assessed by means of a host breeding experiment. The parasite feminised 66% of infected host young and was transovarially transmitted by these individuals to the next host generation. The parasite differed from other feminising microsporidia in G. duebeni in that early embryos had a high parasite burden (288 parasites per embryo) and the infection was pathogenic, causing a reduction in both the growth rate of young hosts and in adult size. This study suggests that feminising microsporidia are a diverse group in which a variety of host/pathogen relationships have evolved.     

Introduction experiments with Gammarus spp. (Crustacea: Amphipoda) in the Isle of Man (British Isles), 1949–1995

This study uses data from field introduction experiments with Gammarus spp. conducted by H. B. N. Hynes in the Isle of Man in the period 1949-1969, together with data from re-sampling programmes by the present authors in 1974/5, 1988 and 1995, to examine the interaction between the native freshwater amphipod G. duebeni and the introduced G. pulex. Although Hynes' deliberate introductions of G. pulex into streams in the Isle of Man at first seemed to give equivocal results, their examination in the light of subsequent evidence indicates that G. duebeni is, under some as yet unknown condition(s), sometimes able to withstand the impact of invasions by its competitive rival G. pulex. The presentation of Hynes' data is thus a belated but valuable contribution to knowledge in this field, although we must stress that such experiments involving transplantations of species should not be carried out owing to the ecological damage that can follow. In addition, we discuss our discovery of a truly exotic amphipod in the Isle of Man, the N. American Crangonyx pseudogracilis .     

Osmotic and ionic haemolymph concentrations in the Baltic Sea amphipod Gammarus oceanicus in relation to water salinity

The aim of this work was to determine the osmotic and ionic (Na(+), K(+), Ca(2+), Mg(2+) and Cl(-)) haemolymph concentrations in Gammarus oceanicus at different salinity levels. Being a species of marine origin it inhabits brackish waters of the Baltic Sea. G. oceanicus specimens were collected in January 2003 from the Gulf of Gdansk (salinity 7 psu). The animals were gradually acclimated to eight different salinity levels (5, 7, 14, 20, 25, 30, 35 and 41 psu) at a temperature of 5 degrees C and 100% oxygen saturation. The haemolymph osmolalities correlated positively with external salinity, from 545.4+/-17.3 mOsm in 5 psu to 1185.9+/-34.6 mOsm in 41 psu. G. oceanicus hyperregulated within the 5-31.5 psu range; above 31.5 psu it hyporegulated its body fluids in comparison to the external medium. At 31.5 psu (1017 mOsm) the haemolymph concentration of G. oceanicus was isoosmotic with the habitat. The haemolymph concentrations of all the studied ions, except K(+), correlated positively with their concentrations at the various salinity.     

Reevaluation of phylogeny in the Drosophila obscura species group based on combined analysis of nucleotide sequences.

The Drosophila obscura species group has served as an important model system in many evolutionary and population genetic studies. Despite the amount of study this group has received, some phylogenetic relationships remain unclear. While individual analysis of different nuclear, mitochondrial, allozyme, restriction fragment, and morphological data partitions are able to discern relationships among closely related species, they are unable to resolve relationships among the five obscura species subgroups. A combined analysis of several nucleotide data sets is able to provide resolution and support for some nodes not seen or well supported in analyses of individual loci. A phylogeny of the obscura species group based on combined analysis of nucleotide sequences from six mitochondrial and five nuclear loci is presented here. The results of several different combined analyses indicate that the Old World obscura and subobscura subgroups form a monophyletic clade, although they are unable to resolve the relationships among the major lineages within the obscura species group.