Population Structure of the Baikalian Amphipod <Emphasis Type="Italic">Gmelinoides fasciatus</Emphasis> (Stebbing)

Using the data on 71 individual sequences of the gene for the mitochondrial cytochrome-c-oxidase subunit one, molecular and phylogenetic characterization of the Baikalian amphipod, Gmelinoides fasciatus (Crustacea, Amphipoda), was performed. Interspecific polymorphism was demonstrated. Four main amphipod populations, Southeastern, Southwestern, Northern, and Central, were distinguished. A low level of genetic diversity typical of Southwestern population was revealed. For its explanation, the bottleneck hypothesis was proposed.__________Translated from Genetika, Vol. 41, No. 8, 2005, pp. 1108–1114.Original Russian Text Copyright © 2005 by Gomanenko, Kamaltynov, Kuzmenkova, Berenos, Sherbakov.     

Patterns of gammaridean amphipod abundance and species composition associated with dominant subtidal macroalgae from the western Antarctic Peninsula

The communities of gammaridean amphipods associated with eight dominant macroalgal species were examined near Palmer Station, Western Antarctic Peninsula. A total of 78,415 individuals belonging to 32 amphipod taxa were identified with mean densities ranging up to 20 individuals/g algal wet wt. The most abundant amphipod taxon, Metaleptamphopus pectinatus, was found to associate predominately with the brown alga Desmarestia menziesii, while the second most common taxon, Jassa spp. occurred primarily on the red alga Gigartina skottsbergii. Non-metric multidimensional scaling analysis demonstrated that the population densities of each amphipod species and amphipod species composition were similar on the same algal species but dissimilar on different species of algae. Comparisons of amphipod communities associated with a given algal species but from different sampling sites indicated that although the structure of species-specific macroalgal-associated amphipod communities can vary across spatial scales of 3 km, 50% of the macroalgal species examined showed no significant inter-site differences in associated amphipod community structure. Spearman rank correlation analyses showed that higher abundances of amphipods occurred on the macroalgae with the highest number of branches. As many Antarctic amphipods are known consumers of macroalgae, their remarkable abundances are likely to play a significant role in mediating energy and nutrient transfer in nearshore Antarctic Peninsular macroalgal communities.     

The importance of shore height and host identity for amphipod assemblages

The spatial distribution of organisms associated with marine intertidal macroalgae may be a direct result of their tolerance to air exposure or an indirect consequence of the distribution of their host. We compared amphipod assemblages from five intertidal macroalgae to investigate their relationship with algal identity. To test the effect of height regardless of algal characteristics, we transplanted coralline algal turfs to three different levels within the intertidal zone and compared amphipod assemblages after 1 and 14 days. Interstitial volume was positively correlated to the abundance of amphipods, suggesting that this attribute may correspond better to the potential space for their occupation when compared to algal biomass, thallus volume or the ratio between thallus and interstitial volume. Algal level determined the structure of the amphipod assemblages. Upper-level (Acanthophora spicifera and Caulerpa racemosa) and intermediate-level (coralline) algae host similar amphipod assemblages dominated by Apohyale media, but different from lower-level algae (Padina gymnospora and Sargassum cymosum), which were dominated by Hyale niger. Ten of the 15 amphipod species reported from natural communities were found in the transplanted plots. Distinct pools of amphipod species colonized coralline transplants at upper and lower levels after 1 day. However, regardless of the position on the shore, transplanted coralline turfs supported similar assemblages after 14 days, indicating that algal identity is also important for species assemblages. Our results suggest that both height on the shore and host identity combine to determine the vertical structure of amphipod assemblages in the rocky intertidal.     

EFFECT OF ROCKY INTERTIDAL AMPHIPODS ON ALGAL RECRUITMENT: A FIELD STUDY1

Evidence about the potential of mobile marine invertebrates to act as algal spore dispersal agents is presently circumstantial. Using a field correlational and experimental protocol, our study tested the hypothesis that amphipods can increase the spore recruitment of the red alga Iridaea laminarioides Bory. Iridaea laminarioides spore recruitment onto glass slides was measured at a site with high amphipod abundance and a site with low density of amphipods. To evaluate the effect of an Ulva canopy on recruitment, replicated glass slides with and without a surrounding Ulva canopy were installed at both sites. The number of I. laminarioides spores recruited on the glass slides was four to eight times higher at the high amphipod abundance site than at the low density site. However, the presence of an Ulva canopy covering the glass slides did not significantly increase the recruitment of I. laminarioides. Because the abundance of I. laminarioides, the proportion of cystocarpic plants, and the percentage of open cystocarps only differed slightly between the low and high abundance amphipod sites, we suggest that the variation in recruitment between the sites is due to the differences in amphipod abundance (and their movements) and not to differences in spore production. Moreover, the presence of I. laminarioides cystocarps showing amphipod grazing scars was significantly higher at the high amphipod density site than at the low density site.     

Prey selection by an intertidal beetle: field test of an optimal diet model

Summary Adult beetles Thinopinus pictus LeConte (Staphlyinidae) live on sand beaches in temporary burrows from which they emerge at night to prey on amphipods Orchestoidea calforniana (Brandt). I constructed models of amphipod size selection by beetles, using the size distributions of amphipods measured on the beach, and the results of laboratory experiments on capture success, reaction distance and feeding rates. Capture success decreased and the probability that an amphipod was detected increased with increasing amphipod size. Beetles observed during beach searches selected larger sizes of amphipods than predicted from availability and vulnerability of different sizes. To apply an optimal foraging model, I estimated the profitability of different sizes of amphipods from the number of amphipods of a given size required to satiate a beetle in the laboratory. Profitability was highest for large amphipods and lowest for small amphipods and isopods. However, amphipod abundance on the beach was always below the threshold at which specialization on larger sizes was predicted to occur.     

Is invertebrate shredding critical for collector invertebrates? A test of the shredder–collector facilitation hypothesis

A laboratory experiment was conducted to test the hypothesis that leaf processing by Japanese crayfish (Cambaroides japonicus de Haan) enhances the growth and reduces the mortality of collector amphipods (Sternomoera yezoensis Ueno) through fine particulate organic matter (FPOM) production. Two treatments (crayfish shredding, no shredding control) were established using flow-through artificial streams and permitting differential FPOM production rates. An amphipod enclosure, associated with juvenile amphipods and preconditioned leaf packs, was placed at the downstream end of each channel. During a 4-week period, shredding by crayfish greatly increased the amount of drifting FPOM compared to that in the control channels, in which only shredder-independent FPOM occurred. Despite the substantial contribution of crayfish to FPOM production, amphipods in both treatments grew during the 4-week period and neither amphipod survival nor growth differed between the two treatments. Furthermore, the residual leaf mass in the amphipod enclosures did not differ between the two treatments. However, residual leaf mass in amphipod enclosures was about 20% less than that expected from the processing rates of the leaf packs in the absence of invertebrate shredding. It is likely that amphipods were directly utilizing leaf packs as their food source regardless of FPOM abundance. These results indicate that juvenile amphipods, despite their classification as collectors, were plastic in their foraging habits, and that the FPOM produced by crayfish was not critical for amphipod growth or survivorship.     

Population decline of amphipod Monoporeia affinis in Northern Europe: consequence of food shortage and competition?

In the present study, we investigate the effects of food quality (with three distinct algal diets) and quantity (high vs. low carbon and nitrogen contents) and competition (with natural polychaete competitor, Marenzelleria spp) on the semelparous amphipod Monoporeia affinis fitness and reproduction. Contrary to other studies on this species, our results showed that amphipod females have the ability to adjust their offspring investment when conditions were significantly altered before mating in terms of food quantity, while food quality was of less importance. In fact, there was only a low beneficial effect on amphipod reproduction and embryonic development of a presumed high quality diatom diet. Also, the presence of a natural competitor did not affect amphipod reproductive outcome. The results are viewed in the context of a dramatic decline observed on the amphipod populations in the Gulf of Bothnia. Though, several plausible hypotheses have been suggested for the decline, including competition, new anthropogenic substances, hypoxia and predation, we hypothesize that the population decline is related to food shortage and malnutrition due to an increased percentage low quality terrestrial carbon (rich in humus) from river outflow into the Gulf of Bothnia. Concomitantly, the bacterial food web was enhanced, which has a lower trophic efficiency. We also suggest that a secondary effect of malnutrition is an increased susceptibility to other types of stressors such as contaminants and parasites.     

Impact of acanthocephalan parasites on aggregation behavior of amphipods (Gammarus pseudolimnaeus)

Acanthocephalan parasites can manipulate the behavior of their amphipod intermediate hosts in ways that increase the amphipod's risk of being eaten by a predator that serves as the final host for the parasite. Some asocial amphipod species have been shown to increase the likelihood of aggregation in response to chemical cues associated with predators. If such aggregation has anti-predation benefits, it might be subject to manipulation by parasites. We tested this hypothesis by comparing the preference of parasitized and unparasitized amphipods (Gammarus pseudolimnaeus) for associating with a group of unparasitized conspecifics, both in the presence and absence of chemical cues from predatory brook sticklebacks (Culaea inconstans). Amphipods with encysted parasites (Corynosoma sp.) avoided aggregating, whereas unparasitized amphipods preferred to aggregate. We also found that the risk of predation by sticklebacks faced by an individual amphipod was significantly lower when the amphipod was in a group compared to when it was alone. This suggests that the aggregation response of unparasitized amphipods is an adaptive response to escape predation. This study provides evidence for a novel parasitic manipulation of intermediate host behavior that is likely to increase transmission to the definitive host.     

Is the reduced metabolism of hypogean amphipods solely a result of food limitation?

The epigean amphipod Gammarus lacustris possessed a rate of oxygen uptake (MO2) three times greater that of the hypogean amphipod Stygobromus sp. While much of the difference between these two species could be attributed to different feeding regimes, the hypogean amphipod still exhibited a lower rate of metabolism than the epigean species. This suggests that there can be both a genetic and an environmental (reduced food availability and/or hypoxia) component to the reduced metabolism characteristic of many hypogean animals. The results of this study have re-emphasised the pitfall of making species comparisons without knowledge of the extent of physiological variation within a species. This revised version was published online in July 2006 with corrections to the Cover Date.     

Micrograzers and spore release in Iridaea laminarioides Bory (Rhodophyta: Gigartinales)

Preferential consumption of algal reproductive tissues has been predicted to potentially reduce algal fitness by reduction of reproductive output. This study shows that the amphipod Hyale media (Dana) has a marked trophic preference for mature cystocarpic tissues of Iridaea laminarioides Bory. However, during the feeding process the amphipod tears the cystocarps releasing large numbers of spores into the water column. Germination and growth rate experiments indicate that grazer-mediated release does not affect further spore development. Field populations of I. laminarioides might have unopened cystocarps even in senescent, decaying fronds, while the total number of open cystocarps in mature and senescent fronds increases at higher amphipod density sites, suggesting a facilitation mechanism. Laboratory observations indicate spores can stick to the legs and body sides of the amphipods while a fraction of the ingested spores survives passage through the amphipod digestive tract. Thus, the amphipod seems ecologically important not only as a grazer but also as spore releaser and disperser.     

Population Structure of Humpback Whales from Their Breeding Grounds in the South Atlantic and Indian Oceans

Although humpback whales are among the best-studied of the large whales, population boundaries in the Southern Hemisphere (SH) have remained largely untested. We assess population structure of SH humpback whales using 1,527 samples collected from whales at fourteen sampling sites within the Southwestern and Southeastern Atlantic, the Southwestern Indian Ocean, and Northern Indian Ocean (Breeding Stocks A, B, C and X, respectively). Evaluation of mtDNA population structure and migration rates was carried out under different statistical frameworks. Using all genetic evidence, the results suggest significant degrees of population structure between all ocean basins, with the Southwestern and Northern Indian Ocean most differentiated from each other. Effective migration rates were highest between the Southeastern Atlantic and the Southwestern Indian Ocean, followed by rates within the Southeastern Atlantic, and the lowest between the Southwestern and Northern Indian Ocean. At finer scales, very low gene flow was detected between the two neighbouring sub-regions in the Southeastern Atlantic, compared to high gene flow for whales within the Southwestern Indian Ocean. Our genetic results support the current management designations proposed by the International Whaling Commission of Breeding Stocks A, B, C, and X as four strongly structured populations. The population structure patterns found in this study are likely to have been influenced by a combination of long-term maternally directed fidelity of migratory destinations, along with other ecological and oceanographic features in the region.     

中国淡水钩虾一新种(甲壳纲:端足目:钩虾科)

记述了采自四川九寨沟自然保护区的淡水钩虾1新种,四川钩虾Gammarus sichuanensisi sp.nov.新种的形态特征和与近似种的区别在文中均有详细的论述,同时附有详细的特征图,模式标本保存于中国科学院动物研究所。     

Parasite volume as an indicator of competition: the case of Acanthocephalus tumescens and Pseudocorynosoma sp. (Acanthocephala) in their intermediate host

In Lake Mascardi (Patagonia), 2 acanthocephalan species, Acanthocephalus tumescens and Pseudocorynosoma sp., share an amphipod intermediate host but have different definitive hosts. Because both acanthocephalan species are potentially capable of manipulating amphipod behavior, one of the parasites may, therefore, have no opportunity to complete its life cycle; accordingly, negative interactions between them can be expected. The purpose of the present work was to examine the possibility of competition in the intermediate host through a comparison of A. tumescens and Pseudocorynosoma sp. cystacanth volume. Specimens of the amphipod Hyalella patagonica were collected monthly over almost 2 yr. Amphipods were measured (total length), necropsied, and cystacanths collected. Cystacanths were also measured, and their volume was calculated. Size of both acanthocepalan species was positively associated with amphipod total length. Competition, during 3 different infection periods, was assessed: high level of Pseudocorynosoma sp. infection (HP), high level of A. tumescens infection (HA), and high level of mixed infection (HM). In Pseudocorynosoma sp., intra-specific competition in HM was the only interaction found. In contrast, in A. tumescens, inter-specific competition in HP, intra-specific competion in HA, and intra- and inter-specific competition in HM were found. We suggest that Pseudocorynosoma sp. is a non-plastic species mostly found in single infections, while A. tumescens is a more variable species occurring more frequently in co-infections.     

Distributional responses to small-scale habitat variability by early juvenile silver hake, Merluccius bilinearis

Early juvenile (0-year) silver hake, Merluccius bilinearis, occurred at higher densities on bottoms with greater amphipod tube cover at a 55 m deep site in the Middle Atlantic Bight. The size range of individuals at this site was 1.5–5 cm total length. Additional observations at other sites showed that 0-year silver hake only occurred on silt-sand bottom with amphipod tubes at bottom water temperatures of 8.7–11.4 °C. This distribution pattern could be the result of either selective settlement into appropriate habitats or differential predation with higher survivorship in more complex habitats. We posit that 0-year silver hake occur in patches of dense amphipod tube cover to avoid visual predators and co-occur with preferred prey (i.e., amphipods and shrimps).     

Exploitation of sediment bacterial carbon by juveniles of the amphipod Monoporeia affinis

1. Carbon budget parameters were measured for young-of-the-year Monoporeia affinis in a combined field and laboratory (microcosm) study, designed to quantify the role of sediment bacteria as a carbon source for juvenile amphipods. Special emphasis was placed on the stimulative effects of amphipod activity (foraging, feeding, bioturbation) on sediment bacterial production and abundance by including the carbon thus generated in carbon budget calculations. 2. Amphipod production was clearly higher at lower densities, suggesting strong intraspecific interactions. Negative production was recorded at amphipod densities of 10000 and 20000 ind. m^?2. Negative production was not accompanied by a decrease in amphipod total lipid content, however, probably due to the lack of easily mobilized lipids in juvenile amphipods. Amphipod respiration rate was 0.45 μg O₂ ind.^?1 h^?1, or O.15 μg C ind.^?1 h^?1. Sediment bacterial carbon content averaged 1.31 and 0.90 mg g^?1 DW under field and laboratory conditions, respectively. 3. Bacterial carbon was not quantitatively important for Monoporeia. Due to higher bacterial abundance and production in natural, stratified sediment, assimilation of bacterial carbon was highest for the field population, providing 6.3% of the amphipods' carbon requirement. In microcosm populations, bacterial carbon accounted for between 1.7 and 5.2% of overall amphipod carbon demand, increasing with amphipod density and bioturbation. 4. Ingestion rate, rather than the quantity of bacterial carbon in the sediment, was found to limit absorption of bacterial carbon from the sediment.     

Direct evidence of the cyclooxygenase pathway of prostaglandin synthesis in arthropods: Genetic and biochemical characterization of two crustacean cyclooxygenases

Prostaglandins, well-known lipid mediators in vertebrate animals, have also shown to play certain regulatory roles in insects and other arthropods acting on reproduction, immune system and ion transport. However, knowledge of their biosynthetic pathways in arthropods is lacking. In the present study, we report the cloning and expression of cyclooxygenase (COX) from amphipod crustaceans Gammarus spp and Caprella spp. The amphipod COX proteins contain key residues shown to be important for cyclooxygenase and peroxidase activities. Differently from all other known cyclooxygenases the N-terminal signal sequence of amphipod enzymes is not cleaved during protein expression in mammalian cells. The C-terminus of amphipod COX is shorter than that of mammalian isoforms and lacks the KDEL(STEL)-type endoplasmic reticulum retention/retrieval signal. Despite that, amphipod COX proteins are N-glycosylated and locate similarly to the vertebrate COX on the endoplasmic reticulum and nuclear envelope. Both amphipod COX mRNAs encode functional cyclooxygenases that catalyze the transformation of arachidonic acid into prostaglandins. Using bioinformatic analysis we identified a COX-like gene from the human body louse Pediculus humanus corporis genome that encodes a protein with about 30% sequence identity with human COX-1 and COX-2. Although the COX gene is known to be absent from genomes of Drosophila sp., Aedes aegypti, Bombyx mori, and other insects, our studies establish the existence of the COX gene in certain lineages within the insect world.     

Complete Carbon and Nitrogen Budgets for the Carnivorous Amphipod,Calliopius laeviusculus (KRØYER)

The marine amphipod Calliopius laeviusculus was grown in the laboratory under maximum food levels at 8°C, 12°C, and 15°C. The effects of body size and temperature on all budget parameters were determined and equations describing each parameter as a function of body carbon and nitrogen content were used to construct and check the balance of the budgets. The energetics of the amphipod are discussed.     

Short-term predator avoidance behavior by invasive and native amphipods in the Great Lakes

Understanding predator avoidance behavior by prey remains an important topic in community and invasion ecology. Recently, the Ponto-Caspian amphipod Echinogammarus ischnus (Stebbing 1898) was accidentally introduced into the Great Lakes. Since its introduction, it has displaced the native amphipod, Gammarus fasciatus (Say 1818), from several locations in the lower lakes. To assess whether behavioral differences in predator avoidance might be a causal mechanism increasing the success of the invasive amphipods, two experiments were conducted examining (1) native and invasive amphipod behavioral responses to five fish species with different foraging behaviors, and (2) amphipod responses to different densities of round gobies, a hyper-abundant benthic invertivore. Echinogammarus reduced its distance moved in the presence of all fish species tested, whereas Gammarus reduced its distance moved only after exposure to round gobies, black crappies, and rainbow darters. Both amphipod species increased the time spent motionless following exposure to round gobies, but not after encountering the scent of most of the remaining fish predators. The exception was that Echinogammarus also responded to black crappie scent whereas Gammarus did not. Although both amphipod species exhibited behavioral responses to many of the fish predators, the magnitude of their responses differed only after exposure to the brown bullhead. In the bullhead trials, Echinogammarus reduced its distance traveled significantly more than Gammarus. Both amphipod species increased their avoidance response to increasing goby density, however, the pattern of avoidance behavior was different. Invasive E. ischnus exhibited a consistently strong avoidance response to round gobies over the test duration. Native G. fasciatus initially avoided goby scent, but then either ceased their avoidance response or showed a hyper-avoidance response, depending on goby density. These results suggested (1) both species of amphipods were able to differentiate and react to a variety of fish predators, (2) invasive Echinogammarus amphipods avoided a larger range of fish predators than the native Gammarus, (3) increased avoidance behavior was associated with an increased density of fish, and (4) the avoidance response patterns of invasive Echinogammarus when faced with round goby predators might lead to increased predation on native Gammarus in habitats where they co-occur.     

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.     

Alternative reproductive strategies in the progenetic trematode Coitocaecum parvum: comparison of selfing and mating worms

The progenetic opecoelid trematode Coitocaecum parvum can reproduce either precociously by selfing in its second intermediate amphipod host or by mating in its normal definitive fish host. In this study, we describe and compare the infection parameters and some life history traits of both egg-producing worms and non-egg producing worms in both their second intermediate and definitive hosts. We showed that 58% of worms start to produce eggs while still in the amphipod. The relative abundance of progenetic worms increased with amphipod size, and egg-producing worms achieved greater size in amphipods than in fish. These 2 findings support the reproductive insurance hypothesis. No difference in size was revealed between eggs produced in the amphipods and those produced in the fish. Although more information is needed to thoroughly assess the respective costs and benefits of selfing and mating in this species, our conclusion is that adopting progenesis may have few, if any, long-term negative consequences for the parasite.