Growth and reproduction ofCaprella danilevskii (Crustacea: Amphipoda) reared in the laboratory

Caprella danilevskii Czerniavski, an epifaunal amphipod crustacean, was successfully reared for two generations under laboratory conditions. Amphipods were maintained in pairs or fours in a Petri dish. Temperature and photoperiod were maintained at 20°C, and 14 h light: 10 h dark, respectively. Colonies of the diatomCylindrotheca closterium (Ehrenberg) Reumann and Lewin were provided as food source. The red algaGelidium amansii (Lamouroux) Lamouroux was used to provide an attachment substrate for the caprellids. Juveniles that emerged from the brood pouch were described as instar I. Subsequent instars were identified by molts. Juveniles molted successively at 2.5 to 6.5 d intervals. The body length of males at each instar increased exponentially, while that of females followed a sigmoid curve. A different pattern of flagellar segment addition in the antenna I of males and females was revealed. At the age of 20.8 d, females reached instar VII, and produced their first embryos. After 5.1 d, juveniles emerged from the brood pouch. On average, females produced 5.4 clutches successively at 5.0 d intervals. The number of offspring per spawning increased from 6.3 at instar VII to 22.0 at instar XII. The total number of offspring was 69.0 for a female throughout her life span.     

What do caprellids (Crustacea: Amphipoda) feed on?

The present study represents the first comprehensive work dealing with the dietary analysis of Caprellidea. We studied 743 specimens of 31 genera and 62 species from all around the world. Analysis of digestive contents revealed that caprellids are mainly detritivores (detritus represented the 86% of the caprellid diet), but a small percentage of species, those lacking molars belonging to the Phtisicinae, can be considered as obligate predators and feed mainly on small crustaceans (copepods and other amphipods) and polychaetes. The contribution of sponges, hydroids, macroalgae, diatoms and dinoflagellates to the caprellid diet was very low (<2%). Apart from the clear relationship between the absence of molar process and predators, no other correlations between digestive contents and mouthpart structure were found. Cluster analysis based on the dietary data indicated a patent segregation between the Phtisicinae (obligate predators) and Caprellinae (detritivores, detritivores/predators or opportunistics) and could support the hypothesis of basal divergence in two major lines of evolution: Phtisicinae and Caprogammaridae–Caprellinae. Consequently, the debate questioning if the taxon Caprellidea is a monophyletic group or not is still open. Additional morphological, molecular and behavioral studies are necessary to define the evolutionary relationships in this group of crustaceans.     

Feeding and digestion in Corophium volutator (Crustacea: Amphipoda)

New observations on the feeding behavior of Corophium volutator, collected from the Menai Strait, Anglesey, UK in 1981, show that detritus drawn into one entrance of the U-shaped burrow is pushed out at the opposing entrance either uningested or as faeces. Periodically, the amphipod turns around in the burrow and recommences feeding, so both the uningested material and the faeces may be reworked by the mouthparts. A feeding individual produces, on average, 16 faecal pellets every 10 min, at a seawater temperature of 18°C. When fed on detritus dyed with azo-carmine, approximately 12 pellets are produced before the foregut, intestine and hindgut are completely clear of previously ingested material and the dye appears in the faeces. Dye which enters the ventral caeca takes between 12 and 48 h to clear this tissue and, furthermore, it is only cleared when the amphipod is feeding. It is concluded that ingested coarse material is subjected only to a primary phase of digestion in the stomach, and that it takes 4 to 24 min to clear the gut. Fine material which enters the ventral caeca is subjected to a secondary phase of digestion and absorption which takes 24 to 48 h. Particles of thorium dioxide and ferritin incorporated in the diet are absorbed by the B- and ageing RF-cells in the ventral caeca. Non-specific esterases occur in the apical regions of the same cells, the mature cells of the anterior dorsal caeca and the cells at the anterior of the intestine. Protease activity is greatest in the lumen of the ventral caeca and the large vacuole of the B-cells. Apart from the lumen of the posterior caeca, there is some protease activity throughout the lumen of the gut. Carbohydrates were localised primarily in the R/F-cells towards the proximal region of the ventral caeca. Lipid was confined to the R/F-cells in the same region.     

Trace-metal detoxification in the ventral caeca of Orchestia gammarellus (Crustacea: Amphipoda)

The talitrid amphipod crustacean Orchestia gammarellus (Pallas) was collected from metal-contaminated (Dulas Bay, Gironde) and control (Millport) sites in the UK and France. Irrespective of site of origin, the amphipods showed the same physiological mechanism of trace-metal detoxification, involving the ventral caeca. Copper was always present in lysosomal residual bodies in the ventral caeca. Following laboratory exposure to zinc and cadmium, the lysosomes usually contained both copper and zinc but cadmium was not detectable. The lysosomal copper concentration is positively correlated to that of sulphur, while the concentration of lysosomal zinc is related to that of phosphorus. Results are interpreted in terms of the differential rates of turnover of metallothioneins chelating copper, zinc or cadmium. Received: 9 February 1999 / Accepted: 2 December 1999     

Environmental influence on the locomotor activity rhythm of Talitrus saltator (Crustacea: Amphipoda)

The persistence and precision of the endogenous, nocturnal, circadian locomotor rhythm of the sand-beach amphipod Talitrus saltator is characterised, and the influence of substrate availability, photoperiod, temperature and relative humidity as potential environmental synchronizers of the rhythm is assessed. Individual, cyclic light-dark and temperature regimes synchronize and modify the laboratory activity pattern, but substrate availability and relative humidity have no significant long-term effect. Under simulateneous experimental regimes simulating field conditions of photoperiod, temperature and relative humidity the rhythm is entrained solely by photoperiod. The implications are discussed in relation to field behaviour.     

Lipid biochemistry and reproductive biology in two species of Gammaridae (Crustacea: Amphipoda)

Gammarus oceanicus Segerstråle, 1947 and Echinogammarus marinus (Leach, 1815) were sampled during the breeding season from Oslofjord in 1984, and their lipid composition examined in relation to reproductive condition. In G. oceanicus, female lipid content increased as the ovary matured. Both the amount of lipid stored and the rate of accumulation were greater in spring than in winter. Spring eggs contained 12.4 g lipid, of which 63% was triacylglycerol and 27% phospholipid. Both fractions decreased steadily during embryonic development. Winter eggs contained 19.2g lipid, of which 52% was triacylglycerol and 43% phospholipid. During the early stages of embryonic development the amount of phospholipid decreased sharply, whereas that of triacylglycerol increased, suggesting that some of the fatty acid released from phospholipid was sequestered temporarily as triacylglycerol. When newly spawned, both winter and spring eggs were richer in monoenoic fatty acids than adult amphipods and these acids were the major fuel consumed during development. 6 fatty acids were utilised more slowly than 3 acids, and egg carotenoid pigment content remained constant. Female E. marinus increased in lipid content as the ovary matured. Spring eggs contained 14.7 g lipid when newly spawned and this increased to 16.6 g during the early stages of development. This increase was entirely triacylglycerol, which declined in later stages; the source of the extra lipid was unclear. Eggs contained very little phospholipid or sterol, and both of these components remained at a steady low level during development. E. marinus eggs were not significantly rich in thonoenoic acids compared with adults, and saturated, monoenoic and polyenoic acids were utilised about equally during development. Both adults and eggs were rich in 20.46, which was utilised at a slower rate than the 3 polyunsaturated acids during embryonic development; again, egg carotenoid pigment content remained constant. In both species there was a decrease in the size of the egg (and as a result, of the newly hatched juvenile), but an increase in total reproductive output (i.e., the total weight of the egg clutch) per female as the breeding season proceeded. The reproductive output of an individual female is probably related to food availability during the period of ovarian maturation, whereas the size of an individual egg is dictated largely by feeding conditions for the juveniles once they are independent of the female. The different patterns of lipid utilisation during development found in this study emphasize the flexibility of response in the reproductive biology of gammarid amphipods. It is not yet possible, however, to relate the differing patterns in a simple way either to egg size or total female reproductive output. Two outstanding problems are the source of extra triacylglycerol during the early stages of development of E. marinus and the metabolic cost of brooding eggs.     

Interaction between solar orientation and landscape visibility in Talitrus saltator (Crustacea: Amphipoda)

A series of experiments on the littoral amphipod Talitrus saltator (Montagu) was carried out between April and September, 1978–1981, both under natural conditions and inland with artificial landscapes of different heights on the horizon, in order to assess the visual importance of the landscape in zonal orientation in populations from the Mediterranean coast, and to determine interactions between solar orientation and orientation based on the landscape. Inland, orientation in controls (permitting only vision of the sky and the sun) was compared to that of the experimental individuals, who could see a simulated landscape positioned landwards to them and seawards. In nature, sandhoppers released in a level arena with the landscape screened from view were compared with others released in an unscreened arena and on the sand in absolutely natural conditions. Situations where solar orientation contradicted local cues were produced both by releasing the sandhoppers on a shore diversely orientated to their own, and by shifting their internal clock by nine hours. Results show that T. saltator uses the landscape as a cue in its orientation towards the sea, in conjunction with solar orientation: the latter being the principal factor involved even when the sandhoppers are separated from the local optical factor in the sky (in trials at a distance from the sea). In fact, with the artificial landscape set seawards, none of the populations we studied showed any orientation based on the landscape comparable in accuracy to orientation based exclusively on the sun. From the experiments carried out in natural conditions, it is possible to deduce that conflicting conditions gave rise to two types of results: deviation from the mean direction and an increase in dispersion, up to total dispersion when the local factors were in total contrast to solar orientation (clock-shifted sandhoppers released on the sand).     

Marine Gammaridea (Crustacea: Amphipoda) from the Indian region. Family Ampithoidae

This paper deals with 6 species of marine gammaridean amphipods belonging to the family Ampithoidae. The specimens described were collected from Mandapam (Gulf of Mannar), India and Thankasserry (Quilon, Kerala), India. The collection includes 3 new species, namely Ampithoe (Ampithoe) serraticauda, Ampithoe (Pleonexes) auriculata and Cymadusa imbroglio. Ampithoe (Ampithoe) kergueleni Stebbing (1888) is a new record for this region, while Ampithoe (Ampithoe) ramondi Audouin (1826) and Cymadusa filosa Savigny (1816), the two well-known tropicopolitan members, are briefly redescribed. The study supports Barnard's (1970, p. 23) contention that the genus Pleonexes Bate (1857) (since reduced to subgeneric status under the genus Ampithoe Leach, 1814) represents only a grade of evolution, but suggests that the structure of the 1st maxillary and mandibular palps and the outer lobes of the lower lip should also be taken into consideration, in combination with the telsonic processes, for distinguishing Pleonexes from Ampithoe. Based on this concept, a reappraisal of some of the species of the genera is suggested. The subgenus Ampithoe is created to hold those species of Ampithoe showing typical characteristics of the genus.     

Effects of copper and cadmium on growth,swimming and predator avoidance in Eurytemora affinis (Copepoda)

In this study we demonstrate the sensitivity of swimming behavior and predator-escape responses of nauplii of the estuarine copepod Eurytemora affinis to sublethal doses of Cu and Cd. Behavior was generally altered at metal doses below those affecting growth rates or survival of the copepods. Swimming velocities of Cu-dosed nauplii were different from controls at all concentrations of Cu tested (10–50 g l^-1 total Cu) after 24- to 48-h exposure, whereas development rate of nauplii was significantly reduced only after 96 h at 25 g l^-1. The 96 h LC50 for Cu was approximately 30 g l^-1 Cu. Naupliar swimming velocity was also affected by Cd. Swimming speeds were reduced after 24 h at 130 g l^-1, and development was slowed after 48 h at 116 g Cd l^-1. The 96-h LC50 was >120 g l^-1. Little is known of the adaptive role of specific motile behaviors in the success of larval copepods. We investigated the relationship of swimming speed to predator — prey interactions of the nauplii using both real and simulated predators. Nauplii exposed to Cu for 24 h were observed to be generally hyperactive, a condition which could increase their encounter frequency with predators. Reduced numbers of escape responses of nauplii to a simulated predator, another indication of increased vulnerability to predation, were observed only after 48-h exposure to Cu. Nevertheless, feeding rates of non-dosed larval striped bass on dosed nauplii (24 h at 25 g Cu l^-1) were significantly higher than on control nauplii. Feeding rates of larval mysid shrimp, however, were not higher on similarly dosed nauplii; 24 h exposure of nauplii to >30 g Cu l^-1 did result in increased predation by mysids.Contribution No. 272 of the US EPA Environmental Research Laboratory, Narragansett, Rhode Island 02882, USA     

Microhabitat segregation of the amphipod genus Gammarus (Crustacea: Amphipoda) in the Northern Baltic Sea

Closely related species may occupy very similar niches but are often found to diverge by one or more traits when they share the same habitat. Five indigenous and sympatric Gammarus species are characteristic for the Baltic rocky littoral ecosystem. Yet, the species-specific distribution of these sympatric gammarids has not been well studied in the northern Baltic Sea. This study was undertaken to assess the spatial distribution of gammarid amphipods along wave exposure and depth gradients to study whether they show segregation in their microhabitat use. We sampled 12 rocky sublittoral shores along a wave exposure gradient over a period of 5 years. Samples differed with respect to depth and macroalgal type. Three of the five gammarid species occurred mainly in different depth zones and among different macroalgae at the exposed shores. In contrast, on protected shores, where algal zonation is weaker, a link to zonation and macroalgal type was almost absent. Moreover, the microhabitat use was strongest during the reproductive seasons of the species. The observed microhabitats of the three gammarid species fit well to their species-specific mean body sizes.     

Interspecific competition for mates and habitat selection in five species of Gammarus (Amphipoda: Crustacea)

Mating competition due to the formation of interspecific precopulas is involved in the evolution and maintenance of the habitat selection shown by the amphipod gammarids in the Limfjord, Denmark. The mating competition is discussed in relation to possible pheromones involved in initiating the formation of precopulas and in relation to the phylogeny of the species populations involved.     

Studies on differential fitness of PGI genotypes with regard to temperature in Gammarus insensibilis (Crustacea: Amphipoda)

This paper deals with an experimental study of survival, combined with estimates of biochemical activity, of different genotypes at the PGI (phosphoglucose isomerase) locus in Gammarus insensibilis, in relation to temperature. Samples were collected in the lagoon of Venice during 1987. No mortality occurred at 10°C whereas at 27°C, where mortality reached the value of 50%, heterozygotes exhibited significantly higher survival than homozygotes. Experiments conducted in order to evaluate the PGI biochemical activity of homo- and heterozygote genotypes at three different temperatures (4°, 20° and 37°C) showed in all genotypes an increased activity from 4° to 20°C and a fall of activity from 20° to 37°C. Heterozygotes exhibited higher activity at all temperatures tested. The difference between homo- and heterozygotes became more obvious at 37°C. Our results suggest that in G. insensibilis the PGI locus, as already shown in other organisms, may be subject to selection and that the heterozygous genotypes possess superior fitness. The biochemical bases of the observed differences between genotypes are briefly discussed.     

Advantages and a disadvantage of large size for male gammarus pulex (Crustacea: Amphipoda)

Summary The breeding system of the freshwater amphipod Gammarus pulex includes a precopulatory guarding phase by a male. The length of this guarding phase is investigated with respect to a male's size and the number and size of his competitors. As the absolute number of competitors increases, so does the guarding time but as the absolute number of available females increases, the guarding time decreases. Takeovers of the females by unpaired males are more frequent in longer precopulas (Table 2). In contests for females, larger males have two advantages over smaller males; they are better able to make a takeover (Table 2) and better able to resist takeover attempts while paired (Table 3). Males increase the length of the guarding phase as the mean size of their competitors increases (Table 4). When not paired males are usually searching for available females, perhaps in the stream current. Females are unaffected by current speed but increasing current causes decreased male survivorship (Table 5) and increased precopula duration (Table 5). Searching in currents is more dangerous for larger males than smaller ones. It is proposed that the male size distribution observed is the result of selection pressure to increase size from male-male competition balanced by selection against large size while searching for females in the current.     

Accumulation of copper within the “Hepatopancreatic” caeca of Corophium volutator (Crustacea: Amphipoda)

The concentrations of various metals in specimens of Corophium volutator (Pallas) which have been taken from a site that receives freshwater drainage with a high concentration of copper, zinc and manganese, are compared with those in individuals from a site with a normal concentration of these metals for coastal waters. The amphipods at the contaminated site contain 259 g g⁺¹ dry weight of copper, which is three times that of individuals from the uncontaminated site. The concentrations of the other metals do not differ substantially between the two populations. The hepatopancreatic caeca of the midgut of amphipods with a high concentration of copper have numerous granules of homogeneous electron-dense material which can aggregate within the multivesicular bodies. Some of the amphipods with a lower concentration of copper have similar granules, but these are fewer in number. X-ray microporbe analysis shows that these granules contain copper and sulphur, and occasionally calcium. Various tests on the granules in frozen section indicate that they are relatively insoluble in a wide range of reagents and that the copper is probably complexed with organic matter.     

Genetic adaptation to local habitats and speciation processes within the genus Gammarus (Amphipoda: Crustacea)

A recent event of allopatric speciation (a time span of about 4 000 years) is reported from a comparison between two guilds of amphipod gammarids from the central Baltic Sea and from the Limfjord (inner Danish waters), respectively. For at least two of the five species populations involved, a genetically fixed habitat specialization has led to the establishment of reproductive barriers. It has, however, not been possible to correlate this speciation event with electrophoretically determined isozyme changes. It is argued that the lack of correlation is due to the presence of an initial time lag before a speciation event can be detected as isozyme differences between newly formed species populations as predicted by the neutrality hypothesis for evolution at the molecular level.     

Anatomy of structures associated with air-breathing in Orchestia gammarellus (Crustacea: Amphipoda: Talitridae): coxal plates and gills

The structure of the coxal gills and coxal plates of the semi-terrestrial beachflea Orchestia gammarellus (Pallas) (Crustacea: Amphipoda: Talitridae) is described in relation to their possible use for aerial gas exchange and ion exchange. Anatomical evidence is presented to support the hypothesis that the medial surface of the coxal plates functions as an extrabranchial aerial gas-exchange site in O. gammarellus. Thus, the effective diffusion distance across the medial (or inside-facing) surface of O. gammarellus coxal plates (mean±SD=5.4±0.3 m; n=9, cuticle thickness 4.4±0.5 m, n=21) is only a third of the equivalent distance across both the coxal gills (18.4±6.0 m, n=10; cuticle thickness 1.7±0.6 m, n=7) and the lateral (or external) surface of the coxal plates (19.4±0.7 m, n=5; cuticle thickness 8.7±0.8 m, n=7). Chloride-ion-permeable areas were located using a silver-staining technique. All ten coxal gills appeared to be equally permeable to chloride ions after examination with a light microscope. However, the coxal plates and the rest of the integument do not appear to be chloride-permeable.     

Larval development of Ocypode quadrata (Brachyura: Crustacea) under laboratory conditions

The larvae of Ocypode quadrata (Fabricius) have been reared in the laboratory, from hatching to megalopa stage, at 35 S, 25°C. The five zoeal stages and the megalopa are described, including functional appendages of each stage. On the basis of morphological characteristics, the first zoeal and megalopa stages of O. quadrata can be distinguished from similar stages of closely related Ocypodinae. At 25°C, the megalopa appeared in a minimum of 34 days following hatching.     

The ecophysiological complex of Bathyporeia pilosa and B. pelagica (Crustacea: Amphipoda). II. Effects of exposure

The resistance to high and low temperatures, starvation and desiccation effects in the sand dwelling amphipods Bathyporeia pilosa Lindström and B. pelagica (Bate) have been tested. B. pilosa was the more tolerant species in all experiments. Gravid females showed a greater resistance to high temperatures than adult males in both species, and starvation tolerance was in the order gravid females>juvenile males> adult males. Time-temperature relationships, however, would seem to be of greater ecological significance than upper or lower lethal temperatures, and desiccation effects become obvious well within any limits set by starvation. Exposure would appear to be an important concept limiting the intertidal distribution of sand dwelling animals, particularly those confined to the surface layers of sediment. The amplitude, rate and degree of environmental change and its effect on feeding and reproduction offer severe limitations to the distribution of the two Bathyporeia species studied.     

Population biology of Dyopedos monacanthus (Crustacea: Amphipoda) on estuarine soft-bottoms: importance of extended parental care and pelagic movements

The suspension-feeding amphipod Dyopedos monacanthus (Metzger, 1875) is a common epibenthic amphipod that lives on self-constructed “mud whips” (built from filamentous algae, detritus and sediment particles) in estuaries of the northern North Atlantic Ocean. The population biology of D. monacanthus at a shallow subtidal site in the Damariscotta River Estuary (Maine, USA) was examined between July 1995 and July 1997. The resident population at the study site was dominated by adult females during most months of the year. High percentages of subadults were found in late summer/early fall. Often, between 10 and 20% of the adult females were paired with males, and the percentage of ovigerous females varied between 40 and 100%, indicating continuous reproduction. The percentage of parental females varied between 40 and 80% during most months, but dropped to levels below 20% during summer/early fall. The average size of amphipods on their own mud whips was ∼4 mm during the summer/early fall, after which it increased continuously to >7.0 mm in March or April, and then dropped again. In March and April, the average number of eggs and juveniles female⁻¹ was ∼100 eggs and 55 juveniles, while during the summer/early fall the average number of eggs female⁻¹ was <20 and that of juveniles female⁻¹ was <10. Many juveniles grew to large sizes (>1.4 mm) on their mothers' whips in winter/early spring but not in the summer/fall. The average number of amphipods at the study site was low in late summer/early fall (<50 individuals m⁻²), increased steadily during the winter, and reached peak densities of >3000 individuals m⁻² in April 1996 (>1600 individuals m⁻² in May 1997), after which densities decreased again. The decrease of the D.␣monacanthus population at the study site coincided with a strong increase of amphipods found pelagic in the water column. This behavioural shift occurred when temperatures increased and benthic predators became more abundant and active on shallow soft-bottoms, suggesting that D. monacanthus at the study site is strongly affected by predation. The effects are direct (by predation on amphipods) and indirect (by reducing duration of extended parental care and enhancing pelagic movements). Both extended parental care and pelagic movements are important behavioural traits of D.␣monacanthus (and other marine amphipods), and significantly affect its population dynamics. Received: 18 January 1998 / Accepted: 27 May 1998