Benthic predators and zooplanktonic prey: predation by Crangonyx shoemakeri (Crustacea; Amphipoda) on Daphnia obtusa (Crustacea; Cladocera)

Amphipods and cladocerans are common inhabitants of seasonal ponds throughout North America. Although amphipods are usually considered to be benthic detritivores, Crangonyx shoemakeri was found to capture and consume mosquito larvae and Daphnia obtusa. The rate of capture of Daphnia was independent of the amount of decomposing leaf matter available. However, this rate was dependent on prey density and the presence of light, indicating that these amphipods are visual predators.     

Life cycle ofCorophium insidiosum (Crustacea,Amphipoda) in laboratory culture

The life cycle ofCorophium insidiosum (Crawford) was investigated for the first time in laboratory cultures. This amphipod is mainly a suspension feeder, but it can also switch to deposit feeding. It was cultivated in standing, unaerated finger bowls, feeding on detritus, living or dried algal matter, rotifers (Brachionus plicatilis), or large-sized phytoplankton (e. g. the flagellateScrippsiella faeroense). A mixture of these items gave best results and hence was used for long-term cultivation. Preliminary results are presented on ingestion rate (suspension feeding), digestion rate, starvation resistance, and elemental and biochemical composition. In the life cycle ofC. insidiosum, several factors were found to play an important role: temperature, individual age, sex, and in contrast to other amphipod species thus far studied also the age of the mother animal at the time of breeding. Increasing temperature reduces the total life span, the age and size at the time of attaining sexual maturity, and the duration of marsupial development. It increases growth and moulting rate. At increasing individual age, the growth rate, and in males also the moulting rate, decrease, while the number of offspring per brood and surprisingly also the duration of its marsupial development increase. Females generally have a longer life span than males, and they show a higher number of moults, higher moulting frequency and growth rate, and a larger maximum body size. Body length and age at the time of reaching sexual maturity are smaller in males than in females. Furthermore the age of the mother animal at the time of breeding proved to be of particular importance: Individuals from early broods have an apparently longer life span than those originating from late broods, and they have more moults, mostly a higher growth rate, higher number of broods, higher total number of offspring, and, surprisingly, also a longer period of incubating their broods. These major factors have differing combined effects.     

The survival and growth of Gammarus tigrinus Sexton (Crustacea: Amphipoda) in relation to salinity and temperature

Field collections from an inland saline lake indicated that a rapid increase in numbers of a population of Gammarus tigrinus was positively correlated with high summer temperatures and salinities. The laboratory experiments on growth are an attempt to determine whether high summer temperatures or optimum salinity were primarily responsible for the rapid increase in numbers. Furthermore, G. tigrinus was not found in either of two adjacent lakes; one non-saline, the other at a higher salinity. The laboratory experiments on survival are an attempt to determine whether the restricted distribution of G. tigrinus was related to salinity. The implications of the field and laboratory studies are discussed and compared with other data from Europe and North America.     

Swimming behaviour in Monoporeia affinis (Crustacea: Amphipoda) - dependence on temperature and population density

Swimming speed and swimming activity of the nocturnally active benthic amphipod Monoporeia affinis were measured in water temperatures from 3 to 18 degrees C and different population densities in the laboratory. Swimming speed increased with increasing temperature. Increasing water temperature reduced the percentage of active animals in the population, as measured by a "freeze frame" technique. At 7 and 10 degrees C a higher percentage of the population was active in higher animal densities. In all tested conditions swimming activity was highest at about 1 h after light-off and lowest shortly before the predicted time of light-on. The consequences of the documented behavioural responses to environmental stimuli are discussed in relation to population dynamics.     

The influence of temperature on the duration of egg development in West European grasshoppers (Orthoptera: Acrididae)

Summary The relationship between embryonic postdiapause development (PDD) and temperature in ten Acridid species was studied by culturing eggpods from diapause onwards at constant temperatures (ranging from 15.0° C to 37.5° C). In six species PDD was also studied at fluctuating temperatures (12 h at 27.5° C and 12 h at 13.0° C). The PDD duration was strongly temperature dependent in all species studied (Q₁₀ values between 3.0 and 4.1) and differed greatly between species. To assess whether these differences affect habitat determination, PDD duration was related to habitat microclimate. We found that species with a relatively long PDD are restricted to relatively warm grasslands, while species with a short PDD are also found in colder grasslands. Two species have a more limited occurrence than predicted from PDD duration. It is argued that the length of PDD (and consequently hatching date) is crucial to the completion of the annual cycle. The results are applicable to conservation of grasshoppers in grasslands subject to eutrophication. Here increase of vegetation density and height will lead to lower maximum temperatures in the egg environment (i.e. near the soil surface) and consequently to a delay in hatching and loss of thermophilous species. Grassland management rules are proposed that should aid conservation of these species.     

Embryonic development and expression analysis of Distal-less in Caprella scaura (Crustacea, Amphipoda, Caprellidea)

The Caprellidea generally possess rudimentary abdomens and degenerated third and fourth pereopods. Previous molecular phylogenetic studies support the concept that their unique body plan is derived from a gammarid-like body plan from which the abdomen or third and fourth pereopods have been lost in the Caprellidea. To understand the developmental and genetic mechanisms for the morphological evolution of the Caprellidea, we observed the embryonic development of Caprella scaura. Although in the early embryonic stage limb buds appeared in all of the pereonites, we found that elongation of the limb buds did not occur in the third and fourth pereonites; instead, only oval projections (possibly primordial gills) were observed. We next examined the gene expression of Distal-less (Dll) by in situ hybridization and found that Dll was not expressed in the third and fourth pereonites. This suggests that the suppression of Dll expression is responsible for the reduction of Caprellidea pereopods.     

Effect of temperature on the duration of egg, nauplius and copepodite development of some freshwater benthic Copepoda

SUMMARY. The development times of the egg, nauplius and copepodite stages of seven species of freshwater benthic copepods ( Paracyclops fimbriatus, Canthocamptus staphylinus, Attheyella crassa, Moraria brevipes, M. mrazeki, Bryocamptus echinatus and Paracamptus schmeili ) were determined at constant temperatures ranging from 1.5 to 24°C using detritus as food. Several regression models used earlier to describe the temperature dependence of development were tested on this material.
Species differed both in the rapidity of development and in the magnitude of the effect of temperature. Development times usually decreased with increasing temperature, but in M. brevipes temperatures exceeding 16°C retarded postembryonic development. P. fimbriatus developed at a rate comparable to that reported earlier for littoral cyclopoids. All the harpacticoid species developed more slowly than planktonic, littoral or benthic copepods previously studied, but faster than subterranean species. The effect of temperature was most marked in species reproducing in warm water.
The relationship between rate of development and temperature was not linear. None of the curvilinear temperature functions tested was statistically adequate in all cases. However, three of the models gave a reasonable fit to all egg development data, and one of these, the semilogarithmic quadratic equation, ln D = In a + T In b + T² In c , also satisfactorily described postembryonic development. This model accommodates the retardation of development at higher temperatures, and can therefore be recommended for further testing.     

Digestive anatomy of Halella azteca (Crustacea,Amphipoda)

The digestive tract of the freshwater amphipod Hyalella azteca is a straight but differentiated tube consisting of foregut, midgut, and hindgut divisions. The foregut is subdivided into a tubular esophagus, a cardiac stomach, and a pyloric stomach. The cuticular lining of the cardiac stomach is elaborated into a set of food-crushing plates and ossicles, the gastric mill, while the pyloric cuticle forms a complex straining and pressing mechanism. Nine caeca arise from the midgut, seven anteriorly and two posteriorly. Four of the anterior caeca, the hepatopancreatic caeca, are believed to be the primary sites of digestion and absorption. The remaining caeca may be absorptive, secretory, or both. The much-folded hindgut wall is capable of great distention by extrinsic muscle action for water intake to aid in flushing fecal material out of the anus; such action also may stimulate antiperistalsis by intrinsic rectal muscles.     

The effect of temperature on the post-embryonic growth of Neomysis intermedia Czernlawsky (Crustacea, Mysidacea) under laboratory conditions

The effect of temperature on post-embryonic growth of Neomysisintermedia was investigated under unlimited food conditionsin the laboratory. The effect of temperature on the size ofnewly released animals was negligibly small, but body size wasinversely related to temperature in adults. This was mainlycaused by the difference in the number of molts before maturation.The specific growth rate of N. intermedia increased exponentiallywith a temperature coefficient, Q₁₀ of 4.6 from 0.018 d^–13C to 0.21 d^–1 at 20C in juveniles, and with a temperaturecoefficient of 2.7 from 0.006 d^–1 at 3C to 0.05 d^–1at 25C in adults. The rate in juveniles levelled off above20C, and dropped at 29C. Brood size and brood interval decreasedwith temperature increase, while the daily specific reproductionrate increased. The specific growth rate of gravid females,including production of egg matter, increased exponentiallywith a temperature coefficient of 3.3 from 0.015 d^–1 at10C to 0.093 d^–1 at 25C. The present laboratory experiments confirmed the temperaturecontrol on the growth of N. intermedia suggested in a hyper-eutrophiclake.     

The behaviour of Corophium volutator (Crustacea: Amphipoda)

The behaviour of Corophium volutator (Pallas) is outlined. Swimming, crawling, burrowing and feeding activities are described in detail. Animals usually swim on their backs. Every few seconds, swimming alternates with passive sinking. Animals can crawl over surfaces in and out of water. Out of water they do so by a looping motion using their second antennae and telson. When out of water animals crawl away from light and down slopes. In water they swim towards light. Burrowing is initiated by rapid beating of the pleopods; the animal then sinks below the surface by a concerted action of pereiopods, pleopods, telson, uropods and second antennae; within a few minutes, a shallow burrow is formed. The formation of permanent burrows is dependant on particle size, on adhesive properties of detritus and primary films on sand particles, and on a secretion produced by the animal itself. Individuals can turn about in permanent burrows. The species is essentially a detritus feeder. Animals normally feed only when in their burrows, by using their second antennae to scrape material from the substrate surface into the entrance of the burrow. This material is then transported to the mouth by the feeding appendages and respiratory current. The behaviour of small and large animals differs; small animals burrow rapidly and permanently, and do not emerge spontaneously; furthermore, they only swim occasionally. Large animals swim more frequently, spend more time on the substrate surface, and periodically move burrows. It is suggested that new habitats are colonized by large animals which have already bred once.     

Comparative analysis of the circulatory system in Amphipoda (Malacostraca, Crustacea)

We present data on the haemolymph vascular system (HVS) in four representatives of the major amphipod lineages Gammaridea, Hyperiidea and Caprellidea based on corrosion casting and three‐dimensional reconstructions of histological semi‐thin sections. In all these species the HVS comprises a dorsal pulsatile heart, which is continued in the body axis by the anterior and posterior aortae. The heart is equipped with three pairs of incurrent ostia. The number of cardiac arteries that lead off the heart varies among species: in the studied Gammaridea four pairs occur, in Hyperia galba only the three posterior pairs of cardiac arteries occur, while in Caprella mutica cardiac arteries are absent. In all the studied species the posterior aorta leads as a simple tube into the pleon attached to the dorsal diaphragm. The anterior aorta runs from its origin in the anterior part of the second thoracic segment into the cephalothorax. Both pairs of antennae have an arterial supply off the anterior aorta. An overview of previously studied species including our present findings shows the amphipod HVS to be relatively uniform and the gammarid form is discussed as being closest to the ground pattern of Amphipoda.     

Experimental studies on the life cycle ofJassa falcata (Crustacea,Amphipoda)

Jassa falcata (Leach), an unselective suspension feeder, was cultivated in standing, unaerated finger bowls, feeding on a mixture ofBrachionus plicatilis, Scrippsiella faeroense, Ulva spec., and natural detritus. This amphipod can also be maintained with diets composed of dead or live material of both plant and animal origin, but an addition of living zooplankton is necessary for longterm cultivation. Starvation resistance is higher in females than in males, and it is increased by lower temperatures. The life span ofJ. falcata increases with decreasing temperature, and it is generally higher in females (maximum: 252 days at 10°C) than in males. In laboratory culture, a bimodal mortality pattern is typical with high juvenile death rates, low mortality during the reproductive phase, and again increasingly high death rates toward the end of the life cycle. Growth rate depends on temperature, sex, and individual age. The temperature dependence of growth is particularly high in males, and it is higher in adults than in juveniles. The total number of moults is lower in males (5 to 6) than in females (7 to 9). Sexual maturity is attained at moult IV to V. The average incubation time of eggs is about 9 to 16 days (highest value at 10°C). Three to 4 broods were observed, with largest numbers of offspring at 10°C.     

Karyotypes of the Echinogammarus berilloni-group (Crustacea,Amphipoda) from Spain

The chromosome number and karyological features of Iberian populations of seven species of the Echinogammarus berilloni-group (Crustacea, Amphipoda) have been studied. For comparison, Gammarus gauthieri, belonging to the G. pulex-group was also studied. Four species of the berilloni-group share the same number n=27. Other numbers found were n=25, n=26 and n=28. The chromosomes of these species have a centromeric region surrounded by large heterochromatic blocks at late prophase. There-after, the centromere splits precociously.C. gauthieri has n=26, the same number found in the pulex-group. This species has larger chromosomes than the former but it does not show these karyological peculiarities.Cytological observations confirm both the close relationship among species of the berilloni-group and the differentiation with respect to the pulex-group. On the other hand, the existence of different numbers confirms other results that reject the older idea that speciation within Gammaridea occurred with minor changes in karyotypic characters.     

On the nutrition of two Antarctic acanthonotozomatidae (Crustacea: Amphipoda)

Summary Two species of Antarctic acanthonotozomatid amphipods (Echiniphimedia hodgsoni and Maxilliphimedia longipes) have been investigated in regard to their food preference. Examinations of food remains in foreguts and midguts indicate that Echiniphimedia hodgsoni feeds on sponges and Maxilliphimedia longipes ingests Cnidaria. These foregut analyses are supported by a study of the functional morphology of the mouthparts. The structure of the mandibles in particular can be interpreted as an adaptation to the presumed food source. The right mandible of Echiniphimedia hodgsoni bears a lacinia mobilis which works as an additional cutting edge. By means of this cutting mechanism Echiniphimedia hodgsoni should be able to bite out tough sponge material. The mandibular endites of Maxilliphimedia longipes are medially excavated, the incisors are regulary toothed and the molars vestigial. Such kinds of mandibles are adapted to cut large fragments of soft food, i.e. the mucous tissue of Cnidaria.     

Parasite altered micro-distribution of Gammarus pulex (Crustacea: Amphipoda)

In a river survey, Gammarus pulex amphipods both unparasitised and parasitised with the acanthocephalan Echinorhynchus truttae were distributed similarly with respect to flow regimen, tending to be more abundant in faster, shallower, riffle patches. However, there was a higher prevalence of parasitism in faster, shallower areas than in slower, deeper areas and abundance correlated with macrophyte coverage for unparasitised but not parasitised amphipods, indicating subtle differences in habitat usage. A laboratory 'patch' simulation indicated that parasitism influenced micro-distribution. There were higher proportions of unparasitised amphipods in/under stone substrates and within weed. In contrast, there were higher proportions of parasitised amphipods in the water column and at the water surface. As the experiment progressed, unparasitised but not parasitised amphipod habitat usage shifted from those micro-habitats above the substrate and in the water column to those in/under the substrates. Experiments also demonstrated that parasitised amphipods were more active and had a greater preference for illumination. Previous studies of the effects of acanthocephalan parasitism of amphipod hosts have focussed on how drift behaviour is altered, now we show that subtle differences in micro-habitat usage could translate to greatly increased vulnerability to fish predation. We discuss how aggregation of parasitised individuals within specific habitats could promote parasite transmission.