Allozyme frequencies in western European populations of Asellus aquaticus (L.) Isopoda and their association with water pollution

A study was made of allozyme variation in western European populations of Asellus aquaticus. Two enzymes were examined glucose phosphate isomerase (CPI) and phosphoglucomutase (PGM).
The populations show significant latitudinal clincs for GPI and PGM with the GPI-2 and PGM-2 alleles increasing in more southerly latitudes. While GPI-2 frequencies in British populations are consistent with the overall clinc, considered separately they show a reverse cline. This appears to be the result of a strong association of GPI-2 frequencies with water pollution combined with the geographic distribution of the polluted sites.
The association of high GPI-2 frequencies with high levels of water pollution is present in two independent sets of populations in Britain, and is more specifically associated with low levels of environmental oxygen. This latter association also occurs independently in temporal studies made at three locations. However, an additional temporal association of high GPI-2 frequencies with high temperatures also exists, consistent with the observed latitudinal cline. A study of adult mortality by oxygen deprivation at different temperatures suggests that both temperature and oxygen concentrations may act selectively with the GPI 2-2 genotype to be favoured under certain conditions. In contrast to GPI, PGM allozymes do not appear to be associated with pollution related variables.
The findings of the study point to selection acting on the two loci examined, though most convincingly for GPI. However, it remains to be demonstrated that selection is acting directly on the loci, and if so, how it operates to produce the patterns of allozyme variation observed in nature.     

Comparative ecology of Gammarus pulex (L.) and Asellus aquaticus (L.) II: fungal preferences

This paper continues to explore niche differentiation in Gammarus pulex and Asellus aquaticus by analysis of their food preferences. Individuals from both species discriminated between leaf discs colonized by different fungal species and exhibited strong preferences for Anguillospora longissima and Heliscus lugdunensis. Fungal preferences were not correlated with the relative abundance of fungi in the field and there was considerable intra-population variability in food preferences — both between individuals and for the same individual through time. Niche overlap between animals from all four study populations was high and there was no evidence of differences in the potential trophic niches of animals from sympatric and allopatric populations.     

Toxicity of heavy metals to Asellus aquaticus (L.) (Crustacea,Isopoda)

Effects of heavy metals on the isopod Asellus aquaticus (L.) are studied by static toxicity tests. Results demonstrate that the species is sensitive to Cd⁺², Cr⁺⁶, Cu⁺², Fe⁺³, Hg⁺², Ni⁺² Pb⁺² and Zn⁺², but the toxicity of each metal is different. Differences are also found between adults and between adults and juveniles. The comparative analysis of all data on the toxicity has been performed on the concentrations of metal ions and not on metal compound concentrations.Criteria for establishing water quality in order to guarantee protection of the environment are discussed.     

Comparative ecology of Gammarus pulex (L.) and Asellus aquaticus (L.) I: population dynamics and microdistribution

Gammarus pulex and Asellus aquaticus generally occupy different zones in rivers; the former occurs in upper reaches but is replaced by the latter in lower reaches. Microdistribution and life-history patterns of G. pulex and A. aquaticus in sympatry and allopatry, were analyzed. Both species exhibited similar patterns of microhabitat selection, with larger individuals associated predominantly with large-sized substratum particles, and juveniles with weed. Coexisting populations of G. pulex and A. aquaticus had similar densities and population dynamics. Within each species, differences in population dynamics of allopatric and sympatric populations were observed. Although variation in population dynamics of G. pulex may be explained in terms of competition between the two species, the evidence is weak and equivocal. Differences in the dynamics of the two A. aquaticus populations were possibly a consequence of coal-mine and organic pollution, reducing the survival of offspring in the allopatric population.     

Epibionts of Asellus aquaticus(L.) (Crustacea, Isopoda): an SEM study

1. This study presents a qualitative and quantitative survey of epibionts infesting two populations of the freshwater isopod Asellus aquaticus (L.). Using scanning electron microscopy, the prevalence, mean intensity, abundance, spatial preferences and distribution of organisms on various external surfaces were ascertained.
2. A diverse community, consisting primarily of protozoa and rotifers, utilised A. aquaticus as a substrate organism. Every individual A. aquaticus supported some form of epizoic life. Peritrich species comprised 89.2% of all epibionts. Carchesium polypinum, Pseudocarchesium aselli, Pseudocarchesium asellicola, Pseudocarchesium simulans and Opercularia hebes dominated the epifauna.
3. Highest epibiont burdens occurred on the mouthparts, the first few ventral segments and the gills and largely comprised the above peritrich species. Most epibionts exhibited some degree of site preference on the host. A distinct gill epifauna existed. Apart from Acineta tuberosa and Vorticella rotunda , which had equal prevalences on dorsal and ventral surfaces in one culture, most species largely avoided the dorsal surface.
4. Epibionts exhibited varying degrees of adaptation to life on a living substrate. They ranged from facultative species such as A. tuberosa , which are capable of colonising abiotic substrata, to Gymnodinoides aselli whose life cycle relies on interaction with A. aquaticus . Highly specialised species tended to exhibit the most pronounced and consistent site restriction.
5. Asellus aquaticus offers a highly tractable system for further study of substrate species–epibiont relationships.     

Light-dark cycle and mitotic index in Asellus aquaticus (L.) (Crustacea,Isopoda)

The circadian variation of the mitotic index during spermiohistogenesis was studied in Asellus aquaticus (L.). The actual number of metaphases and prometaphases was determined at the end of each hour of light or darkness over a 24 h period in animals bred under LD 12:12. The number of the metaphases and prometaphases decreases during the light period and sharply increases in the last 3 hrs of the dark period. This variation in the proliferative activity suggests that photoperiod can play a role in the synchronization of mitosis.     

Effect of chronic exposure to cadmium and copper on Asellus aquaticus (L.) (Crustacea,Isopoda)

The effects of chronic exposure to 5 g·1^–1 cadmium or copper on the crustacean Isopod Asellus aquaticus (L.) were studied by analyzing survival and body growth in the first stages of the life-cycle and by determining fecundity and survival of embryo-bearing females. Juveniles survival is differently affected by the two metals in that embryonic development is more sensitive to cadmium while juvenile development is more sensitive to copper. Juvenile body growth is stimulated by cadmium and depressed by copper. Embryo-bearing female survival and fecundity are significantly reduced by cadmium but are not affected by copper. The consequence of environmental contamination by a sublethal cadmium or copper concentration is discussed.     

Effects of Elevated Temperature on Sex Ratio in a Population of Hog Slaters (Asellus aquaticus L.)

Seasonal changes in the abundance and sex ratio in the hog slater were monitored in nature throughout the annual cycle. It was shown that the sex ratio was balanced at a relatively low abundance in the autumn-winter period. The number of males could exceed 1.5-fold that of females during the period of mass reproduction in spring and summer. The experimental results suggest that the summer shift of sex ratio towards males was due to their higher tolerance to elevated temperature at the early ontogenetic stages.     

The predation on Asellus aquaticus (L.) by perch,Perca fluviatilis (L.), in a small forest lake

Asellus aquaticus (L.) was the most important benthic food item for perch, Perca fluviatilis (L.), in a small, extremely humic forest lake in southern Finland. The proportion of A. aquaticus in the diet of perch varied according to the former's availability, which, in turn, depended on its life cycle. Perch 11.0–12.9 cm (total length) most frequently fed on A. aquaticus; smaller and larger perch fed more frequently on crustacean zooplankton and aquatic insect larvae, respectively. The high density of the perch population, the importance of A. aquaticus in the benthos of the study lake and the general high activity level of the prey resulted in a high predation (0.1–1.8% per day). The population of A. aquaticus was also limited by the scarcity of macrophytic vegetation and the small area of oxygenated littoral in the lake.     

Sensitivity of Asellus aquaticus (L.) and Proasellus coxalis Dollf. (Crustacea,Isopoda) to Copper

The effects of Copper on the life-cycle of two crustacean isopods, Asellus aquaticus (L.) and Proasellus coxalis Dollf., are studied. ST₅₀ indicates that females and males are differently sensitive in comparison with juveniles. The two species do not show differences in sensitivity in the range of 0.01–15 mg·1^-1 between adults and juveniles. The effect of 0.005 mg·1^-1 Copper sulphate was strongest on embryonic and larval stages. Ecological implications are discussed.     

A comparison of the population ecology of Asellus aquaticus (L.) and Asellus meridianus rac. in the reed beds of the Tjeukemeer

The population ecology of Asellus aquaticus and Asellus meridianus was studied in a Tjeukemeer reed bed from March to October. The densities of the two species are similar at the beginning and end of the reproductive season, although A. meridianus is up to 3 times more abundant in between. In both species egg production is positively correlated to body length and summer brood sizes are smaller than in the spring. A. meridianus begins to reproduce at smaller sizes than A. aquaticus and is also more fecund for overlapping size classes. Over the season as a whole both species have the same reproductive output. The life cycles of the two species are very similar with three main periods of reproduction and the populations being replaced twice during the year. Despite the differences between the species no factors are found which gives one species an obvious competitive advantage against the other.Henry and Magniez (1970) have proposed the name Proasellus meridianus for this species.     

Effects of pH,humic substances and animal interactions on survival and physiological status of Asellus aquaticus L. and Gammarus pulex (L.)

Summary The mortality and physiological status (body water content) of Asellus aquaticus (Isopoda) and Gammarus pulex (Amphipoda) were measured after 25 days exposure in 20 natural streams with a pH range of 4.3–7.5 and a colour range of 8–280 mg Pt L^–1. In addition, the effects of keeping the animals as single species or together were studied. The response of Gammarus to low pH was an increased mortality and lower physiological status of surviving individuals in streams with a pH lower than 6.0. In Asellus the physiological status was correlated with pH, while the mortality was not pH dependent. The effects of humus on the physiological status of Asellus was significant when fitted to a second order polynomial function. The influence of humus can, however, be regarded as small relative to pH. The interactions between the species could be described as asymmetric under optimal conditions of high pH and low humus concentrations, where the presence of Gammarus decreased the survival and physiological status of Asellus. Acid stress did not seem to reverse the direction of this asymmetry, but the presence of Gammarus improved the physiological status of Asellus at pH lower than 6.0. Since the presence of Asellus did not increase the mortality or decrease the physiological status of Gammarus, this could be explained by Asellus feeding on Gammarus that died from physiological stress solely. This mechanism suggests that food quality, and thus effects of diffuse competition, can be important for the ability to withstand acid stress. The results, though, give no support for the hypothesis that competition from Asellus is important for the disappearance of Gammarus during the acidification of streams.     

Phylogeography of subterranean and surface populations of water lice Asellus aquaticus (Crustacea: Isopoda)

The water louse Asellus aquaticus is a widespread, euryoecious species, mostly uniform throughout its range. However, six subspecies are known from the Dinaric karst in the northwestern Balkans. They include some specialized subterranean populations. The pattern of genetic variation among subterranean and surface populations in this hydrographically highly fragmented karst region was investigated using a 653 bp fragment of the mitochondrial gene (COI). Sequencing of 168 individuals from 25 localities revealed 72 haplotypes. amova and methods of phylogenetic reconstruction all uncovered hydrographic structuring of genetic variation of the populations. Nested clade analysis pointed out several fragmentation events, along with some range expansions within hydrographical systems. By superimposing the subterranean mode of life on the phylogeographical pattern, three independent cave colonizations could be inferred within a distance of < 100 km. Caves were invaded after the ancestral surface populations became isolated through vicariant fragmentation. A possible scenario of hydrographic history of the region was constructed combining the molecular data with palaeogeographical information.     

The ultrastructure of the heart of Oniscus asellus L. and Asellus aquaticus L. (Crustacea,Isopoda)

Summary The endocardium of Oniscus asellus L. and Asellus aquaticus L. consists of lipid cells. The epicardium consists of a layer of cells with a vesiculated cytoplasm covered by a thick extracellular fibrous sheet. The myocardium is a single layer of cells, the sarcolemma invaginates at Z disc level forming transverse tubules, and longitudinal tubules branch off from these. At the A-I level' longitudinal tubules form transverse systems, which form couplings with the sarcoplasmic reticulum. The sarcoplasmic reticulum appears as perforated sheets enveloping the myofibrils. Two types of nerve terminal are found: one is embedded in a myocardial cell process, the other lies in a myocardial cell depression. They contain clear and dense-cored synaptic vesicles.This work was supported by grants from the Norwegian Research Council for Science and the Humanities     

Effect of heavy metal pollution on mineral absorption in sunflower (Helianthus annuus L.) hybrids

The present study was conducted in a potted experiment to examine the effects of chromium pollution on absorption of mineral nutrients and some morpho-physiological attributes of two sunflower (Helianthus annuus L.) hybrids (FH-331 and FH-259) in the presence and absence of ethylene diamine tetra acetic acid (EDTA) used as a chelating agent. Four concentrations of chromium (Cr³⁺) i.e., 0, 20, 30 and 40 mg kg^?1 with and without 0.3 g kg^?1, EDTA as chelating agent were applied to 25-day-old sunflower plants. A gradually decreasing trend in absorption of all minerals and other parameters studied were observed. Different treatments of Cr³⁺ as well as Cr³⁺ and EDTA significantly reduced root and shoot fresh weight; however, root, shoot and achene Cr³⁺ contents of two sunflowers hybrids under higher chromium and EDTA stress varied significantly whereas movement of Cr³⁺ contents to leaves was non-significant. Absorption of Na⁺, K⁺, N₂ and P through roots and shoots significantly reduced with increasing concentration of Cr³⁺ treatments. In fact addition of EDTA to the medium further enhanced the toxicity of chromium.