The chemical ecology of some British freshwater gastropod molluses: behavioural responses to short chain carboxylic acids and maltose

SUMMARY. 1. The behavioural responses of six species of British freshwater gastropods to chemical gradients of short chain carboxylic acids (C-2 to C-5, C-8) and maltose were investigated by means of diffusion olfactometers.
2. The species were ranked as follows on the basis of the number of significant behavioural responses to the test chemicals: Lymnaea peregra > Planorbis contortus > Physa fontinalis > Planorbis planorbis > Bithynia tentaculata > Planorbis vortex. These differences were not a result of differences in activity but reflect real differences in ehemoreception.
3. Propanoate (C-3) was a significant attractant or arrestant to five snail species, C-4, C-8 and maltose to four species and C-5 to three species. Acetate (C-2) was a significant attractant to L. peregra and P. fontinalis but it was the only acid to act as a repellent, to P. planorbis and B. tentaculata.
4. Lymnaea peregra continued to respond to repeated butanoate application. Response levels could be enhanced by increasing concentration (minimum thresholds 10^-4M to 10⁻⁵ M), pH (above 6) and food deprivation.
5. The ecological relevance of the results are discussed with particular reference to the distributional patterns of the chemicals and snails and the feeding niches of the latter.     

Shell variation in sympatric freshwater Lymnaea peregra and L. ovata (Gastropoda: Lymnaeidae)

Snails of the genus Lymnaea are morphologically variable and their taxonomy is unclear. In particular, the forms peregra and ovata , distinguished by shell shape, are often considered variants of the same species, L. peregra. We studied a rare situation in a Swiss mountain lake where both forms are sympatric. First, we found that the forms shows complete separation for a number of allozymes. Second, we examined the response of the two snail forms to infection by the trematode Diplostomum phoxini . For the ovata form, there was a transitory, 10% increase in the growth of infected snails compared to uninfected controls. The peregra form showed no gigantism and had higher parasite-induced mortality. Third, we assessed differences between the forms in reproduction under different environmental conditions. Density negatively influenced egg production to the same degree in both forms. However, decreasing water levels, characteristic of part of the lake studied, led to a 30% decrease in egg production for the ovata form, but only a 10% decrease for the peregra form. These differences are discussed in relation to the microdistributions of the snails in the lake and we conclude that the two forms are almost certainly separate species.     

Toxic effects of cadmium and zinc on the transmission of Echinoparyphium recurvatum cercariae

The toxicity of cadmium, zinc and Cd/Zn mixtures to the transmission of Echinoparyphium recurvatum (Digenea: Echinostomatidae) cercariae into the snail second intermediate hosts was investigated at concentrations ranging from 100 microg l-1 to 10 000 microg l-1 in both soft and hard water. A differential response in the infectivity of metal-exposed cercariae into Lymnaea peregra and Physa fontinalis was demonstrated which was dependent on the snail species being infected. Exposure of L. peregra, P. fontinalis, and L. stagnalis to heavy metals caused a differing susceptibility to E. recurvatum cercariae depending on the snail species being exposed. The mechanism and effects of metal toxicity, together with the importance of the parasite/host strain on cercarial transmission are discussed.     

Spiniferites cruciformis: a fresh water dinoflagellate cyst?

Palynological studies of cored lacustrine sediments from the late Quaternary of Lake Kastoria, northern Greece, revealed a Late Glacial interval with abundant dinoflagellate cysts. Cyst assemblages include two identifiable species, Spiniferites cruciformis and Gonyaulax apiculata. The presence of the fresh water species G. apiculata is consistent with the lacustrine setting of these deposits, but that of S. cruciformis is anomalous. Previously, this species has only been recorded in abundance from presumed brackish marine sediments from the Black Sea and Marmara Sea sediments where geochemical data clearly record brackish salinities. Therefore, it has been regarded as a low salinity cyst type with a wide range of morphological variation that some workers have suggested to reflect salinity fluctuations. Specimens from Greece display only part of the range of morphological variability previously described from these (brackish) marine settings. Encountered morphological variation includes ellipsoidal/pentameral and cruciform endocyst shapes with rare intermediate shapes, and highly variable septa development. Specimens characterized by extremely reduced ornamentation known from (brackish) marine environments have not been recorded. Our records of S. cruciformis indicate that: (1) it could thrive in fresh water conditions; and (2) that apparently most of the strong morphological variations of the cysts are an intrinsic phenomenon for this taxon, and may only partly be linked to salinity variations as suggested earlier. We suggest that S. cruciformis essentially is a fresh water taxon, and that its records in (brackish) marine environments, with the exception of specimens with strongly reduced ornamentation, may be due to transportation, to short-lived fresh water surface conditions in such environments, or to tolerance of the species to brackish conditions.     

Cadmium toxicity and snail-digenean interactions in a population of Lymnaea spp

The toxicity of cadmium to a population of Lymnaea peregra and L. stagnalis naturally infected with a range of digeneans and collected from a number of sites in the lower Thames Valley, UK was investigated. Lymnaeid snails were exposed to 100 microg l-1 cadmium and the effects on host survival and emergence of cercariae recorded. Overwintered L. peregra, but not L. stagnalis, showed significantly reduced survival compared to seasonally infected snails, i.e. snails which have acquired an infection during the spring or summer. A significant increase in survival with increasing snail size was demonstrated for L. stagnalis and for seasonally infected L. peregra only. Only L. stagnalis infected with Diplostomum spathaceum and L. peregra infected individually with D. spathaceum, Sanguinicola inermis, Echinoparyphium recurvatum and Notocotylus attenuatus demonstrated a significantly reduced survival compared to laboratory-bred controls. The exposure of L. stagnalis to cadmium resulted in a significant reduction in the emergence of D. spathaceum over a 5-day period but cadmium-exposed L. peregra showed no difference in the emergence of E. recurvatum cercariae over a 3-day exposure period. The mechanisms and importance of metal toxicity to snail-digenean interactions are discussed.     

Variations in the retinal designs of pulmonate snails (Mollusca, Gastropoda): squaring phylogenetic background and ecophysiological needs (I)

Abstract. The eyes of aquatic pulmonates differ from those of terrestrial pulmonates; the latter, in species such as Cepaea nemoralis and Trichia hispida , possess conventional, cup-shaped retinas, but the aquatic species Lymnaea stagnalis, Radix peregra, Physa fontinalis , and Planorbarius corneus have retinas that are partitioned into dorsal and ventral depressions ("pits"). The pits are separated by an internal ridge, called the "crest", and on account of their pigmentation can be seen in vivo . The dominant cellular components of the retinae of terrestrial as well as aquatic snails are pigmented cells and microvillar photoreceptors, the latter occurring in two morphologically distinct types (I and II). Aquatic snails with preferences for shallow water possess eyes with both type I and type II photoreceptive cells, but Pl. corneus , an inhabitant of deeper water, only has type-I receptors, supporting an earlier finding that type I cells represent dim- and type II cells bright-light receptors. On the basis of histological and optical comparisons, we conclude that the eyes of L. stagnalis and R. peregra , species that are known to escape and seek temporary refuge above the water surface, are well adapted to function in water as well as air, but that the eyes of P. fontinalis and Pl. corneus are less modified from those of their terrestrial ancestors.     

Strain variation and geographic endemism in Streptococcus iniae

Twenty-six Israeli isolates of Streptococcus iniae from both marine and fresh/brackish water sources were compared with each other and with 9 foreign isolates. All the isolates were tentatively identified according to their biochemical profile. Direct sequencing of approximately 600 bp PCR products of the 16S rDNA confirmed their identification as S. iniae at the molecular level and revealed a new (one-nucleotide) variant among Israeli isolates, in addition to 2 variants that had been previously reported. Strain variation was further examined by subjecting the isolates to randomly amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) analyses. The RAPD method allowed separation of the isolates into only 2 groups, one including 5 Israeli fresh/brackish water isolates and one including all the other isolates. The AFLP method grouped the Israeli marine isolates into one homogeneous cluster, although they had been obtained in different years (1995 to 2001) from different species of fish, and from wild (Red Sea) as well as cultured (both Mediterranean and Red Sea) sources. The Israeli fresh/brackish water isolates and foreign isolates separated into distinct entities that clustered at generally high degrees of similarity. The distance between the clusters of the Israeli marine and fresh/brackish water isolates indicates that the S. iniae streptococcosis that has been afflicting the aquaculture industries in the 2 environments in recent years was caused by distinct strains. AFLP showed superior discriminative properties over RAPD in detecting intraspecific variation and proved to be an important tool for the characterization of S. iniae. A correlation between strain variation and geographic endemism was established.     

Contrasting patterns of quantitative and neutral genetic variation in locally adapted populations of the natterjack toad, Bufo calamita

The relative importance of natural selection and genetic drift in determining patterns of phenotypic diversity observed in nature is still unclear. The natterjack toad (Bufo calamita) is one of a few amphibian species capable of breeding in saline ponds, even though water salinity represents a considerable stress for them. Results from two common-garden experiments showed a pattern of geographic variation in embryonic salinity tolerance among populations from either fresh or brackish environments, consistent with the hypothesis of local adaptation. Full-sib analysis showed increased variation in survival among sibships within population for all populations as osmotic stress was increased (broad-sense heritability increased as salinity raised). Nevertheless, toads native to the brackish water environment had the highest overall survival under brackish conditions. Levels of population genetic differentiation for salinity tolerance were higher than those of neutral genetic differentiation, the latter obtained through the analysis of eight microsatellite loci. Microsatellite markers also revealed little population differentiation, lack of an isolation-by-distance pattern, and moderate gene flow connecting the populations. Therefore, environmental stress tolerance appears to have evolved in absence of geographic isolation, and consequently we reject the null hypothesis of neutral differentiation.     

Fixed focal-length optics in pulmonate snails (Mollusca, Gastropoda): squaring phylogenetic background and ecophysiological needs (II)

Abstract. Our results suggest that freshwater pulmonates like Lymnaea stagnalis, Radix peregra, Physa fontinalis , and Planorbarius corneus have inherited from their terrestrial ancestors eyes with a spherical, immobile lens with fixed focal-length optics. Unable to change the dioptric apparatus to form an image under water, modifications to the retina had to occur if sharp vision was required. Computer-assisted calculations and 3-D eye reconstructions demonstrate that the photoreceptors in the deeper, ventral pit are in a position to perceive focused images under water. Vision in air, however, would favour photoreceptive cells located in the shallower, dorsal pit. On the basis of histological, ethological, and optical comparisons, we conclude that the eyes in L. stagnalis and R. peregra , species that are known to escape and seek temporary refuge above the water surface, are well adapted to function in water as well as air, but that the eyes in P. fontinalis and Pl. corneus are less modified from those of their terrestrial ancestors. We also conclude that good resolving power may be of greater importance in the aquatic pulmonates than the terrestrial species, since the former have to locate thin, vertical stems of reeds and sedges to ascend in order to reach the surface to breathe.     

Variation in Scolex Morphology within and between Some Species of the Genus Proteocephalus Weinland (Cestoda, Proteocephala) with References to Strobilar Morphology

The scolex morphology of some Proteocephalus species from fish caught in fresh and brackish waters in Norway, as revealed by scanning and transmission electron microscopy and light microscopy, is described. The size and form of the fifth apical sucker proved to be a very pure character for identification. In spite of this, however, the scoleces of different species revealed specific characters which together with strobilar characters should be well suited for species discrimination and identification.     

Biochemical identification of a brackish water type ofPungitius pungitius,and its morphological and ecological features in Hokkaido,Japan

A brackish water type ofPungitius pungitius (Gasterosteidae) is newly reported from Japan. Genetic differences, based on 13 loci of 6 enzymes and muscle protein, were examined between fresh and brackish water types in the Biwase River in the eastern part of Hokkaido. The alleles onGpd, Pgi andPgm were displaced between them, even though their distributions partially overlapped in the river. The brackish water type was also statistically different from the fresh water type on the basis of three morphological characters, such as number of dorsal spines, gill-rakers and vertebrae, although ranges overlapped. Segregation of spawning sites and differing nuptial colors of the male were found between fresh and brackish water types. These facts suggest that the brackish water type is reproductively isolated from the fresh water type and that both types should be regarded as independent species.     

The Mollusca of the exposed zone of Øvre Heimdalsvatn

The molluscan fauna was surveyed monthly in 1972 during the ice free period. Densities were low and the most common species were the gastropods Gyraulus acronicus (Férussac) and Lymnaea peregra (Müll.).     

Changes of the serotonergic system activity in fish tissues during an increase of water salinity

Changes of environment parameters produce essential effects on the serotonergic system activity in the body tissues. This paper describes study of the serotonergic system activity in various tissues of half-migratory fish - the Caspian roach Rutilus rutilus caspicus and the bream Abramis brama orientalis - caught in the fresh and brackish water. Using the method of indirect solid-phase ELISA test, the serotonergic system activity was assessed by determining in the studied fish tissues of the amount of serotonin-modulating anticonsolidation protein (SMAP) that is in the linear correlation with serotonin level. A significant change of the SMAP level in the Caspian roach and bream brain was found under effect on increased water salinity. Analysis of the SMAP amount in the bream liver did not reveal any differences in the animals caught in the brackish and fresh water. At the same time, in the bream gill there was a small rise of the SMAP content in the fish caught in the brackish water. The revealed in this experiment elevation of the SMAP amount in the Caspian roach and bream brain reflecting a corresponding increase of the serotonergic system activity indicates involvement of adaptive readjustments in the animal body.     

Biological Differences between Brackish and Fresh Water-Derived Aedes aegypti from Two Locations in the Jaffna Peninsula of Sri Lanka and the Implications for Arboviral Disease Transmission

The mainly fresh water arboviral vector Aedes aegypti L. (Diptera: Culicidae) can also undergo pre-imaginal development in brackish water of up to 15 ppt (parts per thousand) salt in coastal areas. We investigated differences in salinity tolerance, egg laying preference, egg hatching and larval development times and resistance to common insecticides in Ae. aegypti collected from brackish and fresh water habitats in Jaffna, Sri Lanka. Brackish water-derived Ae. aegypti were more tolerant of salinity than fresh water-derived Ae. aegypti and this difference was only partly reduced after their transfer to fresh water for up to five generations. Brackish water-derived Ae. aegypti did not significantly discriminate between 10 ppt salt brackish water and fresh water for oviposition, while fresh water-derived Ae. aegypti preferred fresh water. The hatching of eggs from both brackish and fresh water-derived Ae. aegypti was less efficient and the time taken for larvae to develop into pupae was prolonged in 10 ppt salt brackish water. Ae. aegypti isolated from coastal brackish water were less resistant to the organophosphate insecticide malathion than inland fresh water Ae. aegypti. Brackish and fresh water-derived Ae. aegypti however were able to mate and produce viable offspring in the laboratory. The results suggest that development in brackish water is characterised by pertinent biological changes, and that there is restricted genetic exchange between coastal brackish and inland fresh water Ae. aegypti isolates from sites 5 km apart. The findings highlight the need for monitoring Ae. aegypti developing in coastal brackish waters and extending vector control measures to their habitats.     

长江口水域鱼卵、仔稚鱼种类组成和数量的分布与变化

根据2005年4和11月、2006年4和9月在长江河口水域进行的鱼卵、仔稚鱼种类和数量调查,并结合1990年9月和1991年3月的历史数据,对该水域的鱼卵、仔稚鱼群落结构的种类组成和数量的季节变化作了研究,其结果共发现鱼卵、仔稚鱼36种(类),以海洋鱼类种类最多。秋季航次鱼卵、仔稚鱼的平均种类数和丰度均高于春季。河口咸淡水区鱼卵总数显著高于淡水区,而仔稚鱼总数略低于淡水区。与1990—1991年数据相比,2005—2006年春、秋季的鱼卵和仔稚鱼丰度均有所增加。1990、2006年秋季(9月)鱼卵、仔稚鱼种类组成差异较大,特别是翘嘴红鲌和太湖新银鱼丰度差异较大。这些都说明近20年来,长江河口水域鱼卵、仔稚鱼种类组成和数量均发生了明显的改变。     

The Definition of British Water Beetle Species Pools (Coleoptera) and their Relationship to Altitude, Temperature, Precipitation and Land Cover Variables

Pooled water beetle species lists from 1826 British national grid 10-km squares were analysed using multivariate ordination and classification methods. The relationships of pool groups to the climate, altitude and land cover variables were assessed using constrained and partial ordinations. Ordination of the species pool data indicated a major trend between squares in the north-west of Scotland and those in southern England, illustrating differences in acid and basic water standing water. Secondary variation was from acid standing water to fast-flowing streams and rivers. Classification generated nine species pool groups. These showed a distinct north-west to south-east trend but there was no obvious coastal or brackish water effect on distribution. The climatic and land cover variables were all significantly related to each other, and to north-south variation in grid square location, but the constrained ordination results indicated that that the most important influence on water beetle species pool distribution was mean summer temperature. Although the amount of variation explained by the environmental variables was low, spatial variation in the environmental predictors was almost as important as the environmental variables themselves in determining species pool composition. Mean annual temperature was also strongly correlated with species pool distribution with two land cover variables slightly less important. Altitude and precipitation had the least influence. The water beetle national recording scheme database appears to be of sufficiently high quality for environmental investigations at the British scale. There is considerable potential for the synthesis of invertebrate species distribution, land cover and climate change predictions in the assessment of environmental change. The results, together with previous work on other invertebrate species, indicate that changing summer temperatures may have a considerable influence on the distribution British invertebrate species.     

Interactions between the leech Glossiphonia complanata and its gastropod prey

Summary Predator-prey interactions between the predatory leech, Glossiphonia complanata, and its gastropod prey were investigated in laboratory experiments, including behavioural observations with the aid of time-lapse video technique. Six gastropod species were investigated, viz. Lymnaea peregra, Planorbis planorbis, Physa fontinalis, Ancylus fluviatilis, Bithynia tentaculata, and Theodoxus fluviatilis. The species studied exhibited anti-predator defences, which had their maximum efficiency at different stages of encounter with G. complanata. The activity of B. tentaculata decreased with increasing leech activity, but was relatively higher when food was present than when not. Handling times were dependent on the time elapsed since the previous meal was captured (intercatch interval), which in turn was related to the size of the previous prey. Handling time was also related to the size of both predator and prey. The capture efficiency was high for small prey and the leeches spent more time in patches with higher yield. They were, however, unable to discriminate between patches of different prey density.     

Infectivity of Echinostoma friedi miracidia to different snail species under experimental conditions

The infectivity of Echinostoma friedi (Trematoda: Echinostomatidae) miracidia was studied experimentally in a range of laboratory-reared snails that coexist in the same natural locality, namely Radix peregra, Lymnaea fuscus, L. truncatula (Lymnaeidae), Gyraulus chinensis, Helisoma duryi (Planorbidae) and Physella acuta (Physidae), and snails from different geographical origins acting naturally or experimentally as intermediate hosts of Schistosoma spp., namely Planorbarius metidjensis (from Málaga, Spain), Biomphalaria glabrata (Guadeloupe), B. alexandrina (Egypt) (Planorbidae), Bulinus cernicus (Mauritius), B. globosus (Zambia), B. natalensis (South Africa) and B. truncatus (Niger) (Bulinidae). Six species of snails were found to be susceptible, with the rate of infection ranging from 0 to 36.7%. The highest infection was detected in R. peregra. The low host specificity of E. friedi might have an epidemiological significance as a requisite for a recent establishment in a new geographical area.     

Fish communities along an oxygen-poor salinity gradient (Zeeschelde Estuary, Belgium)

Fish living in the tidal fresh and brackish water reaches of the Zeeschelde Estuary were studied in samples collected from the cooling-water inlets of three power stations. Between July 1994 and June 1995, 42 different species were recorded including 26 marine migrants, 14 freshwater species and two diadromous species. Species number as well as fish abundance were correlated significantly with salinity and oxygen concentration. The community structure was analysed with a correlation biplot based on principal component analysis of the root-root transformed fish abundance. Four separated communities could be distinguished since the first principal component expressed a salinity and the second a temperature gradient. During summer and fall Pomatoschistus microps, P. minutus, P. lozanoi and Syngnathus rostellatus were most abundant in the brackish-water reach. At this time, freshwater species seemed to avoid the freshwater area. During winter, Sprattus sprattus, Clupea harengus and Dicentrarchus labrax were the dominant species of the brackish-water zone while the freshwater reaches were dominated by Gasterosteus aculeatus . Migrating fish such as Pleuronectes flesus, Lampetra fluviatilis, Anguilla anguilla and Osmerus eperlanus were restricted to the brackish environment.     

Distribution and antibacterial drug resistance ofAeromonas spp. from fresh and brackish waters in Southern Turkey

The frequency of antibiotic resistance was compared inAeromonas spp. isolated from fresh and brackish water in Southern Turkey. A total of 97Aeromonas spp. strains were isolated from four zones (three from fresh and one from brackish water). Most of the strains isolated from all samples wereAeromonas hydrophila (79.4%), while the amount ofAeromonas sobria andAeromons caviae, were rather lower in the samples examined (17.5% and 3.1% respectively). A high proportion of isolates from all water sources showed resistance to cephalotin (86.6%) and trimethoprim-sulphamethoxazole (69%). On the other hand, a low proportion of bacteria showed resistance to tetracycline (14.4%), chloramphenicol (11.3%), gentamicin (7.2%) and nitrofurantoin (6.8%). Only one strain showing resistance to amikacin was found. Multiple Antibiotic Resistance Index (MARI) to at least two antibiotics was highest in brackish water (zone 4), followed by fresh water (zone 3). MARI values ranging from 0.2 to 0.8 for the bacteria isolated from brackish water. This study suggest that, multiple antibiotic resistantAeromonas spp., especiallyA. hydrophila, can be easily recovered from fresh and brackish water sources in Turkey and these sources may play as a reservoirs responsible for disease pathogen aeromonads.