The diatoms ingested by freshwater snails: temporal,spatial, and interspecific variation

Seventeen species of diatoms, representing a broad range of sizes, shapes, and growth habits, were collected from rocks in rapidly-flowing sections of the Mitchell River, North Carolina. The diatoms ingested by adult Goniobasis proxima, juvenile Leptoxis carinata, and adult Physa sp. co-occurring in this habitat were indistinguishable from one another, in spite of great differences in radular morphology. All snails sampled the diatom flora almost randomly, with only one or two of the larger diatom species under-represented in the gut contents. Some snails also seemed to selectively ingest the smaller individuals of the larger diatom taxa, and larger individuals of the smaller diatom taxa. The diatoms identifiable in juvenile Goniobasis guts were somewhat more distinctive, although this seemed to be due at least partly to more mechanical breakage. The diatom flora of quiet, muddy pools was much different from that of shallow, rocky areas, but once again, Goniobasis seemed to sample the available flora randomly. Seasonal variation was also apparent in the diatom diet of Goniobasis. We suggest that in some cases, it may be reasonable to use snails to sample the diatom assemblage present in a particular habitat, if more direct methods are impractical.     

Development of polymorphic microsatellite loci in the hermaphroditic freshwater snails Drepanotrema surinamense and Drepanotrema depressissimum

We characterized new variable microsatellites in two congeneric species of hermaphroditic freshwater snails (Drepanotrema depressissimum and D. surinamense), as well as conditions for multiplexing and simultaneously genotyping sets of loci. D. depressissimum had high mean gene diversity (> 0.8) and large number of alleles (= 10.9) per population. Most loci and populations were at Hardy–Weinberg equilibrium. The F_ST estimates were low among lesser Antilles populations and larger with a Venezuelan population. Far less diversity was found in D. surinamense with mean number of alleles and gene diversity per population of 2.8 and 0.34, respectively. Very few heterozygous individuals were observed. The most likely explanation is a high selfing rate (> 0.825) in this species. Unsurprisingly, the F_ST estimates among populations were much higher than in D. depressissimum. Cross‐species amplification in three congeneric species was on the whole unsuccessful.     

Interactions between freshwater snails and tadpoles: competition and facilitation

Summary Freshwater snails and anuran tadpoles have been suggested to have their highest population densities in ponds of intermediate size where abiotic disturbance (e.g. desiccation) is low and large predators absent. Both snails and tadpoles feed on periphytic algae and, thus, there should be a large potential for competitive interactions to occur between these two distantly related taxa. In a field experiment we examined the relative strength of competition between two closely related snail species, Lymnaea stagnalis and L. peregra, and between L. stagnalis and tadpoles of the common frog, Rana temporaria. Snail growth and egg production and tadpole size at and time to metamorphosis were determined. Effects on the common food source, periphyton, were monitored with the aid of artificial substrates. Periphyton dry weight was dramatically reduced in the presence of snails and/or tadpoles. There were no competitive effects on growth or egg production of the two snail species when they were coexisting. Mortality of L. peregra was high (95%) after reproduction, but independent of treatment. Growth of L. stagnalis was reduced only at the highest tadpole densities, whereas egg production was reduced both by intraspecific competition and by competition with tadpoles. Differences in egg production were retained after tadpole metamorphosis. Tadpole larval period increased, weight of metamorphosing frogs decreased and growth rate was reduced as a function of increasing tadpole density. However, contrary to expectation, snails had a positive effect on tadpole larval period, weight and growth rate. Further, in experimental containers without snails there was a dense growth of the filamentous green alga Cladophora sp. We suggest that the facilitative effects of snails on tadpoles are due to an indirect mutualistic mechanism, involving competition between food sources of different quality (microalgae and Cladophora sp.) and tadpoles being competitively dominant over snails for the preferred food source (microalgae). In the presence of tadpoles snails will be forced to feed on low-quality Cladophora, increasing nutrient turnover rates, which results in enhanced productivity of microalgae, increasing tadpole food resources. Thus, tadpoles have a negative effect on snails through resource depression, while snails facilitate tadpole growth through an indirect enhancement of food availability.     

The effects of spatial habitat structure on population variability of freshwater snails

Experiments were conducted to examine the effects of a habitat's spatial structure on population variability in two species of freshwater snails (Physa acuta and Austropeplea ollula). To alter the spatial structure of the habitat, vinyl chloride plates were hung in experimental tanks, providing three types of spatial structure: Complex structure, Simple structure and Control (no structure). In Experiment 1, the average number of individuals in a tank did not differ among the three types of structure 2 months after the introduction of the snails, but the variability of the number of individuals in the Complex structure tanks was lowest, whereas the variability in the Control tanks was highest. In Experiment 2, in addition to the spatial structure of the habitat, three types of species interaction were designed as experimental treatments: only P. acuta was introduced into the tanks (P. acuta tanks), only A. ollula was introduced into the tanks (A. ollulatanks) and both P. acuta and A. ollula were introduced into the tanks (two-species tanks). For the P. acuta tanks, the variability of the number of P. acuta individuals in the Complex structure tanks was lowest, and the variability in the Control tanks was highest when the effect of the number of individuals in a tank was subtracted. For the A. ollula tanks and the two-species tanks, there were no significant differences in the variability of the population size among the different treatments of spatial structure. The spatial distribution of P. acuta was more uniform than the distribution of A. ollula on the plates of complex structure. Our results indicate that the spatial structure of the habitat influences the variability of population size (the variance of the number of individuals in different populations during the earlier period after the introduction of the snails), but the effects depend on the spatial behavior of individuals and the interaction with other species.     

Relationships between life-history strategies of European freshwater fish species and their habitat preferences

1. Focusing on the current environmental characteristics, the ‘habitat template’ theory proposes that life‐history strategies summarise how evolution has shaped species to cope with the temporal and spatial variability of their present environment. The hierarchical ‘landscape filters’ concept predicts that the distribution of species reflects their specific traits that allow them to pass through multiple habitat filters. Together, these theories showed the importance of identifying the functional relationships of species to selective habitat forces in order to predict the organisation and response of communities to the environment. 2. We test the relationships between life‐history traits of European freshwater fish species’ and their habitat preferences, to detect the strategies adopted by fish to cope with their current habitat. For this purpose, we use published data on species traits and habitat preferences (microhabitat hydraulics, temperature and oxygen level). We use multivariate analyses to classify fish species’ strategies and test the relationships between strategies and habitat preferences. 3. We identified a continuum of life‐history patterns between two extremes, with opportunistic and periodic species. Our study supports the idea that microhabitat hydraulics plays a more important role as a template for these species ecological strategies than temperature and oxygen level. Indeed, riffle habitats may select opportunistic species whereas weak relationships are found between species strategies and both their temperature and oxygen level preferences. In addition, the ratio between mortality and growth rate (dimensionless trait), reflecting a trade‐off between growth and survival, varied among species according to the use of their hydraulic habitat, with species using deep habitats exhibiting the highest values. 4. These general relationships between hydraulics and traits may be of importance in community ecology to develop predictive models to understand how fish communities change with the hydraulic environment.     

Freshwater snails of East Caprivi and the lower Okavango River Basin in Namibia and Botswana

A systematic account is given of the aquatic gastropod fauna of the lower Okavango River in Namibia and Botswana, and of the East Caprivi area in Namibia, based on collections made mostly in 1983–86 from about 100 different sites. A total of 20 living species are reported, 9 of them for the first time from this area: Bellamya monardi, Lobogenes michaelis, Cleopatra elata, Afrogyrus coretus, Segmentorbis angustus, S. kanisaensis, Bulinus scalaris, B. depressus and B. tropicus. All are found outside this area and most are widely distributed Afrotropical species. Some do not occur farther south than the Okavango Delta, while others reach a south-western limit here but occur at greater latitude in the eastern tropical corridor on the coast of Natal. Bulinus globosus and Biomphalaria pfeifferi occur throughout the study area and are intermediate hosts for schistosome parasites of man and livestock.     

Geographic and ecological patterns in Turkish land snails

The distribution of Turkish land snails has been examined, using data from a monograph by H. Schütt (1993). Turkey has been divided into eight regions for purposes of describing localization of fauna. On average, species occupy 1.7 regions. About 36% of the fauna is known from Turkey alone. There are affinities with Europe, the Caucasus, the eastern Mediterranean and the Levant and Middle East. The influence of neighbouring faunas shows up when the similarities of the eight regions are clustered. As usual, the fauna contains a high spired and a discoidal mode of shell shape, with species covering a wide range of sizes. Clausiliacea occupy a higher mode than other high spired species, while Helicacea become progressively more equidimensional from small to large species. The pattern of shell size and shape varies between regions, smaller and high spired species being most common in cooler and damper parts, larger discoidal species in parts with Mediterranean or continental dry climates. A test for evidence that animals of the same shape and size are more likely to be allopatric than sympatric failed to show that they were. The fauna is dominated by a few families to a greater extent than that of Europe, and is more like that of the isolated Madeiran archipelago. It is suggested that the Turkish fauna still shows evidence of external penetration with some local radiation, in the manner of the oceanic islands, and has not evolved to become a balanced assemblage such as is seen in Europe.     

Foodborne uptake and sublethal effects of copper and zinc to freshwater snails

Snail habitat selection was strongly influenced in thisresearch by measured copper (Cu) contribution from a powerplant discharge. Laboratory feeding studies showed that thesnail Leptoxis praerosa significantly bioconcentrated Cuwhen fed aufwuchs containing 564 (±269) µg Cu g^-1but did not have significant cellulolytic enzyme activityimpairment. No foodborne zinc (Zn) bioconcentration was foundfrom aufwuchs containing up to 20 000 (±18 400) µg Zn g^-1. These results suggest that water column Cuconcentrations leading to impairment via feeding mechanismscan be an order of magnitude higher than concentrations causingimpairments via waterborne exposures. Therefore, foodborneuptake might be expected to contribute to toxicity rather thandominate toxicity in most conditions where waterborneconcentrations of metals occur. Changes in food qualityappeared to have a greater overall effect on snail populationsthan foodborne uptake of metals alone. Snail populations took2 years to recover following intensive metal treatment on theplant discharge and subsequent reduction of measured metalconcentrations in both water and aufwuchs.     

Latitudinal, habitat and substrate distribution patterns of freshwater ascomycetes in the Florida Peninsula

Freshwater ascomycetes are important decomposers of dead woody and herbaceous debris in aquatic habitats. Despite evidence of their ecological importance, latitudinal, habitat and substrate distributional patterns of freshwater ascomycetes are poorly understood. In this study, we examined the latitudinal and habitat distributional patterns, and substrate recurrences of freshwater ascomycetes by collecting dead submerged woody and herbaceous debris in lentic and lotic habitats at five selected sites along a north-central-south, temperate–subtropical latitudinal ecotone in Florida. One hundred and thirty-two fungal taxa were collected during the study. Seventy-four were meiosporic and 56 were mitosporic ascomycetes, while two species were basidiomycetes. Canonical analyses of principal coordinates (CAP) and Sørenson’s similarity index of species based on presence/absence data revealed a high turnover in species composition between the northern and southern sites, indicating a change in species composition along the temperate–subtropical latitudinal ecotone of the Florida Peninsula. Results from the ordination analysis indicated that freshwater ascomycete community composition is not significantly different between lentic and lotic habitats in Florida. The geographically broadly distributed species and species commonly found in Florida occurred in both habitats, whereas a number of new or rare species occurred in either lentic or lotic habitats, but not both. The same freshwater ascomycete species did not necessarily occur on both woody and herbaceous debris; of the 132 taxa collected, 100 were reported only on woody debris; 14 species occurred exclusively on herbaceous debris; and 18 species were found on both woody and herbaceous debris in lentic or lotic habitats. Implications of data from this study to the conservation and knowledge of biodiversity for freshwater ascomycetes is discussed.     

Australian land snails: a review of ecological research and conservation approaches

Land snails are an important yet often neglected component of Australia's biological diversity. Despite high levels of diversity within this group and the identification of many narrow range endemic species as being of conservation concern, there have been few detailed studies that document the ecology and conservation requirements of the group. A range of threats has been suggested, yet relatively few have been rigorously assessed. Whilst factors such as land clearing are readily apparent and have resulted in extinctions, other threats such as climate change are not well understood. This paper reviews studies conducted on terrestrial molluscs in Australia and highlights the need for further targeted ecological research, given the likely level of on-going threats. We urge researchers to apply rigorous approaches to data collection that will enable a deeper understanding of the factors governing distribution and abundance. Approaches used in other areas of conservation biology offer considerable scope for application to land snails and for the development of appropriate conservation strategies.     

Distribution and ecology of freshwater sponges in Connecticut

A survey of Connecticut lakes and rivers revealed the presence of 7 species of freshwater sponge: Spongilla lacustris, Ephydatia muelleri, Eunapius fragilis, Anheteromeyenia ryderi, A. argyrosperma, Corvomeyenia carolinensis, and Corvospongilla novaeterrae in order of decreasing frequency of occurrence. Corvomeyenia carolinensis has not been reported previously beyond its type locality in South Carolina. In addition, microscleres of Spongilla lacustris, Anheteromeyenia-like megascleres, Ephydatia muelleri-like megascleres, and smooth megascleres (amphioxeas), which could not be assigned to a particular species, were found in surface sediments from lake cores. Spongilla lacustris inhabiting small rivers produced brown, thick-capsuled gemmules during the summer and yellow, thin-capsuled gemmules during the fall. The thick-capsuled gemmules, but not the thin-capsuled gemmules, are tolerant of desiccation; and populations of Spongilla lacustris and Ephydatia muelleri survived severe drying of their habitats during the summer.     

Crayfish predation on the common pond snail (Lymnaea stagnalis): the effect of habitat complexity and snail size on foraging efficiency

Optimal foraging theory was used to explain selective foraging by the introduced signal crayfish (Pacifastacus leniusculus) on the thin-shelled common pond snail (Lymnaea stagnalis). Crayfish predation efficiency was studied in relation to habitat complexity and snail size. In a pool experiment (area 1.3 m²) single adult crayfish were allowed to feed on four size classes of snails for one week. A pair-wise preference trial (aquarium experiment) tested if adult crayfish selectively predated on particular size classes of snail and if prey value (expressed as snail dry mass per handling time) could explain the size range of snails chosen. Crayfish preferred the smallest size classes of snails in both pool and aquaria experiments. In the pool experiment crayfish had a strong effect on snail survival. Habitat complexity did not affect overall snail survival, but resulted in reduced predation pressure on the smallest size classes of snails. Handling time and shell-thickness increased exponentially with increasing snail size, and the two smallest size classes had the highest prey values. The results suggest that crayfish can structure the abundance and size distribution of thin-shelled snails, through size-selective predation and reduction of macrophytes. The mechanisms behind the choice of snails may be based on prey value and reduced exposure time to predators and conspecifics. Crayfish effects on snail size distribution may be less pronounced in complex habitats such as macrophyte beds. This revised version was published online in July 2006 with corrections to the Cover Date.     

Relative importance of direct and indirect interaction among individual snails

Individual organisms interact directly through behavior, and indirectly through resource consumption and environment modification. The effects of different kinds of interactions on individual growth and reproduction will differ. Freshwater snails may interact directly for food resources and indirectly through substances dissolved in water. I separated the effects of the direct behavioral interaction and indirect interaction through waters using laboratory experiments with freshwater snails Physa acuta. Behavioral direct interaction have negative effects on the growth, but indirect interaction through water environments has positive effect on the growth. The importance of distinction of different kinds of interactions were discussed.     

The freshwater snails (Gastropoda) of Iran, with descriptions of two new genera and eight new species

Using published records and original data from recent field work and revision of Iranian material of certain species deposited in the collections of the Natural History Museum Basel, the Zoological Museum Berlin, and Natural History Museum Vienna, a checklist of the freshwater gastropod fauna of Iran was compiled. This checklist contains 73 species from 34 genera and 14 families of freshwater snails; 27 of these species (37%) are endemic to Iran. Two new genera, Kaskakia and Sarkhia, and eight species, i.e., Bithynia forcarti, Bithynia starmuehlneri, Bithynia mazandaranensis, Pseudamnicola georgievi, Kaskakia khorrasanensis, Sarkhia sarabensis, Valvata nowsharensis and Acroloxus pseudolacustris are described as new to science; Ecrobia grimmi (Clessin & Dybowski, 1888), Heleobia dalmatica (Radoman, 1974) and Hippeutis complanatus (Linnaeus, 1758) are reported for the first time from Iran. Additional field work is highly desirable for a more appropriate evaluation of the extant freshwater snail biodiversity in Iran.     

中国驴的地理生态和种群生态

一、驴的起源、驯养与生态环境的关系驴(Equus asinus Vulgaris)在动物分类学上与马是同属而异种。野生驴种有两种:(1)騑驴(E.asinus Taeniopus),亦称非洲野驴,它包括在中央撒哈拉生存的努比亚驴和从埃塞俄比亚到红海沿岸生存的索马驴,栖息在非洲东北部到南部;(2)骞驴(E.hemionus),亦称亚洲野驴,分布于中亚细亚、阿拉伯和中国西部。     

Vertical migrations in two hygrophilous species of micro‐snails in relation to time of the year and habitat type

The aim of this study was to investigate vertical migration behaviors in two species of hygrophilous micro‐snails, Vertigo moulinsiana and Vertigo angustior, in relation to the time of the year (spring and summer) at two sites that differ in ground water level (periodically inundated site and non‐inundated site). The study shows different patterns of vertical migrations in the studied species. Vertigo angustior demonstrated a strong affinity to the litter layer (a weak tendency for vertical movements), independent of the time of year and site studied. By contrast, V. moulinsiana showed a clear tendency for vertical migrations, which differed depending on the time of year and site. These differences may be related to the spatial segregation of microhabitats used by these two species at the sites studied and to differences in the ability to resist inundation. Vertigo angustior is associated with microhabitats which are not subjected to prolonged inundation and tolerates a brief submersion. The periodic character of vertical migrations may suggest the effect of endogenous factors related to reproduction in V. moulinsiana. Some plasticity of this behavior in relation to habitat conditions demonstrated by this species may be an adaptation to live in unpredictably flooded environments.     

Collaboration in scientific research: a critical need for freshwater ecology

1. Collaboration means actively working together to achieve things which could not be done alone. This article attempts to provide an overall, unified, guiding framework for collaboration in freshwater ecology by discussing aspects of collaboration at individual and organizational levels, and addressing international linkages.
2. The essential elements of collaboration are communication and trust, and effective project management. Barriers to effective collaboration include competition, organizational cultures and organizational instabilities.
3. The success of collaboration can be measured by tangible benefits such as increased numbers of peer-reviewed publications, the production of working models and a number of intangible benefits.
4. Interactions between individuals lie at the heart of an effective collaboration; organizational arrangements should facilitate this interaction. Some governments are encouraging collaboration to increase cost efficiency and allocate accountability. This trend should continue on an international level.
5. Collaboration is a key to future research in freshwater ecology.     

Role of fungi in freshwater ecosystems

There are more than 600 species of freshwater fungi with a greater number known from temperate, as compared to tropical, regions. Three main groups can be considered which include Ingoldian fungi, aquatic ascomycetes and non-Ingoldian hyphomycetes, chytrids and, oomycetes. The fungi occurring in lentic habitats mostly differ from those occurring in lotic habitats. Although there is no comprehensive work dealing with the biogeography of all groups of freshwater fungi, their distribution probably follows that of Ingoldian fungi, which are either cosmopolitan, restricted to pantemperate or pantropical regions, or in a few cases, have a restricted distribution. Freshwater fungi are thought to have evolved from terrestrial ancestors. Many species are clearly adapted to life in freshwater as their propagules have specialised aquatic dispersal abilities. Freshwater fungi are involved in the decay of wood and leafy material and also cause diseases of plants and animals. These areas are briefly reviewed. Gaps in our knowledge of freshwater fungi are discussed and areas in need of research are suggested.