Non-indigenous land and freshwater gastropods in Israel

Few comprehensive works have investigated non-indigenous snails and slugs as a group. We compiled a database of non-indigenous gastropods in Israel to explore how they arrived and spread, characteristics of their introduction, and their biological traits. Fifty-two species of introduced gastropods are known from Israel (of which nine species subsequently went extinct): 19 species of freshwater snails and 33 species of terrestrial gastropods. The majority of these species are found only in human-dominated habitats. Most of those found in natural habitats are aquatic species. Most snails are introduced unintentionally from various parts of the Holoarctic region, reaching Israel as stowaways with horticultural imports and the aquarium trade, but some are brought intentionally to be used as pets or for food. Because the study of this group in Israel is very limited, information regarding their distribution in the country and their effects on other species is incomplete. Though only nine species of non-indigenous snails have been found to date in natural habitats, some of these are very abundant. More information and research is required to enable effective management schemes.     

Reproductive systems and breeding condition in Nerita birmanica (Archaeogastropoda: Neritacea) from Malayan mangrove swamps

The complex reproductive systems of the mangrove-dwelling Nerita birmanica are described and related to those of other neritids. Gonad condition in both sexes and numbers of spermatophores in males and females varied slightly during a one-year survey. It is concluded that a slight tendency for larger number of full ovaries with big oocytes to occur in collections taken shortly before full and new moon does not represent a significant lunar cycle of gonad activity since almost all gonads bore gametes in all stages of development at all times of year. It appears merely that ovulation may be held up during relatively rainless periods after which substantial rain is followed by reduced ovaries lacking large oocytes. In brief, breeding appears to be continous with but slight variation which does not consistently follow observable environmental factors.     

Reproduction in the Malayan freshwater cerithiacean gastropod Melanoides tuberculata

Melanoides tuberculata in the Kuala Lumpur area of Malaysia were found to be entirely female, reproducing parthenogenetically. The reproductive system is extremely simple in structure and histology, lacking all the glandular developments common in most mesogastropods. Eggs pass into a cephalic brood-pouch where they develop to juveniles of 5–6 shell whorls before emergence. Numbers of developing young in the brood-pouches increased with shell height of the parents except for a decline in the few very largest snails. The highest brood-pouch count was 265, but average counts were much lower. 85 % of developing young in the brood-pouches were very early stages from eggs to embryos of one whorl only, perhaps implying that many eggs fail to develop successfully to young snails. Three localities studied yielded consistently different brood-pouch counts, implying variation in fecundity. Juveniles emerge from the brood-pouch most commonly between nightfall and midnight and normal emergence seems to require diurnal alternation of light and dark. In continuous darkness, brood-pouch counts increased markedly, perhaps as a result of greater activity and feeding during darkness. Several features of the reproductive biology suggest that Melanoides might become a useful experimental animal in freshwater studies.     

Rissooidean freshwater gastropods from the Vanuatu archipelago

During expeditions to Santo and the Torres islands belonging to the Vanuatu archipelago in 2006 and 2007, ten new species of tateid gastropods confined to springs, the upper most, slowly flowing regions of streams or the groundwater had been discovered. These species were now described based on shell morphology and anatomy. In accordance with geography, these characters placed the species from Vanuatu between those from New Caledonia and Fiji, suggesting a stepping stone-like dispersal across the Pacific with an origin in New Zealand and the far end on the Austral islands. We also assessed the threat status of the new species according to the IUCN Red List criteria and concluded that they should be amended by explicit incorporation of the scale of potential human impact or stochastic natural events relative to the size of the habitat of organisms.     

Global diversity of gastropods (Gastropoda; Mollusca) in freshwater

The world’s gastropod fauna from continental waters comprises ∼4,000 valid described species and a minimum of 33–38 independent lineages of Recent Neritimorpha, Caenogastropoda and Heterobranchia (including the Pulmonata). The caenogastropod component dominates in terms of species richness and diversity of morphology, physiology, life and reproductive modes and has produced several highly speciose endemic radiations. Ancient oligotrophic lakes (e.g., Baikal, Ohrid, Tanganyika) are key hotspots of gastropod diversity; also noteworthy are a number of lower river basins (e.g., Congo, Mekong, Mobile Bay). But unlike many other invertebrates, small streams, springs and groundwater systems have produced the most speciose associations of freshwater gastropods. Despite their ecological importance in many aquatic ecosystems, understanding of even their systematics is discouragingly incomplete. The world’s freshwater gastropod fauna faces unprecedented threats from habitat loss and degradation and introduced fishes and other pests. Unsustainable use of ground water, landscape modification and stock damage are destroying many streams and springs in rural/pastoral areas, and pose the most significant threats to the large diversity of narrow range endemics in springs and ground water. Despite comprising only ∼5% of the world’s gastropod fauna, freshwater gastropods account for ∼20% of recorded mollusc extinctions. However, the status of the great majority of taxa is unknown, a situation that is exacerbated by a lack of experts and critical baseline data relating to distribution, abundance, basic life history, physiology, morphology and diet. Thus, the already considerable magnitude of extinction and high levels of threat indicated by the IUCN Red List of Threatened Species is certainly a significant underestimate. Guest editors: E. V. Balian, C. Lévêque, H. Segers and K. Martens Freshwater Animal Diversity Assessment     

Range size and environmental calcium requirements of British freshwater gastropods

Calcium is an essential requirement for the successful growth and development of gastropod molluscs. Data for British freshwater gastropods were used to examine the relationship between environmental calcium requirements and British and European range sizes. At both spatial scales calciphile species, which require a high level of environmental calcium, had significantly smaller range sizes than species able to exploit a wide range of environmental calcium levels. However, at least in Britain, range size may also be influenced by the availability of suitable habitat. British and European range sizes were significantly correlated. This study provides evidence for niche‐based explanations of range size variation, and suggests that both niche breadth and niche availability are important in determining range size.     

Reproductive ecology of Brazilian freshwater fishes

We used metadata on nine reproductive traits of 67 species of Brazilian iteroparous, oviparous, teleost freshwater fishes to test phenotypes associations to discriminate species that only spawn in large rivers (lotic fishes) from those capable to spawn in lentic habitats (lentic fishes). We tested the hypothesis that lotic fishes present spawning migration, shorter spawning season, single spawning, no parental care, free eggs, higher relative fecundity, faster embryogenesis, and larger size, while lentic fishes present no spawning migration, longer spawning season, multiple spawning, parental care, adhesive eggs, lower relative fecundity, slower embryogenesis, and smaller size. Our analyses supported the hypothesis but not all phenotypic associations satisfied it, specifically with regard to lentic fishes or to pairs of phenotypes typical of lentic fishes. We also concluded that spawning in large rivers is a better predictor of bionomic characters than spawning in lentic habitats, and lotic fishes are specialists compared to lentic fishes.     

Relationship between freshwater gastropods and plant communities reflecting various trophic levels

Plant communities were examined in ponds in Brittany (north-west France) and then classified into six types reflecting different trophic levels: oligotrophic, oligodystrophic, mesotrophic, meso-dystrophic, meso-eutrophic an eutrophic. In 45 of these ponds, aquatic snails were sampled in order to determine the relationship between the gastropod species richness and the water trophic levels as indicated by plant community types. The second aim of this study was to determine whether some gastropod species were characteristic of a particular trophic level. The number of plant communities in the ponds was also taken into consideration.A trophic gradient was found along the F1 axis on the principal plane of the correspondence analyses. The species richnesses low or zero and especially the lymneid, Lymnaea glabra were close to the oligo-dystrophic and oligotrophic communities. In contrast, the highest numbers of snail species (5 and above) were found in the most eutrophic ponds where Hippeutis complanatus, Planorbis planorbis, Lymnaea stagnalis and Planorbarius corneus were particularly common. The latter species inhabited the ponds including on average the greatest number of macrophyte communities but no significant differences were found between snail species. The ponds which contained the greatest numbers of plant communities included the richest gastropod communities (7 and more) but also the poorest ones (0 or 1 species). Relationships between freshwater snails, macrophytes and trophic levels are discussed.Laboratoire de Zoologie et d'Ecophysiologie     

Effects of vertebrate predation on freshwater gastropods: an exclosure experiment

A field experiment with predator exclosures was performed in a pond in Southern Sweden to evaluate the effects of vertebrate predators on the diversity, density and distribution of freshwater gastropods. Ten exclosures (1 × 1 × 1.5 m) were erected in the nearshore vegetation at a waterdepth of 0.5–0.7 m in early June 1983 so that they included different amounts and species of macrophytes. The exclosures and cageless controls were sampled for macrophytes and gastropods at the end of the summer. The density of gastropods in the controls, exposed to predators, was positively correlated to the abundance of macrophytes. No such correlation existed in the exclosures. Further, the density of gastropods was significantly higher in the exclosures than predicted by the regression between gastropods and macrophytes in the controls. There was no difference between species composition of gastropods between controls and exclosures, but the number of species and the density of gastropods were lower in the macrophyte stands dominated byScirpus lacustris than in the more complex stands dominated bySparganium erectum. These results indicate that vertebrate predation is a major structuring force of benthic freshwater gastropod communities.     

Introduction,distribution, spread,and impacts of exotic freshwater gastropods in Texas

We examined the patterns of distribution, vectors of introduction, and potential ecological impacts of freshwater exotic species in Texas over the last 45 years. Currently, five species of exotic gastropods are established: channeled-type applesnail (Pomacea insularum), red-rim melania (Melanoides tuberculatus), quilted melania (Tarebia granifera), giant rams-horn snail (Marisa cornuarietis), and Chinese mysterysnail (Cipangopaludina chinensis). In contrast to the northern part of the US, where shipping appears to be the most important vector for the introduction of aquatic invasive species, aquarium and ornamental trade dominated among unintentional vectors of introduction of all freshwater exotics in Texas, resulting in different patterns of distribution, spread, and ecological impacts. The rate of spread of exotic gastropods in Texas varied from 39 waterbodies colonized over 18 years for P. insularum to only three waterbodies during last 45 years for C. chinensis. Four of five exotic gastropods were found in highly vulnerable aquifer-fed springs and rivers, which contain numerous endemic and endangered species. The fifth species, Pomacea insularum, is an agricultural pest. Potential negative ecological effects of exotic gastropods include impacts on wetlands and wetland restoration, competitive exclusion of native snails, and the introduction of exotic parasites, trematodes, which could infect fish and waterfowl, including federally protected species. Aquifer springs with stable temperature regimes are refuges for both cold and warm intolerant species. Handling editor: D. Dudgeon     

Contrasting demographic history and phylogeographical patterns in two Indo-Pacific gastropods

Marine species with ranges that span the Indo-Australian Archipelago (IAA) exhibit a range of phylogeographical patterns, most of which are interpreted in the context of vicariance between Indian and Pacific Ocean populations during Pliocene and Pleistocene low sea-level stands. However, patterns often vary among ecologically similar taxa, sometimes even within genera. This study compares phylogeographical patterns in two species of highly dispersive neritid gastropod, Nerita albicilla and Nerita plicata, with nearly sympatric ranges that span the Indo-Pacific. Mitochondrial COI sequences from >1000 individuals from 97 sites reveal similar phylogenies in both species (two divergent clades differing by 3.2% and 2.3%, for N. albicilla and N. plicata, respectively). However, despite ecological similarity and congeneric status, the two species exhibit phylogeographical discordance. N. albicilla has maintained reciprocal monophyly of Indian and Pacific Ocean populations, while N. plicata is panmictic between oceans, but displays a genetic cline in the Central Pacific. Although this difference might be explained by qualitatively different demographic histories, parameter estimates from three coalescent models indicate that both species have high levels of gene flow between demes (2Nem>75), and share a common history of population expansion that is likely associated with cyclical flooding of continental shelves and island lagoons following low sea-level stands. Results indicate that ecologically similar, codistributed species may respond very differently to shared environmental processes, suggesting that relatively minor differences in traits such as pelagic larval duration or microhabitat association may profoundly impact phylogeographical structure.     

Reproductive strategies in rain-pool dwellers and the model freshwater insect

Reproductive strategies of principal rain-pool midges, Chironomus imicola and Chironomus pulcher are investigated in field and laboratory. The two species are able to lay at least one full clutch without access to food in the adult stage. Since females are also capable of flying for extended periods without feeding, they carry out both adult functions (i.e. dispersal and reproduction), without taking energy from the terrestrial environment.We argue that independance of the terrestrial environment is adaptively appropriate to animals able to exploit a larval habitat rich in food and low in interspecific competition. However, there are costs to this strategy because freshwaters, and notably rain-pools, are unpredictable habitats inclined to dry up periodically. These species must, therefore, constantly colonise new pools by laying eggs. We show that adult females can resort to feeding and that if they do so the energy acquired goes to the production of further eggs with a consequent increase in colonizing ability.As a test of this hypothesis that there is a relationship between duration of habitat and the number of eggs layed, we have examined a third rain-pool dwelling chironomid, Polypedilum vanderplanki. This species is unique among insects in that larvae are able to survive desiccation of their tissues. For them there is thus not the same incentive to leave before the home pool dries. So, P. vanderplanki does not need to be a colonizer. Observations confirm this view since P. vanderplanki adult females, even when fed, lay no more than one clutch of eggs. Consequently, reproduction and feeding in the adult female are related to the way in which duration of the habitat is perceived. We suggest that, measured against P. vanderplanki, Chironomus species provide a useful model of the ideal freshwater animal.     

Relative vulnerability of six freshwater gastropods to the leech Nephelopsis obscura (Verrill)

SUMMARY. 1. The vulnerability of six species of freshwater snails to the leech Nephelopsis obscura was determined in laboratory predation experiments.
2. Nephelopsis was unable to prey on prosobranch snails with an operculum, but did consume certain pulmonate species though predation rates were low, ranging from one to two snails per leech per night at 20°C. Apparently, Nephelopsis does not actively select prey, but merely consumes those species most easily handled.
3. Among pulmonates, leeches captured species in the following order: Physa gyrina (Say), Helisoma anceps (Menke). Lymnaea emarginata (Say) and Helisoma trivolvis (Say). Susceptibihty of size classes varied among snail species.
4. Neither environmental structure, such as cobble or macrophytes, nor gastropod escape behaviors, such as clamping to substrates or vertical migration away from bottom-feeding leeches, lowered capture rates by Nephelopsis.
5. In 2 years sampling, only one of seven lakes, however, had appreciable abundances of Nephelopsis. It is therefore suggested that the rarity, low feeding rates, and lack of strong gastropod preference limit the effect of Nephelopsis on field gastropod distributions.     

Selfing and outcrossing in hermaphrodite freshwater gastropods (Basommatophora): where, when and why

Hermaphrodite freshwater snails offer the opportunity to study the evolution of selling and outcrossing. Laboratory studies using genetic markers have shown that selling is possible in all species investigated, although outcrossing seems to be favoured in most. Predominance of outcrossing is promoted by sperm storing for up to several months. Studies using electrophoretic markers also suggest that outcrossing is the main breeding system in natural populations. However, heterozygote deficiencies found in some populations could indicate (partial) selfing. The evolution of self-fertilization and cross-fertilization is driven by numerous forces. Inbreeding depression is thought to select for outcrossing, and has been experimentally investigated in hermaphrodite freshwater snails. Other traits have evolved that prevent selfing. On the other hand, selfing could be selected under low density, or to preserve local adaptation, or when aphallic individuals occur within populations.     

Reproductive strategies and early development of three freshwater gobies

Three species of gobiid fish inhabit the freshwater Lake Trichonis of western Greece. Two of these species, Economidichthys pygmaeus and E. trichonis are endemic, and the third is the widespread Knipowitschia caucasica . There are habitat separations between the three species, E. pygmaeus and E. trichonis prefer vegetated areas, the first being fully demersal at all stages of development and the second being semi-demersal. Knipowitschia caucasica prefers sandy bottoms and is distributed in shallower waters. Female E. pygmaeus and E. trichonis spawn in nests prepared by the males in the cavities of broken reeds. The males subsequently guard the eggs until they hatch, with females playing no role in parental care. Economidichthys trichonis is probably the smallest freshwater European species. Its eggs are ovoid, measuring about 0.64 × 0.58 mm, from which tiny, unpigmented and incompletely developed pelagic larvae hatch out after an incubation period lasting less than 1 day at a water temperature of 19.5° C. The eggs of E. pygmaeus are cylindrical and larger, measuring about 2.38 × 0.89 mm, from which relatively large, strongly pigmented and ontogenetically more advanced larvae hatch out after a longer incubation period. Both species reproduce only once in their lifetime, at the age of 1 year, and die shortly after spawning, but the breeding season involves several spawnings by each individual fish. These biological, developmental and reproductive characteristics are discussed in relation to current theories on evolution of life-historics.     

The geography of evolutionary opportunity: hypothesis and two cases in gastropods

Evolutionary innovations that require or provide increased per-capitaenergy budgets and competitive performance should appear attimes and in places where resources are abundant and accessibleand where predators and competitors impose intense selection.By contrast, innovations without functional benefits shouldbecome established in productive environments under conditionsof weak selection from enemies. I confirmed these predictionsin comparative studies of two types of innovation in gastropodshells. The labral tooth, a structure facilitating predation,appeared in 45 Cenozoic clades of marine gastropods, with thehighest concentrations originating during the early Miocene,late Miocene, and Pliocene, all times and sites of high planktonicproductivity, large expanses of warm shallow water, and diversepredator-rich biotas. Left-handed coiling, a condition withno obvious survival benefits, arose 19 times independently inright-handed clades. Most left-handed clades, including eightarising in regions outside the tropics, evolved in productiveregions where the larva and/or the adult is shielded from intensepredation. The times and places of origin of new traits in cladesthus offer insights into the geography of evolutionary opportunity.     

Glacidorbidae (Glacidorbacea: Basommatophora), a new family and superfamily of operculate freshwater gastropods

Some aspects of the anatomy of Glacidorbis hedleyi Iredale are described and its systematic position is reviewed. Glacidorbis is a genus of operculate gastropods found in Australia and South America, the species of which possess a monoseriate or triseriate radula and brood their embryos in the pallial cavity. Glacidorbis hedleyi is a protandrous hermaphrodite with, sometimes, 50% or more of large individuals remaining as males. The reproductive system is diaulic, with the penis being lost in mature females. It feeds on the tissue of freshly killed or wounded animals and has a very simple alimentary canal. A new family and superfamily is created for Glacidorbis within the Basommatophora. A new subgenus, Gondwanorbis , is introduced for Glacidorbis magallanicus Meier-Brook & Smith from Chile, S America.     

Long-term dynamics and community structure of freshwater gastropods exposed to parasitism and other environmental stressors

1. Freshwater communities are subject to various abrupt environmental disturbances and increasing pollution levels in their habitat. According to the nature and the periodicity of disturbances (i.e. punctuated, recurrent or continuous), one may expect different kinds of response of the target gastropod communities. 2. The gastropod community of a French lake has been investigated for 10 years to study its responses to three main environmental disturbances: supra‐seasonal droughts, recurrent proliferations of cyanobacteria and parasitism by trematodes. The relationship between this latter factor, considered as a continuous stressor, and the gastropod community was a particular focus. 3. A total of 13 280 gastropods belonging to 17 species (mostly Pulmonata with Planorbidae as the dominant family) have been sampled in the lake over the 10‐year time series. Species composition of the gastropod community varied strongly during the study period as did species richness (0–14, mean of 6.5 ± 0.4 species) and abundance of gastropods (0–4456, mean of 192 ± 72 individuals). Trematode larvae belonging to 11 morphotypes of cercariae were detected in 15 of the 17 species of gastropods and had a total prevalence of 2.9%. 4. Droughts (punctuated stressor) were responsible for the disappearance of nearly all gastropod species, and thus represent a severe environmental stressor for them. Nevertheless, the extent of this stressor was limited since the gastropod community was highly resilient. 5. Recurrent proliferations of toxic cyanobacteria (recurrent stressor) coincided with the large decline of the gastropod community, corresponding to a strong decrease in abundance and species richness. Intoxication of gastropods by toxic cyanobacteria was demonstrated by the bioaccumulation of microcystins in all gastropod tissues. 6. Trematode parasitism (continuous stressor) did not affect the gastropod community despite the possibly strong impact of parasites on some host species (those with monthly prevalence as high as 100% at some times). Indeed, abundance and species richness of gastropods were scarcely influenced by trematode prevalence or species richness.     

Shell as an indicator of the growth rate of freshwater gastropods of the family Bithyniidae

Snails of the family Bithyniidae (Gastropoda: Prosobranchia) of 29 populations (14 014 individuals) from West Siberia were examined. Guidelines for studying the growth rate of the Gastropoda based on shells were proposed. Data on the effect of abiotic and biotic factors on the Gastropoda growth rate were analyzed. The effect of trematode parthenitae on the shell growth rate was investigated for Bithynia troscheli (Paasch, 1842).