A nomenclator of extant and fossil taxa of the Valvatidae (Gastropoda,Ectobranchia)

A compilation of all supra- and (infra-) specific taxa of extant and fossil Valvatidae, a group of freshwater operculate snails, is provided, including taxa initially described in this family and subsequently classified in other families, as well as names containing errors or misspellings. The extensive reference list is directly linked to the available electronic source (digital view or pdf-download) of the respective papers.     

Radiation of crenobiontic gastropods on an ancient continental island: the Hemistomia-clade in New Caledonia (Gastropoda: Hydrobiidae)

A vast radiation of hydrobiid spring snails endemic to New Caledonia, a continental island in the Southwest Pacific known for its unique flora and fauna, is described. This radiation comprises a total of 54 named species of which 50 are new. The majority of the species belong to the most basal genus, Hemistomia, which happens to be the first one described from New Caledonia. The remaining species are attributed to four genera, Kanakyella, Pidaconomus, Caledoconcha, and Leiorhagium, which are all introduced in this paper. The radiation as a whole is characterized by the formation of the digestive gland, the stomach with an additional, ciliated proximal chamber, and the subdivision of the pallial oviduct. Whether or not a denticle situated behind the outer lip is a synapomorphy of the whole group cannot be stated with certainty. The genera are distinguished mainly by features of the genital system. For the cladistic analysis, which resulted in 419 equally parsimonious trees, only five characters could be used, and even those were not free of homoplasy. The genera Hemistomia and Pidaconomus are paraphyletic according to this analysis. In contrast to the widely accepted principles of phylogenetic systematics we retain these paraphyletic genera, because otherwise the diversification, i.e. the evolution, which has taken place within the clade could not be expressed in the classification. The majority of the species occur in very restricted areas. Twenty-six (48%) species were found in a single locality and only six species (11%) in ten or more places. The hydrobiid diversity of west coast drainages is much higher than that of river systems draining to the east. This is, at least partly, explained by the differing precipitation regimes and geological conditions of the regions considered. The west coast receives much less rainfall so that in continuous periods of drought the area of a species would be fragmented by drying up of springs and consequently gene flow between the remaining populations reduced, enhancing speciation. In addition, the west is geologically more heterogenous. Unfavourable, insular ultramafic mountains represent barriers for the dispersal along the west coast. Many of the taxa are highly threatened to become extinct in the closer future as a consequence of human activities, such as deforestation, agriculture, surface mining, or uncontrolled fires. The conservation of the unique New Caledonian radiation of crenobiontic gastropods requires a transformation of land management practices on privately-owned sites, and a more global reappraisal of the impact of fire and deforestation on water resources. This revised version was published online in July 2006 with corrections to the Cover Date.     

Physiological adjustment of the genus Limicolaria (Gastropoda: Pulmonata) during aestivation and activity in tropical agro-ecosystem

Comparisons of sympatric species inhabiting the same ecological habitat may elucidate adaptive processes. We studied the physiological patterns of two species of the genus Limicolaria (L. aurora and L. flammea) that thrive in a hot tropical habitat. We examined changes in water content, biochemical fuel reserves and haemolymph enzyme activities during aestivation and activity. Our results indicate that both species had the potential to conserve body water during aestivation. A definite pattern in foot muscle biochemical fuel reserves was observed. Both species depleted glycogen during aestivation while building up lipids. Catabolism of protein was observed during aestivation. Lactate levels and the activity of lactate dehydrogenase both decreased during aestivation, and both variables later increased at the onset of activity. Significantly higher enzyme activities were recorded during aestivation than during the active period. Stepwise discrimination analysis revealed lactate as the significant predictor of differences between the two periods, with 97.9% of the cases correctly classified. No significant correlation was observed between the measured variables and climatic data. Our results suggest that the physiological adaptation of Limicolaria is not environmentally predictable, rather it is inherently determined for ensuring physiological adjustment for survival in the tropics.     

Apomorphic and plesiomorphic ITS-1 rDNA patterns in morphologically similar snails (Stylommatophora: Vallonia), with estimates of divergence time

Morphological classification of snail shells is sometimes arbitrary and misleading in correct species delimitation. This topic is investigated in four nominal species of the minute gastropods of the genus Vallonia ( V. pulchella , V. excentrica , V. costata and V. enniensis ). First, individuals are classified according to their shell morphology. Second, variation in ribosomal internal transcribed spacer 1 DNA (ITS-1 rDNA) is analysed. Using a cladistic approach, the nucleotide positions of the ITS-1 are elucidated on apomorphic and plesiomorphic character states (outgroup= Acanthinula aculeata ; Valloniidae). The molecular data yield evidence that the morphospecies V. excentrica is a paraphyletic group, comprising just a loose arrangement of individuals with similar shells. Data on fossil shells and putative divergence time are also elucidated. In the monograph on Vallonia it has been suggested that the split between the branch of V. costata and the branch of V. pulchella , V. excentrica and V. enniensis could have been in the upper Cretaceous. Based on the ITS-1 sequence alignment and the number of variable nucleotide positions, it is suggested that the last common ancestor of both branches lived at some time during the Miocene or even the Pliocene. Therefore, the fossil stem lines of Vallonia should be newly interpreted.     

Life cycle and production of Hydrobia acuta Drap. (Gastropoda: Prosobranchia) in a hypersaline coastal lagoon

The life cycle and annual production of Hydrobia acuta was studied in a hypersaline lagoon (s = 39 in summer), forming a part of solar salt works. Quantitative random samples were taken at regular intervals over a period of 15 months using a corer, and snails collected were counted and measured. Weight and biomass was calculated from a length-weight relationship and from measurements of ash content. H. acuta was a strictly annual species in the study lagoon. Recruitment takes place over a brief period in May and June, after which the breeding population dies. Growth of the new generation was slow during summer, probably due to the unfavourably high salinity. A period of rapid growth took place in autumn coinciding with a drop in salinity caused by rainfall. In winter Hydrobia hibernated by burrowing deeply into the sediment. Growth recommenced in spring when the lagoon was reflooded, but by this time the number of survivors was low.The maximum density of snails was 6 000 m^–2 and maximum biomass 500 mg organic dry wt · m^–2. Annual cohort production was estimated as 786 mg organic dry wt · m^–2 · a^–1. These figures are low compared to other studies on hydrobiid snails, and for production in inland waters, but the value for annual P/B = 4.5 is typical for a univoltine species. The relevance of the results to foraging by wading birds (the main consumers), is discussed.     

Characterization of 13 polymorphic microsatellite loci for two land snail species, Trochulus villosus and T. sericeus (Gastropoda: Pulmonata: Hygromiidae)

Thirteen new microsatellite loci were isolated and tested on two land snail species, Trochulus villosus and T. sericeus (Pulmonata: Hygromiidae), resulting in a set of eight polymorphic markers for each species. The expected heterozygosity was high for all loci and species (between 0.616 and 0.944). Such levels of variability will allow detailed insights into the population genetic structure of some Trochulus species.     

Conchometrics, systematics and distribution of Melanopsis (Mollusca: Gastropoda) in the Levant

In this conchometric study, the systematics and distribution of the freshwater gastropod Melanopsis in the Levant are described. Of the ten species found, three are widespread, two have narrow distributions and five are known only from their type locality. Five smooth‐shelled species are recognized (buccinoidea, ammonis, dircaena, khabourensis and meiostoma). Within M. buccinoidea, Jordan Valley populations may belong to a separate subspecies. M. ammonis is clearly differentiated from buccinoidea of the nearby Jordan Valley, but less so from buccinoidea of more distant sites; differences between ammonis and meiostoma are significant but not diagnostic. Five species have ribbed shells. Within costata, four subspecies are recognized (in the northern Orontes, upper Jordan, Sea of Galilee, and in southernmost parts of the Levant). Throughout the Levant, M. buccinoidea frequently hybridizes with M. costata and fossil evidence suggests that these species have been hybridizing for the last 1.5 Myr. M. saulcyi differs from M. costata in its narrower shell and shorter, bumpier ribs and frequently hybridizes with M. buccinoidea throughout the Levant. Specimens from Homs differ from those of the Jordan Valley in their higher figurativity index, fewer ribs and lower rib density. M. germaini differs from M. costata in its more numerous ribs, M. pachya in its shorter ribs, and M. infracincta in its bumpy shell in which each rib has huge tubercles, with a pronounced ridge flanking the columella. Our conclusion that there are ten species in the Levant differs from previous studies that suggested only two subspecies of one species (or superspecies). This difference could stem from (1) our use of nonstandard as well as standard conchometrics, (2) a reappraisal of the importance of the shell vs. the radula in intrageneric systematics, and (3) differences of opinion on the subspecies concept. © 2005 The Linnean Society of London, Zoological Journal of the Linnean Society, 2005, 144 , 229?260.     

Fatty acid composition of Goniobasis virginica, Physa sp. and Viviparus malleatus (Mollusca: Gastropoda) from Lake Musconetcong, New Jersey

Gas—liquid chromatographic studies were done to determine the fatty acid composition of Goniobasis virginica Physa sp., and Viviparus malleatus (Mollusca: Gastropoda), from Lake Musconetcong, NJ, U.S.A. Palmitic acid was the predominant saturated fatty acid, followed by stearic acid, in all three molluscan species. The chief monoenes were 16:n−7, 18:1n−7; 20:1n−11+9, and 22:1n−11+13, which together accounted for all monoene fatty acids and one-quarter of the total fatty acids. Considerable amounts of linolenic acid (2.7−4.1%) and arachidonic acid (7.8−12%) were found in all three species. The percentage composition of docosahexaenoic acid (22:6n−3) was low compared to that of eicosapentaenoic acid (22:5n−3). Non-methylene interrupted dienes (20:2 NMID), characteristic of marine molluscs, ranged from 2 to 3% in the three species of freshwater snails.     

A new approach to an old conundrum--DNA barcoding sheds new light on phenotypic plasticity and morphological stasis in microsnails (Gastropoda, Pulmonata, Carychiidae)

The identification of microsnail taxa based on morphological characters is often a time-consuming and inconclusive process. Aspects such as morphological stasis and phenotypic plasticity further complicate their taxonomic designation. In this study, we demonstrate that the application of DNA barcoding can alleviate these problems within the Carychiidae (Gastropoda, Pulmonata). These microsnails are a taxon of the pulmonate lineage and most likely migrated onto land independently of the Stylommatophora clade. Their taxonomical classification is currently based on conchological and anatomical characters only. Despite much confusion about historic species assignments, the Carychiidae can be unambiguously subdivided into two taxa: (i) Zospeum species, which are restricted to karst caves, and (ii) Carychium species, which occur in a broad range of environmental conditions. The implementation of discrete molecular data (COI marker) enabled us to correctly designate 90% of the carychiid microsnails. The remaining cases were probably cryptic Zospeum and Carychium taxa and incipient species, which require further investigation into their species status. Because conventional reliance upon mostly continuous (i.e. nondiscrete) conchological characters is subject to fallibility for many gastropod species assignments, we highly recommend the use of DNA barcoding as a taxonomic, cutting-edge method for delimiting microsnail taxa.     

Associations with habitat versus geographic cohesiveness: size and shape of Bembicium vittatum Philippi (Gastropoda: Littorinidae) in the Houtman Abrolhos Islands

In the Houtman Abrolhos Islands, Western Australia, the direct-developing littorine snail Bembicium vittatum occupies a wide range of habitats, which are replicated across the three major groups of islands. Earlier studies showed that allozyme similarities followed patterns related to gene flow, independent of habitat, providing an excellent opportunity to test for associations with habitat for traits more likely to be adaptively important. As the first test for adaptive divergence, we examined variation in size and shape of shells among 131 populations in the Abrolhos Islands. Two-fold variations were found in width of adults, the allometric coefficient of height with width, and shell height scaled to a standard width. Quantification of habitat characteristics was summarized by principal components analysis. In contrast with the patterns of divergence for allozymes, shell height, adjusted for width, was strongly associated with habitat: flatter shells are found on exposed, vertical shores, while domed, more globose shells predominate in sheltered sites. This association was stronger for shape of adult-sized snails than for height scaled to an arbitrary size, highlighting the importance of using biologically relevant measures. Even highly isolated and allozymically less variable populations in tidal ponds conformed to this association. Because differences in shape are highly heritable in B. vittatum , this association of shape with habitat, independent of patterns of gene flow, indicates local adaptation. Shell size also varied with habitat, but because growth rate is highly plastic, variation in size cannot be interpreted simply in terms of adaptation. Nevertheless, the pattern of variation indicates that, within realized limits, larger size is generally favourable, but may be constrained by local conditions. Thus, variation in size signals the potential for adaptive divergence of life histories among the many, isolated populations of this species.     

Patterns and processes in a non-adaptive radiation: Alopia (Gastropoda,Clausiliidae) in the Bucegi Mountains

We studied the door-snail genus Alopia in the Southern Carpathians in Romania to better understand non-adaptive radiations and the processes that determine their course. Alopia in the Bucegi Mountains offers the opportunity to study all stages of a radiation within a few kilometres. The species (as defined by the differential fitness species concept) in the most advanced stage of the radiation differs from other species in the genitalia and co-occurs with other species. The least advanced stages are genetically differentiated clusters of populations that are geographically separated from other clusters but are not yet morphologically differentiated. Differentiation does not increase with a constant rate as shown by a lineage that was separated early in the evolution of the genus but fused with other taxa upon secondary contact. Since non-adaptive radiation cannot be accelerated by divergent natural selection beyond the slow pace of speciation that is possible by genetic drift alone, sexual selection plays a crucial role in non-adaptive radiations. This is supported by the differences in the genitalia found in the most advanced stage of the speciation which indicate that the speciation process was accelerated by a co-evolutionary arms race resulting in the elongation of spermatophore-producing and spermatophore-receiving organs. Another process that facilitates non-adaptive radiation is long-distance dispersal that results in geographically isolated populations that can differentiate without gene flow and that have a higher likelihood of speciation due to the founder event. Several taxa that were considered distinct species until now, but fuse upon contact should better be classified as subspecies of a polytypic species.     

The life cycle, population dynamics, growth and secondary production of the snail Xeropicta arenosa Ziegler (Gastropoda: Pulmonata) in northern Greece

The life cycle, population dynamics and secondary production of the xerothermophilic land snail Xeropicta arenosa were studied in northern Greece. The study of biology and the demographic analysis of the populations of X. arenosa revealed that it is a semelparous annual species. Reproduction takes place in autumn and the majority of the adults die after egglaying. Growth is continuous throughout the year and no seasonal fluctuations occur. Estimation of annual secondary production with the Hynes' size frequency method revealed a mean standing crop ( aa ) of 0.075 g m^-2 year^-1 and a productivity ( P ) of 0.267+ 0.043 gm^-2 year^-1. The annual turnover ratio ( P/ ) was equal to 3.56.     

The pattern of geographical and altitudinal variation in the land snail Albinaria idaea from Crete (Gastropoda: Clausiliidae)

Certain morphological characters in the Mediterranean land snail genus Albinaria arc believed not to be closely related to ecological conditions. Recently this view has been challenged by a study on A. idaea from central Crete (Greece) claiming that shell characters such as rib density, apcrtural lamella sizes and shell size parameters depend on ecological variables related to altitude. The present study suggests that variation in apertural lamellae, shell size parameters and shell shape were not related to altitude. Neither were they closely related to expected temperature gradients, nor to Drilits beetle predation pressure, nor to vegetational cover (forests/open land). The rib density was the only factor responding to altitude, but after accounting for altitude, altitude-independent regional variation was also of importance. The correlation with altitude was possibly caused by a response to temperature gradients.     

Divergent demographic patterns and perspectives for conservation of endemic species in extreme environments: a case study of the springsnail Melanopsis etrusca (Gastropoda: Melanopsidae)

We studied the distribution, size structure, growth, and diet of the freshwater prosobranch Melanopsis etrusca in experimental and natural population samples. This snail is endemic to isolated headwaters of thermal springs in central Italy. In recent times, several anthropogenic pressures such as water extraction and stream contamination have caused population declines and local extinctions of M. etrusca. Consequently, this species was included on the IUCN Red List of Threatened Species. The streams inhabited by M. etrusca had oligohaline waters; however, some physicochemical variability existed among sites. We found that the two variables most directly related to the patterns of distribution and life history of M. etrusca were water pH and temperature. In particular, individual growth was faster in streams with water temperatures constantly >30°C, which was reflected by a shorter life cycle than in cooler streams (13°–26°C), where snails showed a seasonal pattern of growth. Finally, we observed that individuals in a population that is exposed to extreme temperatures (>35°C) performed a peculiar behavior, spending long periods outside the water. We also found that the diet of M. etrusca reflected the local composition of the periphytic community and was dominated by macrophyte fragments. Our data suggest that heat‐adapted populations of M. etrusca hold the greatest potential for recolonization after collapse events. From a conservation perspective, reintroduction programs could be useful to avoid local extinction or bottleneck effects but at the risk of the loss of evolutionary innovations that may have emerged at the population level.     

Multiple scale patterns of shell and anatomy variability in land snails: the case of the Sicilian Marmorana (Gastropoda: Pulmonata, Helicidae)

Certain major aspects of phenotypic diversity are still largely unexplained. When phenotypic patterns do not relate to habitat variables, fine analysis of morphological patterns and their distribution sheds light on the origin of diversity. Among invertebrates, snails are an ideal model for studying the roles of the neutral processes and selection involved in creating diversity. To understand patterns and processes of variability on different scales (regional: areas; local: sites), morphological variability of two sets of characters (shell and genitalia) was quantified in a group of rock-dwelling land snails of the genus Marmorana (Pulmonata, Helicidae). To analyse shell variability, partitioning of the overall variation into size and shape components was analysed by a principal component-based approach. Shell shape and size variability is not significantly influenced by any environmental pressure. Variability at site scale is mainly attributed to shell size, which is a trait demonstrated to have a high degree of phenotypic plasticity. No sharp changes were observed for genitalia. Moreover, allometries between shell size and genitalia measurements involve a few populations. The observed multiple scale patterns are in line with the hypothesis that genital variance may be selectively controlled to maintain function.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 359–370.     

Natural selection and the distribution of shell colour morphs in three species of Littoraria (Gastropoda: Littorinidae) in Moreton Bay, Queensland

The distribution of yellow, brown and red morphs of sympatric species of Littoraria were recorded on mangrove trees of the genus Avicennia within Moreton Bay, Queensland. The roles of background mimicry (leaf vs. bark, dark vs. light), niche selection and thermal tolerance (sunny vs. shaded positions and height above ground) were examined. The yellow advantage found previously in the area was tested. Total yellow morph frequency adjusted to a reduction in leaf background on pruned trees. Morph frequencies in Littoraria species reflect differences in habitat use. L. filosa (high yellow frequency) was more frequently found on leaves at the highest tree levels, while L. luteola (high brown frequency) was more frequently found on branches at lower levels. It is therefore argued that morphs mimic background elements. Previously reported niche selection by yellow and brown morphs of leaf and bark backgrounds is shown to be a result of the distribution of L. luteola on branches and L. filosa on leaves. At warmer times of the year, yellow L. filosa were more common in sunny positions; this is thought to be a result of thermal tolerance. There appears to be some advantage to particular morphs on particular tree types, but this relationship needs to be examined further. Mangrove-dwelling Littoraria are a promising model to investigate molluscan polymorphism. In the past, erroneous identification of sympatric species may have influenced the accuracy of reported patterns. We used allozyme electrophoretic markers as a precise identification technique. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 75 , 219–232.     

The taxonomic identity of a population of terrestrial Leiopelma (Anura: Leiopelmatidae) recently discovered in the northern king country,New Zealand

Abstract

A terrestrial endemic frog resembling Leiopelma archeyi was discovered in the Whareorino Forest, northern King Country, New Zealand, in 1991, where it is broadly sympatric with L. hochstetteri. To clarify its taxonomic status, allozyme electrophoresis of toe tissue was used to compare it genetically with four other populations of terrestrial Leiopelma (L. archeyi from Tapu and Tokatea, Coromandel; L. hamiltoni from Stephens Island; L. pakeka from Maud Island). Thirteen presumed genetic (allozyme) loci could be consistently scored for the five populations. At 11 loci, no genetic differences were found between the Whareorino frog and the two Coromandel L. archeyi populations. Allelic frequencies differed slightly at two loci. We therefore conclude that the terrestrial Whareorino frog represents a western population of L. archeyi. L. hamiltoni from Stephens Island is genetically closer to L. archeyi than is L. pakeka from Maud Island. The Whareorino L. archeyi population is morphologically similar to Coromandel L. archeyi populations, although multivariate analysis suggests subtle morphological differences, including the relative position of the nostril. Size comparisons between Whareorino and three Coromandel sites (Moehau, Tapu, Tokatea) show there were more larger frogs (35–38 mm snout‐vent length) at Whareorino and Tokatea compared with Moehau and Tapu, where maximum snout‐vent lengths were 34 and 36 mm, respectively.     

Comparing patterns of nuclear and mitochondrial divergence in a cryptic species complex: the case of Iberian and North African wall lizards (Podarcis, Lacertidae)

Combining different sources of information is essential for a complete understanding of the process of genetic differentiation between species. The Iberian and North African wall lizard ( Podarcis ) species complex has been the object of several studies regarding morphological and mitochondrial DNA variation but, so far, no large-scale survey of nuclear variation within this group has been accomplished. In this study, ten polymorphic allozyme loci were studied in 569 individuals collected across the Iberian Peninsula and North Africa. The obtained data were analysed using both conventional population genetic tools and recent Bayesian model-based clustering methods. Our results show that there are several well-differentiated entities corroborating the major splits observed in mtDNA analyses. These groups correspond not only to the fully recognized species Podarcis bocagei , Podarcis carbonelli , and Podarcis vaucheri but also to multiple forms within the polytypic Podarcis hispanica , all of which have a similar level of differentiation to that observed between the acknowledged species. However, relationships between forms are weakly supported both by population and individual clustering methods, suggesting a scenario of a rapid diversification that contrasts to the clear bifurcating model assumed from previous mtDNA analyses. Individual multilocus analyses report few individuals misassigned or apparently admixed, some of which are most likely explained by the persistence of high levels of ancestral polymorphism. Other admixed individuals, however, are probably the result of limited levels of gene flow between forms.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 121–133.     

Phylogeography of Plectostylus Beck, 1837 (Gastropoda: Stylommatophora: Orthalicoidea): Origin and isolation of the Fray Jorge forest relicts in northern Chile

Among the questions surrounding the biogeographical history of the Chilean biota, none has gathered more interest than the origin of the Fray Jorge (FJ) forest relict and its biota. Inserted in a semi‐desert area, this forest enclave exists due to the existence of a very particular microclimate in this region. The age of the disjunction and the historical relationship between the FJ biota with the remaining components of South America are explained by two distinct, competing hypotheses: the first suggests that it would have become isolated during the climatic changes of the Paleogene/Neogene, while the second suggests that the isolation is a product of Quaternary glaciations. To discriminate between these competing hypotheses, we used DNA sequence phylogeny methods and molecular genetic dating to the study of a genus of land snails (Plectostylus) that occurs in the FJ relict and throughout Chile. The phylogeny shows a clear distinction between forest and arid clades, and each of these clades is formed by many geographically circumscribed populations. The FJ fragment snails form a clade that is sister to all other forest clades. The separation between the Fray Jorge clade and the other forest clades dates back to the Paleogene/Neogene. Our data suggest that the FJ forest is a relict from the forests that occupied that landscape during the Paleogene/Neogene and retreated due to the aridification of the region. We also observe that the current taxonomy of the Plectostylus genus must be re‐evaluated.