Multiple unfolding states of glutathione transferase from Physa acuta (Gastropoda [correction of Gastropada]: Physidae)

The equilibrium unfolding of the major Physa acuta glutathione transferase isoenzyme (P. acuta GST(3)) has been performed using guanidinium chloride (GdmCl), urea, and acid denaturation to investigate the unfolding intermediates. Protein transitions were monitored by intrinsic fluorescence. The results indicate that unfolding of P. acuta GST(3) using GdmCl (0-3.0M) is a multistep process, i.e., three intermediates coexist in equilibrium. The first intermediate, a partially dissociated dimer, exists at low GdmCl concentration (approximately at 0.7M). At 1.2M GdmCl, a dimeric intermediate with a compact structure was observed. This intermediate undergoes dissociation into structural monomers at 1.75M of GdmCl. The monomeric intermediate started to be completely unfolding at higher GdmCl concentrations (>1.8M). Unfolding using urea (0-7.0M) and acid-induced structures as well as the fluorescence of 8-anilino-1-naphthalenesulfonate in the presence of different GdmCl concentrations confirmed that the unfolding is a multistep process. At concentrations of GdmCl or urea less than the midpoints or at the midpoint pH (pH 4.2-4.6), the unfolding transition is protein concentration independent and involved a change in the subunit tertiary structure yielding a partially active dimeric intermediate. The binding of glutathione to the enzyme active site stabilizes the native dimeric state.     

Effects of environmental calcium deprivation on the egg masses of Physa marmorata Guilding (Gastropoda: Physidae) and Biomphalaria glabrata Say (Gastropoda: Planorbidae)

Eggs of the basommatophoran snails Physa marmorata and Biomphalaria glabrata were cultured in low concentrations of calcium to determine effects on growth and development. In both species there was some development in media with 0.12 mg/l Ca²⁺ but embryos were unable to hatch. 61.04% of embryos of P. marmorata could develop to hatching in 0.22 mg/l Ca²⁺ but those of B. glabrata required a level of 0.42 mg/l Ca²⁺, to attain even a 31.07% hatch. Marked effects on growth rate, embryo size and on time taken to achieve hatching were noted in both species at very low calcium levels. The possibility of cation-controlling mechanisms in the egg membrane is discussed.     

Invasion of ancient Lake Titicaca by the globally invasive Physa acuta (Gastropoda: Pulmonata: Hygrophila)

A vital population of Physa acuta, a globally invasive species of freshwater gastropods was dicovered in ancient Lake Titicaca in April 2007. The population was found near Chucuito (Bahia de Puno) on the Peruvian side in close proximity to a boat landing of the aquaculture facility of the University of Puno. Physids occured in great abundances at this site on macrophytes in depths from 0 to 2 m. Physa acuta was associated with members of the Heleobia andicola species complex as well as with Heleobia otorni, Biomphalaria andecola, and Uncancylus crequi. Species identity was confirmed by morphological and molecular methods. We discuss the mode of introduction and raise a cautionary note on the potential impact of this global invader on the endemic gastropod fauna of ancient Lake Titicaca.     

Introduction to Physidae (Gastropoda: Hygrophila); biogeography, classification, morphology

Physidae, a world-wide family of freshwater snails with about 80 species, are reclassified by progressive characters of the penial complex (the terminal male reproductive system): form and composition of penial sheath and preputium, proportions and structure of penis, presence or absence of penial stylet, site of pore of penial canal, and number and insertions of penial retractor muscles. Observation of these characters, many not recognized previously, has been possible only by the technique used in anesthetizing, fixing, and preserving. These progressive characters are the principal basis of 23 genera, four grades and four clades within the family. The two established subfamilies are divided into seven new tribes including 11 new genera, with diagnoses and lists of species referred to each. Proposed as new are: in Aplexinae, Austrinautini, with Austrinauta g.n. and Caribnautu harryi g.n., nom.nov.; Aplexini; Amecanautini with Amecanauta jaliscoensis g.n., sp.n., Mexinauta g.n., and Mayabina g.n., with M. petenensis, polita, sanctijohannis, tempisquensis spp.nn., Tropinauta sinusdulcensis g.n., sp.n.; and Stenophysini, with Stenophysa spathidophallus sp.n.; in Physinae, Haitiini, with Haitia moreleti sp.n.; Physini, with Laurentiphysa chippevarum g.n., sp.n., Physa mirollii nom.nou.; and Physellini, with Chiapaphysa g.n., and C. grijalvae, C. pacifica spp.nn., Utahphysa g.n., Archiphysa g.n., with A. ashmuni, A. sonomae spp.nn., Physella hemphilli sp.n., and Ultraphysella sinaloae g.n., sp.n. The simplest reproductive system is found in Austrinauta of the Aplexinae; its penial complex approaches that in the related family Lymnaeidae. Within Physinae a close approximation is found in Haitia. By these two genera the two subfamilies are drawn close together. Four grades of progressive complexity are recognized: (I) penial sheath entirely muscular; (II) penial sheath with both glandular and muscular tissue; (III) penis with penial stylet or other specialization of the tip of the penis; and (IV) pore of penial canal lateral rather than terminal as in the lower grades. In both subfamilies there are clades with glandular tissue in the penial sheath, a penial sheath subdivided into two parts, and tip of penis specialized in various ways. These clades are formalized as new tribes. Of 23 genera of Physidae, 17 occur in Pacific drainages of North and Central America, eight of these restricted to the region. Concentration of primitive genera along the Pacific coast from Mexico to Costa Rica conforms to previous observations that primitive pulmonate families are concentrated within, or along the continental margins of, the Pacific Ocean. An ancestral origin of Physidae along an ancient eastern Pacific coast is probable. From this region the several lineages have spread north, south and east in the Americas, and through Siberia to Europe. Although Physinae have fewer genera than Aplexinae (11 v. 12), they have more species (47 v. 34). Greater land area in the temperate zone has provided more opportunity for speciation of Physinae, in contrast to the generally tropical and warm-temperate range of Aplexinae. Furthermore, 10 species of Physinae are localized in individual lakes, whereas Aplexinae are not lake-dwellers. Both well-developed egg strings and capsular strings are found in the spawn of Sibirenauta elongatus. These structures have been known in Lymnaeidae, but not hitherto in Physidae; they are a link with some marine groups, such as Siphonariidae. Spiral color bands and white streaks in the shell of Mexinauta recall those in Lancidae (Lymnaeacea), whereas the radula of Physidae is like that of Chilinidae. Physidae thus show affinities to various basal stocks of aquatic pulmonates; no clear-cut sister-group can be recognized. Most species have a restricted range; out of 55 with sufficiently detailed information for analysis, 25 are limited to a single 1 degrees x 1 degrees quadrangle. Only a few species are widespread, on one or even two continents. Accordingly, more species of Physidae are threatened by habitat destruction than in other families of Hygrophila with generally wider distributions. Other features are a key to genera; catalog of more than 430 names applied to living Physidae, with original reference, type locality, and location of type specimens; summary of museums with types; and glossary.     

First occurrence of Schistosomatidae infecting Aplexa hypnorum (Gastropoda, Physidae) in France

Due to the recrudescence of cercarial dermatitis in the world, larval Schistosomatidae have been researched during 20 months in gastropods of stagnant fresh waters in a wetland. Brevifurcate ocellate cercariae have been detected after crushing in a species of Physidae, Aplexa hypnorum, with a prevalence of 6.52%. Up to now, this species had never been found infected by larval trematodes. Lymnaeidae, Planorbidae and other Physidae didn't harbour schistosomatids. Cercariae of A. hypnorum present furcal fin-folds and the length of the tail stem is inferior to that of the body. Only cercariae of Heterobilharzia americana, Schistosomatidae of Carnivora in America, have also these two features. This species, not described in Physidae, is an agent of the human cercarial dermatitis. Schistosomatid cercariae in american species of Physidae have been compared with that of A. hypnorum. Brevifurcate ocellate cercariae of A. hypnorum, possible agent of the cercarial dematitis, probably belong to a new species with unknown genus.     

DNA multigene sequencing of topotypic specimens of the fascioliasis vector Lymnaea diaphana and phylogenetic analysis of the genus Pectinidens (Gastropoda)

Freshwater lymnaeid snails are crucial in defining transmission and epidemiology of fascioliasis. In South America, human endemic areas are related to high altitudes in Andean regions. The species Lymnaea diaphana has, however, been involved in low altitude areas of Chile, Argentina and Peru where human infection also occurs. Complete nuclear ribosomal DNA 18S, internal transcribed spacer (ITS)-2 and ITS-1 and fragments of mitochondrial DNA 16S and cytochrome c oxidase (cox)1 genes of L. diaphana specimens from its type locality offered 1,848, 495, 520, 424 and 672 bp long sequences. Comparisons with New and Old World Galba/Fossaria, Palaearctic stagnicolines, Nearctic stagnicolines, Old World Radix and Pseudosuccinea allowed to conclude that (i) L. diaphana shows sequences very different from all other lymnaeids, (ii) each marker allows its differentiation, except cox1 amino acid sequence, and (iii) L. diaphana is not a fossarine lymnaeid, but rather an archaic relict form derived from the oldest North American stagnicoline ancestors. Phylogeny and large genetic distances support the genus Pectinidens as the first stagnicoline representative in the southern hemisphere, including colonization of extreme world regions, as most southern Patagonia, long time ago. The phylogenetic link of L. diaphana with the stagnicoline group may give light to the aforementioned peculiar low altitude epidemiological scenario of fascioliasis.     

Body size-dependent gender role in a simultaneous hermaphrodite freshwater snail, Physa acuta

We examined whether gender role in the simultaneous hermaphroditefreshwater snail, Physa acuta, is determined by relative bodysize in a manner predicted by the size-advantage model. We observedthe body-size combinations of pairs in the laboratory by usingfield-collected populations. Smaller individuals tended to playthe "male" role (sperm donor), and larger snails the "female"(sperm recipient). Next, we analyzed the mating behaviors involvedin gender-role decision in snail pairs of three different body-sizecombinations, using "large" and "small" snails. Smaller snailswere more likely to approach the partner as a male in different-sizecombination (large/small), whereas frequent initial approachesas a male and rejection behavior as a female were observed inthe large/large combination. Third, we examined the body sizepreference when a snail can freely choose the partner from twoother individuals of different body sizes (large/large/smallor large/small/small). Small individuals had a significant tendencyto act as the male and positively selected large snails as thefemale partner in both triple combinations. However, the largeindividual acted as both the male and the female with nearlyequal frequency. In the size-differing pairings, copulationsoccurred after fewer male approaches and fewer rejections thanin pairings involving two large snails, suggesting that bodysize difference is one of the behavioral solutions in genderconflict. Clear gender-role switching associated with body sizewas not seen. Smaller snails thus have a tendency to play themale role more frequently but adopt both gender roles when theirbody size is sufficiently large.     

Experimental infection of Physa heterostropha, Helisoma trivolvis, and Biomphalaria glabrata (Gastropoda) with Echinostoma revolutum (Trematoda) Cercariae

Gross and histologic studies were done on laboratory-raised Physa heterostropha, Helisoma trivolvis, and Biomphalaria glabrata snails exposed individually to 100 cercariae of Echinostoma revolutum. Cercariae showed a predisposition for the kidneys of snails. They entered the nephridiopore, migrated up the tubular kidney, and encysted in the saccular kidney within 2 hr. Considerably more cysts were in the kidney of B. glabrata at 24 hr than in H. trivolvis or P. heterostropha kidneys. Encysted metacercariae were not infective to domestic chicks at 2 hr, but were infective by 4 hr. Biomphalaria glabrata exposed to about 1,000 cercariae/snail and necropsied either 10 or 16 wk postexposure contained 300-500 cysts/kidney; about one-half the cysts were viable and infective to chicks. Biomphalaria glabrata is an excellent second intermediate host for the laboratory propagation of E. revolutum.     

Molecular comparison of topotypic specimens confirms Anopheles (Nyssorhynchus) dunhami Causey (Diptera: Culicidae) in the Colombian Amazon

The presence of Anopheles (Nyssorhynchus) dunhami Causey in Colombia (Department of Amazonas) is confirmed for the first time through direct comparison of mtDNA cytochrome c oxidase I (COI) barcodes and nuclear rDNA second internal transcribed spacer (ITS2) sequences with topotypic specimens of An. dunhami from Tefé, Brazil. An. dunhami was identified through retrospective correlation of DNA sequences following misidentification as Anopheles nuneztovari s.l. using available morphological keys for Colombian mosquitoes. That An. dunhami occurs in Colombia and also possibly throughout the Amazon Basin, is of importance to vector control programs, as this non-vector species is morphologically similar to known malaria vectors including An. nuneztovari, Anopheles oswaldoi and Anopheles trinkae. Species identification of An. dunhami and differentiation from these closely related species are highly robust using either DNA ITS2 sequences or COI DNA barcode. DNA methods are advocated for future differentiation of these often sympatric taxa in South America.     

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.     

The effects of calcium in mediating the inducible morphological defenses of a freshwater snail,Physa acuta

Predation risk is known to induce numerous, often adaptive, plastic changes in the morphology, life history, and behavior of prey. However, little is known about how abiotic factors such as environmental nutrient availability affect these responses. In this experiment, a freshwater pulmonate snail (Physa acuta) was used to determine how predator-induced shell morphology was affected by the availability of an abiotic nutrient important for shell growth (calcium). Each snail was reared individually in a factorial experiment consisting of two predator treatments (chemical cues from crayfish present or absent) and three calcium concentrations (20, 45, or 70 mg/L). Calcium induced larger, heavier, and thicker shells, while predator cues induced heavier and thicker shells. Importantly, the magnitude of the predator effect on shell thickness (i.e., the inducible defense) increased with additional calcium availability. Our results demonstrate the importance of nutrient availability in mediating and limiting the amount of adaptive predator-induced plasticity.     

Planorbidae, Lymnaeidae and Physidae of Ecuador (Mollusca: Basommatophora)

In the course of a trip to Ecuador I had the opportunity of collecting topotypic specimens of the following nominal species of pulmonate molluscs: Biomphalaria cousini Paraense, 1966; Planorbis equatorius Cousin, 1887; P. canonicus Cousin, 1887; Lymnaea cousini Jousseaume, 1887 and P. boetzkesi Miller, 1879. Additional findings were: Helisoma trivolvis (Say, 1817), Biomphalaria peregrina (Orbigny 1835), Drepanotrema anatinum (Orbigny, 1835), D. kermatoides (Orbigny, 1835), D. lucidum (Pfeiffer, 1839), D. surinamense (Clessin, 1884), Lymnaea columella Say, 1817 and Physa acuta Draparnaud, 1805. P. boetzkesi and P. canonicus are considered junior synonyms of Gyraulus hindsianus (Dunker, 1848) and Biomphalaria peregrina (Orbigny, 1835), respectively.     

The different sources of variation in inbreeding depression, heterosis and outbreeding depression in a metapopulation of Physa acuta

Understanding how parental distance affects offspring fitness, i.e., the effects of inbreeding and outbreeding in natural populations, is a major goal in evolutionary biology. While inbreeding is often associated with fitness reduction (inbreeding depression), interpopulation outcrossing may have either positive (heterosis) or negative (outbreeding depression) effects. Within a metapopulation, all phenomena may occur with various intensities depending on the focal population (especially its effective size) and the trait studied. However, little is known about interpopulation variation at this scale. We here examine variation in inbreeding depression, heterosis, and outbreeding depression on life-history traits across a full-life cycle, within a metapopulation of the hermaphroditic snail Physa acuta. We show that all three phenomena can co-occur at this scale, although they are not always expressed on the same traits. A large variation in inbreeding depression, heterosis, and outbreeding depression is observed among local populations. We provide evidence that, as expected from theory, small and isolated populations enjoy higher heterosis upon outcrossing than do large, open populations. These results emphasize the need for an integrated theory accounting for the effects of both deleterious mutations and genetic incompatibilities within metapopulations and to take into account the variability of the focal population to understand the genetic consequences of inbreeding and outbreeding at this scale.     

Ultrastructure of the sensory epithelia of oral tube,fungiform sensory bodies,and terminal knobs of tentacles of Ovatella myosotis Draparnaud (Archaeopulmonata,Gastropoda)

Sensory epithelia of the oral tube, a fungiform body anterior to the tentacles and of the terminal knob of tentacles, were studied in Ovatella myosotis by electron microscopy. All three epithelia consist of columnar support cells, sensory cells, and, except in the oral tube, numerous goblet cells. The epithelia differ significantly in their apical differentiations. In the oral tube an outer layer is formed by irregularly bent villi of support cells completely embedded in a surface coat. Cilia and cytofila of the dendrites of sensory cells intertwine throughout the entire depth of the villous layer. In the fungiform sensory body some of the villi of support cells are singly branched. Their basal region is free of a surface coat. In this region cytofila and cilia of dendrites form a spongy layer, some cytofila extending into the surface coat. In the tentacular terminal knob the villi of the support cells branch dichotomously once or twice, a single villus thus ending with 2–4 tips. Only these terminal twigs are invested with the surface coat. The cytofila and dendritic cilia are confined to a broad spongy layer underneath. Three types of dendrites are present. They differ in their number of cilia, structure of basal bodies and occurrence in the three epithelia. Dendritic cytofila are most abundant in the tentacular terminal knob and least numerous in the oral tube. The observations are discussed with respect to corresponding epithelia in other pulmonates, the homology of the fungiform body, and possible functional correlates of structural features.     

Grazing-filtration as feeding mechanisms in motile specimens of Crepidula fecunda (Gastropoda: Calyptraeidae)

Quantification of ingestion by grazing and by filtration in Crepidula fecunda showed that during the motile phase of the life cycle (<28 mm in shell length), the species depends on both feeding strategies to supply it's energetic requirements. This species improves the energetic quality of the material ingested by exercising preferential selection for organic material from all the materials that are available on the substrate, with an average organic enrichment of 13%. The ontogenetic change in the relative importance of grazing and filter feeding appear to be species-specific within the genus; some species have motile forms in earlier life stages which need to move about the substrate to obtain food and locate aggregations of conspecifics. After growing to about 28 mm in length, C. fecunda become sessile females and depend solely on filter feeding to meet their nutritional requirements.     

Linnaeus' Neptunea (Mollusca: Gastropoda)

Three species of the arcto-boreal, large gastropod Neptunea , described by Linnaeus in 1758 and 1771, occur in large numbers over wide areas of the inshore North Atlantic and adjacent Arctic seas and are conspicuous among Pliocene and Pleistocene molluscs in the Icelandic, North Sea, and western Mediterranean basins. Selections of lectotypes for these species from shells in the collection of the Linnean Society of London, and designations of their type localities, establish the identity of Linnaeus' neptunes and more accurately determine their geographic and geologic distribution. The geographic range of Neptunea (Neptunea) antiqua (L.), the type species, now extends from southern Norway to the northern Biscay coast of France and from the westernmost Baltic Sea to southwestern Ireland; this species also occurs in Pliocene-Holocene marine deposits in West and East Germany, Sweden, the Netherlands, England and France. Its type locality is determined to be the North Sea. N. (Neptunea) despecta (L.) lives in the eastern Canadian Arctic, off southern Greenland, the Barents Sea, and North Atlantic as far south as Massachusetts and Portugal; it also occurs in Pliocene-Holocene strata of eastern Canada, east-central Greenland, Norway (including Svalbard), the Soviet Union, Sweden and England. Its type locality is determined to be the postglacial deposits at Uddevalla in southwestern Sweden. N. (Sulcosipho) contraria (L.) now extends from the southern Biscay coast of France to Cape Spartel, Morocco; this species also occurs in Pleistocene and lower Holocene sequences of the western Mediterranean. Its type locality is determined to be Vigo Bay, Spain. A closely related fossil species, N. (S.) angulata (S. V. Wood), occurs in Pliocene and Pleistocene deposits of the North Sea basin.