Fingernail Clams Research Articles

Off the conservation radar: the hidden story of Europe's tiny pea clams (Bivalvia: Sphaeriidae)

AbstractThis study highlights the conservation problems faced by the tiny freshwater bivalves of the family Sphaeriidae, also known as pea, pill, or fingernail clams (or mussels) in Europe. Despite their global distribution, assumed ecological importance, and potential uses, basic knowledge about their taxonomy, biology, and ecology is very limited and much lower than for the larger freshwater bivalve taxa. Immediate scientific priorities are required to fill knowledge gaps regarding their taxonomy, genetic diversity, distribution, reproductive cycle, ecosystem functions, and population trends. Such fundamental knowledge is necessary to identify specific threats and develop appropriate conservation actions. Deploying environmental DNA analysis at a large scale could be a valuable way to fill gaps in distribution and strengthen monitoring in areas where local taxonomic knowledge is lacking. Until taxon-specific management plans can be developed, we recommend that efforts concentrate on the general protection and restoration of wetland habitats, implementing pollution control measures, and managing invasive species. These actions should be complemented by community engagement through citizen science initiatives. Additionally, prioritising data collection to fill existing knowledge gaps and updating conservation statuses (Red Lists) based on comprehensive assessments will be crucial. Implementing these actions will provide a starting point for the broader protection of freshwater ecosystems, thus benefiting pea clams and other interconnected species within these habitats.

Evidence that bivalve burrowing is mediated by serotonin receptors: activation of foot inflation and protrusion by serotonin, serotonergic ligands and SSRI-type antidepressants in three species of freshwater bivalve

ABSTRACT Foot inflation and protrusion in bivalve molluscs is part of a sequence of events necessary for burrowing into the substrate. Although this process been observed after exogenous exposure to the neurotransmitter serotonin [5-hydroxytryptamine (5-HT)] and by some selective serotonin reuptake inhibitor (SSRI) type antidepressants, no study has shown that foot inflation and protrusion as a precursor to burrowing is under serotonergic control. In order to elucidate the physiological mechanism mediating this response, we tested over 2,000 freshwater bivalves in three species by exposing them to 5-HT, two 5-HT receptor agonists, two receptor antagonists and five antidepressants. Fingernail clams (Sphaerium striatinum), Asian clams (Corbicula fluminea) and unionid mussels (Elliptio complanata) all showed significant foot inflation or foot protrusion when exposed to 5-HT and the serotonergic agonists 8-OH-DPAT and alpha-methyl 5-HT. Some SSRI-type antidepressants (fluoxetine and fluvoxamine) also significantly induced these responses in all three species but were not as potent at the concentrations tested. In S. striatinum and C. fluminea, a 2-h exposure to the 5-HT2 receptor antagonists mianserin and cyproheptadine effectively blocked foot inflation induced by 5-HT and 8-OH-DPAT. The 5-HT receptor mediating this response is thus sensitive to mammalian 5-HT1 and 5-HT2 receptor ligands, supporting the hypothesis that serotonin mediates the initial step in burrowing.

Nonindigenous Aquatic Mollusks in Illinois

Nonindigenous aquatic species (NAS), some of which are referred to as aquatic invasive species (AIS) or non-native aquatic species, are those aquatic organisms that have become established beyond their native ranges. They often inhabit a variety of habitats and physicochemical conditions, reach high densities, and alter ecosystem function. Understanding the distribution of nonindigenous aquatic species is vital to protecting native biodiversity in invaded ecosystems. A search of museum collections, literature accounts, and field surveys conducted in recent years by biologists from the Illinois Natural History Survey, Illinois Department of Natural Resources, and other agencies revealed 13 nonindigenous aquatic mollusk species reported to occur in Illinois. Ten species (five bivalves and five gastropods) have viable reproducing populations. One species, the Big-eared Radix Radix auricularia (Linnaeus, 1758), is no longer extant in Illinois, and two species, the European Stream Valvata Valvata piscinalis (Müller, 1774) and European Fingernail Clam Sphaerium corneum (Linnaeus, 1758), have an unknown status. Some species, such as the Basket Clam Corbicula fluminea (Müller, 1774), Zebra Mussel Dreissena polymorpha (Pallas, 1771), and Chinese Mysterysnail Cipangopaludina chinensis (Gray in Griffith and Pidgeon, 1833), are widespread and abundant. However, other species like the Mottled Fingernail Clam Eupera cubensis (Prime, 1865) and New Zealand Mudsnail Potamopyrgus antipodarum (Gray, 1843) are currently restricted to a particular location or drainage. Other nonindigenous aquatic mollusks with the potential for becoming established in Illinois or border waters are also discussed.

Efficacy and Nontarget Effects of a Spinosad-Based Larvicide in Minnesota Vernal Pools and Cattail Marshes.

Larvicides that contain spinosad, a bacterial metabolite, are used to control mosquitoes in diverse aquatic habitats. These same habitats are home to other invertebrates, including Crustacea-fairy shrimp, isopods, and amphipods-and mollusks-fingernail clams and freshwater snails. A double-blind study evaluated the effects of Natular® G, a granular treatment containing spinosad, on spring Aedes spp. and nontarget invertebrates in vernal wetlands. Within 14 days after application, Natular G controlled larvae of spring Aedes by 53-84%, depending on species, but had no significant effects on numbers of fairy shrimp, fingernail clams, or freshwater snails. A second double-blind study evaluated effects on Coquillettidia perturbans and nontarget isopods and amphipods in cattail marshes. Treatment reduced emergence of Cq. perturbans by 25% but did not change numbers of isopods or amphipods. The 2 experiments indicate Natular G could be effective against spring Aedes in vernal wetlands, less so against Cq. perturbans in cattail marshes, and yet pose minimal risk to crustaceans and mollusks in either vernal wetlands or cattail marshes.

Passive transport of Eastern Elliptio (<i>Elliptio complanata</i>) by freshwater turtles in New England

Dispersal of freshwater mussels (order Unionida) is primarily as glochidia on the fins and gills of host fish. Adult mussels are more sessile, generally moving short distances (<2 m/week) along lake and river beds. Between 2007 and 2016, we observed seven instances of adult Eastern Elliptio (Elliptio complanata) and one instance of a fingernail clam (Sphaerium sp.) attached to the feet of freshwater turtles in streams and ponds of New England, United States. Observations included five instances of mussels attached to Wood Turtles (Glyptemys insculpta) in Maine and Massachusetts, one instance of a mussel attached to the fingernail of an Eastern Painted Turtle (Chrysemys picta) in Massachusetts, one instance of a mussel attached to a Snapping Turtle (Chelydra serpentina) in Massachusetts, and one instance of a fingernail clam attached to the fingernail of an Eastern Painted Turtle in Massachusetts. We suggest that Eastern Elliptio may be susceptible to transport by freshwater turtles foraging in mussel beds and that transport of adult mussels by freshwater turtles could result in otherwise atypical long-distance, upstream, or overland dispersal between waterbodies.

Documentation of Freshwater Mussels (Unionidae) in the Diet of Round Gobies (Neogobius melanostomus) within the French Creek Watershed, Pennsylvania

The round goby (Neogobius melanostomus) was discovered in 2013 in the French Creek (Allegheny River Drainage) watershed and is the first documented invasion outside of the Lake Erie basin in Pennsylvania. The round goby throughout the Laurentian Great Lakes is known to eat dressenid mussels (Dreissenidae), but consumption of either dressenids or native mussels (Unionidae) in tributaries to Lake Erie is minimal based on low populations of any bivalves. The French Creek watershed, on the other hand, harbors 29 species of native freshwater mussels as well as introduced fingernail clams (Sphaeriidae; Corbicula fluminea). The objectives of this study were to document the diet of round gobies in the French Creek watershed to determine whether consumption of native freshwater mussels was occurring. Round gobies were collected in the summer months (May–Sept.) of 2016 via kick seine in four locations, dissected, and their stomach contents identified to lowest possible taxa. We separated the gobies into categories based on length classes, in order to determine if diet changed with increased size and age. Unionid mussels were consumed by all length classes, particularly in length class one (30–44 mm), but diet shifted to a dominance of sphaeriids in length class four (≥75 mm). Round gobies also consumed benthic aquatic insects, a large percentage of which were chironomids (greater than 24% in all size classes). This is the first documentation of unionid consumption by the round goby in Pennsylvania that poses possible threats to native mussels in the French Creek watershed.

Microhabitat and biology of Sphaerium striatinum in a Central New York stream

In many lotic systems, drastic declines in freshwater bivalve populations, including fingernail clams (Sphaeriidae), have created concerns about biodiversity and future ecosystem services. We examined the local occurrence of the historically common fingernail clam, Sphaerium striatinum, in a central New York stream. We sampled the density of sphaeriids and measured the associated habitat variables (substrate, depth, water flow) to test within-stream multivariate benthic microhabitat association. Size distribution, density, and diel feeding periodicity were measured as focal aspects of fingernail clam biology and ecology. S. striatinum tended to be found in microhabitats that had harder substrates and faster flow. The Labrador Creek fingernail clam local population had positive indicators (size distribution, density). There was significant diel periodicity in feeding behavior. The clams fed most actively during the 0400–0800 h periods. This kind of behavioral periodicity can indicate a significant ecological interaction between predators and bivalve prey. Increased understanding of the behavioral ecology of small native freshwater bivalves in an unimpacted headwater stream is a fundamental building block for development of overall ecological conservation goals for freshwater bivalves and their lotic habitats.

Salinization triggers a trophic cascade in experimental freshwater communities with varying food-chain length.

The application of road deicing salts in northern regions worldwide is changing the chemical environment of freshwater ecosystems. Chloride levels in many lakes, streams, and wetlands exceed the chronic and acute thresholds established by the United States and Canada for the protection of freshwater biota. Few studies have identified the impacts of deicing salts in stream and wetland communities and none have examined impacts in lake communities. We tested how relevant concentrations of road salt (15, 100, 250, 500, and 1000mgCl- /L) interacted with experimental communities containing two or three trophic levels (i.e., no fish vs. predatory fish). We hypothesized that road salt and fish would have a negative synergistic effect on zooplankton, which would then induce a trophic cascade. We tested this hypothesis in outdoor mesocosms containing filamentous algae, periphyton, phytoplankton, zooplankton, several macroinvertebrate species, and fish. We found that the presence of fish and high salt had a negative synergistic effect on the zooplankton community, which in turn caused an increase in phytoplankton. Contributing to the magnitude of this trophic cascade was a direct positive effect of high salinity on phytoplankton abundance. Cascading effects were limited with respect to impacts on the benthic food web. Periphyton and snail grazers were unaffected by the salt-induced trophic cascade, but the biomass of filamentous algae decreased as a result of competition with phytoplankton for light or nutrients. We also found direct negative effects of high salinity on the biomass of filamentous algae and amphipods (Hyalella azteca) and the mortality of banded mystery snails (Viviparus georgianus) and fingernail clams (Sphaerium simile). Clam mortality was dependent on the presence of fish, suggesting a non-consumptive interactive effect with salt. Our results indicate that globally increasing concentrations of road salt can alter community structure via both direct and indirect effects.

Development of functional trait biomarkers for trace metal exposure in freshwater clams (Musculium spp.)

Exposure to trace metals typically causes oxidative stress; these consequences are better-characterized in estuarine and marine species than in freshwater species. How cellular-level responses to metal pollution influence whole-organism and population-level traits is poorly understood. We tested whether exposure to single metals (zinc and cadmium) and to metal mixtures (water in equilibrium with sediment from a highly polluted lake) alters two ecologically-relevant traits in freshwater clams, locomotion and reproduction. Fingernail clams (Musculium spp.) from unimpacted habitats were exposed to single metals and the metal mixture for up to 49days. The single metal doses (≤5mg/L Zn and ≤20μg/L Cd) were not toxicologically meaningful as clam survival, burial, and climbing activity did not differ across treatments. Water in equilibrium with the lake sediment contained cadmium, copper, lead, and zinc. Clams exposed to this metal mixture had decreased climbing activity but no change in burial activity. Metal-exposed clams had lower fecundity (number of shelled juveniles extruded by adult clams) and patterns in metal accumulation corresponded with lake sediment dose and clam activity. In contrast to the functional traits, stress protein expression and whole-clam glycogen content did not vary across treatment groups. These results indicate that fingernail clams of the genus Musculium are appropriate for development as sentinel species for metal pollution and can serve as a model for determining how metal pollution alters metabolic allocation patterns in freshwater organisms.

The effect of chronic exposure to phosphorus-inactivation agents on freshwater biota

The phosphorus (P)-inactivation agents alum or modified zeolite (Aqual-P TM ) are used in eutrophic lake remediation. Lake managers must evaluate the benefits of P-removal against potential adverse effects on lake biota. Laboratory mesocosms were used to determine whether a 2 month exposure to alum or Aqual-P had lethal or sublethal effects on native benthic-dwelling macroinvertebrates or fish. The P-inactivation agents were applied while the organisms were present to evaluate both acute- and longer-term effects. A gradient of doses up to 344 g alum m -2 ((7 mm capping layer thickness) and a single 200 g Aqual-P m -2 dose were applied with no detectable acute effects on survival or behaviour. After 2 months, there was no significant effect of alum or Aqual-P on the survival or growth of the crayfish, mussels or fish, but aluminium accumulation was measurable in some treatments. Fingernail clams were held in a sub-mesocosm to prevent predation, which resulted in exposure to intact capping layers. The highest alum dose significantly decreased fingernail clam survival and reburial rates, while 200 g Aqual-P m -2 caused highly variable survival. Our findings can be used by lake managers to assist the selection of site- specific application rates for these P-inactivation agents.

Targeting riparian buffers and grassed waterways to address freshwater species decline

Targeting conservation practices greatly increases economic efficiency (1) if the resource problem occurs primarily within a small geographic area and (2) if the conservation practice is targeted within the area where it works most effectively. Over 73% of United States' freshwater mussel species, 35% of amphibians, and 37% of fish have been classified as vulnerable, imperiled, or endangered (Henley et al. 2000; Williams et al. 1993). These species' problems are concentrated in certain Southeastern streams and rivers, where an estimated (Neves et al. 1997) 91% of the United States' freshwater mussels, 53% of fingernail clams, and 61% of snails reside. For rare mussel species most in need of protection, 98% of these species occur in the Southeast (Neves et al. 1997).

Importance of methane-derived carbon as a basal resource for two benthic consumers in arctic lakes

Microbial processing of detritus is known to be important to benthic invertebrate nutrition, but the role of dissolved (DOC) versus particulate organic carbon (POC), and pathways by which those resources are obtained, are poorly understood. We used stable isotopes to determine the importance of DOC, POC, and CH4-derived carbon to benthic invertebrate consumers from arctic Alaskan Lakes. Intact sediment cores from Lake GTH 112 were enriched with 13C-labeled organic matter, including algal detritus, algal-derived DOC, methyl-labeled acetate, and carboxyl-labeled acetate, and incubated for 1 month with either caddisflies (Grensia praeterita ) or fingernail clams (Sphaerium nitidum), two invertebrate species that are important to fish nutrition. Both species used basal resources derived from POC and DOC. Results generally suggest greater reliance on POC. Differential assimilation from acetate treatments suggests Sphaerium assimilated CH4-derived carbon, which likely occurred through deposit-feeding. Grensia assimilated some microbially processed acetate, although its survivorship was poor in acetate treatments. Our data extend previous studies reporting use of CH4-derived carbon by Chironomidae and oligochaetes. Taken together, these results suggest that the use of CH4-derived carbon is common among deposit-feeding benthic invertebrates.

An ~11,200 year paleolimnological perspective for emerging archaeological findings at Quartz Lake, Alaska

Wetlands and lakes in the Tanana Valley, Alaska, have provided important resources for prehistoric humans who inhabited this region. We examine an ~11,200 cal yr BP record of environmental and paleolimnological changes from Quartz Lake in the middle Tanana Valley. Our data are also presented in the context of recent archaeological findings in the lake’s general vicinity that have 18 associated AMS 14C dates. We analyzed the stable-carbon and nitrogen isotope composition of total organic matter from the core, coupled with oxygen and carbon isotope analyses of Pisidiidae shells (fingernail clams), in addition to chironomid assemblage changes. Lacustrine sediments began to accumulate at ~11,200 cal yr BP. Initially, autochthonous production was low and allochthonous organic input was negligible between 11,000 and 10,500 cal yr BP, and were associated with relatively cool conditions at Quartz Lake at ~10,700 cal yr BP. After 10,500 cal yr BP, autochthonous production was higher coincident with a shift to chironomid assemblages dominated by taxa associated with warmer summer climates. A decrease in δ13C values of total organic carbon (TOC) and organic content of the sediment between 9,000 and 4,000 cal yr BP may indicate declining autochthonous primary production. This period ended with an abrupt (~7 ‰) decrease in the δ18O values from Pisidiidae shells at ~3,000 cal yr BP, which we hypothesize represented an episodic connection (flood) of the lake with flow from the nearby (~6 km) Tanana River. Our findings coincide with evidence for major flooding at other locations connected to the Tanana River and further afield in Alaska. From ~3,000 cal yr BP Quartz Lake subsequently appeared to become a relatively closed system, as indicated by the δ18OPisidiidae and δ13CPisidiidae data that are positively correlated and generally higher, which also correlates with a shift to moderately higher abundances of littoral chironomids. The cause of the transition to closed-basin conditions may have been geomorphic rather than climatic. This evidence of a progressively stronger evaporative influence on the lake’s closed hydrology after ~3,000 cal yr BP is consistent with our modern δ18O and δD water data from Quartz Lake that plot along a regional evaporative line we base on isotopic measurements from other local lakes and rivers.

Associations between small dams and mollusk assemblages in Alabama streams

Small dams are ubiquitous yet poorly understood features in many streams. Dam removal is being used increasingly in stream restoration projects as a means to enhance habitat connectivity and ecosystem function. However, habitat- and assemblage-level effects of small dams on stream mollusk assemblages are poorly documented. We examined associations between stream physicochemical habitat variables and mollusk assemblages at 22 small (<10 m) dams in 3rd–5th order Alabama streams. We sampled 66 reaches (3 reaches/dam) associated with intact, breached, and relict small dams. For each dam, we designated 3 study reaches: 1) immediately downstream from the dam, 2) 500 to 5000 m downstream, and 3) 500 to 5000 m upstream from the impounded or formerly impounded zone. We used principal components analysis (PCA) to examine variation in physical-habitat conditions across all sites. Four principal components accounted for ∼72% of the variation in physical-habitat conditions across sites. One PC score (PC1, corresponding to increased substrate size) was negatively associated with several mollusk metrics including total mussel abundance, taxon richness, catch-per-unit-effort (CPUE), and density. We observed few significant differences between simple habitat variables at sites up- and downstream of dams. However, streams with intact dams had significantly higher mussel catch rates (CPUE) and taxon richness than did streams with breached or relict dams. We used forward-stepwise multiple regression to model the effects of habitat variables (as standardized PC scores) on mollusk assemblage metrics. PCs representing substrate composition were the strongest predictors of total mussel abundance and richness. Abundance of other mollusks including deposit-feeding snails, the exotic bivalve Corbicula fluminea, and fingernail clams was correlated with PC scores describing variability in substrate organic matter composition or stream gradient. We think these data indicate that some intact dams enhance mollusk habitat in downstream reaches. Streams with intact dams appear to be more geomorphically stable than streams with breached or relict dams and conditions in the mill reach may reflect preconstruction stream conditions. Breached dams warrant higher prioritization for removal than intact structures because habitat degradation may persist for decades and impede re-establishment of native mollusk populations.

Acute Toxicity of Nitrate and Nitrite to Sensitive Freshwater Insects, Mollusks, and a Crustacean

Both point- and nonpoint-sources of pollution have contributed to increased inorganic nitrogen concentrations in freshwater ecosystems. Although numerous studies have investigated the toxic effects of ammonia on freshwater species, relatively little work has been performed to characterize the acute toxicity of the other two common inorganic nitrogen species: nitrate and nitrite. In particular, to our knowledge, no published data exist on the toxicity of nitrate and nitrite to North American freshwater bivalves (Mollusca) or stoneflies (Insecta, Plecoptera). We conducted acute (96-h) nitrate and nitrite toxicity tests with two stonefly species (Allocapnia vivipara and Amphinemura delosa), an amphipod (Hyalella azteca), two freshwater unionid mussels (Lampsilis siliquoidea and Megalonaias nervosa), a fingernail clam (Sphaerium simile), and a pond snail (Lymnaea stagnalis). Overall, we did not observe a particularly wide degree of variation in sensitivity to nitrate, with median lethal concentrations ranging from 357 to 937 mg NO(3)-N/l; furthermore, no particular taxonomic group appeared to be more sensitive to nitrate than any other. In our nitrite tests, the two stoneflies tested were by far the most sensitive, and the three mollusks tested were the least sensitive. In contrast to what was observed in the nitrate tests, variation among species in sensitivity to nitrite spanned two orders of magnitude. Examination of the updated nitrite database, including previously published data, clearly showed that insects tended to be more sensitive than crustaceans, which were in turn more sensitive than mollusks. Although the toxic mechanism of nitrite is generally thought to be the conversion of oxygen-carrying pigments into forms that cannot carry oxygen, our observed trend in sensitivity of broad taxonomic groups, along with information on respiratory pigments in those groups, suggests that some other yet unknown mechanism may be even more important.

A fingernail clam (Sphaerium sp.) shows higher reproductive success in hypoxic waters

Low dissolved O2, or hypoxia, is becoming increasingly prevalent in aquatic habitats and is considered to be stressful for aerobic organisms. However, hypoxia also can be beneficial by decreasing cellular stress, particularly that related to free radicals. Therefore, an animal’s ideal habitat may have the minimum O2 necessary to sustain aerobic metabolism, with excess O2 increasing the need to scavenge free radicals and repair free radical damage. Here we show that a natural population of small (&lt;9 mm shell length) freshwater clams (genus Sphaerium Scopoli, 1777) lives along a dissolved O2 gradient from extreme hypoxia to moderate hypoxia. We tested the hypothesis that clams living in extreme hypoxia would have higher reproductive success than clams that live in moderate hypoxia. Clam abundance was highest in water with very low dissolved O2, conditions previously demonstrated to decrease cellular stress. The internally brooding clams reproduced year-round and had higher reproductive output in extreme hypoxia than in moderate hypoxia. The findings demonstrate that the apparent cellular-level benefits of hypoxia may translate into increased fitness, especially for small organisms.

Influence of water hardness and sulfate on the acute toxicity of chloride to sensitive freshwater invertebrates

Total dissolved solids (TDS) represent the sum of all common ions (e.g., Na, K, Ca, Mg, chloride, sulfate, and bicarbonate) in freshwater. Currently, no federal water quality criteria exist for the protection of aquatic life for TDS, but because the constituents that constitute TDS are variable, the development of aquatic life criteria for specific ions is more practical than development of aquatic life criteria for TDS. Chloride is one such ion for which aquatic life criteria exist; however, the current aquatic life criteria dataset for chloride is more than 20 years old. Therefore, additional toxicity tests were conducted in the current study to confirm the acute toxicity of chloride to several potentially sensitive invertebrates: water flea (Ceriodaphnia dubia), fingernail clams (Sphaerium simile and Musculium transversum), snail (Gyraulus parvus), and worm (Tubifex tubifex), and determine the extent to which hardness and sulfate modify chloride toxicity. The results indicated a significant ameliorating effect of water hardness (calcium and magnesium) on chloride toxicity for all species tested except the snail; for example, the 48-h chloride median lethal concentration (LC50) for C. dubia at 50 mg/L hardness (977 mg Cl(-) /L) was half that at 800 mg/L hardness (1,836 mg Cl(-) /L). Conversely, sulfate over the range of 25 to 600 mg/L exerted a negligible effect on chloride toxicity to C. dubia. Rank order of LC50 values for chloride at a given water hardness was in the order (lowest to highest): S. simile < C. dubia < M. transversum < G. parvus < T. tubifex. Results of the current study support the contention that the specific conductivity or TDS concentration of a water body alone is not a sufficient predictor of acute toxicity and that knowledge of the specific ion composition is critical.

The discovery of the nonindigenous, mottled fingernail clam, Eupera cubensis (Prime, 1865) (Bivalvia: Sphaeriidae) in the Chicago Sanitary and Ship Canal (Illinois River Drainage), Cook County, Illinois

The nonindigenous mottled fingernail clam, Eupera cubensis is reported from the Upper Mississippi River Basin for the first time. This record represents a significant northern range expansion for the species in the United States. It appears to be presently confined to a 35-km stretch of the Chicago Sanitary and Ship Canal (CSSC), an artificial waterway that connects the Mississippi River drainage to the Great Lakes. Although the introduction of this species to the Great Lakes basin poses uncertain risks to the general aquatic community, the immediate effects of Eupera cubensis on the fauna of the CSSC are expected to be minimal.

Alternative Life Cycle Strategies and Colonization of Young Anurans by Gorgoderina attenuata in Nebraska

Studies on life cycles and epizootiology of North American frog bladder flukes indicate that adult frogs become infected predominantly by ingesting tadpoles or other frogs that serve as second intermediate hosts for gorgoderid metacercariae. Other studies have indicated that newly metamorphosed frogs are rarely infected with these parasites because they are gape-limited predators that cannot feed on large intermediate hosts such as tadpoles and other frogs. We examined the role of potential intermediate hosts in the recruitment of the frog bladder fluke, Gorgoderina attenuata, to metamorphosed northern leopard frogs, Woodhouse's toads, and bullfrogs from western Nebraska. We completed the life cycle of G. attenuata in the laboratory in 3 anuran species by experimentally infecting a variety of hosts. In addition, we generated and compared DNA sequence data from life cycle stages collected from a variety of naturally infected hosts. Our field and laboratory data indicate that in Nebraska G. attenuata has a truncated, 2-host life cycle that includes fingernail clams and anurans. Cercariae are ingested directly by tadpoles; unencysted juvenile worms then develop in the kidneys of tadpoles before moving to, and maturing in, the urinary bladder when tadpoles metamorphose. Additionally, G. attenuata can infect metamorphosed leopard frogs, bullfrogs, and toads when metacercariae in damselfly second intermediate hosts are ingested. These worms can also infect adult bullfrogs when they feed on other infected anurans possessing worms in their kidneys. Comparison of our material to published accounts of G. attenuata morphology and life cycles in Massachusetts suggests that previous work may have inadvertently involved 2 different species of gorgoderids. Our comparative approach to life cycle studies in different anuran life stages and multiple species of hosts suggests that tadpoles and metamorphosed anurans have favored alternative life cycle strategies in this trematode.

Norfluoxetine Induces Spawning and Parturition in Estuarine and Freshwater Bivalves

Fluoxetine, a commonly prescribed antidepressant (Prozac), has been detected in sewage effluent. Its active metabolite norfluoxetine is more potent and has been detected in sewage influent and in fish tissues. We tested the effects of norfluoxetine on spawning and parturition in bivalves. Norfluoxetine induced significant spawning in zebra mussels and dark false mussels at concentrations as low as 5 microM. Norfluoxetine induced significant parturition in fingernail clams at 10 microM. Fluoxetine also induced spawning in dark false mussels at concentrations as low as 100 nM. Implications for environmental impacts of norfluoxetine and fluoxetine on native and exotic bivalves are discussed.