Littorina Littorea Research Articles

Experimental Evaluation of Seaweeds as a Vector for Microplastics into Marine Food Webs.

The ingestion of microplastics has been shown for a great variety of marine organisms. However, benthic marine mesoherbivores such as the common periwinkle Littorina littorea have been largely disregarded in studies about the effects of microplastics on the marine biota, probably because the pathway for microplastics to this functional group of organisms was not obvious. In laboratory experiments we showed that the seaweed Fucus vesiculosus retains suspended microplastics on its surface. The numbers of microplastics that adhered to the algae correlated with the concentrations of suspended particles in the water. In choice feeding assays L. littorea did not distinguish between algae with adherent microplastics and clean algae without microplastics, indicating that the snails do not recognize solid nonfood particles in the submillimeter size range as deleterious. In periwinkles that were feeding on contaminated algae, microplastics were found in the stomach and in the gut. However, no microplastics were found in the midgut gland, which is the principle digestive organ of gastropods. Microplastics in the fecal pellets of the periwinkles indicate that the particles do not accumulate rapidly inside the animals but are mostly released with the feces. Our results provide the first evidence that seaweeds may represent an efficient pathway for microplastics from the water to marine benthic herbivores.

Accumulation of Sellafield-derived radiocarbon (14C) in Irish Sea and West of Scotland intertidal shells and sediments

The nuclear energy industry produces radioactive waste at various stages of the fuel cycle. In the United Kingdom, spent fuel is reprocessed at the Sellafield facility in Cumbria on the North West coast of England. Waste generated at the site comprises a wide range of radionuclides including radiocarbon (14C) which is disposed of in various forms including highly soluble inorganic carbon within the low level liquid radioactive effluent, via pipelines into the Irish Sea. This 14C is rapidly incorporated into the dissolved inorganic carbon (DIC) reservoir and marine calcifying organisms, e.g. molluscs, readily utilise DIC for shell formation. This study investigated a number of sites located in Irish Sea and West of Scotland intertidal zones. Results indicate 14C enrichment above ambient background levels in shell material at least as far as Port Appin, 265 km north of Sellafield. Of the commonly found species (blue mussel (Mytilus edulis), common cockle (Cerastoderma edule) and common periwinkle (Littorina littorea)), mussels were found to be the most highly enriched in 14C due to the surface environment they inhabit and their feeding behaviour. Whole mussel shell activities appear to have been decreasing in response to reduced discharge activities since the early 2000s but in contrast, there is evidence of continuing enrichment of the carbonate sediment component due to in-situ shell erosion, as well as indications of particle transport of fine 14C-enriched material close to Sellafield.

Yearly shifts in shell quality for the hermit crab Pagurus longicarpus in coastal Massachusetts

Global warming is expected to result in milder New England winters. In this study we monitored changes in hermit crab shell quality at Nahant, Massachusetts, USA, at intervals during 17 yr between 1997 and 2014 for a single species of hermit crab Pagurus longicarpus occupying the shells of the intertidal periwinkle Littorina littorea. The incidence of hermit crabs occupying damaged shells, shells housing the symbionts Hydractinia, Crepidula plana, and C. convexa, and showing poor shell fit varied significantly among years. Shell quality was especially bad in the summer of 2012, following one of the warmest winters on record: more than 60% of the sampled hermit crabs were found living in damaged shells and more than 50% of the shells bore symbionts. Moreover, an unusually low number (only 15%) of the hermit crabs sampled that summer were found in shells that were undamaged, without symbionts, and of adequate size, compared with 50 to 55% of hermit crabs being found in such 'perfect' shells in 1997 and 2013. We suggest that new, high-quality shells are added to hermit crab populations at our study site largely through the freeze-induced mortality of intertidal periwinkles, and that the poor shell quality documented in summer 2012 reflects reduced periwinkle mortality during the unusually warm preceding winter. If so, then P. longicarpus might serve as a coastal 'canary in the coal mine': documenting yearly shifts in the quality of shells used as shelters by coastal marine hermit crabs in New England may provide a convenient means of monitoring the impact of climate change on intertidal populations.

Tributyltin pollution biomonitoring under the Water Framework Directive: Proposal of a multi-species tool to assess the ecological quality status of EU water bodies

The Water Framework Directive (WFD) is a key legislative action developed by the European Union in order to protect aquatic ecosystems. One of the concerning pollutants, listed in this directive as a priority hazardous substance, is tributyltin (TBT), a biocide largely used in antifouling paints and identified as a causative agent of imposex/intersex in gastropods. In order to integrate TBT pollution monitoring within this legislative framework, a practical exercise is here proposed to assess the evolution of surface water ecological status in Ria de Aveiro (NW Portugal). Three bioindicators – the caenogastropods Nucella lapillus, Nassarius reticulatus and Littorina littorea – were used under the general WFD benthic invertebrate quality element, and the vas deferens sequence index (VDSI) and the intersex index (ISI) were selected as biomarkers for the purpose of assessing the condition of this quality element regarding the impact of TBT pollution. Levels of VDSI in N. lapillus and N. reticulatus, and ISI in L. littorea, were surveyed in 2013 and compared with previous data available for the same species and study area in 1998 and 2005, providing a time lapse for a period of 15 years. VDSI and ISI values were converted into Ecological Quality Ratios (EQR) and EQR boundaries were set for each species in order to define the five ecological status classes (High, Good, Moderate, Poor and Bad). We propose N. lapillus as key bioindicator, however the combined use of further species is very useful to cover a wider study area. Based on the proposed method, it is concluded that the ecological status of the surface waters surveyed in Ria de Aveiro, concerning the impact of TBT pollution on the above benthic invertebrate taxa, improved considerably since 1998 and achieved a Good Ecological Status in 2013, thus meeting the WFD environmental objectives for this priority hazardous substance even before 2015.

Anti-oxidative cellular protection effect of fasting-induced autophagy as a mechanism for hormesis

The aim of this investigation was to test the hypothesis that fasting-induced augmented lysosomal autophagic turnover of cellular proteins and organelles will reduce potentially harmful lipofuscin (age-pigment) formation in cells by more effectively removing oxidatively damaged proteins. An animal model (marine snail - common periwinkle, Littorina littorea) was used to experimentally test this hypothesis. Snails were deprived of algal food for 7 days to induce an augmented autophagic response in their hepatopancreatic digestive cells (hepatocyte analogues). This treatment resulted in a 25% reduction in the cellular content of lipofuscin in the digestive cells of the fasting animals in comparison with snails fed ad libitum on green alga (Ulva lactuca). Similar findings have previously been observed in the digestive cells of marine mussels subjected to copper-induced oxidative stress. Additional measurements showed that fasting significantly increased cellular health based on lysosomal membrane stability, and reduced lipid peroxidation and lysosomal/cellular triglyceride. These findings support the hypothesis that fasting-induced augmented autophagic turnover of cellular proteins has an anti-oxidative cytoprotective effect by more effectively removing damaged proteins, resulting in a reduction in the formation of potentially harmful proteinaceous aggregates such as lipofuscin. The inference from this study is that autophagy is important in mediating hormesis. An increase was demonstrated in physiological complexity with fasting, using graph theory in a directed cell physiology network (digraph) model to integrate the various biomarkers. This was commensurate with increased health status, and supportive of the hormesis hypothesis. The potential role of enhanced autophagic lysosomal removal of damaged proteins in the evolutionary acquisition of stress tolerance in intertidal molluscs is discussed and parallels are drawn with the growing evidence for the involvement of autophagy in hormesis and anti-ageing processes.

Wave action modifies the effects of consumer diversity and warming on algal assemblages.

To understand the consequences of biodiversity loss, it is necessary to test how biodiversity-ecosystem functioning relationships may vary with predicted environmental change. In particular, our understanding will be advanced by studies addressing the interactive effects of multiple stressors on the role of biodiversity across trophic levels. Predicted increases in wave disturbance and ocean warming, together with climate-driven range shifts of key consumer species, are likely to have profound impacts on the dynamics of coastal marine communities. We tested whether wave action and temperature modified the effects of gastropod grazer diversity (Patella vulgata, Littorina littorea, and Gibbula umbilicalis) on algal assemblages in experimental rock pools. The presence or absence of L. littorea appeared to drive changes in microalgal and macroalgal biomass and macroalgal assemblage structure. Macroalgal biomass also decreased with increasing grazer species richness, but only when wave action was enhanced. Further, independently of grazer diversity, wave action and temperature had interactive effects on macroalgal assemblage structure. Warming also led to a reversal of grazer-macroalgal interaction strengths from negative to positive, but only when there was no wave action. Our results show that hydrodynamic disturbance can exacerbate the effects of changing consumer diversity, and may also disrupt the influence of other environmental stressors on key consumer-resource interactions. These findings suggest that the combined effects of anticipated abiotic and biotic change on the functioning of coastal marine ecosystems, although difficult to predict, may be substantial.

Parasites and personality in periwinkles (Littorina littorea): Infection status is associated with mean-level boldness but not repeatability

We demonstrate the presence of animal personality in an inter-tidal gastropod, Littorina littorea, both in a sample of individuals infected by the trematode Cryptocotyle lingua and in an uninfected sample. On average infected individuals behaved more cautiously than individuals free of infection, but the parasite did not affect repeatability. Although the parasite is not associated with greater diversity of behaviour amongst infected individuals, infection might be associated with state-dependent personality differences between infected and non-infected individuals.

Consistent effects of consumer species loss across different habitats

Our knowledge of the effects of consumer species loss on ecosystem functioning is limited by a paucity of manipulative field studies, particularly those that incorporate inter‐trophic effects. Further, given the ongoing transformation of natural habitats by anthropogenic activities, studies should assess the relative importance of biodiversity for ecosystem processes across different environmental contexts by including multiple habitat types. We tested the context‐dependency of the effects of consumer species loss by conducting a 15‐month field experiment in two habitats (mussel beds and rock pools) on a temperate rocky shore, focussing on the responses of algal assemblages following the single and combined removals of key gastropod grazers (Patella vulgata, P. ulyssiponensis, Littorina littorea and Gibbula umbilicalis). In both habitats, the removal of limpets resulted in a larger increase in macroalgal richness than that of either L. littorea or G. umbilicalis. Further, by the end of the study, macroalgal cover and richness were greater following the removal of multiple grazer species compared to single species removals. Despite substantial differences in physical properties and the structure of benthic assemblages between mussel beds and rock pools, the effects of grazer loss on macroalgal cover, richness, evenness and assemblage structure were remarkably consistent across both habitats. There was, however, a transient habitat‐dependent effect of grazer removal on macroalgal assemblage structure that emerged after three months, which was replaced by non‐interactive effects of grazer removal and habitat after 15 months. This study shows that the effects of the loss of key consumers may transcend large abiotic and biotic differences between habitats in rocky intertidal systems. While it is clear that consumer diversity is a primary driver of ecosystem functioning, determining its relative importance across multiple contexts is necessary to understand the consequences of consumer species loss against a background of environmental change.SynthesisThe roles of species may vary with environmental context, making it difficult to predict how biodiversity loss affects ecosystem functioning across multiple habitats. We tested how natural algal assemblages in two distinct intertidal habitats responded to the removal of different combinations of key consumer species. Despite an initial habitat‐dependent effect of consumer loss, habitat type did not modify the longer‐term responses of algal assemblages to either the identity or number of consumer species removed. Our findings show that, in certain systems, consumer diversity remains a primary driver of ecosystem functioning across widely different environmental contexts.

Opposing selective pressures decouple pattern and process of parasitic infection over small spatial scale

Species face multiple selective pressures that may require opposing responses to mitigate. On rocky shorelines, fitness of the intertidal snail Littorina littorea is determined by both parasitism and predation. We experimentally demonstrated that L. littorea was at greatest risk of infection from trematode parasites high in the intertidal zone where it was in closest proximity to abundant gull feces (the vector for the snail's parasites). However, because of extreme, size‐selective predation pressure at low tidal elevations, small snails often live high in the intertidal until they have grown sufficiently large. By prolonging their exposure to infection higher on the shore, ontogenetic responses to predation risk accentuate parasite risk. Counterintuitively, snails exhibited the highest trematode prevalence at the lowest tidal elevations where they had almost no risk of contracting infection. By carrying contracted infections into the lowest tidal zones, the larger, predation‐resistant snails invert hotspots of infection risk and prevalence, underscoring that size‐dependent selection pressures can decouple infection process and pattern even over small scales.

Long-Term Effects of an Invasive Shore Crab on Cape Cod, Massachusetts

Invasive species can cause dramatic changes in the structure of intertidal communities. In some systems, however, abundance or impacts of invaders may peak 10–20 years after invasion and decline thereafter. Hemigrapsus sanguineus (Asian Shore Crab) has been established at Sandwich, MA, on the north side of Cape Cod, since the mid-1990s. This study documented population dynamics of the Asian Shore Crab and 3 species of prey or competitors (Carcinus maenas [Green Crab], Mytilus edulis [Blue Mussel], and Littorina littorea [Common Periwinkle]) over 10 years. An additional goal of the study was to determine whether population growth of the Asian Shore Crab has slowed since its initial establishment. Density of the Asian Shore Crab increased over time, with no evidence of a density-dependent decrease in per capita growth rates. Concurrently, density of the Green Crab and the Blue Mussel declined, but there was no significant temporal trend in density of the Common Periwinkle. If observations at Sandwich are representative of sites north of Cape Cod, populations of the Asian Shore Crab are growing rapidly, and dramatic changes in community structure may be widespread.

Immunological and physiological responses of the periwinkle Littorina littorea during and after exposure to the toxic dinoflagellate Alexandrium minutum

Species of the dinoflagellate genus Alexandrium produce phycotoxins responsible for paralytic shellfish poisoning. Blooms of Alexandrium minutum reach very high concentrations of vegetative cells in the water column; and when these blooms occur, large numbers of toxic cysts can be produced and deposited on sediments becoming available to benthic species. The present study investigated the potential effect of exposure to toxic cysts of A. minutum on the periwinkle Littorinalittorea. Snails were exposed for nine days to pellicle cysts of toxic and non-toxic dinoflagellates, A. minutum and Heterocapsa triquetra, respectively, followed by six days of depuration while they were fed only H. triquetra. Toxin accumulation, condition index, immune and histopathological responses were analyzed. Histological alterations were also monitored in snails exposed to a harmful A. minutum bloom, which naturally occurred in the Bay of Brest. Snails exposed to toxic cysts showed abnormal behavior that seems to be toxin-induced and possibly related to muscle paralysis. Periwinkles accumulated toxins by preying on toxic cysts and accumulation appeared dependent on the time of exposure, increasing during intoxication period but tending to stabilize during depuration period. Toxic exposure also seemed to negatively affect hemocyte viability and functions, as ROS production and phagocytosis. Histological analyses revealed that toxic exposure induced damages on digestive organs of snails, both in laboratory and natural systems. This study demonstrates that an exposure to the toxic dinoflagellate A. minutum leads to sublethal effects on L. littorea, which may alter individual fitness and increase the susceptibility of snails to pathogens and diseases.

Short-Term Variation of the Macrobenthic Fauna Structure on Rocky Shores after the Hebei Spirit Oil Spill, West Coast of Korea

Jung, Y.-H.; Yoon, K.-T.; Shim, W.-J., and Park, H.-S., 2015. Short-term variation of the macrobenthic fauna structure on rocky shores after the Hebei Spirit oil spill, west coast of Korea.This study was conducted to determine the initial response, such as ecological status, to the disturbance in macrobenthic fauna on a rocky shore after an oil spill. Sites polluted with oil spilled during the Hebei Spirit accident on December 7, 2007, showed continuous decreases in species of the Bivalvia class, including Lasaea undulata and Mytilus galloprovincialis, and no gastropods were observed. In addition, at polluted sites, the cold-water barnacle Chthamalus challengeri and the common periwinkle were present in low densities, whereas they appeared relatively stable at control sites. In this study, the macrobenthic community structure was distinct between polluted sites and control sites because of differences in species composition and densities of dominant species. Therefore, it is believed that the oil spill accident could lead to mass mortalities of the major macrobenthic fauna in the study area, by smothering or reducing breeding activities or recruitment, and thereby altered rocky shore ecosystems.

Osphradial chemosensory organ as a probable trigger of the cardiac system adaptive reaction to the effect of heavy metals in aquatic molluscs

The responses of osphradium in the fresh-water mollusk Viviparus sp. and single osphradial neurons in the pond snail Lymnaea stagnalis to L-glutamine and L-asparagine as well as the changes in these responses under the effect of heavy metals (Cu, Cd) were recorded electrophysiologically. The functional connections of osphradium with the identified neurons of the central pattern generator of respiratory movements and cardiac activity as well as the modification of these connections under the effect of short-term application of HgCl2 solution on the snail's osphradium were investigated. The cardiac rhythm in the mollusk Littorina littorea under the effect of Cu ions was registered non-invasively in long-lasting experiments. The dose-dependent short-term effects of heavy metals changes after osphradium injury were revealed. The implication of osphradium in adaptive reactions of the cardiac system in aquatic mollusks to the environmental heavy metal pollution is suggested. The dependence of cardiac rhythm on the degree of accumulation of copper ions in the mollusk tissues was detected. The results obtained are essential for unraveling neural mechanisms and pathways allowing heavy metals to affect the functional state of hydrobionts, particularly, the cardiac activity frequency characteristics of which are widely used as informative biomarkers to assess physiological condition of aquatic invertebrates.

Lectin-like molecules in transcriptome of Littorina littorea hemocytes

The common periwinkle Littorina littorea was introduced in the list of models for comparative immunobiology as a representative of phylogenetically important taxon Caenogastropoda. Using Illumina sequencing technology, we de novo assembled the transcriptome of Littorina littorea hemocytes from 182 million mRNA-Seq pair-end 100 bp reads into a total of 15,526 contigs clustered in 4472 unigenes. The transcriptome profile was analyzed for presence of carbohydrate-binding molecules in a variety of architectural contexts. Hemocytes' repertoire of lectin-like proteins bearing conserved carbohydrate-recognition domains (CRDs) is highly diversified, including 11 of 15 lectin families earlier described in animals, as well as the novel members of lectin family found for the first time in mollusc species. The new molluscan lineage-specific domain combinations were confirmed by cloning and sequencing, including the fuco-lectin related molecules (FLReMs) composed of N-terminal region with no sequence homology to any known protein, a middle Fucolectin Tachylectin-4 Pentaxrin (FTP) domain, and a C-terminal epidermal growth factor (EGF) repeat region. The repertoire of lectin-like molecules is discussed in terms of their potential participation in the receptor phase of immune response. In total, immune-associated functions may be attributed to 70 transcripts belonging to 6 lectin families. These lectin-like genes show low overlap between species of invertebrates, suggesting relatively rapid evolution of immune-associated genes in the group. The repertoire provides valuable candidates for further characterization of the gene functions in mollusc immunity.

The smell of sex: water-borne and air-borne sex pheromones in the intertidal gastropod Littorina littorea

We investigated whether individuals of the intertidal snail Littorina littorea may be attracted by waterborne and air-borne pheromones from conspecifics. The potential relative role of water-borne and air-borne pheromone in the behavioural and reproductive biology of L. littorea was assessed through chemotactic assays. These involved a series of choice experiments with snails, snail smell and snail mucus as stimuli in a T-maze under conditions of immersion and emersion, and during the nonmating and mating seasons. During the nonmating season, L. littorea did not choose the snail-conditioned side of the T-maze significantly more frequently than the control side under conditions of both immersion and emersion. During the mating season, under condition of immersion both males and females chose the side of the T-maze conditioned with individual of the opposite sex significantly more frequently than the control side, and did not show any preference for the side conditioned with individuals of the same sex. Under conditions of emersion, only males were significantly more attracted by cues from the opposite sex than by the control. These results indicate that L. littorea are not attracted by conspecifics during the nonmating season; the cues of conspecifics are then unlikely to play a role in the orientation or the aggregation behaviour of this species. The results also suggest that males and females are attracted by the odour of conspecifics of the opposite sex, which contains both water-borne and air-borne pheromones in females and only water-borne pheromones in males. Also the similar behaviours observed with snails, water-borne and air-borne snail smell, and snail mucus, as stimuli indicate that male and female sex pheromones are both present in mucus. Temperature manipulations conducted during both seasons did not affect any of the observed behavioural changes, hence suggesting that the chemoreceptive abilities of L. littorea may be driven by exogenous and/or endogenous factors that are decoupled from direct control by temperature. This is in sharp contrast to the locomotor activity of L. littorea, which consistently increased with temperature. We also report the possibility of mate-tracking in females, a behaviour that has yet to be reported in gastropods, since males are typically believed to be the active sex that searches for females. Our results build on previous evidence of the function played by mucus-trail following in the reproductive success of intertidal gastropods, through the ability of L. littorea to remotely detect the water-borne and air-borne sex-specific cues that are incorporated in their mucus.

English

Leaf blight caused by Rhizoctonia solani is one of the most serious diseases that cause damage to turmeric crop. Fifty percent disease incidence was observed in turmeric growing areas of Andhiyur (Erode district) and Mettur (Salem district) of Tamil Nadu, India. The antifungal efficacy of botanicals, bioagents and fungicides were tested against R. solani in vitro. It was observed that seed extract and oil cake of Madhuca longifolia suppressed the mycelia growth (34.81; 49.63%), sclerotial formation (100%) and production of biomass (2.18; 2.41 mg) of R. solani followed by leaf extracts of Azadirachta indica and Littorina littorea. Among the bioagents native isolate of BSoya1 of Bacillus spp., Cg1 of Chaetomium spp., Pf1 of Pseudomonas spp. and Tv1 of Trichoderma spp. shown more than 50% antagonistic effect on mycelia growth and 100% on sclerotial formation. The complete fungal growth inhibition was observed in Nativo and Bavistin fungicides amended medium. Then, the basal soil application of mahua cake and T. viride in the ratio of 1:2 (1 g of mahua cake mixed with 2 g T. viride per kg of pot soil) followed by foliar spray of Nativo @ 0.5% significantly mitigated the leaf blight (8.6%) over the inoculated control (50.51%) in pot culture experiments. Key words: Turmeric, efficacy, fungicides, bioagents, botanicals, Rhizoctonia solani.

Himasthla elongata: Implantation of rediae to the specific iteroparous long-living host, Littorina littorea, results in the immune rejection

All semelparous short-lived gastropods studied so far for the experimental transplantation of trematode parthenitae, from one specific host to another, showed more or less successful acceptance of implanted parasites. We implanted echinostomatid rediae, Himasthla elongata, to the specific iteroparous long-living host, coenogastropod Littorina littorea. Using simple and low-invasive implantation techniques we have tested 680 snails injected with 75 redia microhemipopulations (MHP) harvested from naturally infected snails. Neither young nor mature rediae were able to survive in the recipient periwinkles in the course of 30 days post-implantation. A strong immune response from the host was already evident within the first week after implantation: initial inactivation of motile rediae with toxic humoral immune factors, following encapsulation of the implants and increased hemocyte counts. In contrast, rediae from the same MHPs showed perfect survival rates in primary in vitro axenic cultures. The failure of the transplantation experiments is explained in terms of the compatibility matching phenotype model. In the studied host-parasite combination all periwinkles are potentially susceptible and all rediae MHPs are potentially infective, however the probability of the compatible phenotypes matching is virtually low. Low investment in L. littorea annual reproduction would result in increased investment in self maintenance and immune mechanisms, causing the general resistance to the trematode infestation. Presumably, this resistance is relatively higher in long-lived iteroparous gastropods compare to semelparous short-lived mollusks such as pulmonates.

Community context mediates the top-down vs. bottom-up effects of grazers on rocky shores.

Interactions between grazers and autotrophs are complex, including both top-down consumptive and bottom-up facilitative effects of grazers. Thus, in addition to consuming autotrophs, herbivores can also enhance autotroph biomass by recycling limiting nutrients, thereby increasing nutrient availability. Here, we evaluated these consumptive and facilitative interactions between snails (Littorina littorea) and seaweeds (Fucus vesiculosus and Ulva lactuca) on a rocky shore. We partitioned herbivores' total effects on seaweeds into their consumptive and facilitative effects and evaluated how community context (the presence of another seaweed species) modified the effects of Littorina on a focal seaweed species. Ulva, the more palatable species, enhanced the facilitative effects of Littorina on Fucus. Ulva did not modify the consumptive effect of Littorina on Fucus. Taken together, the consumptive and facilitative effects of snails on Fucus in the presence of Ulva balanced each other, resulting in no net effect of Littorina on Fucus. In contrast, the only effect of Fucus on Ulva was to enhance consumptive effects of Littorina on Ulva. Our results highlight the necessity of considering both consumptive and facilitative effects of herbivores on multiple autotroph species in order to gain a mechanistic understanding of grazers' top-down and bottom-up roles in structuring communities.

Molecular cloning of α-2-macroglobulin from hemocytes of common periwinkle Littorina littorea

We report the sequence of the proteinase inhibitor with a wide inhibition spectrum, α-2-macroglobulin (α2M), belonging to the thioester superfamily of proteins. This is the first α2M sequence from coenogastropod prosobranch snails. The full-length cDNA was cloned by RACE method, spans 7897 bp and contains an open reading frame of 5460 bp. The ORF encodes a protein of 1819 amino acids. The deduced mature protein contains 1795 amino acids with a molecular weight of 200 kDa and isoelectric point of 5.00. Littorina littorea α2M bears 4 conserved α2M domains and one internal thioester. Phylogenetic analysis showed that the sequence forms well supported cluster with Mollusca species and other representatives of Lophotrochozoa.

Caste formation in larval Himasthla elongata (Trematoda) infecting common periwinkles Littorina littorea

Reproductive division of labour is well-known in several animal groups but the ecological factors driving the evolution of such social organization are still being discussed. Recent studies have discovered social organization in four marine species of trematode parasites having two distinct castes specialized for reproduction and defence of the clonal intra-molluscan larval colony, respectively. Here, we provide novel evidence for social structure also in colonies of the trematode Himasthla elongata infecting the common periwinkle Littorina littorea. We found two types of rediae, the parthenogenetic larval offspring of the parasite: small non-reproductive rediae and considerably larger reproductive rediae. Both redial types possessed a digestive system, collar and posterior appendages and, hence, aside from dimensions, were morphologically similar. However, in vitro experiments showed that non-reproductive morphs attacked heterospecific competing parasites at a higher rate (2–3 fold) than reproductive morphs did. No within-colony antagonism was observed. In contrast to a previous study on a congeneric trematode species, our findings suggest a relatively weak caste formation in H. elongata, possibly resulting from a corresponding weaker level of interspecific competition.