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The shell of Ensis species is vulnerable and can easily be damaged. In response to a paper of Cadée (2018) a particular case of malformation of a specimen of Ensis leei Huber by the intrusion of a littorinid shell is elucidated

Heavily damaged and malformed shells of Ensis leei found on the Dutch coast are suggested to be due to commercial fishery on this species with a specialized dredge. All specimens smaller than 10 cm length are discarded and returned to the sea. Some may survive the damage and scavengers and repair their shell

A malformed specimen of Ensis leei Huber, 2015, with a dead specimen of Littorina littorea (Linnaeus, 1758) inside is reported upon. It is argued that the malformation of the bivalve was due to the intrusion of the littorinid. Despite this intrusion, that happened when the Ensis specimen had a shell length of c. 4 cm, the bivalve animal grew to a shell length of 12 cm. This is the first record of such a phenomenon.

Invasive species have the ability to outcompete natives, and can create a monoculture if not mitigated by herbivores or some other mechanism. Limited information exists on the ecology of the invasive macroalga Grateloupia turuturu and how it is impacted by herbivores. Using laboratory mesocosm experiments, we investigated the ability of two invasive herbivore species common in Rhode Island, the snail Littorina littorea and Asian shore crab Hemigrapsus sanguineus, to control Grateloupia populations. In the first trial, Grateloupia was provided to a single herbivore (either Littorina or Hemigrapsus) or both herbivores together. Grateloupia controls were in the same mesocosms as each treatment, but were separated by a mesh partition to allow water flow and account for possible facilitation by herbivore presence. Mesocosms were kept at 13°C and at 0, 2, 4, and 6 days, the algae was weighed and water samples were taken. Preliminary results indicate that Littorina do indeed graze on Grateloupia, with an average decrease in mass of 44.6% after 6 days. There was no significant change in mass of Grateloupia in the presence of Hemigrapsus only or with Littorina and Hemigrapsus together. Future trials will include two common species of marine macroalgae along with the Grateloupia, to investigate herbivore feeding preference when exposed to multiple food choices. The ultimate results of these trials are intended to indicate the success of the continued invasion of Grateloupia in Rhode Island waters, and predict the role of invasive herbivores in controlling Grateloupia populations.

Unravelling the form of selection acting on hybrids of ecotypes undergoing ecological speciation is essential to understand the mechanisms behind the evolution of reproductive isolation in the face of gene flow. Shell phenotype is known to be affected by natural selection and is involved in the fitness of the marine snail Littorina saxatilis. Here, we studied the association between shell traits and fitness in hybrids in order to determine the relative role of exogenous and endogenous selection in this hybrid zone of L.saxatilis. We show that directional selection is the predominant mode of selection among hybrids. We also show its heterogeneity, affecting different shell traits, within populations at the level of the microhabitat. Therefore, endogenous selection mechanisms are most probably lacking in this hybrid zone and exogenous barriers (pre- and post-zygotic) are possibly one of the main forces behind the evolution of barriers to gene flow between these ecologically divergent ecotypes. This study shows how this barrier might represent an important type of reproductive isolation within ecological speciation, and this should be taken into account in future studies of speciation in hybrid zones.

Hybrid zones of ecologically divergent populations are ideal systems to study the interaction between natural selection and gene flow during the initial stages of speciation. Here, we perform an amplified fragment length polymorphism (AFLP) genome scan in parallel hybrid zones between divergent ecotypes of the marine snail Littorina saxatilis, which is considered a model case for the study of ecological speciation. Ridged-Banded (RB) and Smooth-Unbanded (SU) ecotypes are adapted to different shore levels and microhabitats, although they present a sympatric distribution at the mid-shore where they meet and mate (partially assortatively). We used shell morphology, outlier and nonoutlier AFLP loci from RB, SU and hybrid specimens captured in sympatry to determine the level of phenotypic and genetic introgression. We found different levels of introgression at parallel hybrid zones and nonoutlier loci showed more gene flow with greater phenotypic introgression. These results were independent from the phylogeography of the studied populations, but not from the local ecological conditions. Genetic variation at outlier loci was highly correlated with phenotypic variation. In addition, we used the relationship between genetic and phenotypic variation to estimate the heritability of morphological traits and to identify potential Quantitative Trait Loci to be confirmed in future crosses. These results suggest that ecology (exogenous selection) plays an important role in this hybrid zone. Thus, ecologically based divergent natural selection is responsible, simultaneously, for both ecotype divergence and hybridization. On the other hand, genetic introgression occurs only at neutral loci (nonoutliers). In the future, genome-wide studies and controlled crosses would give more valuable information about this process of speciation in the face of gene flow. © 2013 European Society For Evolutionary Biology.

Determining the magnitude of dispersal and connectivity between populations has important implications for marine conservation. Species with limited dispersal capabilities exhibit restricted gene flow leading to isolation and, ultimately, differentiated populations. In this ecological study I investigated the gastropods Austrolittorina antipodum (Philippi, 1847) and Austrolittorina cincta (Quoy and Gaimard, 1833) to determine how ecology and behaviour influence the dispersal and connectivity of these species. The aim of this study was to determine population size and structure, settlement, fecundity, and adult movement rates. Methodologies included: population surveys, deployment of settlement pads and adult density manipulations, dissections, and a tagging study. These elements of a species ecology and behaviour can enhance or restrict population connectivity by: cohort partitioning resulting from habitat requirements, fluctuating settlement due to variable larval mortality or adult densities impacting dispersal, skewed sex ratios and effective populations sizes altering larval production, and adult movement leading to behavioural isolation or facilitating gene flow, along with other possible effects. Population surveys revealed both species had a Vermeij (1972) "type 1 distribution" (shell size increasing from the low to high shore), with the highest density of individuals on the low shore and the majority of mature adults on the high shore. Overall, A. antipodum was 16 times more abundant than A. cincta. Shifts to a smaller mean size of both species, along all shore heights following periods of peak settlement indicates settlers are potentially triggering competitive interactions or ontogenetic migrations in other cohorts.Settlement surveys revealed that peak settlement for Austrolittorina spp. was from February to April, declining at the beginning of March. Multiple peaks in settlement may act as a buffer limiting the potential of stochastic events to hinder dis

Determining the magnitude of dispersal and connectivity between populations has important implications for marine conservation. Species with limited dispersal capabilities exhibit restricted gene flow leading to isolation and, ultimately, differentiated populations. In this ecological study I investigated the gastropods Austrolittorina antipodum (Philippi, 1847) and Austrolittorina cincta (Quoy and Gaimard, 1833) to determine how ecology and behaviour influence the dispersal and connectivity of these species. The aim of this study was to determine population size and structure, settlement, fecundity, and adult movement rates. Methodologies included: population surveys, deployment of settlement pads and adult density manipulations, dissections, and a tagging study. These elements of a species ecology and behaviour can enhance or restrict population connectivity by: cohort partitioning resulting from habitat requirements, fluctuating settlement due to variable larval mortality or adult densities impacting dispersal, skewed sex ratios and effective populations sizes altering larval production, and adult movement leading to behavioural isolation or facilitating gene flow, along with other possible effects. Population surveys revealed both species had a Vermeij (1972) "type 1 distribution" (shell size increasing from the low to high shore), with the highest density of individuals on the low shore and the majority of mature adults on the high shore. Overall, A. antipodum was 16 times more abundant than A. cincta. Shifts to a smaller mean size of both species, along all shore heights following periods of peak settlement indicates settlers are potentially triggering competitive interactions or ontogenetic migrations in other cohorts.Settlement surveys revealed that peak settlement for Austrolittorina spp. was from February to April, declining at the beginning of March. Multiple peaks in settlement may act as a buffer limiting the potential of stochastic events to hinder dis

Determining the magnitude of dispersal and connectivity between populations has important implications for marine conservation. Species with limited dispersal capabilities exhibit restricted gene flow leading to isolation and, ultimately, differentiated populations. In this ecological study I investigated the gastropods Austrolittorina antipodum (Philippi, 1847) and Austrolittorina cincta (Quoy and Gaimard, 1833) to determine how ecology and behaviour influence the dispersal and connectivity of these species. The aim of this study was to determine population size and structure, settlement, fecundity, and adult movement rates. Methodologies included: population surveys, deployment of settlement pads and adult density manipulations, dissections, and a tagging study. These elements of a species ecology and behaviour can enhance or restrict population connectivity by: cohort partitioning resulting from habitat requirements, fluctuating settlement due to variable larval mortality or adult densities impacting dispersal, skewed sex ratios and effective populations sizes altering larval production, and adult movement leading to behavioural isolation or facilitating gene flow, along with other possible effects. Population surveys revealed both species had a Vermeij (1972) "type 1 distribution" (shell size increasing from the low to high shore), with the highest density of individuals on the low shore and the majority of mature adults on the high shore. Overall, A. antipodum was 16 times more abundant than A. cincta. Shifts to a smaller mean size of both species, along all shore heights following periods of peak settlement indicates settlers are potentially triggering competitive interactions or ontogenetic migrations in other cohorts.Settlement surveys revealed that peak settlement for Austrolittorina spp. was from February to April, declining at the beginning of March. Multiple peaks in settlement may act as a buffer limiting the potential of stochastic events to hinder dis

Determining the magnitude of dispersal and connectivity between populations has important implications for marine conservation. Species with limited dispersal capabilities exhibit restricted gene flow leading to isolation and, ultimately, differentiated populations. In this ecological study I investigated the gastropods Austrolittorina antipodum (Philippi, 1847) and Austrolittorina cincta (Quoy and Gaimard, 1833) to determine how ecology and behaviour influence the dispersal and connectivity of these species. The aim of this study was to determine population size and structure, settlement, fecundity, and adult movement rates. Methodologies included: population surveys, deployment of settlement pads and adult density manipulations, dissections, and a tagging study. These elements of a species ecology and behaviour can enhance or restrict population connectivity by: cohort partitioning resulting from habitat requirements, fluctuating settlement due to variable larval mortality or adult densities impacting dispersal, skewed sex ratios and effective populations sizes altering larval production, and adult movement leading to behavioural isolation or facilitating gene flow, along with other possible effects. Population surveys revealed both species had a Vermeij (1972) "type 1 distribution" (shell size increasing from the low to high shore), with the highest density of individuals on the low shore and the majority of mature adults on the high shore. Overall, A. antipodum was 16 times more abundant than A. cincta. Shifts to a smaller mean size of both species, along all shore heights following periods of peak settlement indicates settlers are potentially triggering competitive interactions or ontogenetic migrations in other cohorts.Settlement surveys revealed that peak settlement for Austrolittorina spp. was from February to April, declining at the beginning of March. Multiple peaks in settlement may act as a buffer limiting the potential of stochastic events to hinder dis

Littorina littorea shells found broken on a cycle-track next to where they lived, are thought to be broken by shell-dropping birds. Shells broken experimentally by dropping them from 6 m height on a concrete floor showed very similar damage: a hole in the last whorl, whereas the aperture rim remained intact. Examples from the literature indicate this shell damage to be characteristic for shell-dropping by birds. We suspect carrion crows as the culprit, but field observations have to prove this.

At present, the periwinkle, Littorina littorea (Linné, 1758), is not found living in Iceland. The only confirmed occurrence of the species in Icelandic sediments is in the Middle Pleistocene upper littoral conglomerate at Búlandshöfdi, Snaefellsnes, West Iceland. These layers were deposited during an interglacial stage, slightly older than 1.1 Ma. The species apparently evolved from the Pacific L. squalida Broderip & Sowerby, 1829, after the trans-Arctic/North Atlantic migration from the Pacific, possibly in response to cooling and increasing environmental energy. The oldest fossil occurrence of L. littorea is in the British Red Crag Formation, between 2.55 and 2.4 Ma; it is unknown from the Pliocene Tjörnes deposits in N Iceland, older than 2.6 Ma. This indicates that the species separation postdates the deposition of the uppermost Serripes Zone of Tjörnes, after the tide of the migration wave passed Iceland, but before it reached the North Sea area and Britain, between 2.6 and 2.4 Ma. The taxonomic diversity and palaeobiogeography of North Atlantic molluscs were greatly affected by the major climatic changes that resulted in an extensive glaciation at about 2.5 Ma.

The results of a 14-year survey of the populations of L. saxatilis and L. obtusata from one locality in the Kandalaksha Bay of the White Sea are presented. The periwinkles were found to be hosts of 10 castrating trematode species. Microphallus piriformes was the most abundant species with infection prevalence often exceeding 50%. Year-to-year variation of the infection prevalence was correlated in the two host species, probably reflecting fluctuations in the influx of trematode eggs to the shore. Long-term changes in population density are associated with the variation of the age structure of the winkles, suggesting a dependence of the population density on the success of the recruitment. Fluctuations in abundance and age composition were correlated in L. saxatilis sub-populations inhabiting macrophytes, gravel and stone surfaces, but were asynchronous with changes in abundance and age composition of L. obtusata population. No significant influence of variations in trematode infection upon the hosts' abundance or age structure was found in either species of the winkles. It is assumed that despite a strong negative influence of trematodes on reproduction of the host individual, there are no disastrous consequences for the population level; this, in turn, suggests the existence of some compensating mechanisms ensuring a stability of the host-parasite co-action.

The results of a 14-year survey of the populations of L. saxatilis and L. obtusata from one locality in the Kandalaksha Bay of the White Sea are presented. The periwinkles were found to be hosts of 10 castrating trematode species. Microphallus piriformes was the most abundant species with infection prevalence often exceeding 50%. Year-to-year variation of the infection prevalence was correlated in the two host species, probably reflecting fluctuations in the influx of trematode eggs to the shore. Long-term changes in population density are associated with the variation of the age structure of the winkles, suggesting a dependence of the population density on the success of the recruitment. Fluctuations in abundance and age composition were correlated in L. saxatilis sub-populations inhabiting macrophytes, gravel and stone surfaces, but were asynchronous with changes in abundance and age composition of L. obtusata population. No significant influence of variations in trematode infection upon the hosts' abundance or age structure was found in either species of the winkles. It is assumed that despite a strong negative influence of trematodes on reproduction of the host individual, there are no disastrous consequences for the population level; this, in turn, suggests the existence of some compensating mechanisms ensuring a stability of the host-parasite co-action.

The results of a 14-year survey of the populations of L. saxatilis and L. obtusata from one locality in the Kandalaksha Bay of the White Sea are presented. The periwinkles were found to be hosts of 10 castrating trematode species. Microphallus piriformes was the most abundant species with infection prevalence often exceeding 50%. Year-to-year variation of the infection prevalence was correlated in the two host species, probably reflecting fluctuations in the influx of trematode eggs to the shore. Long-term changes in population density are associated with the variation of the age structure of the winkles, suggesting a dependence of the population density on the success of the recruitment. Fluctuations in abundance and age composition were correlated in L. saxatilis sub-populations inhabiting macrophytes, gravel and stone surfaces, but were asynchronous with changes in abundance and age composition of L. obtusata population. No significant influence of variations in trematode infection upon the hosts' abundance or age structure was found in either species of the winkles. It is assumed that despite a strong negative influence of trematodes on reproduction of the host individual, there are no disastrous consequences for the population level; this, in turn, suggests the existence of some compensating mechanisms ensuring a stability of the host-parasite co-action.

The results of a 14-year survey of the populations of L. saxatilis and L. obtusata from one locality in the Kandalaksha Bay of the White Sea are presented. The periwinkles were found to be hosts of 10 castrating trematode species. Microphallus piriformes was the most abundant species with infection prevalence often exceeding 50%. Year-to-year variation of the infection prevalence was correlated in the two host species, probably reflecting fluctuations in the influx of trematode eggs to the shore. Long-term changes in population density are associated with the variation of the age structure of the winkles, suggesting a dependence of the population density on the success of the recruitment. Fluctuations in abundance and age composition were correlated in L. saxatilis sub-populations inhabiting macrophytes, gravel and stone surfaces, but were asynchronous with changes in abundance and age composition of L. obtusata population. No significant influence of variations in trematode infection upon the hosts' abundance or age structure was found in either species of the winkles. It is assumed that despite a strong negative influence of trematodes on reproduction of the host individual, there are no disastrous consequences for the population level; this, in turn, suggests the existence of some compensating mechanisms ensuring a stability of the host-parasite co-action.