Genetic isolation by distance among populations of the netted dog whelk Nassarius reticulatus (L.) along the European Atlantic coastline.
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Estimates of the average distances by which marine larvae disperse are generally poorly described, despite the central role that larval dispersal plays in the demographic connectivity of populations across geographic space. Here, we describe the population genetic structure and average dispersal distance of the netted dog whelk Nassarius reticulatus (L.) (Mollusca, Gastropoda, Prosobranchia), a widespread member of European intertidal communities, using DNA sequence variation in a fragment of the mitochondrial gene cytochrome c oxidase subunit I (COI). An analysis of 156 individuals from 6 locations spread across approximately 1700 km of the European Atlantic coastline revealed weak and nonsignificant population structure (overall Phi(ST) = 0.00013). However, pairwise Phi(ST) values revealed a slight but significant increase in genetic isolation with geographic distance (IBD), suggesting that populations are not panmictic across the sampled geographic range. If we assume that the isolation by distance is maintained by a stable, stepping stone model of gene flow, then the slope of the IBD is consistent with an average larval dispersal distance of approximately 70 km per generation. The spatial scale of larval dispersal in N. reticulatus is consistent with the life cycle of the species (planktotrophic veliger lasting 30-60 days before competent to settle). A mismatch analysis of the COI sequences revealed a signature of an ancient demographic expansion that began 61 500-160,000 years ago, well before the most recent Pleistocene glaciation event. The greatest levels of genetic diversity occur within the middle latitudes of the whelk's geographic range, consistent with the notion that historic populations of N. reticulatus might have expanded northward and southward from the centrally located Bay of Biscay. (+info)
Shrinking to fit: fluid jettison from a haemocoelic hydrostatic skeleton during defensive withdrawals of a gastropod larva.
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Although most of the basic animal body plans are supported by hydrostatic skeletons consisting of fluid maintained at constant volume, studies on how animals have solved biomechanical scaling dilemmas during evolution of large body size have emphasized cases where skeletons are formed by rigid solids. Larvae of gastropod molluscs swim using ciliated velar lobes supported by a constant volume hydrostatic skeleton. Defensive behaviour involves rapid withdrawal of the velar lobes and foot into a protective biomineralized shell. Some gastropod larvae grow to giant size and the velar lobes enlarge allometrically, but the lobes and foot of many can still withdraw completely into the mineral-stiffened shell. I dyed internal fluid of a large gastropod larva with fluorescein to show that fluid supporting the extended velar lobes is expelled from discrete release sites during defensive withdrawals. Scanning electron microscopy suggested that release sites are distinctive papillae on the upper velar epidermis. Ultrathin sections revealed that branched tracks of microvilli-free membrane on the surface of these papillae were formed by very thin epithelial cells, which may rupture and re-anneal during and after defensive withdrawals. Behaviours facilitated by fluid discharge from a haemocoelic (non-coelomic) body compartment have been rarely reported among aquatic invertebrates, but may be more widespread than currently recognized. (+info)
The role of MAPK signaling in patterning and establishing axial symmetry in the gastropod Haliotis asinina.
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Gastropods are members of the Spiralia, a diverse group of invertebrates that share a common early developmental program, which includes spiral cleavage and a larval trochophore stage. The spiral cleavage program results in the division of the embryo into four quadrants. Specification of the dorsal (D) quadrant is intimately linked with body plan organization and in equally cleaving gastropods occurs when one of the vegetal macromeres makes contact with overlying micromeres and receives an inductive signal that activates a MAPK signaling cascade. Following the induction of the 3D macromere, the embryo begins to gastrulate and assumes a bilateral cleavage pattern. Here we inhibit MAPK activation in 3D with U0126 and examine its effect on the formation and patterning of the trochophore, using a suite of territory-specific markers. The head (pretrochal) region appears to maintain quadri-radial symmetry in U0126-treated embryos, supporting a role for MAPK signaling in 3D in establishing dorsoventral polarity in this region. Posterior (posttrochal) structures - larval musculature, shell and foot--fail to develop in MAPK inhibited trochophores. Inhibition of 3D specification by an alternative method--monensin treatment--yields similar abnormal trochophores. However, genes that are normally expressed in the ectodermal structures (shell and foot) are detected in U0126- and monensin-perturbed larvae in patterns that suggest that this region has latent dorsoventral polarity that is manifested even in the absence of D quadrant specification. (+info)
Ocean acidification disrupts induced defences in the intertidal gastropod Littorina littorea.
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Carbon dioxide-induced ocean acidification is predicted to have major implications for marine life, but the research focus to date has been on direct effects. We demonstrate that acidified seawater can have indirect biological effects by disrupting the capability of organisms to express induced defences, hence, increasing their vulnerability to predation. The intertidal gastropod Littorina littorea produced thicker shells in the presence of predation (crab) cues but this response was disrupted at low seawater pH. This response was accompanied by a marked depression in metabolic rate (hypometabolism) under the joint stress of high predation risk and reduced pH. However, snails in this treatment apparently compensated for a lack of morphological defence, by increasing their avoidance behaviour, which, in turn, could affect their interactions with other organisms. Together, these findings suggest that biological effects from ocean acidification may be complex and extend beyond simple direct effects. (+info)
New caulerpenyne-derived metabolites of an Elysia sacoglossan from the South Indian coast.
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Chemical analysis of the secondary metabolite pattern of the sacoglossan mollusc Elysia cf. expansa, collected along South Indian coasts, showed the presence of the typical Caulerpa-derived sesquiterpene caulerpenyne (1) and two new minor co- occurring metabolites, the compounds dihydrocaulerpenyne (4) and expansinol (5). The chemical characterization of these molecules, structurally related to 1, is reported. (+info)
InhA-like protease secreted by Bacillus sp. S17110 inhabited in turban shell.
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A strain producing a potent protease was isolated from turban shell. The strain was identified as Bacillus sp. S17110 based on phylogenetic analysis. The enzyme was purified from culture supernatant of Bacillus sp. S17110 to homogeneity by ammonium sulfate precipitation, SP-Sepharose, and DEAE-Sepharose anion exchange chromatography. Protease activity of the purified protein against casein was found to be stable at pH 7 to pH 10 and around 50 degrees . Approximately 70% of proteolytic activity of the enzyme was detected either in the presence of 100 mM SDS or Tween 20. The enzyme activity was enhanced in the presence of Ca2+, Zn2+, Mg2+, but was inhibited by EDTA, indicating that it requires metal for its activity. The purified enzyme was found to be a monomeric protein with a molecular mass of 75 kDa, as estimated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and gel filtration chromatography. The purified enzyme was analyzed through peptide fingerprint mass spectra generated from matrix-assisted laser desorption ionization-time-of-flight-mass spectrometry (MALDI-TOF-MS) and a BLAST search, and identified as immune inhibitor A (inhA) deduced from nucleotide sequence of B. cereus G9241. Since InhA was identified as protease that cleave antibacterial proteins found in insect, inhA-like protease purified from Bacillus sp. S17110 might be pathogenic to sea invertebrates. (+info)
Shewanella haliotis sp. nov., isolated from the gut microflora of abalone, Haliotis discus hannai.
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A motile, rod-shaped, pink-orange pigmented bacterium, designated strain DW01(T), was isolated from the gut microflora of abalone collected from the South Sea (Republic of Korea). Cells were Gram-negative, facultatively anaerobic, catalase- and oxidase-positive. The major fatty acids were iso-C(15 : 0) (17.7 %), C(16 : 0) (13.4 %), iso-C(15 : 0) 2-OH and/or C(16 : 1)omega7c (12.5 %) and C(17 : 1)omega8c (10.7 %). The DNA G+C content was 53.7 mol%. A phylogenetic tree based on the 16S rRNA gene sequences showed that strain DW01(T) forms a lineage of the genus Shewanella and is closely related to Shewanella algae ATCC 51192(T) (98.3 % sequence similarity) and to other members of the genus Shewanella (91.0-94.9 %). The phenotypic characteristics and DNA-DNA hybridization relatedness data indicate that strain DW01(T) should be distinguished from S. algae ATCC 51192(T). On the basis of the data presented in this study, strain DW01(T) represents a novel species, for which the name Shewanella haliotis sp. nov. is proposed. The type strain is DW01(T) (=KCTC 12896(T)=JCM 14758(T)). (+info)
Further twists in gastropod shell evolution.
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