Changing Tropical Estuarine Sedimentary Environments with Time and Metals Contamination, Cest Coast of India

Estuaries are one of the major sub-environments of the coastal zone wherein freshwaters interact and mix with saline waters, and facilitate deposition of finer sediments, organic matter, and metals. Intertidal mudflat and mangrove sediment cores collected from estuaries along the central west coast of India were investigated for various sedimentological and geochemical parameters to understand the changes in the sedimentary depositional environments and various factors influencing the processes. Additionally, estuarine biota was examined to understand the bioaccumulation of metals with respect to bioavailability. The results indicated considerable changes in the depositional environments with time owing to sea-level changes; geomorphology of the estuaries; rainfall and river runoff; anthropogenic activities including construction of dams and bridges. The sediments in the estuaries are considerably polluted by metals and pose toxicity risks to the estuarine biota due to high metal bioavailability. Marine gastropods and mangrove plants act as prospective bio-indicators, and the bioremediation potential of mangroves for contaminated sediments was identified. Metal bioaccumulation in edible benthic biota can be harmful to the human health.

Identification of Novel Conotoxin Precursors from the Cone Snail Conus spurius by High-Throughput RNA Sequencing

Marine gastropods of the genus Conus, comprising more than 800 species, have the characteristic of injecting worms and other prey with venom. These conopeptide toxins, highly diverse in structure and action, are highly potent and specific for their molecular targets (ion channels, receptors, and transporters of the prey’s nervous system), and thus are important research tools and source for drug discovery. Next-generation sequencing technologies are speeding up the discovery of novel conopeptides in many of these species, but only limited information is available for Conus spurius, which inhabits sandy mud. To search for new precursor conopeptides, we analyzed the transcriptome of the venous ducts of C. spurius and identified 55 putative conotoxins. Seven were selected for further study and confirmed by Sanger sequencing to belong to the M-superfamily (Sr3.M01 and Sr3.M02), A-superfamily (Sr1.A01 and Sr1.A02), O-superfamily (Sr15.O01), and Con-ikot-ikot (Sr21.CII01 and Sr22.CII02). Six of these have never been reported. To our knowledge, this report is the first to use high-throughput RNA sequencing for the study of the diversity of C. spurius conotoxins.

Comparison of Evolutionary Selection Acting on the Mitochondrial Protein-Coding Genes Between Intertidal and Deep-Sea Gastropods

Marine molluscs are ecologically and economically important group of organisms that survive in the challenging environments of different oceanic zones. Of all the classes of the phylum Mollusca, gastropods have radiated into marine, freshwater and terrestrial habitats, successfully adapting themselves to thrive in changing environmental conditions. Hence, marine gastropods can be considered as an ideal system to study stress adaptation. In order to withstand the constant fluctuations in temperature, salinity and shifts in oxygen concentration of the intertidal zone, the gastropods inhabiting here rely on a modified and adaptive energy metabolism. The same is applicable for gastropods living in the deep sea environment, which is characterized by high hydrostatic pressure, low oxygen concentrations and abundance of heavy metals. Therefore, survival of these organisms may be correlated to their adaptive mitochondrial genome which serves as the principal site for energy metabolism and production in the cell. Here, we estimated selection pressure acting on the mitochondrial protein-coding genes of 13 intertidal and 2 deep sea gastropods based on site and branch-site specific models. The results exhibited higher number of sites under diversifying selection for the mitochondrial protein-coding genes of intertidal gastropods compared to deep sea species. Overall, this study focusses on the adaptive mitogenome evolution of marine gastropods for survival in the dynamic environments of the intertidal zone as well as deep sea.

Microbiome divergence of marine gastropod species separated by the Isthmus of Panama

The rise of the Isthmus of Panama ~3.5 mya separated populations of many marine organisms, which then diverged into new geminate sister species currently living in the Eastern Pacific Ocean and Caribbean Sea. However, we know very little about how such evolutionary divergences of host species have shaped their microbiomes. Here, we compared the microbiomes of whole-body and shell-surface samples of geminate species of marine gastropods in the genera Cerithium and Cerithideopsis to those of congeneric outgroups. Our results show that the effects of the Isthmus on microbiome composition varied among host genera and between sample types within the same hosts. In the whole-body samples, microbiome compositions of geminate species pairs in the focal genera tended to be similar, likely due to host filtering, although the strength of this relationship varied among the two groups and across similarity metrics. Shell-surface communities show contrasting patterns, with co-divergence between the host taxa and a small number of microbial clades evident in Cerithideopsis, but not Cerithium. These results suggest that (i) the rise of the Isthmus of Panama affected microbiomes of geminate hosts in a complex and clade-specific manner and (ii) host-associated microbial taxa respond differently to vicariance events than the hosts themselves.

A phylogeny-aware approach reveals unexpected venom components in divergent lineages of cone snails

Marine gastropods of the genus Conus are renowned for their remarkable diversity and deadly venoms. While Conus venoms are increasingly well studied for their biomedical applications, we know surprisingly little about venom composition in other lineages of Conidae. We performed comprehensive venom transcriptomic profiling for Conasprella coriolisi and Pygmaeconus traillii , first time for both respective genera. We complemented reference-based transcriptome annotation by a de novo toxin prediction guided by phylogeny, which involved transcriptomic data on two additional ‘divergent’ cone snail lineages, Profundiconus , and Californiconus . We identified toxin clusters (SSCs) shared among all or some of the four analysed genera based on the identity of the signal region—a molecular tag present in toxins. In total, 116 and 98 putative toxins represent 29 and 28 toxin gene superfamilies in Conasprella and Pygmaeconus , respectively; about quarter of these only found by semi-manual annotation of the SSCs. Two rare gene superfamilies, originally identified from fish-hunting cone snails, were detected outside Conus rather unexpectedly, so we further investigated their distribution across Conidae radiation. We demonstrate that both these, in fact, are ubiquitous in Conidae, sometimes with extremely high expression. Our findings demonstrate how a phylogeny-aware approach circumvents methodological caveats of similarity-based transcriptome annotation.

An overlooked diversity—the Costellariidae (Gastropoda: Neogastropoda) of the Miocene Paratethys Sea

The Miocene Costellariidae of the Paratethys Sea are revised. In total, 39 species in seven genera are recorded herein, documenting an unexpected diversity of these marine gastropods. The α-diversities of up to 14 species and basin-scale γ-diversities of up to 28 coeval species reveal the Central Paratethys as a unique diversity hot-spot for Miocene Costellariidae. Palaeobiogeographic relationships with the adjacent Proto-Mediterranean Sea are low at species level, and absent for Eastern Paratethyan and north-eastern Atlantic faunas. Antithala nov. gen. and Fedosovia nov. gen. are described as new genera. Bellardithala nov. nom. is introduced as new name for Micromitra Bellardi (1888) [non Meek, 1873]. Eight species are described as new: Antithala claviformis nov. sp., Antithala filipescui nov. sp., Bellardithala kovaci nov. sp., Bellardithala baluki nov. sp., Bellardithala fedosovi nov. sp., Bellardithala dacica nov. sp., Pusia confunda nov. sp., and Vexillum transalpinum nov. sp. Lectotypes are designated for Mitra badensis Hoernes & Auinger, 1880, M. brevior Friedberg, 1911, M. fuchsi Hoernes & Auinger, 1880, M. intermittens Hoernes & Auinger, 1880, M. januszkiewiczi Friedberg, 1928, M. lapugyensis Hoernes & Auinger, 1880, M. laubei Hoernes & Auinger, 1880, M. michelottii Hörnes, 1852, M. moravica Hoernes & Auinger, 1880, M. neugeboreni Hoernes & Auinger, 1880, M. partschi Hörnes, 1852, M. pseudorecticosta Boettger, 1906, M. sturi Hoernes & Auinger, 1880, M. szobbiensis Halaváts, 1884.