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Low connectivity between ‘scaly-foot gastropod’ (Mollusca: Peltospiridae) populations at hydrothermal vents on the Southwest Indian Ridge and the Central Indian Ridge
No full textHydrothermal vents on mid-oceanic ridges are patchily distributed and host many taxa endemic to deep-sea chemosynthetic environments, whose dispersal may be constrained by geographical barriers. The aim of this study was to investigate the connectivity of three populations of the ‘scaly-foot gastropod’ (Chrysomallon squamiferum Chen et al., 2015), a species endemic to hydrothermal vents in the Indian Ocean, amongst two vent fields on the Central Indian Ridge (CIR) and Longqi field, the first sampled vent field on the Southwest Indian Ridge (SWIR). Connectivity and population structure across the two mid-oceanic ridges were investigated using a 489-bp fragment of the cytochrome oxidase c subunit I (COI) gene. Phylogeographical approaches used include measures of genetic differentiation (F ST), reconstruction of parsimony haplotype network, mismatch analyses and neutrality tests. Relative migrants per generation were estimated between the fields. Significant differentiation (F ST?=?0.28–0.29, P?<?0.001) was revealed between the vent field in SWIR and the two in CIR. Signatures were detected indicating recent bottleneck events followed by demographic expansion in all populations. Estimates of relative number of migrants were relatively low between the SWIR and CIR, compared with values between the CIR vent fields. The present study is the first to investigate connectivity between hydrothermal vents across two mid-ocean ridges in the Indian Ocean. The phylogeography revealed for C. squamiferum indicates low connectivity between SWIR and CIR vent populations, with implications for the future management of environmental impacts for seafloor mining at hydrothermal vents in the region, as proposed for Longqi
The ‘scaly-foot gastropod’: a new genus and species of hydrothermal vent-endemic gastropod (Neomphalina: Peltospiridae) from the Indian Ocean
No full textThe ‘scaly-foot gastropod’ is widely recognized as an iconic species of deep-sea hydrothermal vent ecosystems in the Indian Ocean. Uniquely among gastropods, this species carries hundreds of dermal sclerites on its foot and these scales can be covered in iron sulphide that also covers its shell, making it the only extant metazoan known to utilize iron sulphide as part of its skeleton. It has not been formally named, despite attracting great attention from both scientists and the general public alike, although a manuscript name has occasionally been used in various sources. The RRS James Cook JC67 expedition in 2011 sampled the biota of the Longqi vent field (37°47.027?S, 49°38.963?E), Southwest Indian Ridge, for the first time, revealing a previously unknown population of the ‘scaly-foot gastropod’. The present study gives a formal name to the ‘scaly-foot gastropod’, Chrysomallon squamiferum n. gen., n. sp. with Longqi vent field as the type locality. The erection of the new monotypic genus is supported by both morphological and molecular characterization, differentiating it from existing genera of the family Peltospiridae. Analysis of the cytochrome c oxidase subunit I gene reveals a 24–26% pairwise distance between Chrysomallon and five other genera of Peltospiridae, while the range among those five genera is 14–25%. The new genus is placed in the family Peltospiridae based on morphological characteristics, including lack of sexual dimorphism, no copulatory organ, the distal end of marginal teeth being subdivided into many denticles and the ventral margin of the gill leaflets carrying a series of bulges. A five-gene Bayesian phylogenetic reconstruction does not contradict the placement within Peltospiridae
Figure 9. Consensus tree reconstructed from a 489 in A new genus of large hydrothermal vent-endemic gastropod (Neomphalina: Peltospiridae)
No full textFigure 9. Consensus tree reconstructed from a 489-bp fragment of the cytochrome c oxidase subunit I gene using Bayesian inference. Node values represent Bayesian posterior probabilities.Published as part of Chen, Chong, Linse, Katrin, Roterman, Christopher N., Copley, Jonathan T. & Rogers, Alex D., 2015, A new genus of large hydrothermal vent-endemic gastropod (Neomphalina: Peltospiridae), pp. 319-335 in Zoological Journal of the Linnean Society (Zool. J. Linn. Soc.) 175 (2) on page 330, DOI: 10.1111/zoj.12279, http://zenodo.org/record/533841
Microgeographic genetic variation of populations of Idotea chelipes (Crustacea: Isopoda) in lagoons of the southern English coast
No full textAllozyme variability was examined using starch-gel electrophoresis between sub-populations of Idotea chelipes over a small geographic distance (approx. 104 km), in lagoons within the Solent area (Fort Gilkicker Moat; Ashlett Pond)and at one site in Dorset (the Fleet Lagoon). Genetic identity values indicate that all three populations are conspecific (I = 0.967 to 0.995), and mean heterozygosity per locus for all three populations was 8%. Significant levels of genetic differentiation (mean F sub(ST) = 0.119***; p< 0.001) were detected over this small spatial scale, but this mainly resulted from the slow esterase locus (mean F sub(ST) (no esterase) = 0.072***; p< 0.001). Genetic differentiation was moderate given the low geographic distances between populations with only one to two migrants per deme per generation (N sub(e)m(F sub(ST)) = 1.85) from the Fleet to Gilkicker. There was no significant deviation from the genotypes expected under the Hardy-Weinberg equilibrium despite an overall slight excess of heterozygotes (mean F sub(IS) = -0.01). Pairwise F sub(ST) values indicated that there was limited genetically effective migration between the sampled lagoons. This genetic differentiation may have been promoted by the presence of the Southampton Water and Solent estuarine system that may act as a physical barrier to gene flow for this species. The previous use of the esterase (ET2)locus as a sub-specific biochemical marker for Idotea chelipes is placed in doubt by this study. Original Abstract: La variabilite enzymatique de trois populations lagunaires daIdotea chelipes est examinee sur gel daelectrophorese daamidon a faible echelle spatiale (environ 104 km). Les trois populations font partie de la meme espece (I = 0,967 a 0,995) et laheterozygotie moyenne observee est de 8 %. Des valeurs de differenciation genetique significatives sont observees (F sub(ST)= 0,119***; p< 0,001) bien que resultant principalement de laesterase lente (F sub(ST)(sans esterase) = 0,072*** ; p< 0,001). Etant donnee la faible distance geographique separant les populations, le niveau de differenciation genetique reste modere avec un a deux migrants par deme par generation (Nem(F sub(ST)) = 1,85). En depit daun faible exces en heterozygote (F sub(IS) = -0,01), aucune deviation par rapport a laequilibre de Hardy-Weinberg naest observee. Les valeurs de differenciation genetique entre paires de populations indiquent que les echanges entre lagunes sont limites et que cette differenciation aurait pu etre accentuee par la presence du systeme estuarien oSolento qui jouerait le role de barriere au flux genique pour cette espece. Daautre part, lautilisation prealable de laesterase lente (ET2) comme marqueur subspecifique du complexe Idotea chelipes est placee en doute dans la presente etude
Figure 6 in A new genus of large hydrothermal vent-endemic gastropod (Neomphalina: Peltospiridae)
No full textFigure 6. Radula. Overview: A, Gigantopelta chessoia sp. nov.; B. Gigantopelta aegis sp. nov.; scale bars = 100 μm. Central and lateral teeth close-up: C, G. chessoia sp. nov.; D, G. aegis sp. nov.; scale bars = 20 μm. Marginal teeth close-up: E, G. chessoia sp. nov.; F. G. aegis sp. nov.; scale bars = 10 μm.Published as part of Chen, Chong, Linse, Katrin, Roterman, Christopher N., Copley, Jonathan T. & Rogers, Alex D., 2015, A new genus of large hydrothermal vent-endemic gastropod (Neomphalina: Peltospiridae), pp. 319-335 in Zoological Journal of the Linnean Society (Zool. J. Linn. Soc.) 175 (2) on page 326, DOI: 10.1111/zoj.12279, http://zenodo.org/record/533841
Figure 5 in A new genus of large hydrothermal vent-endemic gastropod (Neomphalina: Peltospiridae)
No full textFigure 5. Protoconchs: A, Gigantopelta chessoia sp. nov., scale bar = 100 μm; B, Gigantopelta aegis sp. nov., scale bar = 100 μm. Juvenile operculum: C, G. chessoia sp. nov., scale bar = 500 μm; D, G. aegis sp. nov., scale bar = 500 μm.Published as part of Chen, Chong, Linse, Katrin, Roterman, Christopher N., Copley, Jonathan T. & Rogers, Alex D., 2015, A new genus of large hydrothermal vent-endemic gastropod (Neomphalina: Peltospiridae), pp. 319-335 in Zoological Journal of the Linnean Society (Zool. J. Linn. Soc.) 175 (2) on page 325, DOI: 10.1111/zoj.12279, http://zenodo.org/record/533841
Lower bathyal and abyssal distribution of coral in the axial volcanic ridge of the Mid-Atlantic Ridge at 45°N
No full textThe deep-sea floor below 3000 m occupies 50% of the surface of the planet and is composed mainly of fine sediments. Most studies of deep-sea benthic fauna have concentrated on soft sediments with little sampling in rocky areas and even less on non-vent mid-ocean ridges. To assess the distribution and abundance of coral between 2500 m and 3500 m depths, video footage from the ROV Isis taken during a cruise to the Axial Volcanic Ridge (AVR) of the Mid-Atlantic Ridge at approx 45°30? N was analysed. Abundances per 100 m were calculated and mapped using Arc GIS, with a maximum of 59 being observed. 20 putative species were identified. Scleractinia were absent from the observed area and the coral fauna was dominated by Octocorallia. The data were separated into four substratum types, sediment, sloped rock, flat rock and mixed substratum, with both abundance and community being compared. Sedimented and rocky areas had different coral communities with sediment having a higher occurrence of Pennatulidae and Chrysogorgidae than rock. Sloped rock had the highest abundance of corals. We suggest that this increase in abundance reflects higher food availability as well as the solid substratum on which coral larvae settle
Data from: Connectivity in the cold: the comparative population genetics of vent-endemic fauna in the Scotia Sea, Southern Ocean.
No full textWe report the first comparative population genetics study for vent fauna in the Southern Ocean using cytochrome C oxidase I and microsatellite markers. Three species are examined: the kiwaid squat lobster, Kiwa tyleri, the peltospirid gastropod Gigantopelta chessoia and a lepetodrilid limpet, Lepetodrilus sp. collected from vent fields 440 km apart on the East Scotia Ridge (ESR) and from the Kemp Caldera on the South Sandwich Island Arc, ~95 km eastwards. We report no differentiation for all species across the ESR, consistent with panmixia or recent range expansions. A lack of differentiation is notable for Kiwa tyleri, which exhibits extremely abbreviated lecithotrophic larval development, suggestive of a very limited dispersal range. Larval lifespans may, however, be extended by low temperature-induced metabolic rate reduction in the Southern Ocean, muting the impact of dispersal strategy on patterns of population structure. COI diversity patterns suggest all species experienced demographic bottlenecks or selective sweeps in the past million years and possibly at different times. ESR and Kemp limpets are divergent, although with evidence of very recent ESR-Kemp immigration. Their divergence, possibility indicative of incipient speciation, along with the absence of the other two species at Kemp, may be the consequence of differing dispersal capabilities across a ~1000 m depth range and/or different selective regimes between the two areas. Estimates of historic and recent limpet gene flow between the ESR and Kemp are consistent with predominantly easterly currents in the region and potentially therefore, cross-axis currents on the ESR, with biogeographic implications for the region.,Zip file of input filesIncludes fasta sequence files, microsatellite genotype files, as well as other input filesData_accessibility.zip</span
How the mollusc got its scales: convergent evolution of the molluscan scleritome
Full text linkRadiation of dramatically disparate forms among the phylum Mollusca remains a key question in metazoan evolution, and requires careful evaluation of homology of hard parts throughout the deep fossil record. Enigmatic early Cambrian taxa such as Halkieria and Wiwaxia (in the clade Halwaxiida) have been proposed to represent stem-group aculiferan molluscs (Caudofoveata?+?Solenogastres?+?Polyplacophora), as complex scleritomes were considered to be unique to aculiferans among extant molluscs. The ‘scaly-foot gastropod’ (Neomphalina: Peltospiridae) from hydrothermal vents of the Indian Ocean, however, also carries dermal sclerites and thus challenges this inferred homology. Despite superficial similarities to various mollusc sclerites, the scaly-foot gastropod sclerites are secreted in layers covering outpockets of epithelium and are largely proteinaceous, while chiton (Polyplacophora: Chitonida) sclerites are secreted to fill an invaginated cuticular chamber and are largely calcareous. Marked differences in the underlying epithelium of the scaly-foot gastropod sclerites and operculum suggest that the sclerites do not originate from multiplication of the operculum. This convergence in different classes highlights the ability of molluscs to adapt mineralized dermal structures, as supported by the extensive early fossil record of molluscs with scleritomes. Sclerites of halwaxiids are morphologically variable, undermining the assumed affinity of specific taxa with chitons, or the larger putative clade Aculifera. Comparisons with independently derived similar structures in living molluscs are essential for determining homology among fossils and their position with respect to the enigmatic evolution of molluscan shell forms in deep time
A new genus of large hydrothermal vent-endemic gastropod (Neomphalina: Peltospiridae)
Full text linkRecently discovered hydrothermal vent fields on the East Scotia Ridge (ESR, 56–60°S, 30°W), Southern Ocean, and the South West Indian Ridge (SWIR, 37°S 49°E), Indian Ocean, host two closely related new species of peltospirid gastropods. Morphological and molecular (mitochondrial cytochrome c oxidase subunit I, COI) characterization justify the erection of Gigantopelta gen. nov. within the Peltospiroidae with two new species, Gigantopelta chessoia sp. nov. from ESR and Gigantopelta aegis sp. nov. from SWIR. They attain an extremely large size for the clade Neomphalina, reaching 45.7?mm in shell diameter. The oesophageal gland of both species is markedly enlarged. Gigantopelta aegis has a thick sulphide coating on both the shell and the operculum of unknown function. The analysis of a 579-bp fragment of the COI gene resulted in 19–28% pairwise distance between Gigantopelta and six other genera in Peltospiridae, whereas the range amongst those six genera was 12–28%. The COI divergence between the two newly described species of Gigantopelta was 4.43%. Population genetics analyses using COI (370?bp) of 30 individuals of each species confirmed their genetic isolation and indicate recent rapid demographic expansion in both species. <br/
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