Population structure and environmental niches of Rimicaris shrimps from the Mid-Atlantic Ridge

Abstract Veríssimo, A., McDowell, J. R., and Graves, J. E. 2011. Population structure of a deep-water squaloid shark, the Portuguese dogfish (Centroscymnus coelolepis). – ICES Journal of Marine Science, 68: . The genetic population structure of the deep-water squaloid Centroscymnus coelolepis (the Portuguese dogfish) in the eastern Atlantic was investigated using eight polymorphic nuclear microsatellite markers and a 496-bp fragment of the mitochondrial DNA control region (mtDNA CR). Samples (20–50 individuals per location) were collected off Ireland, Portugal, Madeira, Mauritania, South Africa, and the Azores (Mid-Atlantic Ridge). High levels of genetic diversity were found at the nuclear microsatellite loci (mean A = 17.3; overall Ho = 0.77), although there was low diversity at the mtDNA CR (h = 0.65, π = 0.0018). Genetic diversity for the Portuguese dogfish was homogeneously distributed among sampling locations, resulting in low and non-significant indices of genetic differentiation (e.g. FST = −0.0013 to 0.0096, ΦST = −0.017 to 0.033; p > 0.5), consistent with the absence of population structure within the area sampled. The results indicate that C. coelolepis has a high dispersal potential within the eastern Atlantic, and its apparent spatial segregation by size and maturity stage suggest large-scale migration associated with the reproductive cycle.

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Population structure and environmental niches of Rimicaris shrimps from the Mid Atlantic Ridge

10.1101/2021.06.27.450074 ◽

2021 ◽

Author(s):

Pierre Methou ◽

Ivan Hernandez Avila ◽

Cecile Cathalot ◽

Marie-Anne Cambon Bonavita ◽

Florence Pradillon

Keyword(s):

Population Structure ◽

Hydrothermal Vents ◽

Life Stages ◽

Population Demographics ◽

Juvenile Mortality ◽

Rimicaris Exoculata ◽

Population Structures ◽

Mid Atlantic Ridge ◽

Juvenile Stages ◽

Potential Factors

Among the endemic and specialized fauna from hydrothermal vents, Rimicaris shrimp surely constitutes one of the most important and emblematic component of these ecosystems. In the Mid Atlantic Ridge, two species affiliated to this genus co-occur: Rimicaris exoculata and Rimicaris chacei that differ by their morphology, their trophic regime as well as by their abundance. The first forms large and dense aggregations on active vent chimney walls in close proximity to vent fluid emissions, whereas the second is recognized as much less conspicuous, living mostly in scattered groups or solitary further away from the fluids. However, the recent revision of Rimicaris juvenile stages from the Mid Atlantic Ridge show that R. chacei abundance would be higher than expected at these early life stages. Here, we describe and compare the population structures of R. exoculata and R. chacei at the Snake Pit and TAG vent fields. We show widely distinct population demographics between the two co-occurring shrimps with a large post settlement collapse in R. chacei population suggesting a large juvenile mortality for this species. We also observe important spatial segregation patterns between the two species and their different life stages. Additionally, our results highlight distinct niches for the earliest juvenile stages of both R. exoculata and R. chacei, compared to all the other life stages. Finally, we discuss the potential factors - predation and competitive interactions among others - that could explain the differences we observe in the population structure of these two species.

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Population structure and reproduction of the alvinocaridid shrimp Rimicaris exoculata on the Mid-Atlantic Ridge: variations between habitats and vent fields

10.1101/2021.06.27.450066 ◽

2021 ◽

Author(s):

Ivan Hernandez ◽

Marie-Anne Cambon-Bonavita ◽

Jozee Sarrazin ◽

Florence Pradillon

Keyword(s):

Population Structure ◽

Size Structure ◽

Mature Female ◽

Genetic Connectivity ◽

Intraspecific Interactions ◽

Larval Stages ◽

Rimicaris Exoculata ◽

Hypothetical Scenario ◽

Mid Atlantic Ridge ◽

Sexually Mature

Rimicaris exoculata is a dominant species of deep Mid-Atlantic Ridge (MAR) vent fields and inhabits areas close to vent emissions at depths below 2000 m. Its high abundance and strong genetic connectivity along the MAR point at a remarkable ability to produce dispersing larval stages. However, the reproduction of this species long remained enigmatic because brooding females were rarely observed. Here, we describe the population structure and reproduction of R. exoculata at the Snake Pit and TAG vent fields (3600m depth) for the months of January-February. We observed major differences in population structure between habitats within a single vent field: females widely dominate the large swarms near active venting while inactive peripheries are inhabited by large males. Low temperature diffusion zones are mainly colonized by small juveniles of R. chacei instead of R. exoculata. Size structure of populations from dense active areas is polymodal at both fields, suggesting discontinuous recruitment. Male and female sizes did not vary across habitats and vent fields, with sexually mature female being slightly larger than males. In contrast to previous studies, hundreds of ovigerous females were observed at both vent fields, suggesting seasonal reproduction. Proportion of ovigerous females among sexually mature females were similar between vent fields (36.7 %). However, reproductive output was lower at TAG, where ovigerous females had smaller size-specific fecundity and egg size, and more aborted broods. Broods were colonized by the dirivultid copepod Stygiopontius pectinatus at both vent fields, apparently without deleterious effect on egg development. In the light of the observed variability in R. exoculata population structure, we propose a hypothetical scenario depicting its mating system and brooding behavior, and discuss more generally intraspecific interactions during its benthic life stages.

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