Biology subjects

Pradillon, F.

Publications and source records attributed to Pradillon, F..

3 recordsLinked to original sources

bioRxiv2021

Reproductive strategies in vent shrimps shaped by feeding ecology with intriguing seasonality unlinked to surface productivity

Variations in offspring production according to feeding strategies or food supply have been recognized in many animals from various ecosystems. Despite an unusual trophic structure based on non-photosynthetic primary production, these relationships remain largely under-studied in chemosynthetic ecosystems. Here, we use Rimicaris shrimps from deep-sea hydrothermal vents as a study case to explore relations between reproduction, diets and food supply in these environments. For that, we compared reproductive outputs of three congeneric shrimps differing by their diets. They inhabit vents located under oligotrophic waters of tropical gyres with opposed latitudes, allowing us to also examine the prevalence of phylogenetic vs environmental drivers in their reproductive rhythms. For this we used both our original data and a compilation of published observations on the presence of ovigerous females covering various seasons over the past 35 years. We report distinct egg production trends between Rimicaris species relying solely on chemosymbiosis - R. exoculata and R. kairei - and those relying on mixotrophy - R. chacei - where R. chacei produces broods with higher numbers of smaller eggs. Besides, our data and historical records suggest a reproductive period with substantial proportions of brooding females mostly between January and early April for all examined species whatever the region. Intriguingly, this periodicity does not correspond to seasonal variations in surface production with presence of brooding females during either boreal winter or austral summer. These observations contrast with the long-standing paradigm in deep-sea species for which periodic reproductive patterns have always been attributed to seasonal variations of photosynthetic production sinking from surface. Our results suggest the presence of intrinsic basis for biological rhythms in the deep sea, and bring to light the importance of having year-round observations in order to understand life history of vent animals.

ecology↗

bioRxiv2021

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

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.

ecology↗

bioRxiv2021

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

Among the endemic and specialized fauna from hydrothermal vents, Rimicaris shrimp surely constitutes one of the most important and emblematic components 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 shows 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 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.

ecology↗