Thesis Lipid Content Of Hydrothermal Shrimp The Role Of Habitat Life Cycle And Symbionts M - F H/F Ifremer

Deadline for applications: 29/09/2026

Applications must also be submitted via the platform Amethis : https://amethis.doctorat.org/amethis-client/prd/consulter/offre/3829

Who are we?

The UMR BEEP (Biology and Ecology of Deep-Sea Ecosystems) aims to study the biology and ecology of deep-sea ecosystems using a multidisciplinary and holistic approach, ranging from microorganisms to megafauna, and from molecules to communities. Research focuses on the characterization and dynamics of biological diversity, biotic interactions and interactions with the environment, as well as the adaptation and response of biological systems to natural and anthropogenic stresses. These issues are addressed at different spatial and temporal scales depending on the ecosystems studied: chemosynthetic ecosystems, cold-water corals, seamounts, or abyssal plains.

https://www.umr-beep.fr/

What is the topic of the thesis?

Understanding trophic interactions and energy transfer within hydrothermal ecosystems represents a major gap in our knowledge of the deep sea.

Shrimp of the family Alvinocarididae constitute the main biomass at active hydrothermal sites on the Mid-Atlantic Ridge. Their presence and low genetic diversity along the ridge suggest a high potential for dispersal, which could underpin a major pathway for energy flow between hydrothermal vents. They are therefore the ideal model for studying energy flows and their connectivity at hydrothermal vents.

Their abundance is made possible by symbiotic chemoautotrophic bacteria. These bacteria derive their energy from the oxidation of reduced compounds-sulfur, iron, deuterium, methane-present in the fluids of hydrothermal vents, from which the fixed carbon is then transferred to their host. However, depending on the species and life stage, hydrothermal shrimp differ in their degree of dependence on bacterial symbiosis for nutrition, and these differences-as well as their consequences-remain poorly understood. Lipid biomarkers and their isotopic composition have proven to be useful tools for studying host-symbiont relationships among deep-sea fauna and for determining their reliance on photosynthetic versus chemosynthetic production.

In this context, the two main objectives of this thesis project are:
i) To map the lipid profiles of three species of hydrothermal shrimp.
ii) To characterize the pathways of lipid production and assimilation within shrimp communities.

More broadly, this thesis proposal is part of the ANR GYNET project and will provide the foundational knowledge needed to understand the distribution, origin, and transfer of energy-from primary producers to shrimp communities-by combining molecular approaches in order to apply this information at the meta-system level.

What will your mission and activities be?

As part of the ANR GYNET project, you will describe the lipid compositions (i.e., fatty acids, fatty alcohols, and sterols) of three species of hydrothermal shrimp that differ in their degree of bacterial colonization (Rimicaris exoculata, Rimicaris chaceï, and Alvinocaris markensis). These compositions will be analyzed at different stages of their life cycle (i.e., juvenile and adult) and according to their site of origin. You will be able to describe ontogenetic and spatial variability using samples of juveniles and adults from four sites with contrasting geochemical conditions (i.e., TAG, Hydra, Snake Pit, and Puy des Folles).

The second part of the thesis will focus on identifying the origin of these lipid compounds in order to determine the role of symbionts in their production and transfer. To this end, a dual approach combining lipidomics and compound-specific isotope analysis will be employed. The characterization of active microbial communities will be investigated through the analysis of fatty acids in polar lipids, as well as intact polar membrane lipids. These latter analyses will be conducted in collaboration with the University of Rennes (ECOBIO laboratory). The availability of metagenomes from shrimp symbionts will enable the identification of the genes and enzymes responsible for lipid biosynthesis. Finally, the isotopic composition of fatty acids specific to the symbionts will allow us to identify their origin (photosynthetic vs chemosynthetic).

This doctoral research will be conducted using a variety of biochemical techniques and their associated instruments (i.e., HPTLC, GC-MS, GC-FID, HPLC-HRMS, GC-c-p-IRMS).

Key words :

Deep Sea, Hydrothermal Shrimp, Lipids, Fatty Acids, Fatty Alcohol, Sterols, Intact Polar Membrane Lipids, Life Cycle, Symbiosis

How are your activities organized?

- Laboratory work (lipid analysis)

- Use of statistical analytical tools applied to ecology

- Travel for training and/or conferences in France and international

- Writing scientific articles

- Submission of the thesis manuscript and oral defense