DEEPADAPT · The molecular drivers of deep-sea adaptation in brittle stars

The molecular drivers of deep-sea adaptation in brittle stars

The deep ocean covers about two-thirds of the world’s ocean floors; yet, it is one of the least known environments of the planet. Despite its remoteness, the deep ocean provides critical ecosystem services (e.g. carbon sequestration; nutrient regeneration) and a wealth of resources of interest for humans (e.g. anti-cancer molecules; deep-sea fisheries; mining for rare metals). Given its extreme environmental conditions (crushing hydrostatic pressure, freezing temperature, absence of sunlight), life in the deep sea requires several specific adaptations. Surprisingly, little is known about the molecular mechanisms underlying adaptation to such environments. Which and how many genes are involved in adaptation? What is the extent of convergent evolution across distantly related taxa? Answering these questions is important for society because deciphering mechanisms of stress-driven adaptation will provide insights on the resilience of deep marine biodiversity to the ongoing environmental changes. The objectives of this project are: i) Decipher the molecular mechanisms of adaptation to the deep sea in brittle stars ii) Test the extent of convergent evolution among distantly related families. iii) Generate a reference genome of abyssal brittle stars I found that molecular functions related to the production of proteins are essential components of deep-sea adaptation. Furthermore, I uncovered strong levels of convergent evolution, as the same genes and functions were repeatedly targeted by natural selection in species that shared a common ancestor several millions years ago. I also uncovered that due to the particular life-history traits of deep-sea species (e.g. high longevity), many of them tend to have large genomes essentially composed of repeated regions. I further showed that the evolution of genome size is not an adaptive process in brittle stars. Finally, I generated a reference genome for the abyssal species Ophiosphalma armigerum, and uncovered cryptic speciation and hybridization in the deep ocean. These results bring a better understanding of the molecular mechanisms underlying the formation of species in the deep sea, and shed light on the molecular mechanisms allowing life in the deep ocean.

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