Ocean acidification (OA) has major consequences on marine ecosystems. Survival of species and particularly calcifying species was shown to be decreased at lower pH as the latter directly damages their protective shells. However, the impacts of OA on chemically mediated behaviors have often not been considered or studied. Chemical cues are of major importance for several categories of behavior in marine species: finding habitat/prey/mating partners and avoiding predator. If chemical communication is disrupted, organisms might not find their mating partners or synchronize the release of gametes (in case of spawning species), the reproduction will not occur and the lineages and even the species could in the long-term be extinct.
Acidicc project investigated the impacts of OA on chemical communication in the polychaete Platynereis dumerilii. P. dumerilii is a promising species to investigate the impact of OA on chemical communication and reproduction. Indeed, this new model, is easy to culture, is globally distributed, its genome is sequenced, and its pheromones involved in its mating behavior have been mostly identified. When mature, the males and females become pelagic and reproduce at night (after specific lunar cycle). As broadcast spawner, P. dumerilii males and females use pheromones (5-methyl-3-heptanone, uric acid, ovothiol A, 5-octadiene-2-one) to induce rapid swim speed or to trigger the release of their gametes synchronously.
In this study, we investigated the impacts of OA on the chemical communication process at different steps: alteration of the cue itself or its production, reception of the cue and resulting behavior. The Objective 1 of AcidICC was to quantify the uric acid production in P. dumerilii females from different pH environments, at a lower pH with higher pH fluctuations. By doing so we could determine if the pH influences the production of uric acid and if the females acclimatize to low pH. Objective 2 aimed to quantify the cue detection response in P. dumerilii males from different pH environments at lower pH with higher pH fluctuations, and measure the potential costs of pH adaptation or acclimatization (e.g. survival) in P. dumerilii males and females. Since nothing was known about the genes coding for P. dumerilii pheromone, we aimed to find candidate genes likely coding for the receptor of the sperm release pheromone (uric acid) using comparative transcriptomic and GPCR deorphanization to test ligand activation of candidate GPCRs (Objective 3). Then, Objective 4 was to carry knockout of such candidates using CRISPR/Cas-9 technology to test if the candidate genes are indeed coding for the receptor, and in situ hybridization to detect where it is expressed. Once identified, the Objective 5 aims to determine the conformation changes of such receptors and of the pheromone under different pHs. Finding the receptor is important to investigate the effect of pH on an identified receptor-ligand pair and to genetically dissect the function of the receptor during spawning.
