Inter- and Intra-Specific Transcriptional and Phenotypic Responses of Pseudo-nitzschia under Different Nutrient Conditions

Untangling thefunctionalbasis of divergencebetweenclosely relatedspecies is a steptowardunderstanding speciesdynamicswithin communities at both the evolutionary and ecological scales. We investigated cellular (i.e., growth, domoic acid production, and nutrient consumption) and molecular (transcriptomic analyses) responses to varying nutrient concentrations across several strains belonging to three species of the toxic diatomgenus Pseudo-nitzschia. Threemain resultswere obtained. First, strains fromthe same species displayed similar transcriptomic, but not necessarily cellular, responses to the experimental conditions. It showed the importance of considering intraspecific diversity to investigate functional divergence between species. Second, a major exception to the first findingwas a strain recently isolated fromthe natural environment and displaying contrasting gene expression patterns related to cell motility and domoic acid production. This result illustrated the profound modifications thatmay occurwhen transferring a cell fromthe natural to the in vitro environment and asks for future studies to better understand the influence of culture duration and life cycleon expression patterns. Third, transcriptomic responsesweremore similarbetween the two speciesdisplaying similar ecology in situ, irrespective of the genetic distance. This was especially true formolecular responses related to TCA cycle, photosynthesis, and nitrogen metabolism. However, transcripts related to phosphate uptake were variable between species. It highlighted the importance of considering both overall genetic distance and ecological divergence to explain functional divergence between species. © The Author(s) 2019. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.