Search

Understanding the origin and maintenance of genetic diversity is crucial to elucidate population dynamics of unicellular microalgae, their microevolutionary history and their adaptive ability. The planktonic, domoic acid-producing diatom Pseudo-nitzschia multistriata has a ubiquitous distribution in the world oceans and past population genetics studies, based on few genomic loci, have shown a clear temporal structure over different years in the Gulf of Naples (Italy). Despite the ecological and toxicological importance of this organism, detailed information on its diversity across the whole genome and at the population level is still lacking. We collected P. multistriata strains in the Gulf of Naples in five different years, obtained strains from the Adriatic Sea, the Gulf of Mexico and New Zealand coasts, and resequenced the whole genomes of a total of 28 strains at high coverage. While strains from the first three geographical areas were capable of producing the toxin domoic acid, the New Zealand strains had been reported to be non-toxic. A comparison of the domoic acid biosynthetic (dab) genes sequences between toxic and non-toxic strains showed very little variation among the strains, and no disrupting mutation was found in the dab genes in the non-toxic strains. On the other hand, the dab genes showed higher levels of expression in toxic strains than in non-toxic strains, suggesting that, in this species, absence of toxicity is explained by gene regulation rather than dab sequence divergence. Variant analysis showed stronger spatial than temporal genetic structuring and a clear separation was observed between the New Zealand strains and the others, the former having a greater content of genes under selection. Overall, the genomes of the different groups, including strains from a clonal bloom, did not appear to contain major rearrangements. Our findings contribute to enlarging our understanding of diatom diversity, a key factor underlying diatom success, and provide novel data on the longstanding problem of Pseudo-nitzschia toxicity., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

Environmental DNA metabarcoding (eDNA metaB) is fundamental for monitoring marine biodiversity and its spread in coastal ecosystems. We applied eDNA metaB to seawater samples to investigate the spatiotemporal variability of plankton and small pelagic fish, comparing sites with different environmental conditions across a coast-to-offshore gradient at river mouths along the Campania coast (Italy) over 2 years (2020-2021). We found a marked seasonality in the planktonic community at the regional scale, likely owing to the hydrodynamic connection among sampling sites, which was derived from numerical simulations. Nonetheless, spatial variability among plankton communities was detected during summer. Overall, slight changes in plankton and fish composition resulted in the potential reorganization of the pelagic food web at the local scale. This work supports the utility of eDNA metaB in combination with hydrodynamic modelling to study marine biodiversity in the water column of coastal systems. This article is part of the theme issue 'Connected interactions: enriching food web research by spatial and social interactions'.

Understanding the genetic structure of populations and the processes responsible for its spatial and temporal dynamics is vital for assessing species' adaptability and survival in changing environments. We investigate the genetic fingerprinting of blooming populations of the marine diatom Pseudo-nitzschia multistriata in the Gulf of Naples (Mediterranean Sea) from 2008 to 2020. Strains were genotyped using microsatellite fingerprinting and natural samples were also analysed with Microsatellite Pool-seq Barcoding based on Illumina sequencing of microsatellite loci. Both approaches revealed a clonal expansion event in 2013 and a more stable genetic structure during 2017-2020 compared to previous years. The identification of a mating type (MT) determination gene allowed to assign MT to strains isolated over the years. MTs were generally at equilibrium with two notable exceptions, including the clonal bloom of 2013. The populations exhibited linkage equilibrium in most blooms, indicating that sexual reproduction leads to genetic homogenization. Our findings show that P. multistriata blooms exhibit a dynamic genetic and demographic composition over time, most probably determined by deeper-layer cell inocula. Occasional clonal expansions and MT imbalances can potentially affect the persistence and ecological success of planktonic diatoms., (© 2024. The Author(s).)