Cophylogenetic interactions between marine viruses and eukaryotic picophytoplanktonReport as inadecuate

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* Corresponding author 1 BIOM - Biologie intégrative des organismes marins 2 DIPO - Diversité et Interactions au sein du Plancton Océanique ADMM - Adaptation et diversité en milieu marin 3 ADMM - Adaptation et diversité en milieu marin

Abstract : Background: Numerous studies have investigated cospeciation or cophylogeny in various host-symbiont systems, and different patterns were inferred, from strict cospeciation where symbiont phylogeny mirrors host phylogeny, to complete absence of correspondence between trees. The degree of cospeciation is generally linked to the level of host specificity in the symbiont species and the opportunity they have to switch hosts. In this study, we investigated cophylogeny for the first time in a microalgae-virus association in the open sea, where symbionts are believed to be highly host-specific but have wide opportunities to switch hosts. We studied prasinovirus-Mamiellales associations using 51 different viral strains infecting 22 host strains, selected from the characterisation and experimental testing of the specificities of 313 virus strains on 26 host strains. Results: All virus strains were restricted to their host genus, and most were species-specific, but some of them were able to infect different host species within a genus. Phylogenetic trees were reconstructed for viruses and their hosts, and their congruence was assessed based on these trees and the specificity data using different cophylogenetic methods, a topology-based approach, Jane, and a global congruence method, ParaFit. We found significant congruence between virus and host trees, but with a putatively complex evolutionary history. Conclusions: Mechanisms other than true cospeciation, such as host-switching, might explain a part of the data. It has been observed in a previous study on the same taxa that the genomic divergence between host pairs is larger than between their viruses. It implies that if cospeciation predominates in this algae-virus system, this would support the hypothesis that prasinoviruses evolve more slowly than their microalgal hosts, whereas host switching would imply that these viruses speciated more recently than the divergence of their host genera.

Keywords : Specificity Mamiellale Chlorophyta Cophylogeny Prasinovirus Phycodnaviridae

Author: Laure Bellec - Camille Clerissi - Roseline Edern - Elodie Foulon - Nathalie Simon - Nigel Grimsley - Yves Desdevises -



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