Cophylogenetic interactions between marine viruses and eukaryotic picophytoplankton

Abstract

BackgroundNumerous 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.ResultsAll 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.ConclusionsMechanisms 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.

Revision of the Genus Micromonas Manton et Parke (Chlorophyta, Mamiellophyceae), of the Type Species M. pusilla (Butcher) Manton & Parke and of the Species M. commoda van Baren, Bachy and Worden and Description of Two New Species Based on the Genetic and Phenotypic Characterization of Cultured Isolates

“…These sequences were retrieved from GenBank and the National Center for Biotechnology Information (NCBI, http://www.ncbi.nlm.nih.gov/) and included SSU rRNA gene sequence and ITS rRNA sequence of strains which have been previously analysed ( Bellec et al 2014;Guillou et al 2004;Marin and Melkonian 2010;Nakayama et al 1998;Slapeta et al 2006;Worden 2006;) (Table 2), a selection of environmental sequences grouping with Micromonas, and sequences of Mantoniella used as outgroups. Environmental SSU rRNA gene sequences were retrieved from the Protist Ribosomal Reference (PR 2 ) database (Guillou et al 2013) and selected based on their length (> 1695 bp).…”

New lipid envelope-containing dsDNA virus isolates infecting Micromonas pusilla reveal a separate phylogenetic group

“…M. pusilla virus DNA polymerase sequences generated in this study were deposited into GenBank (accession numbers in Table 2). 235 DNA sequences from our MpV isolates were aligned with an additional 35 M. pusilla virus DNA polymerase B partial sequences available through GenBank and previously published (Chen and Suttle (1996) Bellec et al (2014)). Five Ostreococcus virus and two Bathycoccus virus DNA polymerase B partial sequences (Bellec et al 2014) were included as an outgroup.…”

“…235 DNA sequences from our MpV isolates were aligned with an additional 35 M. pusilla virus DNA polymerase B partial sequences available through GenBank and previously published (Chen and Suttle (1996) Bellec et al (2014)). Five Ostreococcus virus and two Bathycoccus virus DNA polymerase B partial sequences (Bellec et al 2014) were included as an outgroup. The sequences were initially aligned using the 240 ClustalX algorithm (Larkin et al, 2007) within MEGA version 6 (Tamura et al, 2013.…”

“…The 80 dsDNA M. pusilla viruses belong to the algal virus family Phycodnaviridae, which is part of a group of viruses known as nucleocytoplasmic large dsDNA viruses (NCLDVs) that replicate in the cytoplasm and in some cases partly in the nucleus of their eukaryotic host cells (Iyer et al 2001). Research stemming from independent studies of M. pusilla-specific viruses has revealed significant genetic diversity within 85 dsDNA M. pusilla viruses (Cottrell & Suttle 1991, 1995, Bellec et al 2014, some knowledge of their infection strategy and effect on host physiology (Mayer & Taylor 1979, Waters & Chan 1982, variation in strain specificity (Sahlsten 1998, and evidence for significant cospeciation between these viruses and their hosts in addition to host switches (Bellec et al 2014). Furthermore, investigations of 90 their dynamics in the environment have shown seasonal and spatial variation in abundance (Cottrell & Suttle 1991, Sahlsten 1998, Zingone et al 1999) and have indicated the importance of viruses as mortality agents of M. pusilla (Evans et al 2003).…”

Origin of a major infectious disease in vertebrates: The timing ofCryptosporidiumevolution and its hosts

“…Host-parasite coevolution examples are numerous (algae and virus, Bellec et al 2014; e.g. pocket gophers and chewing lice, Hafner et al 1994; insects and fungi, Zhang et al 2014) and shaped evolutionary theory (Anderson and May, 1982;May and Anderson, 1983).…”