Abstract
Collectively known as phytoplankton, photosynthetic microbes form the base of the marine food web, and account for up to half of the primary production on Earth. Haptophytes are key components of this phytoplankton community, playing important roles both as primary producers and as mixotrophs that graze on bacteria and protists. Viruses influence the ecology and diversity of phytoplankton in the ocean, with the majority of microalgae-virus interactions described as 'boom and bust' dynamics, which are characteristic of acute virus-host systems. Most haptophytes are, however, part of highly diverse communities and occur at low densities, decreasing their chance of being infected by viruses with high host specificity. Viruses infecting these microalgae have been isolated in the laboratory, and there are several characteristics that distinguish them from acute viruses infecting bloom-forming haptophytes. Herein we synthesise what is known of viruses infecting haptophyte hosts in the ocean, discuss the adaptive evolution of haptophyte-infecting viruses -from those that cause acute infections to those that stably coexist with their host - and identify traits of importance for successful survival in the ocean.
Highlights
Haptophytes are a diverse group of microalgae consisting both of ubiquitous bloom-forming and non-blooming species (Eikrem et al, 2016)
Viruses infecting marine haptophytes display a continuum in infection strategies from acute infections, where the host is rapidly lysed, to more persistent infections resulting in lower host mortality rates (Jacobsen, Bratbak & Heldal, 1996; Sandaa et al, 2001; Castberg et al, 2002; Baudoux & Brussaard, 2005; Johannessen et al, 2015; Wagstaff et al, 2017)
In this review we suggest that the range of infection strategies among marine haptophyte viruses is the result of mutual trade-off processes between the virus and the growth strategy of its algal host
Summary
Haptophytes are a diverse group of microalgae consisting both of ubiquitous bloom-forming and non-blooming species (Eikrem et al, 2016). In this review we suggest that the range of infection strategies among marine haptophyte viruses is the result of mutual trade-off processes between the virus and the growth strategy of its algal host. As resistance was not complete, virulence increased again in response to the host’s resistance (Gandon & Michalakis, 2000; Kerr et al, 2017; Alves et al, 2019) This well-studied example demonstrates how virus–host relationships evolve as each of the two players struggle for survival, and may lead to an oscillation between acute and persistent infections (Fig. 2B). We argue that every new relationship starts as an acute infection, developing into persistent infections with inherent trade-offs (Fig. 1, Table 2). Frequent events of virus host switching maintain a high diversity of virus–host relationships in terms of the balance between infection acuteness and persistence
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