Evolution of mutualism from parasitism in experimental virus populations

Abstract

While theory suggests conditions under which mutualism may evolve from parasitism, few studies have observed this transition empirically. Previously, we evolved Escherichia coli and the filamentous bacteriophage M13 in 96-well microplates, an environment in which the ancestral phage increased the growth rate and yield of the ancestral bacteria. In the majority of populations, mutualism was maintained or even enhanced between phages and coevolving bacteria; however, these same phages evolved traits that harmed the ancestral E. coli genotype. Here, we set out to determine if mutualism could evolve from this new parasitic interaction. To do so, we chose six evolved phage populations from the original experiment and used them to establish new infections of the ancestral bacteria. After 20 passages, mutualism evolved in almost all replicates, with the remainder growing commensally. Many phage populations also evolved to benefit both their local, evolving bacteria and the ancestral bacteria, though these phages were less beneficial to their co-occurring hosts than phages that harm the ancestral bacteria. These results demonstrate the rapid recovery of mutualism from parasitism, and we discuss how our findings relate to the evolution of phages that enhance the virulence of bacterial pathogens.

When enemies do not become friends: Experimental evolution of heat-stress adaptation in a vertically transmitted parasite

“…This may lead to the accumulation of deleterious mutations or loss of function (Dale and Moran 2006;Feldhaar 4 2011), but also facilitate specialisation and co-evolution (Brucker and Bordenstein 2012;Jaenike 2015). These ideas are consistent with the observation that some of the major 70 evolutionary transitions from parasitic to mutualistic relationships are associated with a switch from horizontal to vertical transmission, as shown across the phylogenetic tree (Moran et al 2008;Sachs et al 2011), but also in microcosm experiments (e.g., Dusi et al 2015;Shapiro and Turner 2018).…”

“…Factors determining sign and strength of an interaction are the symbiont transmission mode, environmental conditions, as well as the genetic background of symbiont and host (Ewald 1987;Wolinska and King 2009). Most empirical and 55 experimental work has highlighted the short-term consequences of variation in these factors over one or very few generations (Thomas and Blanford 2003;Wolinska and King 2009;Ebert 2013), but it is still less clear how they drive long-term evolutionary and coevolutionary processes (Mahmud et al 2017;Shapiro and Turner 2018;Hatcher et al 2005).…”

Interactive rhythms across species: the evolutionary biology of animal chorusing and turn‐taking

“…From an evolutionary perspective, phenomena that appear to be cooperative today may have their origins in phenomena that most decidedly were not. For example, mutualism between species may have begun as parasitism . Likewise, animal alarm calls, which provide direct benefit to the receiver but not the caller, might have originated to selfishly manipulate conspecifics’ behavior …”

“…For example, mutualism between species may have begun as parasitism. 91 Likewise, animal alarm calls, which provide direct benefit to the receiver but not the caller, might have originated to selfishly manipulate conspecifics' behavior. 92,93 In brief, alternative hypotheses-both competitive and cooperative-may account for turn-taking b Human language is flexible, however, and in some cases confrontational or "competitive" turn-taking does occur.…”

Understanding the evolution of interspecies interactions in microbial communities

“…For example, when a first species evolves to 504 excrete more of a compound that inhibits a second species, which has a positive effect on the 505 first species, this second species now will be under stronger selection to decrease its help to 506 the first species, or even to start harming it. Clearly, this prediction will not hold for 507 interactions of which the sign cannot change by definition, such as host-parasite interactions 508 (but note that even such interactions may not be constant [116,117]). Nonetheless, microbial 509 communities are dominated by chemically-mediated interactions, suggesting that the 510 selection of indirectly-beneficial mutations may occur also in the case of asymmetric 511…”