Selection of Benevolence in a Host-Parasite System

Abstract

A paradigm for the evolution of cooperation between parasites and their hosts argues that the mode of parasite transmission is critical to the long-term maintenance of cooperation. Cooperation is not expected to be maintained whenever the chief mode of transmission is horizontal: a parasite's progeny infect hosts unrelated to their parent's host. Cooperation is expected to be maintained if the chief mode of transmission is vertical: a parasite's progeny infect only the parent's host or descendants of that host. This paradigm was tested using bacteria and filamentous bacteriophage (f1). When cells harboring different variants of these phage were cultured so that no infectious spread was allowed, ensuring that all parasite transmission was vertical, selection favored the variants that were most benevolent to the host-those that least harmed host growth rate. By changing the culture conditions so that horizontal spread of the phage was allowed, the selective advantage of the benevolent forms was lost. These experiments thus support the theoretical arguments that mode of transmission is a major determinant in the evolution of cooperation between a parasite and its host.

Experimental evolution of a microbial predator's ability to find prey

“…The theory underlying these expectations is similar to the patch model of foraging theory. In some experiments of this type, viruses and plasmids that were deleterious to their hosts became more benign and even beneficial to their hosts when the transmissibility of the agents or the availability of susceptible hosts was limited during evolution (Bouma & Lenski 1988;Bull et al 1991;Bull & Molineaux 1992;Lenski et al 1994), an outcome consistent with theory. In another experiment, however, a plasmid's horizontal and vertical transmission rates did not evolve as expected when host abundance was manipulated (Turner et al 1998).…”

The impact of parasitism on resource allocation in a fungal host: the case of Cryphonectria parasitica and its mycovirus, Cryphonectria Hypovirus 1

“…This result is consistent with a tight association between the fitness of the host and the fitness of its vertically transmitted parasite, suggesting that vertical transmission drives down parasite virulence as expected by the literature (Day & Proulx, 2004; Ewald, 1987; Lipsitch, Siller, & Nowak, 1996). Several experiments in different host–parasite systems have confirmed that vertically transmission usually selects for less virulent parasites (Bull, Molineux, & Rice, 1991; Magalon, Nidelet, Martin, & Kaltz, 2010; Pagán, Montes, Milgroom, & García‐Arenal, 2014; Stewart, Logsdon, & Kelley, 2005). This relationship is even suspected to be responsible for the general avirulence of mycoviruses, especially when high vc‐type diversity in host populations limits the occurrence of horizontal transmission (Brusini et al., 2011).…”

Currencies of Mutualisms: Sources of Alkaloid Genes in Vertically Transmitted Epichloae

“…Only one hybrid species, Epichloë liyangensis , has ever been observed to produce stromata [40], so it appears that the hybrids are generally dependent on vertical transmission. Such a situation is expected to select for mutualism because the fitness of a vertically transmitted symbiont links positively to host fitness [41,42]. A common benefit conferred by epichloae to their hosts is the production of protective alkaloids that can deter, impair or even kill invertebrate and vertebrate herbivores [1,3,4,22,43,44,45,46,47,48,49,50,51,52,53].…”