Evolution and maintenance of microbe‐mediated protection under occasional pathogen infection

Abstract

Every host is colonized by a variety of microbes, some of which can protect their hosts from pathogen infection. However, pathogen presence naturally varies over time in nature, such as in the case of seasonal epidemics. We experimentally coevolved populations of Caenorhabditis elegans worm hosts with bacteria possessing protective traits (Enterococcus faecalis), in treatments varying the infection frequency with pathogenic Staphylococcus aureus every host generation, alternating host generations, every fifth host generation, or never. We additionally investigated the effect of initial pathogen presence at the formation of the defensive symbiosis. Our results show that enhanced microbe‐mediated protection evolved during host‐protective microbe coevolution when faced with rare infections by a pathogen. Initial pathogen presence had no effect on the evolutionary outcome of microbe‐mediated protection. We also found that protection was only effective at preventing mortality during the time of pathogen infection. Overall, our results suggest that resident microbes can be a form of transgenerational immunity against rare pathogen infection.

Sex matters: effects of sex and mating in the presence and absence of a protective microbe

“…This pattern holds during pathogen infection (Figure 1A & 1B) and over a lifetime (Figure 1C-E). The potential of MMP to enhance survival Kloock et al, 2020;Martinez et al, 2016) as well as offspring production (Koehler et al, 2013) has been shown repeatedly. So far, these effects have mainly been considered at the population level.…”

“…We used an obligate outcrossing worm population (line EEVD00 from Henrique Teotonio (Theologidis et al, 2014)) where worms carry the fog-2(q71) mutation, preventing hermaphrodites from producing sperm (Theologidis et al, 2014). Worms were kept on Nematode Growth Medium (NGM) (Brenner, 1974), and fed non-pathogenic Salmonella, hereafter referred to as food (Desai et al, 2019;Diaz et al, 2015;Kloock et al, 2020). For pathogenic infection, the Gram positive Staphylococcus aureus strain MSSA476 (Holden et al, 2004) was used.…”

“…Defensive mutualisms have been observed across kingdoms (reviewed in ). The potential of defensive mutualism to enhance survival as well as offspring production has been observed repeatedly Kloock et al, 2020;Koehler et al, 2013). However, most of these examples have only considered population-level effects, while few studies have focussed on individual behaviours and/or sex differences between the hosts (McLean et al, 2018).…”

Sex Matters: Effects of Sex and Mating in the Presence and Absence of a Protective Microbe

“…We used an obligate outcrossing worm population [line EEVD00 from Henrique Teotonio (Theologidis et al, 2014)] where worms carry the fog-2(q71) mutation, preventing hermaphrodites from producing sperm (Theologidis et al, 2014). Worms were kept on Nematode Growth Medium (NGM) (Brenner, 1974), and fed with nonpathogenic Salmonella enterica, hereafter referred to as food (Diaz et al, 2015;Desai et al, 2019;Kloock et al, 2020). For pathogenic infection, the Gram-positive Staphylococcus aureus strain MSSA476 (Holden et al, 2004) was used.…”

“…Defensive mutualisms have been observed across kingdoms [reviewed in ]. The potential of defensive mutualism to enhance survival as well as offspring production has been observed repeatedly (Koehler et al, 2013;King et al, 2016;Kloock et al, 2020). However, most of these examples have only considered population-level effects, while few studies have focused on individual behaviors and/or sex differences between the hosts (McLean et al, 2018).…”