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RESEARCH PRODUCT

Environmentally triggered evolutionary cascade across trophic levels in an experimental phage-bacteria-insect system

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Abstract Environmental changes can cause strong cascading effects in species communities due to altered biological interactions between species (Zarnetske et al., 2012). Highly specialized interactions arising from the co-evolution of hosts and parasites, such as bacteria and phages, and short generation times of these species could rapidly lead to considerable evolutionary changes in their biotic interactions (Kerr, 2012; Buck and Ripple, 2017), with potential large-scale ramifications to other trophic levels. Here we report experimental evidence of cascading environmental effects across trophic levels in an experimental system where phage-bacteria coevolution in an abiotically altered environment cascaded on bacterial virulence in an insect host. We found that the lytic cycle of the temperate phage KPS20 induced at low temperatures led to selection in the bacterial host Serratia marcescens that tempered the likelihood of triggering the phage’s lytic cycle. These changes in S. marcescens concomitantly attenuated its virulence in an insect host, Galleria mellonella . In addition, our data suggests that this effect is mediated by mutations and epigenetic modifications of bacterial genes moderating the onset of the temperate phage’s lytic cycle. Given the abundance of temperate phages in bacterial genomes (Canchaya et al., 2003), the sensitivity of the onset of their lytic cycle to environmental conditions (Howard-Varona et al., 2017), and the predominance of environmental change due to climate change, our results warrants attention as a cautionary example of the dangers of predicting environmental effects on species without considering complex biotic interactions.