A bacterium from a novel Caenorhabditis niche induces opposing life history responses in C. elegans and C. inopinata

Abstract

Microbes are major drivers of host health, life history responses that influence reproduction and fitness, and evolutionary trajectories for all domains of life. The field of life history research has a rich history, while microbiome research is relatively recent. The evolution of microbe- dependent life history responses in divergent hosts is an avenue where these two fields intersect. Caenorhabditis elegans is a prominent model organism that has been utilized within many fields of biological research and has recently been used to study host-microbe interactions. Here, we use a morphologically and ecologically divergent Caenorhabditis species, C. inopinata, alongside its closest known relative, C. elegans, to investigate how microbe-dependent life history phenotypes evolve in hosts that occupy divergent ecological niches. To do this, we isolated bacteria from the ecological context of C. inopinata, reared both nematode species on these bacterial isolates, and measured life history responses and determined whether the responses have diverged or been conserved depending on what bacteria was consumed. We have identified a fig bacterial isolate, Klebsiella sp. WOUb2, that induces increased population growth in both nematode species in different ways. Individual reproductive output increases for C. elegans raised on Klebsiella sp. WOUb2, while developmental rate is more rapid for C. inopinata. The viability of C. elegans raised on Klebsiella sp. WOUb2 decreases, seemingly demonstrating a trade-off between increased reproductive output and survival. Klebsiella sp. WOUb2 also seems to modulate adult body length of C. elegans. Additionally, both foraging behavior and embryo-laying behaviors of C. inopinata and C. elegans were modulated by Klebsiella sp. WOUb2. We conclude that the evolution of a novel Caenorhabditis niche, the fig, has induced the evolution of microbe-dependent life history responses and behavior in C. elegans and C. inopinata.