Unpredictable soil conditions can affect the prevalence of a microbial symbiosis

Abstract

The evolution of symbiotic interactions may be affected by unpredictable conditions. However, a link between prevalence of these conditions and symbiosis has not been widely demonstrated. We test for these associations using Dictyostelium discoideum social amoebae and their bacterial endosymbionts. D. discoideum commonly hosts endosymbiotic bacteria from three taxa: Paraburkholderia, Amoebophilus and Chlamydiae. Three species of facultative Paraburkholderia endosymbionts are the best studied and give hosts the ability to carry prey bacteria through the dispersal stage to new environments. Amoebophilus and Chlamydiae are obligate endosymbiont lineages with no measurable impact on host fitness. We tested whether the frequency of both single infections and coinfections of these symbionts were associated with the unpredictability of their soil environments by using symbiont presence-absence data from D. discoideum isolates from 21 locations across the eastern United States. We found that symbiosis across all infection types, symbiosis with Amoebophilus and Chlamydiae obligate endosymbionts, and symbiosis involving coinfections were not associated with any of our measures. However, unpredictable precipitation was associated with symbiosis in two species of Paraburkholderia, suggesting a link between unpredictable conditions and symbiosis.

Complex third-party effects in the Dictyostelium–Paraburkholderia symbiosis: prey bacteria that are eaten, carried or left behind

“…We speculate that carrying more prey in prey-poor contexts may represent cooperation between hosts and symbionts that allows the symbiosis to persist over repeated harsh environments. Such harsh conditions are potentially an important force shaping cooperation in this [4,48] and other symbioses [49][50][51]. These studies in symbiotic systems complement research on the role of harsh environments in the evolution of cooperation that has been focused on interactions between members of the same species [52], most commonly in cooperatively breeding birds [53][54][55].…”