Vertically transmitted symbiont reduces host fitness along temperature gradient

Oliver Kaltz contributed to a paper by Eike Dusi and colleagues, investigating the impact of an exclusively vertically transmitted parasite on temperature reaction norms of the freshwater protozoan Paramecium tetraurelia.

Dusi, E., S. Krenek, M. Schrallhammer, R. Sachse, G. Rauch, O. Kaltz, and T. U. Berendonk. 2014. Vertically transmitted symbiont reduces host fitness along temperature gradient. Journal of Evolutionary Biology 27: DOI: 10.1111/jeb.12336

Parasites with exclusive vertical transmission from host parent to offspring are an evolutionary puzzle. With parasite fitness entirely linked to host reproduction, any fitness cost for infected hosts risks their selective elimination. Environmental conditions likely influence parasite impact, and thereby the success of purely vertical transmission strategies. We tested for temperature-dependent virulence of Caedibacter taeniospiralis, a vertically transmitted bacterial symbiont of the protozoan Paramecium tetraurelia. We compared growth of infected and cured host populations at five temperatures (16-32°C). Infection reduced host density at all temperatures, with a peak of 30% (se ± 1.61) at 28°C. These patterns were largely consistent across five infected Paramecium strains. Similar to Wolbachia symbionts, C. taeniospiralis may compensate fitness costs by conferring to the host a ‘killer trait’, targeting uninfected competitors. Considerable loss of infection at 32°C suggests that killer efficacy is not universal and that limited heat tolerance restricts the conditions for persistence of C. taeniospiralis.


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