REVERSE EVOLUTION: SELECTION AGAINST COSTLY RESISTANCE IN DISEASE-FREE MICROCOSM POPULATIONS OF PARAMECIUM CAUDATUM
Article first published online: 13 JUL 2011
© 2011 The Author(s). Evolution© 2011 The Society for the Study of Evolution.
Volume 65, Issue 12, pages 3462–3474, December 2011
How to Cite
Duncan, A. B., Fellous, S. and Kaltz, O. (2011), REVERSE EVOLUTION: SELECTION AGAINST COSTLY RESISTANCE IN DISEASE-FREE MICROCOSM POPULATIONS OF PARAMECIUM CAUDATUM. Evolution, 65: 3462–3474. doi: 10.1111/j.1558-5646.2011.01388.x
- Issue published online: 1 DEC 2011
- Article first published online: 13 JUL 2011
- Accepted manuscript online: 16 JUN 2011 04:28AM EST
- Received January 11, 2011, Accepted May 20, 2011, Data Archived: Dryad doi:10.5061/dryad.4kb77
- Holospora undulata;
Evolutionary costs of parasite resistance arise if genes conferring resistance reduce fitness in the absence of parasites. Thus, parasite-mediated selection may lead to increased resistance and a correlated decrease in fitness, whereas relaxed parasite-mediated selection may lead to reverse evolution of increased fitness and a correlated decrease in resistance. We tested this idea in experimental populations of the protozoan Paramecium caudatum and the parasitic bacterium Holospora undulata. After eight years, resistance to infection and asexual reproduction were compared among paramecia from (1) “infected” populations, (2) uninfected “naive” populations, and (3) previously infected, parasite-free “recovered” populations. Paramecia from “infected” populations were more resistant (+12%), but had lower reproduction (–15%) than “naive” paramecia, indicating an evolutionary trade-off between resistance and fitness. Recovered populations showed similar reproduction to naive populations; however, resistance of recently (<3 years) recovered populations was similar to paramecia from infected populations, whereas longer (>3 years) recovered populations were as susceptible as naive populations. This suggests a weak, convex trade-off between resistance and fitness, allowing recovery of fitness, without complete loss of resistance, favoring the maintenance of a generalist strategy of intermediate fitness and resistance. Our results indicate that (co)evolution with parasites can leave a genetic signature in disease-free populations.