Mixed infections may promote diversification of mutualistic symbionts: why are there ineffective rhizobia?
Article first published online: 3 DEC 2009
© 2009 The Authors. Journal Compilation © 2009 European Society For Evolutionary Biology
Journal of Evolutionary Biology
Volume 23, Issue 2, pages 323–334, February 2010
How to Cite
FRIESEN, M. L. and MATHIAS, A. (2010), Mixed infections may promote diversification of mutualistic symbionts: why are there ineffective rhizobia?. Journal of Evolutionary Biology, 23: 323–334. doi: 10.1111/j.1420-9101.2009.01902.x
- Issue published online: 13 JAN 2010
- Article first published online: 3 DEC 2009
- Received 16 June 2008; revised 21 October 2009; accepted 23 October 2009
- adaptive dynamics theory;
- life-history evolution;
While strategy variation is a key feature of symbiotic mutualisms, little work focuses on the origin of this diversity. Rhizobia strategies range from mutualistic nitrogen fixers to parasitic nonfixers that hoard plant resources to increase their own survival in soil. Host plants reward beneficial rhizobia with higher nodule growth rates, generating a trade-off between reproduction in nodules and subsequent survival in soil. However, hosts might not discriminate between strains in mixed infections, allowing nonfixing strains to escape sanctions. We construct an adaptive dynamics model of symbiotic nitrogen-fixation and find general situations where symbionts undergo adaptive diversification, but in most situations complete nonfixers do not evolve. Social conflict in mixed infections when symbionts face a survival–reproduction trade-off can drive the origin of some coexisting symbiont strategies, where less mutualistic strains exploit benefits generated by better mutualists.