Comparing constitutive and induced costs of symbiont-conferred resistance to parasitoids in aphids
Article first published online: 13 FEB 2013
© 2013 The Authors. Ecology and Evolution published by Blackwell Publishing Ltd.
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Ecology and Evolution
Volume 3, Issue 3, pages 706–713, March 2013
How to Cite
Ecology and Evolution 2013; 3(3): 706–713
- Issue published online: 11 MAR 2013
- Article first published online: 13 FEB 2013
- Manuscript Accepted: 8 JAN 2013
- Manuscript Revised: 28 DEC 2012
- Manuscript Received: 13 DEC 2012
- Swiss National Science Foundation
- Aphis fabae ;
- Hamiltonella defensa ;
- Lysiphlebus fabarum ;
Host defenses against parasites do not come for free. The evolution of increased resistance can be constrained by constitutive costs associated with possessing defense mechanisms, and by induced costs of deploying them. These two types of costs are typically considered with respect to resistance as a genetically determined trait, but they may also apply to resistance provided by ‘helpers’ such as bacterial endosymbionts. We investigated the costs of symbiont-conferred resistance in the black bean aphid, Aphis fabae (Scopoli), which receives strong protection against the parasitoid Lysiphlebus fabarum from the defensive endosymbiont Hamiltonella defensa. Aphids infected with H. defensa were almost ten times more resistant to L. fabarum than genetically identical aphids without this symbiont, but in the absence of parasitoids, they had strongly reduced lifespans, resulting in lower lifetime reproduction. This is evidence for a substantial constitutive cost of harboring H. defensa. We did not observe any induced cost of symbiont-conferred resistance. On the contrary, symbiont-protected aphids that resisted a parasitoid attack enjoyed increased longevity and lifetime reproduction compared with unattacked controls, whereas unprotected aphids suffered a reduction of longevity and reproduction after resisting an attack. This surprising result suggests that by focusing exclusively on the protection, we might underestimate the selective advantage of infection with H. defensa in the presence of parasitoids.