Abstract Detail

Botany 2015 Colloquium: Integrated perspectives on the ecology, genetics and coevolution of intimate mutualisms

Porter, Stephanie [1], Simms, Ellen [2].

Fitness alignment and conflict in the mutualism between plants and nitrogen-fixing rhizobium bacteria.

Mutualistic symbionts and environmental conditions alter the expression of plant traits. However, few studies investigate whether evolution of both plant and symbiont populations could contribute to trait evolution or how environmental quality could impact this process. We grew lineages of the legume, Medicago polymorpha, in the absence or presence of lineages of nitrogen-fixing symbiotic rhizobium bacteria, Ensifer medicae, in two environmental contexts. This allowed us to quantify the effects of symbiotic state, genetic variation, and environmental quality to the expression of commonly measured ecophysiological plant traits. We also examined genotypic selection gradients to measure host-symbiont fitness conflict or alignment over ecophysiological trait values in high vs. low-quality environments.
The presence of rhizobia strongly affected trait expression, with especially large effects in a lower quality environment. We found genetic variation among plant lineages for all focal traits and among rhizobium strains for specific leaf area. Natural selection for plant lineages that flower early but rhizobium lineages that cause plants to flower late suggests hosts and symbionts experience fitness conflict over trait expression and this conflict is more severe in a lower quality habitat. Our results suggest symbiont co-determination of host traits that are not directly related to mutualistic resource exchange can be common and strong. Thus, understanding the evolution of commonly measured ecophysiological traits will be incomplete without explicitly considering the role of symbionts.

1 - University of California, Riverside, Biology, 1229 Speith Hall, 3401 Watkins Drive, Riverside, CA, 92521, USA
2 - University of California, Berkeley, Integrative Biology, 3040 Valley Life Sciences Building # 3140, Berkeley, CA, 94720

Keywords:
legume
rhizobia
mutualism
symbiosis
functional leaf traits
ecophysiological traits.

Presentation Type: Colloquium Presentations
Session: C4
Location: Hall C/The Shaw Conference Centre
Date: Tuesday, July 28th, 2015
Time: 5:15 PM
Number: C4015
Abstract ID:704
Candidate for Awards:None