Presentation Detail

Species Interactions and Coevolution

Lee, Caitlin E. [1], Cruzan, Mitchell [2].

Increased costs of asymmetric, multi-player mutualisms: is outweighing costs with benefits the answer?

Mutualisms are ubiquitous in natural systems and have been shown to provide important ecological benefits; however, evolutionary persistence of mutualisms is not often predicted by natural selection. Theory predicts that cooperation in asymmetric, mutli-player mutualisms are maintained by the benefits outweighing the costs for all players with controls for cheaters. Measuring the fitness gains or losses due to this cost/benefit ratio in nature has proven difficult; additionally, when mutualisms are asymmetric and multiple players are involved, measuring the costs and benefits for each individual is problematic. In mycorrhizal interactions, research shows large variation in the cost/benefit ratio across multiple species and multiple conditions. Traditionally, arbuscular mycorrhizal fungi (AMF) are thought to be beneficial to the plants by providing limiting nutrients while the plants provide photosynthates to the fungi for growth and reproduction. Interestingly, multiple invasive plant species have been reported to have decreased AMF colonization compared with both native plants in the invaded range and the invasive plants in their home ranges, suggesting novel interactions with AMF may have increased costs for plants. To test if novelty of the interaction impacted the cost/benefit ratio and if plants attempted to limit the cost, four clones from nine plants of Brachypodium sylvaticum, an invasive bunch-grass in the northwestern United States, from each of three populations in Eugene, OR, Corvallis, OR, and Europe were grown with and without fertilizer and with and without AMF inoculum. Plants were harvested at three harvest dates (60 days, 90 days, and 120 days)to determine shifts in the cost/benefit ratios due to plant developmental stages, as these have been shown in previous studies. We expected plants in high fertilizer conditions with AMF to experience the highest cost; however,the results indicate a significantly greater decreased plant size and chlorophyll content for plants with AMF inoculum in no fertilizer conditions.Plant survival was significantly decreased for all plants inoculated compared to plants not inoculated, indicating that Oregon derived AMF are costly to B. sylvaticum. We also predicted a greater decrease in growth of European plants based on novelty of the interaction, but there was no significant difference between populations or regions. There was no significant difference in colonization levels of inoculated plants, suggesting plants are not limiting AMF colonization to limit costs. Analysis of spore concentrations will provide insights into the effects of novel interactions and nutrient levels on the fitness of the AMF partners.

1 - Portland State University, Biology, 1719 SW 10th Ave, SRTC Room 246, Portland, Oregon, 97201, USA
2 - Portland State University, Department Of Biology, PO BOX 751, PORTLAND, OR, 97207, USA

Keywords:
invasive species
evolution of mutualisms
endosymbiotic mycorrhizal fungi
evolutionary ecology.

Presentation Type: Regular Oral Presentation
Session: 99
Location: Cotton B/Snowbird Center
Date: Monday, June 24th, 2013
Time: 9:15 AM
Number: 99004
Abstract ID:259
Candidate for Awards:W.D. Hamilton Award for Outstanding Student Presentation