DOI: 10.5061/dryad.hmgqnk9f5
title: Context-dependent variability in the population prevalence and individual fitness effects of plant-fungal symbiosis

description: 1. Heritable symbionts, found within a diverse array of flora and fauna,
 are often observed at intermediate prevalence within host populations,
 despite expectations that positive fitness feedbacks should drive
 beneficial symbionts to fixation. Intermediate prevalence may reflect
 neutral dynamics of symbionts with weak fitness effects, transient
 dynamics of symbionts trending toward fixation (or elimination), or a
 stable intermediate outcome determined by the balance of fitness effects
 and failed symbiont transmission. Theory suggests these outcomes should
 depend on symbiont-conferred effects and vertical transmission efficiency,
 which may both depend on environmental context. 2. We tested these
 alternatives by tracking temporal change in population-level symbiont
 prevalence in a three-year field experiment with grasses and vertically
 transmitted fungal endophytes under the context of manipulated
 precipitation. Precipitation can mediate endophyte effects on host
 grasses, and is a relevant context, as global climate models predict
 changes in precipitation amount and seasonal distribution. 3. We found
 evidence for each of the three proposed mechanisms for intermediate
 symbiont prevalence, but the outcome differed qualitatively across years
 and precipitation treatments. Specifically, within the first study year,
 all populations under ambient precipitation trended toward symbiont
 fixation, whereas elevated precipitation literally neutralized the
 interaction resulting in no long-run equilibrium. The second study year
 yielded a different result with long-run equilibria at an intermediate
 prevalence for both ambient and elevated precipitation treatments. We
 linked these population-level outcomes with individual-level symbiont
 effects on grasses and showed that the benefits of symbiosis were
 concentrated at the seedling stage, especially under drought stress during
 the time period coinciding with recruitment. The drought stress evident
 during the first year of the study was not present in the second year due
 to greater ambient precipitation during this time period. Together, these
 findings provide the first experimental evidence that population-level
 outcomes of host-symbiont interactions, which arise from the composite
 outcome of demographic vital rates and transmission, can be dynamically
 stable and can fluctuate in response to shifts in spatio-temporal context.
 4. Synthesis: Overall, these results indicate that intermediate prevalence
 of heritable microbial symbionts likely reflects a combination of neutral,
 transient, and stable mechanisms, and context-dependent fluctuations among
 them.
description: Data collected from the field and lab. Data presented here is the
 final version for use with the JAGS parameterization R script for the JAGS
 model.
description: The files provide the demographic data collected from the
 fieldsite and the agrinostic assay data for use in parameterizing the JAGS
 models. AGHY is the USDA code for <em>Agrostis
 hyemalis</em>. AGHY_plot_dat.csv   -
 provides plot-level data 
 AGHY_subplot_dat.csv   - provides subplot-level data
 flowering_individuals.csv   - provides
 flowering data for individual demographic plants 
 flowering_plts.csv   - provides flowering data at the
 plot-level 
 flowering_sbplts.csv   - provides flowering data at the
 subplot-level infs_dat.csv   -
 provides inflorescence count data  
 infs_unk_stacked.csv  - provides inflorescence count data for
 plants of unknown symbiont status 
 linreg_dat.csv   - provides data for linear regression for the
 conversion from seed counts to seed mass (g) 
 rec_final.csv   - provides recruitment
 data rec_plot_final.csv   -
 provides plot information for the recruitment data 
 seedmass_dat.csv   - provides seed mass
 data survival_dat2.csv   -
 provides survival data in the correct alignment for use in the recruitment
 model survival_known.csv   -
 provides survival data for plants of known symbiont status
 survival_plot.csv   - provides plot
 information for the survival model 
 survival_unk_sbplt.csv   - provides survival data for plants of
 unknown symbiont status 
 total_plants_infs.csv   - provides data on inflorescences and
 total plants vtrans_dat.csv 
  - provides data on vertical transmission (number of symbiont positive
 seeds and total number of seeds scored for the symbiont)