DOI: 10.5061/dryad.bk3j9kdgd
title: Hosts winnow symbionts with multiple layers of absolute and conditional discrimination mechanisms

description: In mutualism, hosts select symbionts via partner choice and preferentially
 direct more resources to symbionts that provide greater benefits via
 sanctions. At the initiation of symbiosis, prior to resource exchange, it
 is not known how the presence of multiple symbiont options (i.e., the
 symbiont social environment) impacts partner choice outcomes. Furthermore,
 little research addresses whether hosts primarily discriminate among
 symbionts via sanctions, partner choice or a combination. We inoculated
 the legume, Acmispon wrangelianus, with 28 pairs of fluorescently labeled
 Mesorhizobium strains that vary continuously in quality as nitrogen-fixing
 symbionts. We find that hosts exert robust partner choice, which enhances
 their fitness. This partner choice is conditional such that a
 strain's success in initiating nodules is impacted by other strains
 in the social environment. This social genetic effect is as important as a
 strain's own genotype in determining nodulation and has both
 transitive (consistent) and intransitive (idiosyncratic) effects on the
 probability that a symbiont will form a nodule. Furthermore, both absolute
 and conditional partner choice act in concert with sanctions, among and
 within nodules. Thus, multiple forms of host discrimination act as a
 series of sieves that optimize host benefits and select for costly
 symbiont cooperation in mixed symbiont populations.
description: We transformed eight
 <em>Mesorhizobium</em> strains to express fluorescent markers.
 We grew <em>Mesorhizobium</em> in symbiosis with a single
 genotype of the native <em>Acmispon wrangelianus</em> host
 plant as both 1-strain inoculations (8 treatments) and all possible
 2-strain combinations (28 treatments), replicated over 8 blocks. Rhizobia
 and host plant fitness data were measured in the greenhouse experiment
 (symbiosis_phenotype_data.csv).  We also measured reproductive fitness of
 rhizobia in nodules (cfu_data.csv) and measured each strains intrinsic
 axenic growth rate (growth_data.csv).
description: We provide three datasets as csv
 files and one R code file that contains code for analyzing the data in
 these files. In addition, two more csv files are provided to save time but
 these files can also be regenerated using code in the R file. See the
 README file for metadata for each data set. The contents of each file are
 as follows: *
 symbiosis_phenotype_data.csv contains <em>Mesorhizobium
 </em>and host plant fitness data from the greenhouse experiment.
 This file contains a metadata description in the first column.
 * cfu_data.csv contains nodule
 culturing data (counts of colony forming units). This file contains a
 metadata description in the first column. * growth_data.csv contains each of the
 eight <em>Mesorhizobium </em>strains growth rate. This file
 contains a metadata description in the first column. * noduleproportion_models_randomized.csv is
 an extra file that is provided to save time when reproducing part of
 figure S2 (nodule proportion), or the code that generated this output file
 is included in the R code file (Montoya_et_al_2022_code.R) * shootmass_models_randomized.csv is an
 extra file that is provided to save time when reproducing part of figure
 S2 (shoot mass), or the code that generated this output file is included
 in the R code file (Montoya_et_al_2022_code.R) * Montoya_et_al_2022_code.R contains R code
 for importing, processing, and analyzing data from the above datasets. It
 also contains code for producing figures from these data.