DOI: 10.5061/dryad.3bk3j9khx
title: Decreased coevolutionary potential and increased symbiont fecundity during the biological invasion of a legume-rhizobium mutualism

description: Although most invasive species engage in mutualism, we know little about
 how mutualism evolves as partners colonize novel environments. Selection
 on cooperation and standing genetic variation for mutualism traits may
 differ between a mutualism's invaded and native ranges, which could
 alter cooperation and coevolutionary dynamics. To test for such
 differences, we compare mutualism traits between invaded- and native-range
 host-symbiont genotype combinations of the weedy legume, Medicago
 polymorpha, and its nitrogen-fixing rhizobium symbiont, Ensifer medicae,
 which have co-invaded North America. We find that mutualism benefits for
 plants are indistinguishable between invaded- and native-range symbioses.
 However, rhizobia gain greater fitness from invaded-range mutualisms than
 from native-range mutualisms, and this enhancement of symbiont fecundity
 could increase the mutualism’s spread by increasing symbiont availability
 during plant colonization. Furthermore, mutualism traits in invaded-range
 symbioses show lower genetic variance and a simpler partitioning of
 genetic variance between host and symbiont sources, compared to
 native-range symbioses. This suggests that biological invasion has reduced
 mutualists’ potential to respond to coevolutionary selection.
 Additionally, rhizobia bearing a locus (hrrP) that can enhance symbiotic
 fitness have more exploitative phenotypes in invaded-range than in
 native-range symbioses. These findings highlight the impacts of biological
 invasion on the evolution of mutualistic interactions.
description: We generated a collection of <em>Ensifer medicae</em>
 (rhizobia) strains from field soils and used PCR to screen each strain for
 the presence of <em>hrrP</em>, a gene that can change how
 cooperative rhizobia are with their legume hosts. We provide the results
 of the PCR screen for each strain in our collection. A subset of rhizobia
 from this collection was inoculated onto <em>Medicago polymorpha
 </em>plants in a greenhouse experiment, and we measured plant growth
 benefits from inoculation (leaf count, shoot mass) and symbiosis traits
 (number of root nodules, nodule size, and number of colony-forming units
 of <em>E. medicae </em>within the nodules). We provide raw
 plant-level and nodule-level data from this experiment.
description: We provide four datasets as csv files and one R code file that
 contains code for analyzing the data in these files. The first two columns
 of each data file contain the metadata, "Column" and
 "Description", which contain details for understanding the
 remaining columns. The contents of each file are as follows:
 1_PCR_data.csv contains
 the <em>hrrP</em> genotype information for each <em>E.
 medicae</em> strain in the study.
 2_map_data.csv contains geographic information about the
 populations from which we sourced <em>E. medicae </em>strains
 and <em>M. polymorpha</em> plants.
 3_CFU_data.csv contains colony count data from culturing of
 nodule contents in the greenhouse inoculation experiment.
 4_greenhouse_data.csv contains plant-level trait data from the
 greenhouse inoculation experiment.
 Wendlandt_et_al_2020_Evolution_code.R contains R code for
 importing, processing, and analyzing data from the above four datasets. It
 also contains code for producing figures from these data.