DOI: 10.5061/dryad.qz612jmp8
title: Facultative symbiont virulence determines horizontal transmission rate without host specificity in Dictyostelium discoideum social amoebas

description: In facultative symbioses, only a fraction of hosts are associated with
 symbionts. Specific host and symbiont pairings may be the result of
 host-symbiont coevolution driven by reciprocal selection, or priority
 effects pertaining to which potential symbiont became associated with a
 host first. Distinguishing between these possibilities is important for
 understanding the evolutionary forces that affect facultative symbioses.
 We used the social amoeba Dictyostelium discoideum and its symbiont
 Paraburkholderia bonniea to determine whether ongoing coevolution affects
 which host-symbiont strain pairs naturally co-occur within a facultative
 symbiosis. Relative to other Paraburkholderia, including another symbiont
 of D. discoideum, P. bonniea features a reduced genome size that indicates
 a significant history of coevolution with its host. We hypothesized that
 ongoing host-symbiont coevolution would lead to higher fitness for
 naturally co-occurring (native) host and symbiont pairings compared to
 novel pairings. We show for the first time that P. bonniea symbionts can
 horizontally transmit to new amoeba hosts when hosts aggregate together
 during the social stage of their life cycle. Here we find evidence for a
 virulence-transmission trade-off without host specificity. Although
 symbiont strains were significantly variable in virulence and horizontal
 transmission rate, hosts and symbionts responded similarly to associations
 in native and novel pairings. We go on to identify candidate virulence
 factors in the genomes of P. bonniea strains that may contribute to
 variation in virulence. We conclude that ongoing coevolution is unlikely
 for D. discoideum and P. bonniea. The system instead appears to represent
 a stable facultative symbiosis in which naturally co-occurring P. bonniea
 host and symbiont pairings are the result of priority effects.
description: # Data from: Facultative symbiont virulence determines horizontal
 transmission rate without host specificity in Dictyostelium discoideum
 social amoebas These data
 support the Evolution Letters article published under the same title. The
 same data are also available
 [here](https://github.com/noh-lab/social-infection). It contains: *
 **host_fitness.clean.20220711.txt** - Data from host fitness experiment
 with columns in the following order * host identity * symbiont identity *
 MOI (multiplicity of infection) of host-symbiont pairing * date of
 experiment * estimated total number of host spores produced by sample *
 percent of host spored infected by symbiont in sample * percent of spores
 produced by sample relative to mean of uninfected controls * type of
 host-symbiont pairing * **symbiont_transmission.clean.20220711.txt** -
 Data from symbiont transmission experiment with columns in the following
 order * host identity * symbiont identity * MOI of host-symbiont pairing *
 date of experiment * percent of host spores infected by symbiont in sample
 * percent of infected spores that were previously uninfected * type of
 host-symbiont pairing * **bonniea_transmission_2023.R** - R code used to
 run statistical analyses using the data files and generate figures *
 **GFF** files for the three *P. bonniea* genomes - Predicted intact gene
 for each symbiont genome * **assembly_to_set_operations.txt** -
 Description and command-line code for how the GFF files were generated
 including long read assembly, short read polishing, gene annotation,
 pseudogene prediction, and set operations * **virulence_candidates.faa** -
 Protein sequences for the candidate virulence factors identified in the
 study