DOI: 10.5061/dryad.jm63xsjh9
title: High parasite virulence necessary for the maintenance of host outcrossing via parasite-mediated selection

description: Biparental sex is widespread in nature, yet costly relative to uniparental
 reproduction. It is generally unclear why self-fertilizing or asexual
 lineages do not readily invade outcrossing populations. The Red Queen
 hypothesis predicts that coevolving parasites can prevent self-fertilizing
 or asexual lineages from invading outcrossing host populations. However,
 only highly virulent parasites are predicted to maintain outcrossing,
 which may limit the general applicability of the Red Queen hypothesis.
 Here, we tested whether the ability of coevolving parasites to prevent
 invasion of self-fertilization within outcrossing host populations was
 dependent on parasite virulence. We introduced wild-type Caenorhabditis
 elegans hermaphrodites, capable of both self-fertilization and
 outcrossing, into C. elegans populations fixed for a mutant allele
 conferring obligate outcrossing. Replicate C. elegans populations were
 exposed for 24 host generations to one of four strains of Serratia
 marcescens parasites that varied in virulence, under three treatments: a
 heat-killed (control, non-infectious) parasite treatment, a fixed-genotype
 (non-evolving) parasite treatment, and a copassaged (potentially
 coevolving) parasite treatment. As predicted, self-fertilization
 invaded C. elegans host populations in the control and
 fixed-parasite treatments, regardless of parasite virulence. In the
 copassaged treatment, selfing invaded host populations coevolving with
 low- to mid- virulent strains but remained rare in hosts coevolving with
 highly virulent bacterial strains. Therefore, we found that only highly
 virulent coevolving parasites can impede the invasion of selfing.
description: Dataset was collected using mortality assays and male frequency
 counting assays of <em>C. elegans</em> populations in a
 laboratory setting. Data has been processed and visualized in R.
description: .csv data files can be opened in excel or in R, as well as other
 data analysis software programs. The .R data anlysis
 files can be opened in R.
description: # Title of Dataset High parasite virulence necessary for the maintenance
 of host outcrossing via parasite-mediated selection ## Description of the
 data and file structure The file “VTEE ancestral SM virulence.csv”
 contains the virulence (mortality) data for the ancestral host and
 parasite populations. The data in this file is analyzed and visualized in
 the script “slowinskietal2023\_av.R” and is presented in Figure 1.
 Variables: rep - Replicate assay plate number. Mortality rates for each
 strain and mating type were measured on multiple replicate assay plates
 serratia.strain - Strain of Serratia (parasite) used in assay hours.expose
 - Number of hours of exposure to parasite in assay num.plated - Number of
 worms (estimated) plated and exposed to the parasite num.in.op50 - Number
 of live worms counted on the OP50 food section of the plate at the end of
 the assay num.else - Number of live worms counted on the plate but not on
 the OP50 at the end of the assay total - Total number of live worms
 counted on the plate at the end of the assay (num.in.op50 + num.else)
 survival - Proportion of total plated worms on the assay plate that were
 counted alive at the end of the assay (total / num.plated) Mortality -
 Proportion of total plated worms on the assay plate that died by the end
 of the assay (1 - survival) avg.mort - Average mortality across replicate
 mating plates within each Serratia strain and mating system combination
 mating.system - Mating system (obligately outcrossing or mixed mating) of
 the ancestral host strain *** The file “VTEE.coev.vir.csv” contains the
 virulence (mortality) data for the the replicate host populations on their
 contemporary coevolved pathogen populations at passage numbers 12 and 22,
 as well as the virulence (mortality) data for the ancestral mixed mating
 host populations (passage zero). The data in this file is analyzed and
 visualized in the script “slowinskietal2023\_cv.R” and is presented in
 Figure 2 Variables treatment - Experimental evolution treatment. All
 evolved populations in this assay (passages 12 and 22) were from the
 “Coevolution”. The passage zero populations represent the host and
 pathogen ancestors. serratia.strain - Strain of Serratia (parasite) used
 in assay host.replicate.population - Replicate number for the host
 population. Ancestral host populations were divided into replicates that
 were passaged separately within each treatment. Note that replicate host
 population is NA at passage zero because mortality of the ancestral host
 was assayed on each pathogen strain before the ancestral host was divided
 into replicate populations. passage - Number of passages of selection that
 the population has undergone (zero for ancestor) rep - Replicate assay
 plate. The mortality of each host population was assayed on multiple
 replicate assay plates pathogen - Name of the evolved pathogen strain.
 num.plated - Number of worms (estimated) plated and exposed to the
 parasite time - Number of hours of exposure to parasite in assay
 num.in.op50 - Number of live worms counted on the OP50 food section of the
 plate at the end of the assay num.else - Number of live worms counted on
 the plate but not on the OP50 at the end of the assay total - Total number
 of live worms counted on the plate at the end of the assay (num.in.op50 +
 num.else) survival - Proportion of total plated worms on the assay plate
 that were counted alive at the end of the assay (total / num.plated)
 avg.survival - Average survival across replicate mating plates within each
 replicate host population. Note that the average survival is listed once
 only per host population, and is listed as NA for additional replicate
 assay plates of the same host population. Mortality - Proportion of total
 plated worms on the assay plate that died by the end of the assay (1 -
 survival) avg.mort - Average mortality across replicate mating plates
 within replicate host population. Note that the average mortality is
 listed once only per host population, and is listed as NA for additional
 replicate assay plates of the same host population. Mortality was not
 measured for a couple of host replicate populations at a couple of time
 points, in which case "NA" is listed for all survival and
 mortality related variables. *** The file “selfingrates.csv” contains the
 selfing rate data for each replicate host populations. Selfing rates were
 estimated based on male frequencies in the evolved populations
 (generations 8, 16, and 24). Selfing rates were estimated based on the
 starting frequencies of mixed maters and obligate outcrossers in the
 ancestral host populations (generation 0), assuming negligible rates of
 outcrossing in the ancestral mixed mating host populations. The data in
 this file is analyzed in visualized in the script
 “slowinskietal2023\_selfing.R” and is presented in Figure 3. Variables
 generation - Number of passages of selection that the population has
 undergone (zero for ancestor) treatment - Experimental evolution treatment
 parasite - Strain of Serratia marcescens that hosts were passaged on rep -
 Replicate host population males - Number of males counted in male
 frequency assays (evolved populations) or estimated number of males plated
 (ancestral populations) herms.females - Number of worms scored as
 hermaphrodite or female in the male frequency assays (evolved populations)
 or estimated number of hermaphrodites or females plated (ancestral
 populations). Note that hermaphrodites and females are hard to distinguish
 morphologically, and were counted together in the male frequency assays.
 male.freq - Frequency of males (i.e., males / (males + herms.females))
 selfing.rate - Proportion of worms in the population that were produced by
 self fertilization (as opposed to outcrossing). Selfing rates were
 estimated based on male frequencies. ## Code/Software Data analyzed in R
 version 4.3.1 using the packages dplyr, tidyverse, and lmerTest