High parasite virulence necessary for the maintenance of host outcrossing via parasite-mediated selection
Data files
Aug 30, 2023 version files 36.45 KB
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README.md
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selfingrates.csv
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VTEE_ancestral_SM_virulence.csv
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VTEE.coev.vir.csv
Abstract
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.
README: 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
Methods
Dataset was collected using mortality assays and male frequency counting assays of C. elegans populations in a laboratory setting. Data has been processed and visualized in R.
Usage notes
.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.