Genetic variation in parasite avoidance, yet no evidence for constitutive fitness costs
Abstract
Behavioral avoidance of parasites is a widespread strategy among animal hosts and in human public health. Avoidance has repercussions for both individual and population-level infection risk. Although most cases of parasite avoidance are viewed as adaptive, there is little evidence that the basic assumptions of evolution by natural selection are met. This study addresses this gap by testing whether there is a heritable variation in parasite avoidance behavior. We quantified behavioral avoidance of the bacterial parasite Serratia marcescens for 12 strains of the nematode host Caenorhabditis elegans. We found that these strains varied in their magnitude of avoidance, and we estimated the broad-sense heritability of this behavior to be in the range of 11-26%. We then asked whether avoidance carries a constitutive fitness cost. We did not find evidence of one. Rather, strains with higher avoidance had higher fitness, measured by population growth rate. Together, these results direct future theoretical and empirical work to identify the forces maintaining genetic variation in parasite avoidance.
README: Genetic variation in parasite avoidance, yet no evidence for constitutive fitness costs
https://doi.org/10.5061/dryad.1jwstqk2m
Description of the data and file structure
The datasets and code in this repository accompany "Genetic variation in avoidance, yet no evidence for constitutive costs," by Caroline R. Amoroso, Leila L. Shepard, and Amanda K. Gibson.
In the Data folder are two files:
1. "Lawn-leaving assay.csv": the original data collected for this project on the parasite avoidance behavior of C. elegans strains. Explanations of column headers:
Block: experimental block, 1 through 6
Plate_number: replicate plate
Bacterial_strain: OP50 (E. coli control) or Db10 (S. marcescens parasite)
C.elegans_strain: Code corresponding to one of 12 of the C. elegans strains from the CaeNDR "divergent set"" (see https://caendr.org/request-strains/)
Date_time_picked: Date and time that C. elegans hosts were added to the experimental plate
Date_time_counted: Date and time that C. elegans hosts were scored as on or off the bacterial lawn
Worms_ON: count of hosts on the lawn
Worms_OFF: count of hosts off the lawn
N_dead_worms: Number of dead worms (these were always on the lawn)
N_burrowed: Number of worms burrowed into agar (these were always under the lawn of OP50)
Excl_from_sub20: Sum of dead or male worms by subtracting "avoided" from 20 (analysis with a liberal interpretation of avoidance)
2. "Population growth assay.csv": Original data collected for this project on the fitness of 12 strains of C. elegans. Explanations of column headers:
Block: experimental block, 1 through 5
Strain: C. elegans strain code, same as above
Plate: replicate plate number
Drop: Which of 4 to 6 20 ul drops was counted for the number of C. elegans individuals, reflecting the population size after a fixed period of population growth
Count_20ul: Mean of 3 separate counts of each 20ul drop
Burrowing_exclude: removed two replicates because C. elegans individuals had burrowed into agar, interfering with our ability to wash them from plates and count them.
We do not provide a file that we used in the analysis due to copyright restrictions. In our code this file is referred to as "Zhang et al 2021 fecundity data.csv". These data are previously published, independent measures of fitness from another lab for 7 of the 12 strains in the present study. Downloaded from https://github.com/AndersenLab/swept_broods/blob/main/processed_data/FileS3_lifetimeFecundity.csv; from Zhang et al. 2021 Natural variation in fecundity is correlated with species-wide levels of divergence in Caenorhabditis elegans. G3. https://doi.org/10.1093/g3journal/jkab168. The paper is available at https://academic.oup.com/g3journal/article/11/8/jkab168/6275220
Links to other publicly accessible locations of the data:
https://github.com/carolineramoroso/C.elegans_Genetic_variation_in_avoidance
Code/Software
Analysis can be found in "Genetic variation in parasite avoidance_analysis.R" and relies on the above described data files.