10.5061/DRYAD.RF47CP2
Lynch, Zachary R.
Emory University
Penley, McKenna J.
Emory University
Morran, Levi T.
Emory University
Data from: Turnover in local parasite populations temporarily favors host
outcrossing over self-fertilization during experimental evolution
Dryad
dataset
2019
Caenorhabditis elegans
host mating system evolution
Serratia marcescens
parasite turnover
outcrossing
self-fertilization
2019-04-11T00:00:00Z
2019-04-11T00:00:00Z
en
https://doi.org/10.1002/ece3.4150
32962 bytes
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CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
The ubiquity of outcrossing in plants and animals is difficult to explain
given its costs relative to self-fertilization. Despite these costs,
exposure to changing environmental conditions can temporarily favor
outcrossing over selfing. Therefore, recurring episodes of environmental
change are predicted to favor the maintenance of outcrossing. Studies of
host–parasite coevolution have provided strong support for this
hypothesis. However, it is unclear whether multiple exposures to novel
parasite genotypes in the absence of coevolution are sufficient to favor
outcrossing. Using the nematode Caenorhabditis elegans and the bacterial
parasite Serratia marcescens, we studied host responses to parasite
turnover. We passaged several replicates of a host population that was
well-adapted to the S. marcescens strain Sm2170 with either Sm2170 or one
of three novel S. marcescens strains, each derived from Sm2170, for 18
generations. We found that hosts exposed to novel parasites maintained
higher outcrossing rates than hosts exposed to Sm2170. Nonetheless, host
outcrossing rates declined over time against all but the most virulent
novel parasite strain. Hosts exposed to the most virulent novel strain
exhibited increased outcrossing rates for approximately 12 generations,
but did not maintain elevated levels of outcrossing throughout the
experiment. Thus, parasite turnover can transiently increase host
outcrossing. These results suggest that recurring episodes of parasite
turnover have the potential to favor the maintenance of host outcrossing.
However, such maintenance may require frequent exposure to novel virulent
parasites, rapid rates of parasite turnover, and substantial host gene
flow.
Figure-1-dataMortality rates suffered by the ancestral host population
(EW2-30) after 24 hours of exposure to the four parasite strains we used
for experimental evolution. Each of the five replicate host populations
was tested against each parasite strain with three technical replicates
and the average number of dead nematodes was calculated for each
combination. All plates started with 200 nematodes and dead nematodes were
counted 24 hours later.Figure-2-dataCounts of male and hermaphrodite hosts
in each replicate population in the ancestral generation and generations
6, 12, and 18 of experimental evolution. Treatment = parasite strain each
population was passaged with during experimental evolution. Male Frequency
= # males / (# males + # hermaphrodites). Outcrossing Rate = 2*(Male
Frequency – 0.002).Figure-3-dataPercent changes in mean fitness for
generation 18 hosts relative to their ancestors during exposure to the
parasite strain each generation 18 host population was passaged with, as
determined by competitive fitness assays against a GFP-marked tester
strain. See README for further details.Figure-4-dataMortality rates
suffered by evolved generation 18 host populations after 24 hours of
exposure to Sm2170. Each replicate host population was tested in two
technical replicates and the average number of dead nematodes was
calculated. All plates started with 200 nematodes and dead nematodes were
counted 24 hours later. Host = parasite strain the host population was
passaged with during experimental evolution. Parasite = parasite strain
used for the mortality assays.Table-3-dataSurvival rates of hermaphrodites
and males from the ancestral host population (EW2-30) within the selection
regime. Both host sexes were tested against each of the four parasite
strains used for experimental evolution in five replicates. Groups of
nematodes (222 hermaphrodites or 50 males) were placed on the parasite
side of Serratia selection plates (Worms Plated). Nematodes that migrated
out of the parasite lawn and were alive 48 hours after exposure to the
parasite were counted as survivors (Worms Alive).