Data from: Fitness decline under osmotic stress in Caenorhabditis elegans populations subjected to spontaneous mutation accumulation at varying population sizes

The consequences of mutations for population fitness depends on their
individual selection coefficients and the effective population size. An
earlier study of Caenorhabditis elegans spontaneous mutation accumulation
lines evolved for 409 generations at three population sizes found that Ne
= 1 populations declined significantly in fitness whereas the fitness of
larger populations (Ne = 5, 50) was indistinguishable from the ancestral
control under benign conditions. To test if larger MA populations harbor a
load of cryptic deleterious mutations that are obscured under benign
laboratory conditions, we measured fitness under osmotic stress via
exposure to hypersaline conditions. The fitness of Ne = 1 lines exhibited
a further decline under osmotic stress compared to benign conditions.
However, the fitness of larger populations remained indistinguishable from
that of the ancestral control. The average effects of deleterious
mutations in Ne =1 lines were estimated to be 22% for productivity and 14%
for survivorship, exceeding values previously detected under benign
conditions. Our results suggest that fitness decline is due to large
effect mutations which are rapidly removed via selection even in small
populations, with implications for conservation practices. Genetic
stochasticity may not be as potent and immediate a threat to the
persistence of small population as other demographic and environmental
stochastic factors.