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.
Fitness measures at MA generation 100 under osmotic stress
Fitness of C. elegans mutation accumulation (MA lines) following 100 consecutive generations of spontaneous MA. The MA experiment was conducted under benign laboratory conditions. Fitness was tested under hyperosmotic conditions (200mM salt concentration in NGM plates). Manual measurements of two fitness-related traits, survivorship to adulthood and productivity, in long-term mutation accumulation (MA) lines of C. elegans maintained at population bottlenecks of N = 1, 10 and 100 individuals and the pre-MA ancestral control. Data is presented, where available for 20 N=1 lines (lines 1A-1T), ten N=10 lines (10A-10J), five N=100 lines (100A-100E) and 20 ancestral control lines (C1-C20). Where possible, data was collected for five replicates per experimental line. Productivity was measured by the total number of offspring produced by a virgin hermaphrodite over eight days or until day of expiration prior to eight days. Survivorship to adulthood was measured by isolating ten L1 larvae and determining the fraction that had survived to adulthood at 36 hours after initial sequestration. Survivorship data values range from 0-1, with a 0 value representing 100% mortality prior to reaching adulthood, and a value of 1 representing 100% survivorship.
Data File 1.pdf
Fitness measures at MA generation 172 under osmotic stress
Fitness of C. elegans mutation accumulation (MA lines) following 172 consecutive generations of spontaneous MA. The MA experiment was conducted under benign laboratory conditions. Fitness was tested under hyperosmotic conditions (200mM salt concentration in NGM plates). Manual measurements of two fitness-related traits, survivorship to adulthood and productivity, in long-term mutation accumulation (MA) lines of C. elegans maintained at population bottlenecks of N = 1, 10 and 100 individuals and the pre-MA ancestral control. Data is presented, where available for 20 N=1 lines (lines 1A-1T), ten N=10 lines (10A-10J), five N=100 lines (100A-100E) and 20 ancestral control lines (C1-C20). Where possible, data was collected for five replicates per experimental line. Productivity was measured by the total number of offspring produced by a virgin hermaphrodite over eight days or until day of expiration prior to eight days. Survivorship to adulthood was measured by isolating ten L1 larvae and determining the fraction that had survived to adulthood at 36 hours after initial sequestration. Survivorship data values range from 0-1, with a 0 value representing 100% mortality prior to reaching adulthood, and a value of 1 representing 100% survivorship.
Data File 2.pdf
Fitness measures at MA generation 300 under osmotic stress
Fitness of C. elegans mutation accumulation (MA lines) following 300 consecutive generations of spontaneous MA. The MA experiment was conducted under benign laboratory conditions. Fitness was tested under hyperosmotic conditions (200mM salt concentration in NGM plates). Manual measurements of two fitness-related traits, survivorship to adulthood and productivity, in long-term mutation accumulation (MA) lines of C. elegans maintained at population bottlenecks of N = 1, 10 and 100 individuals and the pre-MA ancestral control. Data is presented, where available for 20 N=1 lines (lines 1A-1T), ten N=10 lines (10A-10J), five N=100 lines (100A-100E) and 20 ancestral control lines (C1-C20). Where possible, data was collected for five replicates per experimental line. Productivity was measured by the total number of offspring produced by a virgin hermaphrodite over eight days or until day of expiration prior to eight days. Survivorship to adulthood was measured by isolating ten L1 larvae and determining the fraction that had survived to adulthood at 36 hours after initial sequestration. Survivorship data values range from 0-1, with a 0 value representing 100% mortality prior to reaching adulthood, and a value of 1 representing 100% survivorship.
Data File 3.pdf
Fitness measures at MA generation 409 under osmotic stress
Fitness of C. elegans mutation accumulation (MA lines) following 409 consecutive generations of spontaneous MA. The MA experiment was conducted under benign laboratory conditions. Fitness was tested under hyperosmotic conditions (200mM salt concentration in NGM plates). Manual measurements of two fitness-related traits, survivorship to adulthood and productivity, in long-term mutation accumulation (MA) lines of C. elegans maintained at population bottlenecks of N = 1, 10 and 100 individuals and the pre-MA ancestral control. Data is presented, where available for 20 N=1 lines (lines 1A-1T), ten N=10 lines (10A-10J), five N=100 lines (100A-100E) and 20 ancestral control lines (C1-C20). Where possible, data was collected for five replicates per experimental line. Productivity was measured by the total number of offspring produced by a virgin hermaphrodite over eight days or until day of expiration prior to eight days. Survivorship to adulthood was measured by isolating ten L1 larvae and determining the fraction that had survived to adulthood at 36 hours after initial sequestration. Survivorship data values range from 0-1, with a 0 value representing 100% mortality prior to reaching adulthood, and a value of 1 representing 100% survivorship.
Data File 4.pdf