Data from: Drift load in populations of small size and low density

According to theory, drift load in randomly mating populations is determined by past population size, because enhanced genetic drift in small populations causes accumulation and fixation of recessive deleterious mutations of small effect. In contrast, segregating load due to mutations of low frequency should decline in smaller populations, at least when mutations are highly recessive and strongly deleterious. Strong local selection generally reduces both types of load. We tested these predictions in 13 isolated, outcrossing populations of Arabidopsis lyrata that varied in population size and plant density. Long-term size was estimated by expected heterozygosity at 20 microsatellite loci. Segregating load was assessed by comparing performance of offspring from selfings versus within-population crosses. Drift load was the heterosis effect created by interpopulation outbreeding. Results showed that segregating load was unrelated to long-term size. However, drift load was significantly higher in populations of small effective size and low density. Drift load was mostly expressed late in development, but started as early as germination and accumulated thereafter. The study largely confirms predictions of theory and illustrates that mutation accumulation can be a threat to natural populations.allData_121010txt file with population-cross type means and standard errors of a common garden study on Arabidopsis lyrata with the following columns: oberservationNo, population, site, expectedHeterozygosity, localDensity [m-2], multilocusOutcrossingRate (tm), crossType, multiplicative performance I (MPI), multiplicative performance II (MPII), seedLength [mm], germination (binary), infection 2009 (binary), time to flowering 2009 [days], pedicels 2009 (binary), fruits 2009 (binary), pollenNumber per flower 2009, pollenSize 2009 [um], time to flowering 2010 [days], noPedicels to 2010, noFruits to 2010, noPedicels to 2012, noFruits to 2012.allData_121024.tx