Estimation of genetic purging under competitive conditions

Inbreeding depression for fitness traits is a key issue in evolutionary biology and conservation genetics. The magnitude ofinbreeding depression, though, may critically depend on the efficiency of genetic purging, the elimination or recessive deleteriousmutations by natural selection after they are exposed by inbreeding. However, the detection and quantification of genetic purgingfor nonlethal mutations is a rather difficult task. Here, we present two comprehensive sets of experiments with Drosophila aimedat detecting genetic purging in competitive conditions and quantifying its magnitude. We obtain, for the first time in competitiveconditions, an estimate for the predictive parameter, the purging coefficient (d), that quantifies the magnitude of genetic purging,either against overall inbreeding depression (d 0.3), or against the component ascribed to nonlethal alleles (dNL 0.2). We findthat competitive fitness declines at a high rate when inbreeding increases in the absence of purging. However, in moderate sizepopulations under competitive conditions, inbreeding depression need not be too dramatic in the medium to short term, as theefficiency of purging is also very high. Furthermore, we find that purging occurred under competitive conditions also reduced theinbreeding depression that is expressed in the absence of competition