The genetic contribution of single male immigrants to small, inbred populations: a laboratory study using Drosophila melanogaster

This study examined the genetic contribution of single male immigrants to s mall, inbred laboratory populations of Drosophila melanogaster. Genetic con tribution was assessed by measuring the relative frequency of immigrant mar ker alleles in the first and second generations after immigration, while co ntrolling for any selection effects at the marker locus, and for the experi ence of male immigrants. When immigrants were outbred, the mean frequency o f the immigrant allele was significantly higher than its initial frequency, in both the first and second generations after immigration. There was no s ignificant change in allele frequency for populations receiving inbred immi grants. The increase in allele frequency for outbred immigrants was attribu ted to an initial outbred vigour fitness advantage of immigrant males over resident males experiencing inbreeding depression. Hybrid vigour of immigra nt progeny and the rare-male effect did not have a statistically significan t role in the fitness advantage of the immigrant allele. The results sugges t that inbreeding may have a considerable impact on the contribution of imm igrants to the genetic diversity of populations.