THE INFLUENCE OF LOCAL EXTINCTIONS ON THE PROBABILITY OF FIXATION OF CHROMOSOMAL REARRANGEMENTS

We investigated the influence of local extinctions in a subdivided pop ulation on the probability of fixation of an initially rare allele, fo r different migration rates. The selective regimes considered were str ict underdominance, meiotic drive, and underdominance associated with meiotic drive. We show that local extinctions can increase the probabi lity of fixation of initially rare alleles in underdominant loci for r elatively high migration rates, even when both homozygotes have the sa me fitness. This increase is due to drift during founder events. On th e contrary, local extinctions decrease the probability of fixation of alleles favoured by meiotic drive. For a locus where both meiotic driv e and underdominance act, the effect of local extinctions depends on t he relative strength of the two selective regimes and the initial freq uency of the rare allele. For parameter values such that the rare alle le is initially selected against, local extinctions decrease the proba bility of fixation for low migration rates while they cause an increas e for moderate migration rates. When the parameter values are such tha t the rare allele should always be favoured by selection, local extinc tions always decrease the probability of fixation. In this latter case , we show the existence of an optimal migration rate which maximizes t he probability of fixation.