Convergent evolution of the mating behaviour of founder-flush populations of the housefly

Courtship bouts of six founder-flush populations (two-pair founder-flush) a nd two nonbottlenecked controls of the housefly were videotaped over the co urse of 26 generations in order to evaluate the stability of mating behavio ur. Limited-choice mate preference tests were conducted periodically to ass ess levels of homogamic preference. Both founder-flush and control treatmen ts showed significant evolutionary potential in courtship, along with homog amic and heterogamic preferences. The founder-flush populations were signif icantly differentiated from the controls in courtship repertoire, but all o f the populations pursued convergent evolutionary trajectories in adapting to the laboratory, resulting in dissolution of homogamic preferences. The p henotypic shifts in courtship and mate preferences were unrelated to evolut ionary trends in overall mating vigour; therefore, the convergence in court ship could not be attributed to either a fitness meltdown due to inbreeding or the purge of deleterious alleles. Only one founder-flush population sho wed some independence from the selectional pressures for convergence; there fore, the single two-pair founder-flush event was generally inadequate to s timulate stable incipient speciation. This study thus demonstrates how conv ergent evolution can dissolve founder-flush effects.