INTERSPECIFIC MOVEMENT OF THE PATERNAL SEX-RATIO CHROMOSOME

Here we examine the potential for interspecific movement of a supernum erary or B chromosome and its subsequent stability. B chromosomes diff er from autosomes in that they are nonvital, nonpairing chromosomes wh ich vary in number between conspecific individuals. According to one g enerally accepted hypothesis, B chromosomes originate from the autosom es of their host. However, previous comparisons of B chromosome and ho st autosome sequences have suggested an additional evolutionary route: that B chromosomes originating in one species may be subsequently tra nsferred into another species via interspecific hybridization. To exam ine B chromosome movement, hybrid crosses were utilized to introduce t he paternal sex ratio chromosome (PSR) of Nasonia vitripennis into N. giraulti and N. longicornis. The results demonstrate that these transf ers occur at high rates and that the meiotic drive system of PSR conti nues to function in both species, resulting in the maintenance of PSR at high frequencies. The relevance of these results to origin hypothes es of PSR is discussed here, as are the potential ecological effects o f naturally occurring PSR movement and the potential applied uses of t he mechanisms of PSR.