Interspecific movement of the paternal sex ratio chromosome

Here we examine the potential for interspecific movement of a supernumerary or B chromosome and its subsequent stability. B chromosomes differ from autosomes in that they are nonvital, nonpairing chromosomes which vary in number between conspecific individuals. According to one generally accepted hypothesis, B chromosomes originate from the autosomes of their host. However, previous comparisons of B chromosome and host autosome sequences have suggested an additional evolutionary route: that B chromosomes originating in one species may be subsequently transferred into another species via interspecific hybridization. To examine B chromosome movement, hybrid crosses were utilized to introduce the paternal sex ratio chromosome (PSR) of Nasonia vitripennis into N. giraulti and N. longicornis. The results demonstrate that these transfers occur at high rates and that the meiotic drive system of PSR continues to function in both species, resulting in the maintenance of PSR at high frequencies. The relevance of these results to origin hypotheses of PSR is discussed here, as are the potential ecological effects of naturally occurring PSR movement and the potential applied uses of the mechanisms of PSR.