Sequence diversity in the tetraploid Zea perennis and the closely related diploid Z-diploperennis: Insights from four nuclear loci

Polyploidy has been an extremely common phenomenon in the evolutionary hist ory of angiosperms. Despite this there are few data available to evaluate t he effects of polyploidy on genetic diversity and to compare the relative e ffects of drift and selection in polyploids and related diploids. We invest igated DNA sequence diversity at four nuclear loci (adh1, glb1, c1, and wax y) from the tetraploid Zea perennis and the closely related diploid Z. dipl operennis. Contrary to expectations, we detected no strong evidence for gre ater genetic diversity in the tetraploid, or for consistent differences in the effects of either drift or selection between the tetraploid and the dip loid. Our failure to find greater genetic diversity in Z. perennis may resu lt from its relatively recent origin or demographic factors associated with its origin. In addition to comparing genetic diversity in the two species, we constructed genealogies to infer the evolutionary origin of Z. perennis Although these genealogies are equivocal regarding the mode of origin, sev eral aspects of these genealogies support an autotetraploid origin. Consist ent with previous molecular data the genealogies do not, however, support t he division of Zea into two sections, the section Zea and the section Luxur iantes.