EVOLUTIONARY IMPLICATIONS OF ALLOZYME AND RAPD VARIATION IN DIPLOID POPULATIONS OF DIOECIOUS BUFFALOGRASS BUCHLOE DACTYLOIDES

Buffalograss, Buchloe dactyloides, is widely distributed throughout th e Great Plains of North America, where it is an important species for rangeland forage and soil conservation. The species consists of two wi despread polyploid races, with narrowly endemic diploid populations kn own from two regions: central Mexico and Gulf Coast Texas. We describe and compare the patterns of allozyme and RAPD variation in the two di ploid races, using a set of 48 individuals from Texas and Mexico (four population samples of 12 individuals each). Twelve of 22 allozyme loc i were polymorphic, exhibiting 35 alleles, while seven 10-mer RAPD pri mers revealed 98 polymorphic bands. Strong regional differences were d etected in the extent of allozyme polymorphism: Mexican populations ex hibited more internal gene diversity (H-e = 0.20, 0.19) than did the T exan populations (H-e = 0.08, 0.06), although the number of RAPD bands in Texas (n = 62) was only marginally smaller than in Mexico (n = 68) . F-statistics for the allozyme data, averaged over loci, revealed str ong regional differentiation (mean F-RT = + 0.30), as well as some dif ferentiation among populations within regions (mean F-PR = + 0.09). In order to describe and compare the partitioning of genetic variation f or multiple allozyme and RAPD loci, we performed an Analysis of Molecu lar Variance (AMOVA). AMOVA for both allozyme and RAPD data revealed s imilar qualitative patterns: large regional differences and smaller (b ut significant) population differences within regions. RAPDs revealed greater variation among regions (58.4% of total variance) than allozym es (45.2%), but less variation among individuals within populations (3 1.9% for RAPDs vs. 45.2% for allozymes); the proportion of genetic var iance among populations within regions was similar (9.7% for RAPDs vs. 9.6% for allozymes). Despite this large-scale concordance of allozyme and RAPD variation patterns, multiple correlation Mantel techniques r evealed that the correlations were low on an individual by individual basis. Our findings of strong regional differences among the diploid r aces will facilitate further study of polyploid evolution in buffalogr ass.