Allozyme Variation in Gaillardia pulchella and G. amblyodon (Compositae): Relation to Morphological and Chromosomal Variation and to Geographical Isolation

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Abstract
Gaillardia pulchella and G. amblyodon are obligately outcrossed, diploid annuals that occur sympatrically in Texas. Gaillardia pulchella consists of three parapatric varieties and at least four chromosomally differentiated races. Six of thirteen allozyme loci assayed (46%) are polymorphic in both species. Mean expected heterozygosities are 0.188 for G. pulchella and 0.125 for G. amblyodon. No significant linkage disequilibria were observed between pairs of polymorphic loci, and no deviations from Hardy-Weinberg expectations were detected. Nei''s coefficient of gene differentiation (G-ST) was 0.160 between convarietal populations, 0.021 between varieties of G. pulchella, 0.146 between populations of G. amblyodon, and 0.144 between the two species. Mean values of Nei''s genetic distance (D) were 0.035 among local populations, 0.059 among varieties, and 0.285 between species. There is little allozyme differentiation among varieties of G. pulchella. Clustering (UPGMA) of populations by genetic distance failed to discern either morphological varieties or chromosomal races within this species. Genetic distances are significantly correlated with geographic distances within G. pulchella, suggesting gene flow may be an important deterrent to differentiation. Data from other outcrossing plant taxa are consistent with the contention that strong barriers to gene flow are a prerequisite for allozyme differentiation. It is suggested that allozyme variation within species will often show little concordance with variation in other characters and may therefore be of limited use for delimiting infraspecific taxa.