Allozyme Diversity and Hybridization in Castanea Pumila (Section Balanocastanon, Fagaceae)
Castanea pumila is an outcrossing, woody perennial native to the Southeastern United States. Once considered separate species, C.pumila var. ozarkensis (the Ozark Chinquapin) and C. pumila var. pumila were recently combined due to extensive morphological intergradation. One explanation for the observed geographic variability is hybridization between two incompletely isolated species. To explore this possibility, the geographic distribution of allozyme variation was examined for patterns indicative of a hybrid zone. Only one of six loci assayed was polymorphic, yielding a lower than average estimate of gene diversity (Ht=0.082). For this locus the genetic differentiation among populations (Fst=0.129) is slightly greater than average for species with similar life histories. A significant correlation between genetic distance and geographic distance (Rs=0.633, p=0.000), and the geographic distribution of allozyme frequencies, indicate a broad cline characteristic of secondary contact. This pattern could reflect the presence of an old hybrid zone, but is inconsistent with the presence of two reproductively-isolated groups. Consequently the data support the recent revision of the section.
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