Nuclear and chloroplast DNA sequence variation in Yucca brevifolia (Joshua tree)

To understand further the population structure of the Mojave Desert endemic Yucca brevifolia (Agavaceae), we investigated DNA sequence polymorphism in a 4kb fragment of the gene for the cytosolic phosphoglucose isomerase (PgiC) and from a 300bp fragment within the chloroplast trnD-trnT spacer region. Consistent with previous studies, we find extensive shared ancestral variation in both nuclear and chloroplast DNA sequence, and the geographic distribution of diversity suggests that this species experienced range contraction and expansion following the Pleistocene glaciation. Additionally, sequence variation shows no clear pattern associated with PGI allozyme allelic class, chloroplast haplotype, or proposed subspecies.