Chloroplast DNA Variation in Gliricidia sepium (Leguminosae): Intraspecific Phylogeny and Tokogeny

Abstract

An analysis of chloroplast DNA restriction site variation in Gliricidia sepium reveals two geographically distinct chloroplast lineages, one in the Yucatan Peninsula and the other along the Pacific Coast in Mexico and Central America. Geographical, morphological, biochemical, and habitat distinctions suggest that these two chloroplast lineages reflect organismal lineages. Within the Pacific coastal chloroplast lineage, there exist sublineages that most likely reflect tokogenetic systems of relationship rather than organismal phytogeny, a hypothesis supported by the co-occurrence of more than one of these chloroplast sublineages in a single population. The genetic distance between any two of these chloroplast lineages ranges from 0.0001 to 0.0024 nucleotide substitutions per site and reveals relatively high levels of intraspecific divergence. We suggest that assessing intraspecific chloroplast DNA variation is important generally in higher level phylogenetic analysis because it enables one to obtain truer estimates of homoplasy, detect potentially cryptic species, and distinguish among molecular markers that reflect phylogenetic vs. tokogenetic relationships. This is in addition to determining the extent of potential complicating factors such as introgression and lineage sorting from polymorphic ancestry.