Influence of the geological history of the Trans-Mexican Volcanic Belt on the diversification of Nolina parviflora (Asparagaceae: Nolinoideae)
Correspondence: Eduardo Ruiz-Sanchez, Instituto de Ecología A.C., Centro Regional de Bajío, Red de Biodiversidad y Sistemática, Av. Lázaro Cárdenas 253, 61600 Pátzcuaro, Michoacán, México.
Our aims were to determine the pattern of genetic variation in the endemic shrub Nolina parviflora, and to evaluate the influence of the geological history of the Trans-Mexican Volcanic Belt (TMVB) and nearby mountainous regions on plant population divergence.
Trans-Mexican Volcanic Belt, Sierra Madre Occidental, Sierra Madre Oriental and Sierra Madre del Sur mountain ranges in Mexico.
Twenty-eight populations (210 individuals) were sequenced for one nuclear (rpb2) and two chloroplast (trnL–F and psbA–trnH) DNA markers. Intraspecific phylogenetic relationships among haplotypes were reconstructed, and molecular dating, population genetic analyses and group testing were performed on the data. Isolation-by-distance analysis was conducted for the populations spanning the distribution of the species.
Twenty-four chloroplast marker haplotypes and 36 rpb2 haplotypes were recovered from the populations sampled. The combined marker phylogeny indicates the presence of two well-supported clades within the N. parviflora populations. Clade 1 includes populations from Jalisco and Zacatecas and Clade 2 comprises the remaining populations. We found an east–west geographical pattern of chloroplast DNA (cpDNA) haplotype distribution, indicating a lack of gene flow between these two regions. Divergence time estimates indicate an Oligocene to mid-Miocene divergence between Nolina and Dasylirion. Divergence estimates for Clade 1 are from the mid-Miocene to early Pleistocene, and for Clade 2 from the early Miocene to mid-Pliocene. Values of cpDNA GST (0.702) indicate a strong population structure and differentiation. A spatial analysis of molecular variance indicates 11 groups among the sampled populations and detects various well-supported geographical barriers.
Divergence time estimates suggest a correlation between the time of divergence between distinct N. parviflora populations and periods of uplift in the TMVB. We infer that the orogeny of this mountain range played an important role in driving the diversification of plant populations in central Mexico by creating topographical barriers that limited gene flow.