A population genetics perspective on the evolutionary histories of three clonal, endemic, and dominant grass species of the Qinghai-Tibet Plateau: Orinus (Poaceae).

Abstract

We performed analyses of amplified fragment length polymorphism (AFLP) in order to characterize the evolutionary history of Orinus according to its population genetic structure, as well as to investigate putative hybrid origins of O. intermedius and to provide additional insights into relationships among species. The genus Orinus comprises three clonal grasses that are dominant species within xeric alpine grasslands of the Qinghai–Tibet Plateau (QTP). Here, we used eight selectively obtained primer pairs of EcoRI/MseI to perform amplifications in 231 individuals of Orinus representing 48 populations and all three species. We compared our resulting data to genetic models of hybridization using a Bayesian algorithm within NewHybrids software. We determined that genetic variation in Orinus was 56.65% within populations while the among‐species component was 30.04% using standard population genetics statistics. Nevertheless, we detected that species of Orinus were clustered into three highly distinct genetic groups corresponding to classic species identities. Our results suggest that there is some introgression among species. Thus, we tested explicit models of hybridization using a Bayesian approach within NewHybrids software. However, O. intermedius likely derives from a common ancestor with O. kokonoricus and is probably not the result of hybrid speciation between O. kokonoricus and O. thoroldii. We suspect that recent isolation of species of Orinus in allopatry via vicariance may explain the patterns in diversity that we observed, and this is corroborated by a Mantel test that showed significant positive correlation between geographic and genetic distance (r = 0.05, p < 0.05). Recent isolation may explain why Orinus differs from many other clonal species by exhibiting the highest diversity within populations rather than among them.