Supporting a young age for the North American deserts: Historical biogeography of Grusonia (Cylindropuntieae) in a Plio-Pleistocene temporal framework

Abstract

Grusonia is an opuntioid genus in the Cylindropuntieae, Cactaceae, endemic to the North American deserts in Mexico and the United States. The monophyletic status of the genus and the degrees of endemicity of its species make Grusonia a suitable study group in order to test biogeographic hypotheses such as vicariant or dispersal events, biogeographic barriers and time-calibrated phylogenies in order to propose speciation events in the group. The statistical dispersal-vicariance analysis (S-DIVA) and a statistical dispersal-local extinction-cladogenesis (S-DEC) analyses show general congruence postulating ancestral ranges for the species of Grusonia. They disagree, however, in a clade with four species from the Sonoran Desert, the Baja California Peninsula and one species endemic to the central portion of the Chihuahuan Desert Region. The time-calibrated phylogeny here proposed shows an average age of 3.7 Ma for the genus. Grusonia has two internal clades comprising species most likely generated by allopatric speciation under a vicariant scenario. The results of this study support a young age for the North American deserts and identify the end of the Pliocene and mainly the Plio-Pleistocene boundary as the starting point of the cladogenetic events that gave rise to the two main clades of Grusonia.