Abstract Detail


Breslin, Peter [1], Wojciechowski, Martin [2], Majure, Lucas [3].

Recent divergence, rapid diversification and multiple radiations of Cochemiea and Mammillaria (Cactaceae) in the Baja California, Mexico region: accounting for high species richness and peninsular endemism.

The Mammillaria and Cochemiea (Cactaceae) clades of northwestern Mexico and the southwestern United States constitute a major component of the angiosperm biodiversity of this region. High species richness is combined with peninsular and island endemism in Cochemiea, with 90% of all taxa in that recently expanded genus endemic to Baja California and adjacent islands. While the main center of distribution of Mammillaria is eastern Mexico into the Coahuilan and Chihuahuan Desert Region, this genus also displays species richness and endemism in Baja California and along the adjacent Sonoran/Sinaloan Gulf coast. Past research has suggested that geological and climate heterogeneity at multiple spatial and temporal scales has been important in influencing the floral and faunal biodiversity of Baja California. This study uses a well-supported phylogeny as the basis for reconstructing the historical biogeography, estimating divergence times and finding diversification rate shifts at key nodes for the Mammillaria/Coryphantha/Cochemiea clade. The likely ancestral biogeographical history and high rate of diversification of the genus Cochemiea strongly support its taxonomic circumscription as a genus distinct from Mammillaria. We find that the most recent common ancestor of Cochemiea arrived in the Cape region of Baja California from the Sonoran Desert Region, approximately 5 million years ago (Ma), coinciding with the timing of peninsular rifting from the mainland, suggesting a combination of dispersal and vicariance as drivers of endemism. Several dispersal events to the peninsula from the mainland are indicated, outlining a complex historical biogeography that explains the current distributions within Cochemiea. The diversification rate for Cochemiea is estimated to be four to seven times that of the average estimated background diversification rate for angiosperms as a whole, and two to four times that of the Mammillaria/Coryphantha/Cochemiea (MCC) in which it is nested, characterizing Cochemiea  as a rapidly speciating clade. Divergence time estimation shows that many of the taxa in Cochemiea emerged from common ancestors as recently as 500,000 to 1 million years ago (Ma). Geological and climate forces at multiple spatial and temporal scales are correlated with this rapidly radiating, rapidly diversifying clade.

1 - 172 E Bonita Way, Tempe, AZ, 85281, United States
2 - Arizona State University, School Of Life Sciences, PO Box 874501, Tempe, AZ, 85287, United States
3 - Florida Museum Of Natural History, 1659 Museum Rd. , Gainesville, FL, 32611, United States


Presentation Type: Oral Paper
Session: BIOG2, Biogeography II
Location: Virtual/Virtual
Date: Wednesday, July 29th, 2020
Time: 12:30 PM
Number: BIOG2001
Abstract ID:506
Candidate for Awards:None

Copyright © 2000-2020, Botanical Society of America. All rights reserved