PHYLOGENOMIC DATING AND BAYESIAN BIOGEOGRAPHY ILLUMINATE AN AMPHITROPICAL PATTERN FOR EUCERINE BEES (APIDAE: EUCERINAE)

Aim: This study aims to provide the first comprehensive dated tree for eucerine bees and to reconstruct their biogeographic history; to examine how amphitropical distributions formed in eucerine bees and how geoclimatic events shaped modern distribution patterns; and to investigate the influence of molecular data set size on divergence time estimation.

Methods:Using a published UCE data set, and multiple fossil calibration points, we carried out phylogenomic dating under two different clock models and used multiple strategies to vary matrix composition. We then reconstructed the biogeographic history of eucerine bees using a Bayesian implementation of the Dispersal Extinction Cladogenesis (DEC) model.

Results:Eucerinae is estimated to have started its diversification during the Paleocene, with all its tribes originating during the Paleocene/Eocene transition. We found no evidence that varying the amount of molecular data in analyses influences divergence time estimates. Biogeographic reconstructions highlight the importance of southern South America in the early history of eucerine bees. Our results also provide evidence for at least two range expansions into North America before the full closure of the Isthmus of Panama (Eocene and Early Miocene).

Main conclusions: We describe the early diversification of a fascinating group of bees, Eucerinae, revealing an intimate and persisting association with southern South America. The range evolution of Eucerinae was likely affected by periods of global cooling and aridification, which facilitated dispersal and colonization to other biogeographic regions. Range expansions out of South America are hypothesized to have happened before the full closure of the Isthmus of Panama and were probably associated with expansion of open vegetation habitats. Our results also demonstrate that most uncertainty in phylogenomic divergence time estimation is not due to the amount of molecular data being used.