Bees diversified in the age of eudicots

Abstract

Reliable estimates on the ages of the major bee clades are needed to further understand the evolutionary history of bees and their close association with flowering plants. Divergence times have been estimated for a few groups of bees, but no study has yet provided estimates for all major bee lineages. To date the origin of bees and their major clades, we first perform a phylogenetic analysis of bees including representatives from every extant family, subfamily and almost all tribes, using sequence data from seven genes. We then use this phylogeny to place 14 time calibration points based on information from the fossil record for an uncorrelated relaxed clock divergence time analysis taking into account uncertainties in phylogenetic relationships and the fossil record. We explore the effect of placing a hard upper age bound near the root of the tree and the effect of different topologies on our divergence time estimates. We estimate that crown bees originated approximately 123 Ma (million years ago) (113-132 Ma), concurrently with the origin or diversification of the eudicots, a group comprising 75 per cent of angiosperm species. All of the major bee clades are estimated to have originated during the Middle to Late Cretaceous, which is when angiosperms became the dominant group of land plants.

Figure 1.

Time calibrated phylogeny of bees based on analysis 3 (age of the root node sampled from a normal distribution with a mean of 140 and a s.d. of five and tree constrained to have the same relationships as the MrBayes produced tree at the subfamily and taxonomically higher levels). Horizontal bars indicate 95% HPD of estimated divergence times. Posterior probabilities are shown at the right of each node.

Figure 2.

Variation in age estimates for crown groups of major bee lineages. The Albian to Turonian age when angiosperms became dominant in species numbers is highlighted. The first appearance of tricolpate pollen in the fossil record, which is often equated with the age of eudicot origin (or to signal the rise in abundance and geographical expansion of eudicots), is also indicated.