Strepsirhine divergence dates estimated from mitochondrial gene sequences, and the status of daubentonia madagascariensis

Abstract

Given the paucity of Cenozoic fossils on Madagascar, divergence times for strepsirhines must be calculated from nucleotide sequences. I used four mitochondrial genes (cytochrome b , ND3, ND4, and ND4L) from representatives of all extant lemur families, Lorisidae and Galagidae, to derive Bayesian molecular clock estimates of major clade divergences. Divergence of the Lemuriformes (excluding Daubentonia ) ranged from 31 to 38 million years ago (Mya); when Daubentonia was included, this date was pushed back to 52-53 Mya. The divergence of living Strepsirhini was estimated at 58-59 Mya. These dates are appreciably younger than those reported in most previous studies. Divergence dates for Lemuriformes excluding Daubentonia fall within a 25-42 Mya window when the continental crust was emergent along the Davie Fracture Zone, affording a potential dispersal route between Africa and Madagascar. Despite lemuriform monophyly, multiple colonization events cannot be excluded. Regardless of the gene used, Daubentonia emerged substantially earlier than the other lemuriform families. Coalescence simulations revealed an early duplication of the four genes, probably of the whole mitochondrial genome, which led on one hand to Daubentonia and on the other to the remaining Lemuriformes. This supports the uniqueness of this genus, already demonstrated cytologically and morphologically.