Evolutionary divergence times in the Annonaceae: evidence of a late Miocene origin of Pseuduvaria in Sundaland with subsequent diversification in New Guinea.

BACKGROUND

Phylogenetic analyses of the Annonaceae consistently identify four clades: a basal clade consisting of Anaxagorea, and a small 'ambavioid' clade that is sister to two main clades, the 'long branch clade' (LBC) and 'short branch clade' (SBC). Divergence times in the family have previously been estimated using non-parametric rate smoothing (NPRS) and penalized likelihood (PL). Here we use an uncorrelated lognormal (UCLD) relaxed molecular clock in BEAST to estimate diversification times of the main clades within the family with a focus on the Asian genus Pseuduvaria within the SBC. Two fossil calibration points are applied, including the first use of the recently discovered Annonaceae fossil Futabanthus. The taxonomy and morphology of Pseuduvaria have been well documented, although no previous dating or biogeographical studies have been undertaken. Ancestral areas at internal nodes within Pseuduvaria are determined using dispersal-vicariance analysis (DIVA) and weighted ancestral area analysis (WAAA).

RESULTS

The divergence times of the main clades within the Annonaceae were found to deviate slightly from previous estimates that used different calibration points and dating methods. In particular, our estimate for the SBC crown (55.2-26.9 Mya) is much younger than previous estimates (62.5-53.1 +/- 3.6 Mya and ca. 58.76 Mya). Early diversification of Pseuduvaria was estimated to have occurred 15-8 Mya, possibly associated with the 'mid-Miocene climatic optimum.' Pseuduvaria is inferred to have originated in Sundaland in the late Miocene, ca. 8 Mya; subsequent migration events were predominantly eastwards towards New Guinea and Australia, although several migratory reversals are also postulated. Speciation of Pseuduvaria within New Guinea may have occurred after ca. 6.5 Mya, possibly coinciding with the formation of the Central Range orogeny from ca. 8 Mya.

CONCLUSION

Our divergence time estimates within the Annonaceae are likely to be more precise as we used a UCLD clock model and calibrated the phylogeny using new fossil evidence. Pseuduvaria is shown to have dispersed from Sundaland after the late Miocene. The present-day paleotropical distribution of Pseuduvaria may have been achieved by long-distance dispersal, and speciation events might be explained by global climatic oscillations, sea level fluctuations, and tectonic activity.