Laurasian migration explains Gondwanan disjunctions: evidence from Malpighiaceae

Abstract

Explanations for biogeographic disjunctions involving South America and Africa typically invoke vicariance of western Gondwanan biotas or long distance dispersal. These hypotheses are problematical because many groups originated and diversified well after the last known connection between Africa and South America (approximately 105 million years ago), and it is unlikely that "sweepstakes" dispersal accounts for many of these disjunctions. Phylogenetic analyses of the angiosperm clade Malpighiaceae, combined with fossil evidence and molecular divergence-time estimates, suggest an alternative hypothesis to account for such distributions. We propose that Malpighiaceae originated in northern South America, and that members of several clades repeatedly migrated into North America and subsequently moved via North Atlantic land connections into the Old World during episodes starting in the Eocene, when climates supported tropical forests. This Laurasian migration route may explain many other extant lineages that exhibit western Gondwanan distributions.

Figure 1

Current geographic distribution of Malpighiaceae estimated from Arénes (22). Malpighiaceae, with ≈1,250 species (1), are most diverse in northern South America (22). The ≈180 Old World species, belonging to six lineages (see Fig. 2) are variously represented in Africa (47 species), Australasia (17 species), India (43 species), and Madagascar (80 species) [from Arénes (22)]. Red stars indicate fossil localities from Hungary and Slovenia (17), and Tennessee (21).

Figure 2

Maximum likelihood tree topology (−ln L = 17,333.97) for combined ndhF and PHYC data with bootstrap values (>50%) indicated on branches. Old World lineages are shaded red. Divergence times were calculated on the rate-smoothed topology by calibrating the two nodes indicated by the colored stars with a fossil of Tetrapterys (33 mya; ref. 17). The origin of Malpighiaceae (node 0) is reconstructed as New World and is estimated at 63.6 ± 5.8 mya. The nodes labeled 1–6 correspond to the New/Old World disjunctions estimated from the DIVA reconstruction. Age estimates for nodes 1 through 6 (calibrated with the fossil placed at the green star) are, respectively: 55.1 ± 6.0 mya, 30.4 ± 2.6, 29.4 ± 2.1, 19.1 ± 1.5, 15.1 ± 1.2, and 12.9 ± 0.85. The scale bar indicates major Tertiary epochs (Paleo = Paleocene; Oligo = Oligocene; Plio = Pliocene).

Figure 3

Eocene paleogeographic map [after Parrish (41); modified from Doyle and Le Thomas (35)] summarizing hypothesized Laurasian migration of western Gondwana taxa. The distribution of Malpighiaceae is proposed to have resulted by migration from South America to the Old World (red arrow); green arrow shows a possible pattern of dispersion from the Old World to the New World taken by other tropical angiosperm clades.