A study in press at PNAS on the evolution of Andean Lupins suggests that it is environmental change, in this case the uplift of the andes that is a major driver of phenotypic evolution (1). The uplift of the Andes seems to have created island type conditions with many new ecological niches being formed creating opportunities for an adaptive radiation. There does not seem to have been any key evolutionary innovation in the Andean Lupins so the ecological niches created by the uplift of the Andes are the most likely cause of this rapid diversification in forms:
"Phylogeny of Lupinus. Fifty percent majority rule Bayesian tree from analysis of the combined ITS/LEGCYCIA data sets. Posterior probabilities of major clades are shown below nodes; all nodes had posterior probabilities 0.5. This tree is congruent with the strict consensus derived from parsimony analysis. For clarity, taxon names have been omitted (see supporting information). Branch lengths are proportional to changes on the tree. A and B denote two well supported New World clades: A, eastern New World; B, western North America, Mexico, and the Andes. The map shows the distributions of these two New World clades to be largely allopatric, with limited overlap in the southern U.S. and the south-central Andes. The geographical extent of the main Andean radiation is shown in orange. Chilean accessions of Lupinus microcarpus group with their North American counterparts at the base of clade B, but the occurrence of L. microcarpus in central Chile (shown in red) is doubtfully native. Line drawings illustrate life forms encompassed by species in the Andean Lupinus radiation: a, treelet, Lupinus semperflorens; b, prostrate herb, Lupinus sp. nov; c, perennial woody shrublet, Lupinus smithianus; d, ephemeral annual herb, L. mollendoensis; e, giant stem rosette, Lupinus weberbaueri; f, woody perennial shrub, Lupinus sp. nov; g, acaulescent rosette, Lupinus nubigenus; h, perennial woody shrublet, Lupinus sp. nov; i, dwarf acaulescent rosette, Lupinus pulvinaris; j, prostrate herb, Lupinus prostratus. (Scale bars: 5 cm.)"
This study reminded me of a paper in the current issue of Antiquity (2) that suggests that human evolution could have been driven by the opening of the Great rift valley. Maybe major tectonic events have a more widespread effect on evolution than has been realised.
1) Island radiation on a continental scale: Exceptional rates of plant diversification after uplift of the Andes
Colin Hughes and Ruth Eastwood
PNAS published June 26, 2006, 10.1073/pnas.0601928103
2) Tectonics and human evolution
Geoffrey King and Geoff Bailey.
Antiquity Volume: 80 Number: 308 Page: 265–286