Dispersal is associated with morphological innovation, but not increased diversification, in Cyphostemma (Vitaceae)

Abstract

Multiple processes − including dispersal, morphological innovation, and habitat change − are frequently cited as catalysts for increased diversification. We investigate these processes and the causal linkages among them in the genus Cyphostemma (Vitaceae), a clade comprising ∼200 species that is unique in the Vitaceae for its diversity of growth habits. We reconstruct time-calibrated evolutionary relationships among 64 species in the genus using five nuclear and chloroplast markers and infer the group's morphological and biogeographic history. We test for changes in speciation rate and evaluate the temporal association and sequencing of events with respect to dispersal, habitat change, and morphological evolution using a Monte Carlo simulation approach. In Cyphostemma, neither dispersal nor morphological evolution is associated with shifts in speciation rate, but dispersal is associated with evolutionary shifts in growth form. Evolution of stem succulence, in particular, is associated with adaptation to local, pre-existing conditions following long-distance dispersal, not habitat change in situ. We suggest that the pattern of association between dispersal, morphological innovation, and diversification may depend on the particular characters under study. Lineages with evolutionarily labile characters, such as stem succulence, do not necessarily conform to the notion of niche conservatism and instead demonstrate remarkable morphological adaptation to local climate and edaphic conditions following dispersal.