Biogeography and diversification history of the neotropical plant genus Macrocarpaea (Gentianaceae)

The South American Andes stretch 7000 km from north to south with average elevations of

~ 4000 m. They formed mainly through a crustal thickening associated with Cenozoic (65-

0Ma) subduction and convergence between the Nazca Plate and the South American Plate

(Poulsen et al 2010). Recent studies on Neotropical diversity have underlined the role of this

geological event in promoting phylogenetic lineage diversification, e.g. butterflies

(Lymanopoda: Casner et Pyrcz 2010), Angiosperms (Lupinus: Hughes et Eastwood 2006,

Inga: Richardson et al. 2001), birds (Pionus: Ribas et al 2007), and frogs (Dendrobatidae:

Santos et al 2009). The Andean uplift may have promoted speciation in several ways, such as

by creating a variety of new habitats available for colonization by lowland ancestors,

producing geographical vicariance, favoring allopatric speciation among taxa separated by

deep valleys or impassable peaks, and finally by changing the hydrology and climate of the

entire South American continent (Antonelli et al 2010). The relative contributions of each of

these scenarios is still under debate. To better understand links between the Andean uplift and

mechanisms of lineage diversification additional species-level studies are needed.

Macrocarpaea is a genus of neotropical shrubs and small trees of the Gentianaceae family.

It is a speciose genus (110 species) with interesting patterns of distributions. A recent

phylogenetic study (Struwe et al 2009) has revealed that the basalmost species occur at low to

middle elevations in southeastern Brazil whereas most other known species occur at middle to

high elevations on eastern slopes of the Andes. Most species have narrow distributions, and

some occur in sympatry. Some species of section Magnolifolieae have curious morphological

features in winged seeds and verrucose pollen. We suspect these traits to be key innovations,

which is a term used to refer to traits that contribute to an increase in the intrinsic species

diversification rate of a taxon (Cacho et al. 2010). Because of this diversity, distribution and

morphological characteristics, Macrocarpaea is an excellent model to test hypotheses related

to the role of the Andean uplift on the diversification of plant lineages.

The objectives of this project are to reconstruct the biogeographical history of Macrocarpaea

and investigate its patterns of diversification. Several hypotheses will be tested. Did the

Andean uplift promote an increase of the rate of lineage diversification in the genus? If so, did

the rate of diversification increase due to allopatric speciation caused by barriers to dispersal,

or due to ecological adaptation along altitudinal gradients? Did the acquisition of winged

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seeds and verrucose pollen affect the rate of diversification of lineages that have these

morphological characters? Do these novelties have an influence on the level of genetic

divergence (higher or lower gene flow) between populations of the same species? In order to

answer these questions we will combine molecular phylogenetic and population genetic

approaches.

This project will contribute to a better understanding of the origin of plant diversity in the

tropical Andes and the relative contribution of ecological (adaptation) and geographical

(dispersal limitation) processes on diversification of a speciose Neotropical plant genus.