Phylogenetic relationships within Iochrominae (Solanaceae)
We have a particular interest in inferring relationships among species within recent floral radiations, and to date, this work has focused on Iochrominae, a clade of around 34 species traditionally divided among 6 genera. A nearly complete phylogeny for the group based on three nuclear loci reveals frequent shifts in floral form and color, along with several cases of interspecific hybridization (Smith & Baum, 2006). This diversification has taken place across the Andes, leaving a strong signature of geographic structure on the phylogeny. Hybridization is most common in the relatively young regions of the Andes where it appears that previously isolated clades have come to overlap. Ongoing phylogenetic work in Iochrominae focuses (1) incorporating newly described species and (2) applying a concordance approach (see below) to resolve key nodes and quantify reticulate evolution.
Pollination ecology of Iochroma and its relatives
Interactions with pollinators are thought to be one of the main selective forces underlying the origin of floral diversity. Species of Iochrromina are pollinated by a wide range of animals, including hummingbirds, bees and butterflies. Insect-pollinated species, such as Acnistus arborescens tend to have small nectar rewards and scented flowers while the species that are principally pollinated by hummingbirds tend to have highly rewarding flowers and large displays (Smith et al.,2008a, b). Multiple species can be found living in sympatry and sharing the same pollinator species. However, individual pollinators often show preferential patterns of foraging, favoring one Iochroma species over another. In this way, pollinators may play an important role in maintaining species boundaries in this diverse clade.
Comparative Analysis - Correlated evolution
We are involved in several projects aimed at describing patterns of character evolution and detecting correlated changes. Together with Mark Rausher, Rich FitzJohn and Sally Otto, we are using published phylogenies of several groups (Ipomoea, Antirrhinum, Iochroma) to identify directional patterns of flower color evolution and to determine if losses of floral pigmentation affect the rate of lineage diversification. Also, we are examining the relationship between breeding system transitions (outcrossing to selfing, sexual to asexual) and floral evolution in Oenothera (with Marc Johnson).
Genetic mechanisms of flower color evolution in Iochroma
Flower color is an ideal trait for studying the genetic basis of phenotypic differences because pigment biosynthetic pathways are well characterized at the genetic level and are highly conserved across flowering plants. We are using a candidate gene approach to examine two specific evolutionary transitions: the shift from purple to white flowers in I. loxense and from purple to red flowers in I. gesnerioides. The association of candidate anthocyanin genes with these color transitions is assessed by: 1) examining the cosegregation of candidate genes with flower color phenotypes in interspecific crosses between red and purple and white and purple species; 2) cloning candidate genes showing cosegregation to test their functionality in vitro; and 3) using expression studies to examine possible differences in regulation.
University of Nebraska, Lincoln