Evolutionary genomics in Achimenes
Using comparative genomics in a evolutionary-developmental context allows us to begin understanding the molecular mechanisms underlying floral diversification. Achimenes is a small genus of 26 species native to Mexico that contains enormous variation in floral form that is closely tied to pollinator preferences. Flowers in Achimenes are visited by bees, butterflies, euglossine bees, and hummingbirds, and represent distinct pollination syndromes. We have sequenced, assembled, and annotated the floral transcriptomes in 10 species of Achimenes (Roberts and Roalson 2017, Roberts and Roalson 2018), representing species that display each pollination syndrome. Each species was sampled using two or three time points during flower development in order to take advantage of inter- and intraspecies comparisons.
I have taken multiple strategies to begin understanding flower diversification in Achimenes. First, comparing gene expression within and between species has revealed complex patterns in several pathways that correspond to the different floral forms (Roberts and Roalson 2017). Second, phylogenomic analyses of gene flow and introgression have found widespread phylogenetic discordance and specific cases of introgression occurring between sympatric species pairs that share pollinators (Roberts and Roalson 2018). Third, examination of co-expression networks has found a strong association between gene connectivity and selective constraint (Roberts and Roalson, in Prep).
Macroevolution of Gesneriaceae
Gesneriaceae (African violet family) represents a large lineage (>3500 species) with an enormous amount of diversity, particularly in floral form and growth form. The family is known for its diverse flowers that are visited by a number of different pollinators, as well as containing a high number of epiphytes, lithophytes, and unifoliate plants. Constructing the largest dated phylogeny for gesneriads (nearly a quarter of species) and inferring divergence times has allowed us to test hypotheses related to the affect of geography, floral traits, epiphytism, and growth form on diversification (Roalson and Roberts 2016). Our analyses provide evidence for distinct patterns of evolution across different lineages in the Gesneriaceae. Floral form, pollination syndrome, and epiphytism appear to be important drivers of diversification in the New World subfamily Gesnerioideae, while growth form appears to be important in the Old World subfamily Didymocarpoideae.
Developmental genetics in Achimenes
In order to test the functional role of genes in planta, it is useful to have an efficient regeneration and transformation system. We have developed an successful micropropagation and Agrobacterium-mediated transformation for Achimenes erecta (Roberts et al., in prep). The ability to efficiently transform plant species with high success will be useful to develop Achimenes into a model for evolutionary-developmental studies.