Harvard University
Department of Organismic & Evolutionary Biology

The unifying goal of the lab is to understand molecular mechanisms of evolution and adaptation. Most of our work currently focuses on Arabidopsis arenosa. This lovely relative of A. thaliana is an obligate outcrosser, tetraploid through most of its range, and widely distributed in Europe. There are three main areas we are interested in pursuing with this species:

(1) Adaptation to whole genome duplication. Arabidopsis arenosa is autotetraploid through most of its central and northern European range. We are capitalizing on the availability of extant diploids and tetraploids to ask how A. arenosa adapted to having double the number of chromosomes and how it evolved to orchestrate meiosis in this context. We are using a combination of genomics, transcriptomics, molecular genetics and cytology (the cytological aspect is greatly bolstered by an active collaboration with James Higgins at the University of Leicester, UK, and Chris Franklin at the University of Birmingham, UK) to address how meiosis and other key cellular processes may have evolved in tetraploid evolution. We are analyzing the molecular evolution of meiosis-related genes in diploid and tetraploid A. arenosa and initiating functional studies of a key subset of genes that are strongly differentiated between diploids and tetraploids. More recently, we have found evidence that at least some meiosis genes are non-neutrlly evolving also in diploids, which we are currently exploring further.

For more information, see the "Evolution of Meiosis" and "Population Genomics" tabs at left or below.

(2) Biogeography and Habitat adaptation. Arabidopsis arenosa autotetraploids have adapted to a wide range of habitats, from the apparently ancestral shaded limestone outcrops, to silicaceous outcrops, serpentine, railways, acid bogs, beaches, and heavy metal contaminated mine tailings. We are using RADseq markers and low pass population resequencing to study the evolutionary history of diploid and tetraploid A. arenosa populations and how these might have colonized their present range and habitats. We have found that tetraploid populations found in distinct habitats show striking differences in flowering time, vernalization responsiveness, perenniality and plant architecture. Within the scope of an NSF-funded study, we are using a combination of genetic mapping, transcriptome analyses and phenotyping to better characterize these differences. We have begun to map flowering time and plant architecture traits in segregating F2 populations (focusing at least initially on the contrast of shaded outcrops versus exposed drought-prone railways). We are also beginning studies of the potential role of epigenetic regulation in natural variation for flowering and vernalization responsiveness.

For more information, see the "Mechanisms of habitat adaptation and morphological evolution" tab at left or below.

(3) Gene Network evolution. One striking observation from our initial genome scans is that signatures of selection are often seen in genes whose products are known to interact. These genes are also often connected in networks to additional genes that are differentiated between populations. This pattern suggests that these genes may be adaptating to their genomic context rather than to habitat, and raises the question of whether they are co-evolving as "adaptive modules." We are currently exploring this with a large population resequencing study and will then attempt follow-up experiments to test functional modules of related genes. Currently we are focused particularly on interacting meiosis genes, but hope to extend this work to other functional classes such as core transcription and cell cycle regulators, where we see similar patterns.

For more information, see the "Gene network evolution" tab at left or below.