The Edward Grey Institute of Field Ornithology - EGI Research

Evolutionary Genomics

Evolutionary genomics is the study both the genome itself, and more importantly the way that it encodes the animal. Evolutionary genomics can be used to study the genes underlying adaptations as well as the pattern of selection acting on those genes. Ecological genomics, which often incorporates measures of gene expression, is the study of how selection from the organism's environment acts on the phenotype to affect the encoding genes and gene expression patterns.

Figure 1 Thousands of genes are expressed differently between the sexes, and these different gene expression patterns are the molecular building blocks of sexually dimorphic traits. Shown is the hierarchical clustering of expression patterns from the chicken gonad, where each row represents the expression from an individual gene.

Current Work

New technological advances are making genomic studies possible in non-model organisms, and our current work uses these advances to study the evolution of animal, especially avian, genomes, in response to changing ecologies. Much of our ongoing work, lead by Judith Mank, employs sexually dimorphic phenotypes as a model for how selection, acting on the animal, sculpts the genome.

1. The evolution of sexual dimorphism

The same gene can contribute to alternative phenotypes via different expression levels, and thousands of genes are expressed at different levels in males and females. These sex-biased genes are the protein building-blocks of sexually dimorphic phenotypes, and thus they provide the molecular link connecting sexual selection on the phenotype to the underlying genome. Comparative genomics of sex-biased genes can be used to understand the gene expression patterns underlying sexual dimorphisms, as well as the differences in selection pressures experienced by males and females of the same species..

2. The evolution of sex chromosomes

Sex chromosomes are an interesting contrast to the remainder of the genome, and as such can be used to study the power, pattern and nature of evolution and selection. In addition to the origin and turn-over of sex chromosomes, we're interested in how the genes on sex chromosomes evolve, as they are thought to play an important role in hybridization and speciation. The sex chromosomes are also subject to unbalanced sex-specific selection pressures, and we study how this may relate to the origin of sexually dimorphic traits.

Figure 3. Both female-biased genes (red) and male-biased genes (blue) are expressed in fewer tissues than unbiased genes (green) in birds. This suggests that sexually selected traits are encoded by genes with fewer functions, and that sex-specific selection pressures effect change most often in genes with fewer pleiotropic constraints.

3. Sexual antagonism

Some genes and gene expression patterns have contradictory sex-specific effects, resulting in sexually antagonistic selection pressures. Sex-biased genes can be used as a molecular beacon of sexual antagonism, and the study of the molecular genomic properties of sex-biased genes can reveal how this antagonism arises, how it is resolved, and how it relates to the evolution of sexual dimorphism.