CALANGO: a phylogeny-aware comparative genomics tool for discovering quantitative genotype-phenotype associations across species

Abstract

The increasing availability of genomic, annotation, evolutionary and phenotypic data for species contrasts with the lack of studies that adequately integrate these heterogeneous data sources to produce biologically meaningful knowledge. Here, we present CALANGO, a phylogeny-aware comparative genomics tool that uncovers functional molecular convergences and homologous regions associated with quantitative genotypes and phenotypes across species, enabling the fast discovery of novel statistically sound, biologically relevant phenotype-genotype associations. We demonstrate the usefulness of CALANGO in two case studies. The first one unveils potential causal links between prophage density and the pathogenicity phenotype in Escherichia coli, and confidently demonstrates how CALANGO supports the investigation of basic causal relationships by enabling a level of counterfactual investigation of observed associations in the data. As a second case study, we used our tool to search for homologous regions associated with a complex phenotypic trait in a major group of eukaryotes: the evolution of maximum height in angiosperms. We confidently identify a previously unknown association between maximum plant height and the expansion of the self-incompatibility system, a molecular mechanism that prevents inbreeding and increases genetic diversity. Taller species also have lower rates of molecular evolution due to their longer generation times, a critical concern for their long-term viability. The new mechanism we report could counterbalance this fact, and have far-reaching consequences for fields as diverse as conservation biology and agriculture. CALANGO is provided as a fully operational R package that can be freely installed from CRAN.