Genomics

The role of interspecific gene flow in species diversification has long been debated and is increasingly appreciated. However, the effect of gene introgression on phenotypic divergences and genome heterogeneity remain unclear in case of early speciation. To investigate these questions Poelstra and colleagues studied the hybrid zone between the all-black carrion crows (Corvus corone) and the gray-coated hooded crows (C. cornix). Indeed, the absence of neutral genetic diversity between these two species and successful back-crossing of hybrids strongly contrast with the plumage coloration polymorphism that remained stable in natural populations. Moreover, colour assortative mating has been observed suggesting a prezygotic isolation and ongoing speciation. To investigate the causes of this stable phenotypes the authors first analysed the effect of gene flow on genome heterogeneity and then tried to link the observed gene flow heterogeneity with gene expression and phenotypes. Genetic differentiation between hooded and carrion crows First, they assembled and annotated a high-quality reference genome of one hooded male crow and identified 20’794 protein-coding genes. This reference genome was then used to aligned 60 genomes of unrelated individuals from two populations of carrion and two populations of hooded crows (Fig. 1). They identified 8.44 million of SNPs among which 5.27 …

Convergent evolution is defined by the independent evolution of similar traits in different lineages, in order to adapt to similar environmental conditions. Examples of this phenomenon include adaptations to altitude in humans, independent evolution of flight in birds and bats or the multiple evolution of C4 carbon fixation in plants. Yet, the molecular bases of convergent evolution are often lacking. In this paper, authors shed light on the genomic basis of a classical example of convergent evolution, the adaptation to marine life. Mammals evolved multiple independent times to inhabit the marine environment (Fig 1). Species from three different clades share similar phenotypic adaptations involved in communication, locomotion, thermal regulation, buoyancy… Cetaceans (whales and dolphins) and sirenians (manatees) emerged during the Eocene while pinnipeds (walruses) appeared during Miocene. In this paper, Foote and colleagues investigated the convergent evolution of the genomes of marine mammals at two levels. First, they sought for protein coding genes evolving under positive selection across the three lineages. Second, they studied the convergence of amino acid substitutions within these positively selected genes. Detection of protein coding genes under positive selection The authors performed de novo assembly of the genomes of killer whale, manatee and walrus and completed …