BirdIslandGenomic

Abstract of the Project

In this project, we propose to investigate island evolution from the genomic point-of-view. Understanding the influence of population size variation on molecular evolution is currently a major topic in the field. Since island species have evolved in isolated and small populations, they provide an unique opportunity to study the impact of non-adaptive forces on biological evolution. Here we propose to gather a population genomic dataset composed of two island/mainland pairs of species, using endemic birds of Réunion Island and their mainland south-Africa relative as model organisms. Indeed, we are convinced that mainland/island comparison provide one of the best empirical set-up to study the impact of non-adaptive forces on genome evolution in natural population. Four completely sequenced genomes, eight transcriptomes and a genome-wide polymorphism composed of forty individuals will be used to unravel the influence of population size on the accumulation of deleterious mutations in the genome. Our goal will be to establish if different regions of the genome are differentially affected by the reduction of population size. We will also aim to evaluate the evolution of genome architecture (e.g., on genome size) will be compared between the mainland and the island species. According to recent theory, the evolution of genome architecture could also be influence by non-adaptive force such as genetic drift. So far, however, most of the empirical evidences come from comparison between distantly related species. We argue that the mainland/island comparison provide an unique opportunity to study the micro-evolution of genome architecture and to test the importance of genetic drift in the emergence of genomic complexity. Finally, the very large and comprehensive datasets generate during this project will also be used to tackle two fundamental topics of evolutionary biology: i) the evolution of sex chromosomes and ii) the genomic of speciation.

The Mascarene white-eyes (Zosterops) as model species

In our project, we propose to focus on the small oceanic island of Réunion. This island is situated near the Tropic of Capricorn, 700km east of Madagascar. It is a relatively small volcanic island with an area of ~2,500km (three and a half times smaller than Corsica) forming a loose archipelago, called the Mascarene archipelago, with Mauritius (at ~200km) and Rodrigues (at ~800km). Réunion and Mauritius are volcanic Islands that have never been connected to any large land-mass. Their great isolation is confirmed by the high degree of endemism found in the archipelago (e.g., 85% of the terrestrial birds are endemic) (Thébaud et al. 2009). Among the seven extant terrestrial (near-)endemic bird species, four represent good candidates for this project. These are the Réunion Stonechat (Saxicola tectes), the Réunion Bulbul (Hypsipetes borbonicus), the Mascarene White-eye (Zosterops borbonicus) and the Réunion Olive White-eye (Z. olivaceus). Among the endemic birds of the Réunion Island, the White-eyes stands because i) its phylogeny is well documented (Figure 1), ii) the closest mainland relatives are common birds that have large repartition ranges (suggesting a large population size) in Africa ( the African Yellow White-eye (Z. senegalensis) and the Cape White-eye (Z. pallidus)) and iii) the Mascarene White-eye is currently studied by a French team leaded by Pr. Christophe Thébaut from the University of Toulouse (Milá et al. 2010).