NGS-RINGSPS

Searching genomic regions involved in adaptive evolution and speciation using ring species as a model system and next-generation sequencing

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 Obiettivo del progetto (Objective)

'Understanding the genetic bases of phenotypic variation is one of the most challenging topics faced by evolutionary biologists. Recently next-generation sequencing technologies (NGS) have brought into focus exciting technological advances to cover these aims, to the point that new disciplines such as Evolutionary and Ecological Genomics have recently emerged. Here, we propose to take advantage of one of the very few well-described ring species, the greenish warbler Phylloscopus trochiloides, to embark on the search of genomic regions involved in adaptive evolution and speciation. Ring species are enormously valuable model systems in evolutionary biology due to their scarcity and to the fact that they illustrate how evolution works in living populations. The greenish warbler was once confined to the southern border of its distribution range and then expanded northwards bordering the Himalayas through two independent pathways. Two distinct forms of Greenish warblers now coexist in Central Siberia without interbreeding and are connected by a long chain of gradually changing populations encircling the Tibetan Plateau. Interestingly, phenotypic studies have documented both parallel evolution and strong differentiation in phenotypic traits around the ring. Through the isolation of thousands of genetic markers (Single Nucleotide Polymorphisms) from NGS data we intend to investigate the genetic basis of parallel and divergent evolution across the six different forms comprising the superspecies complex. Specifically, we are interested in disentangling the partial role of neutral evolutionary forces and natural selection during speciation processes. The genetic data obtained in this respect might also add valuable information regarding the chromosomal location of genomic regions of adaptive significance and the impact of variation at protein-coding loci and regulatory elements on evolutionary processes.'

Introduzione (Teaser)

Researchers have studied a songbird species to uncover the secrets of evolution.

Descrizione progetto (Article)

In evolutionary biology, a ring species is formed when populations expand around a geographical barrier, eventually forming two distinct species that are unable to interbreed. It occurs as traits within the connected populations diverge with geographic distance, until the two now-distinct forms meet around the barrier to close the ring.

The EU-funded NGS-RINGSPS project used a ring species as a living evolutionary model to investigate how a single species splits into two new daughter species. NGS-RINGSPS looked at a songbird, the greenish warbler, which inhabits a ring around the Tibetan Plateau, with two distinct, non-interbreeding forms co-existing in central Siberia.

Researchers have long hypothesised that populations diverged when an ancestral species in the south expanded northwards along two pathways either side of the inhospitable plateau. As the greenish warbler's song became more complex from south to north, the birds became reproductively isolated as they could not recognise each other's calls.

NGS-RINGSPS analysed thousands of genetic sequences from greenish warblers to provide further insight into this 'evolutionary divergence' hypothesis. It indeed found evidence for ancient periods of geographical isolation followed by more recent secondary contact (where the two forms meet to close the ring).

Surprisingly, although the two Siberian forms were supposed to be reproductively isolated by the time they established contact, genetic evidence indicates that they interbred. In another twist, genetic analysis revealed that the geographically distinct forms evolved similar traits in isolation, a process known as parallel evolution.

In identifying specific genomic regions that diverged in populations either side of the ring, NGS-RINGSPS has provided compelling evidence for how adaptation and speciation came about. This information will be extremely useful for helping evolutionary biologists understand how genes contribute to physical variation in species.