AfterTheIce · After the Ice: using a hybrid zone as a window into the genes underlying species formation

After the Ice: using a hybrid zone as a window into the genes underlying species formation

The process of species formation is responsible for the global distribution of biodiversity, from the generation of species in habitats as extreme as the arctic or deep-sea thermal vents, to the generations of crop varieties that are locally adapted to different water regimes. Yet, we still understand very little about 1) which genes drive the formation of new species and 2) the nature of selection acting on those genes. Traditionally, genetic studies have either focused on model organisms, which have small and well-characterized genomes but that rarely hybridize in nature, or focused on non-model organisms, which often hybridize in nature but have large and poorly-understood genomes. Although these alternative approaches have offered important insights on the genetic basis of species formation, they often lead to conflicting conclusions on the fundamental questions above. In the project AfterTheIce we integrated both approaches in a single biological system: two grasshopper subspecies that maintain ecomorphologic differentiation despite ongoing hybridization since the end of the last glaciation. This system is ideal for this novel integration between lab- and field-based approaches because: 1) these subspecies can be crossed in controlled laboratorial conditions, where they show phenotypes often found in model-organisms, such as hybrid male sterility; and 2) these subspecies have been hybridizing for 9,000 generations in nature, where they show that natural selection is targeting particular genes but not the whole genome. Yet, this system also shows a limitation that is common across many valuable non-model organisms: its genome is too large to be sequenced and assembled with modern technology. Hence, in AfterTheIce we established three main objectives: 1) building a nearly complete gene catalogue for a species lacking a reference genome, 2) determining which particular genes are targeted by selection in natural hybrid zones, and 3) determining if those same genes are implicated in hybrid male sterility in experimental hybrids. By moving from lab to nature, this integrative framework not only provided unique insights on the field of speciation, but also provided a transferable framework that is applicable to emergent challenges of the modern society. For example, developing genomics tools for non-model organisms lacking reference genomes, which commonly occurs in species of economic interest, and establishing new genomic approaches to associate specific genes to important traits, such as sterility or adaptation to different habitats.

Data: CORDIS, © European Union