Abstract
Understanding why some evolutionary lineages generate exceptionally high species diversity is an important goal in evolutionary biology. Haplochromine cichlid fishes of Africa’s Lake Victoria region encompass >700 diverse species that all evolved in the last 150,000 years. How this ‘Lake Victoria Region Superflock’ could evolve on such rapid timescales is an enduring question. Here, we demonstrate that hybridization between two divergent lineages facilitated this process by providing genetic variation that subsequently became recombined and sorted into many new species. Notably, the hybridization event generated exceptional allelic variation at an opsin gene known to be involved in adaptation and speciation. More generally, differentiation between new species is accentuated around variants that were fixed differences between the parental lineages, and that now appear in many new combinations in the radiation species. We conclude that hybridization between divergent lineages, when coincident with ecological opportunity, may facilitate rapid and extensive adaptive radiation.
Highlights
Understanding why some evolutionary lineages generate exceptionally high species diversity is an important goal in evolutionary biology
Introgression of traits involved in adaptation or reproductive isolation has been demonstrated among members of several adaptive radiations
Using genomic data from riverine haplochromine cichlids sampled from all major African drainage systems, and representative species from all lineages within the Lake Victoria region, we demonstrate here that the Lake Victoria Region Superflock of cichlid fish (LVRS) evolved from a hybrid swarm
Summary
Understanding why some evolutionary lineages generate exceptionally high species diversity is an important goal in evolutionary biology. The hybrid ancestry of some species has been inferred, but a direct link between introgressed traits and speciation awaits further testing (for example, cichlid fishes of Lakes Tanganyika[14,15,16], Malawi[17], Victoria[18,19] and Barombi Mbo[20]) Another hypothesis for a perhaps more fundamental role of hybridization in adaptive radiation, distinct from the ‘syngameon hypothesis’, is the idea that hybridization between distinct lineages may seed the onset of an entire adaptive radiation[3]. It remains to be tested if, in these systems, hybridization occurred before or after the radiation had started, and if hybridization-derived polymorphisms played a role in speciation and adaptive diversification
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