Genomic divergence and adaptive convergence in Drosophila simulans from Evolution Canyon, Israel. Drosophila simulans

Biodiversity refugia formed by unique features of the Mediterranean arid landscape, such as the dramatic ecological contrast of “Evolution Canyon”, provide a natural laboratory in which local adaptations to divergent microclimate conditions can be investigated. Significant insights have been provided by studies of Drosophila melanogaster diversifying along the thermal gradient in Evolution Canyon, but a comparative framework to survey adaptive convergence across sister species at the site was lacking. To fill the void, we now present the analysis of genomic polymorphism and evolutionary divergence of Drosophila simulans, a close relative of D. melanogaster with which it co-occurs on both slopes of the canyon. Results show even deeper inter-slope divergence in D. simulans than D. melanogaster, with extensive signatures of selective sweeps present in flies from both slopes, but enhanced in the population from the hotter and drier South-facing slope. Inter-slope divergence was enriched for genes related to electrochemical balance and trans-membrane transport, likely in response to increased selection for dehydration resistance on the hotter slope. Both species shared genomic regions that underwent major selective sweeps but the level of adaptive convergence was overall low, demonstrating no shortage of alternative genomic solutions to cope with the challenges of the microclimate contrast. Mobile elements were a major source of genetic polymorphism and divergence, affecting all parts of the genome, including coding sequences.