Genome sequencing reveals complex speciation in the Drosophila simulans clade

Area of Science:

• Evolutionary Genetics
• Speciation Research
• Comparative Genomics

Background:

• The Drosophila simulans clade (D. simulans, D. mauritiana, D. sechellia) are key models for speciation genetics.
• Phylogenetic relationships and historical gene flow within this clade remain incompletely understood.
• Previous studies have debated the order, timing, and extent of speciation events and gene flow.

Purpose of the Study:

• To resolve phylogenetic uncertainties and investigate gene flow within the Drosophila simulans clade.
• To analyze whole-genome sequence data to infer evolutionary histories.
• To assess lineage-specific genomic changes and selection efficacy in endemic species.

Main Methods:

• Whole-genome sequence alignment of three D. simulans clade species (D. simulans, D. mauritiana, D. sechellia) and D. melanogaster.
• Analysis of novel, paired short-read sequence data from inbred lines.
• Phylogenetic analysis and detection of gene flow signatures across the genome.

Main Results:

• A species phylogeny with a basal polytomy, dated to approximately 242,000 years ago, could not be rejected.
• Evidence for recent gene flow was detected in up to 4.6% of autosomal and 2.2% of X-linked regions.
• D. sechellia exhibits an excess of deleterious mutations and a deficit of favorable mutations, indicating reduced selection efficacy linked to a reduced effective population size.

Conclusions:

• Gene flow has occurred across the genomes of the D. simulans clade species, despite significant isolation.
• The evolutionary history is complex, involving both divergence and admixture.
• Reduced efficacy of natural selection in D. sechellia may be a consequence of its evolutionary trajectory and population history.