RACE FORMATION, SPECIATION, AND INTROGRESSION WITHIN DROSOPHILA SIMULANS, D. MAURITIANA, AND D. SECHELLIA INFERRED...

Area of Science:

• Evolutionary biology
• Genetics
• Molecular biology

Background:

• Mitochondrial DNA (mtDNA) is crucial for understanding evolutionary relationships due to its maternal inheritance and higher mutation rate.
• Restriction enzyme cleavage maps of mtDNA provide insights into genetic variation and phylogenetic divergence among closely related species.

Purpose of the Study:

• To compare mitochondrial DNA cleavage maps of three homosequential Drosophila species: D. simulans, D. mauritiana, and D. sechellia.
• To infer the evolutionary relationships and potential introgression events among these species based on mtDNA variation.

Main Methods:

• Mitochondrial DNA was isolated from multiple isofemale strains of each species.
• Cleavage maps were generated using 12 different restriction enzymes.
• Phylogenetic analysis was performed based on the generated mtDNA cleavage maps.

Main Results:

• Three cleavage morphs (siI, siII, siIII) were identified in D. simulans and two (maI, maII) in D. mauritiana.
• mtDNA cleavage maps of D. mauritiana (maI) and D. sechellia were found to be internal branches within the D. simulans mtDNA phylogenetic tree.
• A specific morph (siIII) in D. simulans from Madagascar was identical to a morph (maI) found in D. mauritiana.

Conclusions:

• D. mauritiana and D. sechellia likely originated from a D. simulans population carrying an ancestral mtDNA type.
• The data support a hypothesis of recent mitochondrial DNA introgression from Madagascar D. simulans into D. mauritiana.
• Biogeographical and hybridization data are consistent with this introgression hypothesis.