Perpendicular axes of differentiation generated by mitochondrial introgression.

Area of Science:

• Evolutionary Biology
• Genetics
• Ornithology

Background:

• Differential introgression of mitochondrial vs. nuclear DNA can lead to discordant geographic variation.
• Population divergence and speciation can be influenced by varying introgression patterns.

Purpose of the Study:

• To investigate a potential case of mitochondrial introgression causing perpendicular axes of differentiation in the Eastern Yellow Robin (Eopsaltria australis).
• To explain the observed deep mitochondrial split perpendicular to nuclear DNA and plumage color differentiation.

Main Methods:

• Coalescent modeling of ten mitochondrial genes and 400 nuclear DNA loci.
• Analysis of geographic variation in mitochondrial DNA, nuclear DNA, and plumage color.

Main Results:

• A deep mitochondrial split was observed, perpendicular to north-south nuclear DNA and plumage color differentiation.
• Initial mitochondrial and nuclear genome divergence estimated in the early Pleistocene.
• Evidence suggests adaptive mitochondrial introgression and selection against incompatible mitochondrial-nuclear combinations.

Conclusions:

• The study proposes a scenario of initial concerted nuclear and mitochondrial divergence, followed by mitochondrial introgression events.
• Adaptive mitochondrial introgression, rather than neutral introgression, is favored to explain the observed genetic patterns.
• This process likely generated coastal-inland mitochondrial differentiation perpendicular to the north-south nuclear differentiation axis.