Perpendicular axes of differentiation generated by mitochondrial introgression.
Differential introgression of mitochondrial vs. nuclear DNA generates discordant patterns of geographic variation and can promote population divergence and speciation. We examined a potential case of mitochondrial introgression leading to two perpendicular axes of differentiation. The Eastern Yellow Robin Eopsaltria australis, a widespread Australian bird, shows a deep mitochondrial split that is perpendicular to north-south nuclear DNA and plumage colour differentiation. We propose a scenario to explain this pattern: (i) first, both nuclear and mitochondrial genomes differentiated in concert during north-south population divergence; (ii) later, their histories disconnected after two mitochondrial introgression events resulting in a deep mitochondrial split perpendicular to the nuclear DNA structure. We explored this scenario by coalescent modelling of ten mitochondrial genes and 400 nuclear DNA loci. Initial mitochondrial and nuclear genome divergences were estimated to have occurred in the early Pleistocene, consistent with the proposed scenario. Subsequent climatic transitions may have driven later mitochondrial introgression. We consider neutral introgression unlikely and instead propose that the evidence is more consistent with adaptive mitochondrial introgression and selection against incompatible mitochondrial-nuclear combinations. This likely generated an axis of coastal-inland mitochondrial differentiation in the face of nuclear gene flow, perpendicular to the initial north-south axis of differentiation (reflected in genomewide nuclear DNA and colour variation).
School of Biological Sciences Monash University, Clayton Campus, Melbourne, Vic., 3800, Australia.|Centre for Marine Evolutionary Biology, Department of Marine Sciences, University of Gothenburg, Box 461, SE 405 30, Göteborg, Sweden.
Hernán E
http://orcid.org/0000-0002-2964-020X
HE
Morales
School of Biological Sciences Monash University, Clayton Campus, Melbourne, Vic., 3800, Australia.
Paul
P
Sunnucks
Australian National Wildlife Collection, CSIRO National Research Collections Australia, GPO Box 1700, Canberra, ACT, 2601, Australia.
Leo
L
Joseph
School of Biological Sciences Monash University, Clayton Campus, Melbourne, Vic., 3800, Australia.
Alexandra
http://orcid.org/0000-0001-9455-4124
A
Pavlova
D000818:Animals; D001315:Australia; D002467:Cell Nucleus / Q000235:genetics; D004272:DNA, Mitochondrial / Q000235:genetics; D051456:Gene Flow; D054629:Genome, Mitochondrial; D006824:Hybridization, Genetic; D008957:Models, Genetic; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D020308:Songbirds / Q000235:genetics*
D004272:DNA, Mitochondrial
adaptive introgression; coalescence; mitochondria; mitonuclear; selective sweep