Parallel and lineage-dependent mitonuclear evolution in threespine stickleback

Freshwater colonization in Gasterosteus aculeatus is linked to broadly parallel allele-frequency shifts in nuclear OXPHOS genes across Alaska and British Columbia, despite multiple mitochondrial lineages.

• Why it matters: Mitochondrial performance depends on coordinated mitochondrial–nuclear interactions, but it is unclear whether repeated freshwater adaptation produces parallel nuclear changes and how these relate to mitonuclear coupling.
• What they did: The study compared mitochondrial and nuclear OXPHOS evolution across populations with divergent mitochondrial lineages, testing for parallel nuclear shifts and for positive evolutionary rate covariation in Complex IV.
• The result: Nuclear–mitochondrial evolutionary coupling is concentrated in particular OXPHOS modules—especially Complex I—while the strongest freshwater-associated nuclear shifts are largely distinct from loci showing mitonuclear rate covariation, implicating cox4i1.

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