Mitonuclear Discordance in Speciation and Phylogeny

Mitonuclear discordance refers to the mismatch between evolutionary histories inferred from mitochondrial DNA and those reconstructed from nuclear genomes. This phenomenon arises when mitochondrial and nuclear markers tell different stories about lineage divergence, often as a result of processes such as incomplete lineage sorting, hybridisation and introgression. Such discordance can complicate our understanding of species boundaries, biogeographical histories and the timing of speciation events. In many taxa—ranging from mammals and amphibians to invertebrates and plants—reliance on a single mitochondrial marker has led to underestimates or overestimates of diversity, misplacement of branches in phylogenetic trees and misguided conservation priorities. Recent advances in high‐throughput sequencing and integrative analytical methods now enable simultaneous analysis of thousands of nuclear loci alongside complete mitochondrial genomes. This integrative approach has transformed our capacity to disentangle the relative contributions of demographic history, gene flow and stochastic coalescence to observed phylogenetic patterns. Understanding mitonuclear discordance is therefore pivotal for robust species delimitation, accurate reconstruction of evolutionary relationships and informed strategies in biodiversity management.

Research from Nature Portfolio

A foundational genome‐scale analysis of bovine species demonstrated that the divergent mitochondrial lineage of the European bison (wisent) is best explained by incomplete lineage sorting rather than by historical hybridisation with domestic cattle. By comparing nuclear whole‐genome sequences across closely related bovines, researchers found that the frequencies of discordant tree topologies matched coalescent expectations under lineage sorting, overturning the long‐standing hybrid origin hypothesis. This study underscored the necessity of dense nuclear sampling to resolve speciation histories and cautioned against overreliance on mitochondrial markers for phylogenetic inference.

Mitonuclear Discordance in Speciation and Phylogeny publication trend

The graph below shows the total number of articles in mitonuclear discordance in speciation and phylogeny across all publications each year (not limited to Nature Index journals).

Technical terms

Mitonuclear discordance: The phenomenon whereby phylogenetic trees inferred from mitochondrial DNA differ from those based on nuclear genomes, often due to processes like hybridisation, introgression or incomplete lineage sorting.

Incomplete lineage sorting (ILS): A coalescent process in which ancestral genetic variation fails to coalesce immediately following speciation, leading to gene trees that differ from the species tree.

Introgression: The transfer of genetic material from one species or population into another via hybridisation and repeated backcrossing, resulting in mosaic genomes.

Gene tree vs species tree incongruence: The mismatch between the history of individual genes (gene trees) and the overall evolutionary history of species (species tree), often caused by ILS, horizontal gene transfer or introgression.

References

1. Incomplete lineage sorting rather than hybridization explains the inconsistent phylogeny of the wisent. Communications Biology (2018).
2. When standard DNA barcodes do not work for species identification: intermixed mitochondrial haplotypes in the Jaera albifrons complex (Crustacea: Isopoda). Marine Biodiversity (2024).
3. Inferring phylogenetic structure, taxa hybridization, and divergence times within rock voles of subgenus Aschizomys (Cricetidae: Alticola) using quaddRAD sequencing and a cytb dataset. Ecology and Evolution (2023).
4. Across mountains and ocean: species delimitation and historical connectivity in Holarctic and Arctic-Alpine wolf spiders (Lycosidae, Pardosa). Insect Systematics and Diversity (2023).