Variation in the Substitution Rates among the Human Mitochondrial Haplogroup U Sublineages

Area of Science:

• Evolutionary Biology
• Population Genetics
• Ancient DNA Analysis

Background:

• Accurate phylogenetic tree calibration relies on understanding DNA sequence evolution rates.
• Intraspecific variation in molecular rates across genetic lineages has been understudied.
• Tip-calibration using radiocarbon-dated ancient DNA is increasingly feasible for phylogenetic analysis.

Purpose of the Study:

• To assess lineage-specific molecular rates of human mitochondrial DNA (mtDNA).
• To investigate the impact of demographic histories on mtDNA substitution rates.
• To compare divergence times and evolutionary rates among mtDNA subhaplogroups U2, U4, U5a, and U5b.

Main Methods:

• Tip-calibrated Bayesian phylogenetic analyses were performed on human mtDNA genomes.
• Data included ancient (n=234) and contemporary (n=301) mtDNA genomes, plus outgroups.
• Analyses focused on subhaplogroups U2, U4, U5a, and U5b, utilizing radiocarbon-dated samples.

Main Results:

• Molecular rates showed time-dependency and significant variation between haplogroups.
• mtDNA haplogroups U4 and U5a exhibited substantially higher evolutionary rates than U5b.
• Divergence times differed notably: U5a at 17,700 years and U5b at 29,700 years.

Conclusions:

• Lineage-specific demographic histories likely influenced human mtDNA substitution rates.
• The observed rate variation is not attributable to selection, sampling, or sequence quality issues.
• mtDNA haplogroups U4 and U5a's rapid evolution may correlate with population expansions, such as the Yamnaya culture.