Temporal variation in introgressed segments' length statistics computed from a limited number of ancient genomes sheds light on past admixture pulses.

  • publication
  • 22-11-2023

Di Santo LN, Quilodran CS, Currat M. Mol Biol Evol 2023 Nov;():. 10.1093/molbev/msad252. 7441957.

Hybridization is recognized as an important evolutionary force, but identifying and timing admixture events between divergent lineages remains a major aim of evolutionary biology. While this has traditionally been done using inferential tools on contemporary genomes, the latest advances in paleogenomics have provided a growing wealth of temporally distributed genomic data. Here, we used individual-based simulations to generate chromosome-level genomic data for a two-population system and described temporal neutral introgression patterns under a single- and two-pulse admixture model. We computed six summary statistics aiming to inform the timing and number of admixture pulses between interbreeding entities: lengths of introgressed sequences and their variance within-genomes, as well as genome-wide introgression proportions and related measures. The first two statistics could confidently be used to infer inter-lineage hybridization history, peaking at the beginning and shortly after an admixture pulse. Temporal variation in introgression proportions and related statistics provided more limited insights, particularly when considering their application to ancient genomes still scant in number. Lastly, we computed these statistics on Homo sapiens paleogenomes and successfully inferred the hybridization pulse from Neanderthal that occurred approximately 40 to 60 kya. The scarce number of genomes dating from this period prevented more precise inferences, but the accumulation of paleogenomic data opens promising perspectives as our approach only requires a limited number of ancient genomes.

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