Spatial principal component analysis points at global genetic structure in the Western Mediterranean

Area of Science:

• Population Genetics
• Human Evolution
• Genomics

Background:

• The Strait of Gibraltar has been studied for potential genetic barriers between Iberian and North African populations, yielding debated results.
• Understanding gene flow and population structure is crucial for evolutionary and demographic studies.

Purpose of the Study:

• To investigate the genetic differentiation between South European and North African populations.
• To determine if a genetic barrier exists in the Strait of Gibraltar or if gene flow is more continuous.

Main Methods:

• Utilized principal component analysis (PCA) and spatial PCA (sPCA) on genetic data.
• Analyzed four datasets: Alu insertions, single-nucleotide polymorphisms (SNPs), short tandem repeats (STRs), and a combined set of markers.
• Examined genetic variation across 12-13 Western Mediterranean populations.

Main Results:

• PCA plots showed clear visual separation between South European and North African samples along the first principal component.
• sPCA analyses indicated a single global genetic structure for each marker set, without distinct local structures.
• Allele frequencies exhibited a clinal distribution rather than abrupt changes across the Strait.

Conclusions:

• The findings support isolation-by-distance and progressive introgression as primary drivers of genetic differentiation, rather than a complete genetic barrier.
• Gene flow appears to be more continuous, with North African populations potentially introgressing into Southwestern Europe.