Abstract
Elucidating the processes enabling lineage diversification in physically
well-connected yet heterogenous environments is central to our
understanding of ecological speciation. Here, we analyzed fully
sequenced genomes to study speciation patterns in the gray mangrove
(Avicennia marina ) peripheral populations occurring throughout
the environmentally extreme, spatially discontinuous coasts of Arabia.
Phylogenomic and demographic models revealed highly differentiated
lineages across the seas bordering the Arabian Peninsula, and divergence
times coinciding with recent periods of low marine connectivity in
(cryptic) glacial refugia. Genotype‐environment association analyses
recovered signs of multi-loci local adaptation driven by climate
extremes. Marked adaptive divergence and remarkably low levels of gene
flow despite the absence of geographic barriers were detected between
Red Sea populations, providing evidence of incipient, selection-driven
reproductive isolation. Our results document a case of strikingly fast
lineage diversification resulting from the combination of historical
isolation and environmental selection, and reveal peripheral mangrove
populations as relevant sites for ecological speciation.