A low-latitude species pump: Peripheral isolation, parapatric speciation and mating-system evolution converge in a marine radiation

Geologically recent radiation can shed light on speciation processes, but incomplete lineage sorting and introgressive gene flow render accurate evolutionary reconstruction and interpretation challenging. Independently evolving metapopulations of low-dispersal taxa may provide an additional level of phylogeographic information, given sufficiently broad sampling and genome-wide sequencing. Evolution in the marine brown algal genus Fucus in the south-eastern Atlantic was shaped by Quaternary climate-driven range shifts. Over this timescale, divergence and speciation occurred against a background of expansion-contraction cycles from multiple refugia, together with mating-system shifts from outcrossing (dioecy) to selfing hermaphroditism. We tested the hypothesis that peripheral isolation of range edge (dioecious) F. vesiculosus led to parapatric speciation and radiation of hermaphrodite lineages. Species tree methods using 876 single-copy nuclear genes and extensive geographic coverage pro...