Convergent adaptation to a marginal habitat by homoploid hybrids and polyploid ecads in the seaweed genusFucus

Abstract

Hybridization and polyploidy are two major sources of genetic variability that can lead to adaptation in new habitats. Most species of the brown algal genusFucusare found along wave-swept rocky shores of the Northern Hemisphere, but some species have adapted to brackish and salt marsh habitats. Using five microsatellite loci and mtDNA RFLP, we characterize two populations of morphologically similar, muscoides-likeFucusinhabiting salt marshes in Iceland and Ireland. The Icelandic genotypes were consistent withFucus vesiculosus×Fucus spiralisF1hybrids with asymmetrical hybridization, whereas the Irish ones consisted primarily of polyploidF. vesiculosus.