Evolution of coastal forests based on a full set of mangrove genomes.

Genomic studies are now poised to explore whole communities of species. The ~70 species of woody plants that anchor the coastal ecosystems of the tropics, collectively referred to as mangroves, are particularly suited to this exploration. In this study, we de novo sequenced the whole genomes of 32 mangroves, which we combined with other sequences of 30 additional species, comprising almost all mangroves globally. These community-wide genomic data will be valuable for ecology, evolution and biodiversity research. While the data revealed 27 independent origins of mangroves, the total phylogeny shows only modest increases in species number, even in coastal areas of active speciation, suggesting that mangrove extinction is common. A possible explanation for common extinction is the frequent sea-level rises and falls (SLRs and SLFs) documented in the geological record. Indeed, near-extinctions of species with extremely small population size (N) often happened during periods of rapid SLR, as revealed by the genome-wide heterozygosity of almost all mangroves. Reduction in N has possibly been further compounded by population fragmentation and the subsequent accumulation of deleterious mutations, thus pushing mangroves even closer to extinction. Crucially, the impact of the next SLR will be exacerbated by human encroachment into these mangrove habitats, potentially altering the ecosystems of tropical coasts irreversibly.