Evolutionary radiation of shallow-water Lucinidae (Bivalvia with endosymbionts) as a result of the rise of seagrasses and mangroves

摘要

The Lucinidae (Bivalvia) originated in the Silurian Period with adaptations and life habits like those of modern members of this family. Nonetheless, the family remained at very low diversity until beginning a remarkable evolutionary radiation near the end of the Cretaceous Period, when seagrasses and mangroves arose. These marine angiosperms provided protective habitats in which the lucinids suddenly began to flourish, taking advantage of the dysaerobic sediments below roots and rhizomes to acquire sulfides for the endosymbiotic bacteria that they harbor in their gills and employ as food. Lucinids entered a symbiotic relationship with seagrasses, which benefit from the endosymbionts’ uptake of toxic sulfide, and it is in seagrass meadows that they have by far their highest diversity in shallow seas today. The terminal Cretaceous mass extinction had little impact on the taxonomic diversity of lucinids. Presumably they relied heavily on endosymbionts for nutrition at a time when marine pelagic productivity collapsed and many suspension-feeding taxa died out. The lucinids continued their radiation into the Cenozoic Era without interruption.