Molecular phylogeny, taxonomy, and evolution of nonmarine lineages within the American grapsoid crabs (Crustacea : Brachyura)

Grapsoid crabs are best known from the marine intertidal and supratidal. Ho wever, some species also inhabit shallow subtidal and freshwater habitats. In the tropics and subtropics, their distribution even includes mountain st reams and tree tops. At present, the Grapsoidea consists of the families Gr apsidae, Gecareinidae, and Mictyridae, the first being subdivided into four subfamilies (Grapsinae, Plagusiinae, Sesarminae, and Varuninae). To help r esolve phylogenetic relationships among these highly adaptive crabs, portio ns of the mitochondrial genome corresponding to the 16S rRNA gene were sequ enced for all grapsoid genera occurring in America. The resulting phylogeny confirms most of the present grapsid subfamilies but suggests reclassifica tion of some of the genera and recognition of new taxonomic units. The two American gecarcinid genera might not represent a sister group to the Grapsi dae but rather appear to have evolved within the latter. Colonization of in land habitats evolved in several lineages of the grapsoids, resulting in va rious forms of nonmarine life and different degrees of independence from th e sea. (C) 2000 Academic Press.