Evolution in Hawiian cave adapted isopods (Oniscidea: Philosciidae): vicariant speciation or adaptive shifts?

We assessed evolutionary relationships among Hawaiian cave-adapted isopods using a maximum-likelihood criterion to analyze cytochrome oxidase I nucleotide sequences. Results support morphological data that two genera of philosciid isopods have invaded caves independently in the islands. In the genus Littorophiloscia,a sister relationship between a surface-dwelling species, L. hawaiiensis, and an undescribed cave species was corroborated. This evidence,along with the known parapatric distributions between species,supports a speciation event by an adaptive shift on the island of Hawaii from a marine littoral to a terrestrial subterranean habitat. The monophyletic genus Hawaiioscia contains four known obligate cave-dwelling species,each of which occurs on a separate island. However,despite present-day allopatric distributions between Hawaiioscia species,the geographic and phylogenetic patterns are not sufficient to support a vicariant mode of speciation. Instead,we believe that the known species of Hawaiioscia evolved from a widespread ancestral surface species or a group of closely related species through multiple,independent adaptive shifts on each of the islands of Kauai,Oahu,Molokai,and Maui. This is the first molecular investigation of evolutionary relationships between surface-dwelling and cavernicolous arthropods in Hawaii and it suggests that simple vicariance is insufficient to explain the evolution of troglobites in tropical zones.