MOLECULAR-DATA AND BIOGEOGRAPHY - RESOLUTION OF A CONTROVERSY OVER EVOLUTIONARY HISTORY OF A PAN-TROPICAL GROUP OF INVERTEBRATES

Phylogenetic analyses of sequences of 16S rDNA suggest that the curren t hypothesis of the evolution of the pan-tropical fiddler crab genus U ca (Decapoda, Brachyura, Ocypodidae) is false. This hypothesis rests o f the assumption that the increase of complexity of reproductive behav ior, together with a tendency of a habitat shift towards the higher in tertidal, arose only once in the history of the fiddler crabs. The ori gin of fiddler crabs was placed in the IndoPacific, which is widely th ought to be a center of origin for several marine groups. There, relat ively lower intertidal crabs were thought to give rise to a radiation in the Americas in which higher intertidal forms with more complex rep roductive behavior evolved, and finally, derived crabs were thought to disperse back to the IndoPacific from the Americas, In contrast our p hylogeny suggests that the ancestral group, which shows complex reprod uctive behavior, now resides wholly in the American-Atlantic region, a s opposed to the postulated Indo-west-Pacific. Behavioral and ecologic al complexity must have arisen independently in the American and IndoP acific faunal regions. The pan-tropical subgenus Celuca seems to be po lyphyletic, which suggests that the evolution of morphology, ecology a nd behavior involves convergence in geographically separated locales. This study highlights the dangers of postulating evolution from a cent er of origin, even if it fits data that can be assigned to an evolutio nary trend.