PATTERN AND PROCESS IN THE BIOGEOGRAPHY OF SUBTERRANEAN AMPHIPODS

The comparative data from studies of two 'superfamily' groups with large numbers of subterranean taxa, the exclusively freshwater Crangonyctoidea and the predominately marine Hadzioidea, support the hypothesis that distributional patterns and evolutionary processes of stygobiont amphipods are closely linked and that the former can be a useful indicator of the latter. Three major biogeographic patterns are indicated by the distribution of subterranean species in these groups, each apparently reflecting a particular mode of origin: (1) freshwater stygobionts (limnostygobionts) derived from epigean freshwater ancestors through colonizations probably influenced by adaptive shifts, or assisted by stream capture and spring failure; (2) freshwater stygobionts derived from marine/brackish water ancestors by stranding during regression of marine embayments; and (3) marine/brackish water stygobionts (thalassostygobionts) derived from epigean marine/brackish water ancestors through adaptive shifts possibly in concert with fluctuating sea levels.