Biogeographic Relationships of Galapagos Marine Isopod Crustaceans
Abstract:Thirty-five species of marine isopods are reported from the Galapagos region; 18 (51%) are endemic. Of the 17 nonendemic species, 6 are restricted to the Panamic Region, 4 occur in the Panamic Region and Californian Province, and 7 are widespread. For the most part, biogeographic relationships of the Galapagos endemic species are not yet known. Of four species for which sister-group relationships are hypothesized, one has its possible sister-species in Antarctica, one in the Panamic Region, one in Brazil/Australia, and one in New Caledonia (west Pacific). Seventeen species of shallow-water isopods are known from the Galapagos, 11 (65%) of which are endemic, 3 also occur in the mainland Panamic Region, and 3 occur in both the Panamic Region and Californian Province. There is no evidence from separate analyses of endemic and nonendemic species to support a vicariance hypothesis that the archipelago was once connected to the American mainland by shallow submarine corridors along the Carnegie or Cocos Ridge. All Galapagos isopods appear to owe their origin on the islands to dispersal from other regions. Only two species span the east Pacific barrier, and both are parasites on oceanic fishes. Other studies of Galapagos marine biogeography are briefly reviewed. All Galapagos marine taxa that have been examined biogeographically, except pycnogonids, gammarid amphipods and isopods, have a pelagic dispersal stage in their life history. Pycnogonids, gammarids and isopods exhibit higher endemism (75%, 35% and 51%) than any other suprageneric-level taxon yet analyzed from the Galapagos, suggesting a direct correlation between dispersal capabilities and levels of endemism on oceanic islands.
Document Type: Research Article
Publication date: September 1, 1987
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