Eyeless Arthropods of the Galapagos Islands, Ecuador: Composition and Origin of the Cryptozoic Fauna of a Young, Tropical, Oceanic Archipelago

Abstract

Fifty-six species of eyeless and reduced-eyed (obligately cryptozoic) macroscopic arthropods are now known from the Galapagos Islands. These occupy cave, ground water, and soil-litter habitats. Sixteen soil-inhabiting species have become established after their probable inadvertent introduction by humans. The number and diversity of the remaining 40 native and endemic species are remarkable because of the geologic youth (about three million years maximum) and oceanic isolation of the islands. Soil habitats contain ten species whose ancestors naturally arrived on the islands in an already eyeless condition, demonstrating that such taxa have greater powers of overwater dispersal than is generally thought. Caves and soils are inhabited by ten eyeless or reduced-eyed species which have related fully-eyed epigean (sister?) species, usually on the same island, indicating relatively recent (possibly parapatric) adaptive radiation into subterranean environments. Another 20 species have no dose Galapagos relatives, and 15 of these are probably relicts of lineages which became extinct in epigean terrestrial habitats, probably because of repeated periods of intense aridity during the Pleistocene. Similar evolutionary patterns exist in the eyeless arthropods of the Hawaiian and Canary archipelagos, indicating that there are common processes in the origins of such eyeless tropical oceanic island faunas.