|
| |
 A group of marine iguanas on the trail at the south-western corner of Española. Mention the Galápagos Islands, and people generally think of Charles Darwin, evolution, and the giant tortoises (galápagos in Spanish). Lesser known than the island's lumbering "mascot" is the marine iguana, described by Charles Darwin in 1835 as a "hideous looking creature, of a dirty black colour, stupid, and sluggish" (Darwin, 1988). Despite its appearance, Darwin observed the marine iguana closely enough to recognize its main evolutionary adaptations from its land-dwelling Galápagos cousins, the land iguanas, Conolphus pallidus and Conolphus subcristatus. He could not, however, know how genetics and plate tectonics would enable the "lowly" marine iguana to teach us much more. |
When I learned that I would be able to take a once-in-a-lifetime biology class trip to the Galápagos, I began doing research to learn much more about the marine iguana. I was surprised to learn that although the Galápagos Islands have the world's only species of marine iguana, there are seven separate subspecies or races among the islands, each one distinguishable from the next (Dowling, 1962, in Thornton, 1971; Garman, 1892, in Eibl-Eibesfeldt, 1984; Eibl-Eibesfeldt, 1956, 1962, in Thornton, 1971). The subspecies from Española Island, Amblyrhynchus cristatus venustissimus, is frequently mentioned as the most unique of the seven races because of its exceptional coloration and unusual behavioral adaptations. This variation within a single species intrigued me. What factors had caused Española's venustissimus to become so different from the races on other islands? Was it climate? The availability of food? Predators? Geography? Also, how had Española's marine iguanas stayed isolated enough from those on other islands to begin to diverge? Since the marine iguana is an able swimmer, why hadn't there been enough immigration between islands, and thus genetic mixing, to keep the populations on Española the same as on the other islands? During my trip to the Galápagos and especially during my stop on Española Island, I made some observations that provided important clues toward what might be the answers to these questions. |
        
|
|
