Seminar Series 2003

Evolution of Spiders on Oceanic Islands: The Venture of Few and Gain of Many.

Rosemary G. Gillespie
Insect Biology, 201 Wellman Hall, University of California, Berkeley, CA 94720-3112; gillespi@nature.berkeley.edu

The islands of Polynesia are isolated specks in the vast Pacific Ocean. As such, the Hawaiian Islands are well known for some of the most spectacular examples of adaptive radiation, in which a single species gives rise to multiple species adapted to exploit different ecological roles. Knowledge of the biota of French Polynesia is much less complete, with the arthropods known only mostly from early expeditions in the 1920s, and through the extensive work in the Marquesas during the Pacific Entomological Survey (~ 1930s). I have been studying spiders in the genus Tetragnatha to compare (1) their distribution across these remote Polynesian Islands, and test whether representatives on different archipelagos, if present, have used the less remote island groups as stepping-stones to more remote archipelagos. And (2) commonalities underlying patterns of adaptive radiation across archipelagoes. Results to date show that, within each archipelago, the genus has diversified, although the lineages only distantly related. Diversification appears to have been most prolific in the Hawaiian Islands, although much work remains to be done in French Polynesia. Within the Hawaiian Islands, it appears that diversification may occur mostly during the short period immediately following island formation. In addition, at least for one lineage, species on any one island are most closely related to others on the same island, and the same set of ecological forms has evolved repeatedly on different islands. Together these results suggest that adaptive radiation is characterized by rapid and episodic, ecologically-driven diversification of species.