EOCENE PLANT-INSECT ASSOCIATIONAL DIVERSITY AT LAGUNA DEL HUNCO, PATAGONIA, ARGENTINA

Although the early Eocene (52 Ma) lacustrine floras at Laguna del Hunco (LH), in Chubut Province of Argentina, are among the most diverse of the Cenozoic, previously the variety of insect-mediated damage on plant hosts has not been quantitatively or qualitatively assessed. At LH insect herbivore trophic diversity was evaluated to test the hypothesis that the variety of insect herbivory matched the elevated taxic diversity of the flora.

Four functional feeding groups on leaves are present at LH: external foliage feeding, galling, leaf mining, and piercing-and-sucking, in addition to nonfeeding ovipositional damage. Within these groups 52 discrete damage types were documented, using an updated, diagnostic system of recognition. Employing methodologically identical analyses, LH damage diversity was compared to North American floras from the middle Eocene Green River Fm. of NE Utah (Bonanza site, lacustrine), the early Eocene Wasatch Fm. of SW Wyoming (Sourdough, fluvial), and for the first time, the middle Eocene Klondike Mtn. Fm. of NE Washington (Republic, lacustrine). Of the North American floras, Sourdough and Green River currently are the closest to LH for the rarefied number of functional feeding groups and damage types, respectively, per dicot leaf specimen. For the 7 species with the greatest number of damage types, all were from LH; so were 7 of the 8 species with the greatest number of functional feeding groups. Thus higher feeding diversity is associated with greater taxonomic diversity of plant hosts, as measured by bulk flora or individual host species.

The elevated level of herbivory provides evidence for diverse component communities of many plant hosts at LH. One podocarpaceous host harbors a vein galler, blotch miner, piercer-and-sucker and several specialized to generalized external feeders. Similarly, a broad spectrum of galls and lepidopteran leaf mines occur on hosts whose relatives occur today in the Neotropics, such as Lauraceae, Sterculiaceae and Fabaceae. These data indicate an exceptionally diverse plant and insect herbivore biota in South America during the globally warm Eocene, and suggest that high South American multitrophic biodiversity is ancient.