Monday, August 2, 2010

PS 14-110: Herbivore defense in three species of Amazonian Cecropia from Peru

Sarabeth B. Brockley, Molly A. DuVall, and John M. Bevington. Moravian College

Background/Question/Methods Cecropia (Cecropiaceae) is a genus of Neotropical trees widespread throughout the Amazon basin and in Central America. Cecropia trees are fast-growing pioneers that colonize disturbed habitats (tree fall gaps and along river edges). Most species are myrmecophytes; that is, they are ant-plants. Although several ant species inhabit the trees, Azteca ants are most common. The relationship between the trees and their ants has been studied by a number of authors, and it is known that the ants defend the trees against herbivores. However, not all species of Cecropia have ants. In the northwest corner of the Amazon basin several species of non-myrmecophyte Cecropia grow on the eastern slopes of the Andes. Little is known about the herbivore defense strategy in these non-myrmecophyte Cecropia, or why the non-myrmecophyte species are more common in the Andes than in the lowlands. We selected three species from Peru to look at how herbivore defense differs between myrmecophyte and non-myrmecophyte species and how elevation may have changed the relationship between the trees and the ants. We used C. membranaceae, C. sciadophylla, and C. tacuna. The first two species are from the lowland rain forest while the third is an Andean cloud forest endemic. C. membranaceae is a myrmecophyte with Azteca ants. C. sciadophylla and C. tacuna are non-myrmecophyhtes. Results/Conclusions We measured leaf toughness in each species and extracted condensed tannins and total phenolic compounds from mature leaves. Leaf toughness in C. sciadophylla was greater than membranacea (ca. 72%). Levels of condensed tannins in C. membranacea and C. sciadophylla were not significantly different. Leaves of C. membranacea contained significantly more extractable phenolics than C. sciadophylla. C. tacuna contained significantly lower levels of both tannins and phenolics compared to either C. membranacea or C. sciadophylla. The leaves of C. tacuna are at least as tough as those of membranacea, but from our data it was not possible to determine how the toughness of tacuna compares to sciadophylla. C. membranacea seems to be defended by both its ants and by secondary metabolites; C. sciadophylla has tough leaves and high levels of tannins. Low levels of both tannins and phenolics in C. tacuna suggest that high in the Andes (2500 m) lower herbivore pressure may have allowed tacuna to commit less resources to production of secondary metabolites.