Antiherbivore Defenses of Myrmecophytic Cecropia under Different Light Regimes

Abstract

In a greenhouse experiment, we compared presumed biotic, chemical, physical and phenological defenses of six myrmecophytic Peruvian Cecropia species under high and low light regimes. For all species, increased light intensity enhanced both dry mass production of glycogen-rich Millerian bodies (MBs) and levels of condensed tannins and total phenolics. The production of lipid-rich pearl bodies (PBs), the leaf toughness, and the expansion rate of new leaves were not enhanced consistently by higher light intensity. The six species were comprised of three pairs of close congeners; each pair consisted of a of riverine and stream edges or land-slips, and a species from treefall openings in primary forest. Each gap species grew more slowly than did its pioneer counterpart and allocated proportionally more resources to MBs. Gap species produced a greater dry mass of MBs per unit of leaf area, and initiated their production earlier in seedling ontogeny. In comparison with pioneer relatives, gap species also possessed somewhat longer-lived and tougher leaves. Both PB production and leaf expansion rates were greater in pioneers than in closely related gap species. Disparities in the behaviors of MBs and PBs in interspecific comparisons probably reflect differences in the initial construction costs versus continuing or maintenance costs of these two types of ant rewards. Interspecific differences in the production of carbon-based secondary compounds by pioneers and gap species are pair specific and appear to be related to the degree of morphological differentiation within pairs, and, possibly, to time since divergence. We relate our results to current theories of plant defense.