Rolled-leaf Hispine Herbivory of Heliconia spp. (Heliconiaceae) over an Altitudinal Gradient Sarah Bachman Department of Biology, Fairfield University _____________________________________________________________________________________ Abstract Hispine beetles (Coleoptera: Chrysomelidae, Hispinae) are herbivores of the Order Zingiberales (Strong 1977a). In Monteverde area there are three known species of Heliconiaceae (Zingiberales): Heliconia monteverdensis, H. tortuosa, and H. vaginalis (Haber, 1990). H. monteverdensis is a high elevation species (1500 – 1800m) whose range does not overlap with H. vaginalis, a low elevation species (700 – 1300m). H. tortuosa occurs along the elevational gradient from San Luis (1000m) to the forest behind the Estación Biológica de Monteverde (1760m) where this study was performed, and overlaps in geographical range with the other two species. In this study I looked at patterns of hispine herbivory between Monteverde Heliconia species as well as leaf age, and altitude. I did not find turnover in hispine herbivory between species of Heliconia, but found that the amount of herbivory changed between species, elevation, and between leaves of different ages. H. vaginalis had significantly lower herbivory than the other two species (Fisher’s PLSD, p < 0.0001). H. tortuosa and H. monteverdensis showed higher herbivory in older leaves (Fisher’s PLSD, p = 0.0119). Herbivory in H. tortuosa increased with elevation in older leaves (simple regression, p < 0.0001). Elevational trends are best explained as responses to temperature and water availability during the dry season, while differences between Heliconia spp. in amounts of herbivory may be due to differences in leaf phenology. Resumen Cercanas de coleópteros hispinos chrysomélidos están limitadas a vivir sombre familias de la orden Zingiberales (Strong 1977a). Hay tres especies de Heliconia que viven en la región de Monteverde por el lado Pacífico: Heliconia monteverdensis, H. tortuosa, y H. vaginalis (Haber, Pers com). Heliconia monteverdensis es una planta que vive arriba de Monteverde en los altitudines altas. Este planta no vive con H. vaginalis, una planta que vive más bajo en San Luis. Heliconia tortuosa vive en los dos lugares, desde San Luis a la Estación Biológica de Monteverde, donde yo hice este proyecto. En este proyecto, yo buscaba por algunos patrones de daño en las ojas de Heliconia entre los tres especies de plantas, la edad de las ojas, y el altitud. No encontré una diferencia entre los patrones de daño entre especies, pero había algunos diferencias en cuanto daño había sobre especies, la edad de las ojas y la altitud. Heliconia vaginalis tuvo menos daño a las ojas que los otros especies (Fisher’s PLSD, p < 0.0001). Heliconia tortuosa y H. monteverdensis tuvieron más daño en las ojas más viejas (Fisher’s PLSD, p = 0.0119). Probablemente, estas ojas fueron hechos más cerca del invierno. Había más daño en las ojas viejas en los altitudines altas con H. tortuosa (regresión simple, p < 0.0001). Estos patrones son explicados mejor con diferencias entre la temperatura y lluvia que los diferentes altitudes tiene durante el invierno. Introduction Herbivory is an important plant – animal interaction that impacts multiple trophic levels and has many ecological consequences. Tropical forests have higher rates of herbivory and a greater number of specialized herbivores than extra-tropical areas. Higher specialization supports resource – based models of species richness where finer niche partitioning occurs because of specialists (Janzen 1983). Insects are the major herbivores of tropical forests, and in on Barro Colorado Island, specialized insect herbivores caused the most damage to any of the tree species studied (Coley et al. 1996). Specialized herbivores contribute to species richness in other ways as well. Distance – dependence may affect young saplings near parent trees if these trees attract or act as a source for specialist herbivores. Saplings near a parent tree may suffer higher herbivory and reduced fitness for this reason. This opens up room for other tree species and may contribute to the low relative abundance and high plant species richness found in the tropics (Coley et al. 1996). The large number of specialized herbivores has likely played a role in the evolutionary history of both plants and insects. Secondary compounds, extra floral nectaries, and tough leaves are just a few of the plant defenses that have evolved separately in plants as a way to avoid herbivory. These defenses are often expensive for the plant, requiring a large allocation of energy to produce or sustain. Plant defenses may reciprocally drive herbivores towards specialization (Coley et al. 1996). In some groups of insects, specialization has persisted at least some 40 million years, which suggests that they may have little potential to adapt to new plants as food sources. High levels of specialization could mean that the loss of a particular plant species leads to the extinction of specialized herbivores. This has important implications for conservation in the tropics (Futuyma, 1997). For the great ecological impact that specialized insect herbivores have in tropical forests, they are poorly known, and certainly deserve more attention. Hispine beetles (Coleoptera: Chrysomelidae, Hispinae) are herbivores of plants in the Order Zingiberales in the New World tropics (Strong 1977a). Zingiberales contains several families to which hispine beetles exhibit high specificity. Both larvae and adults feed on new leaves, which are produced one at a time at the center of the stalks as cylindrical rolls (Strong 1977a). Plant family host specificity was demonstrated for several hispine spp. between Marantaceae, Costaceae, and Heliconiaceae (all members of the Zingiberales Order) in the San Luis valley in the Monteverde region (Johnson 2000). It is not known whether hispine beetles are specialized within plant families among species. Heliconiaceae is common in sunlit areas, stream banks, swamps, river and road edges, and light gaps (Seifert 1982). Heliconia spp. are known for their showy inflorescences constructed of colorful pendant or erect bracts. Flowers extend out of the bracts when mature and are pollinated by hummingbirds. New leaves are produced as cylindrical rolls, and unfurl within a few days or up to a week depending on plant size and local temperature (Stiles 1975). The plants propagate by rhizomes and some species form large clumps this way (Stiles 1975). Hispine beetles are the major herbivores on Heliconia leaves, which are low in nitrogen (Strong 1982). Three species of Heliconia occur along an altitudinal gradient on the Pacific slope in the Monteverde area: H. monteverdensis, H. tortuosa, and H. vaginalis (Haber 1990). It is not known what factors set the distributional limits for hispine beetles, though species vary geographically (Strong 1977b). Elevation may be a geographic barrier between species. Hispines have a long life cycle relative to other members of the family Chrysomelidae (Strong 1977a). Low food quality has been argued as a reason for their slow development (McCoy 1984). Hispine beetle populations are larger during the wet season when more leaves are produced. In very dry regions, pupae may diapause hidden between overlapping petiole-base tissues on the stalk of the plant close to ground level (Strong 1977a). Larvae are flat and easily slip between the wet appressed surfaces of leaves and stems (Strong 1977b). Both larvae and adults feed only on rolled leaves by “strip mining”, which means that they feed on the leaf surface by dragging their mandibles across plant surface while crawling slowly forward leaving characteristic scars (Strong 1977a). Several species of hispines may be present on a given plant, although these species are not known to interact (Strong 1842). This may indicate that food is not a limiting factor. Strong (1977b) showed that over 95% or rolled leaves were left uneaten by hispines in all regions studied. The purpose of this study was to study the hispine beetles indirectly through the studying the patterns left behind by “strip mining”. I looked for trends in hispine herbivory between H. tortuosa, H. monteverdensis, and H. vaginalis over an altitudinal gradient examining Heliconia species, altitude, and leaf age. By studying a plant family that changes along the elevational gradient, I used the trends in patterns of herbivory to look for changes in hispine herbivory between plant species, leaf age, and elevation. Specialized herbivores play important ecological roles in tropical forest yet we lack even the most basic distribution, and natural history of most species. Hispine herbivory may be a valuable reference point for future research of specialized herbivores. Materials and Methods Study Site I performed this study from April 22nd to May 9th at the end of the dry season at the Estación Biológica de Monteverde, the Ecolodge in San Luis and trail to the Catarata in San Luis, and along the trail leading from Invu San Luis to Monteverde. This spanned from 1000m to 1815m in altitude and included the Premontane Moist, Premontane Wet, and Lower Montane Wet Forest (Holdrige Life Zones: Haber 2000). Heliconia Identification I identified H. tortuosa, H. monteverdensis, and H. vaginalis using vegetative characters (Berry and Kress 1991; Haber 1990; Haber and Zuchowski 1999). Heliconia monteverdensis grows three to six feet tall at high elevations (1500-1800m). It has dark red bracts with creamy pale yellow flowers that