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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 Estac in Biolgica 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 altitud e. 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 0.0001). H. tortuosa and H. monteverdensis 0.0119). Herbivory in H. tortuosa increased with elevation in older lea ves (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 phenolog y. Resumen Cercanas de colepteros hispines chrysomlidos estn limitadas a vivir sombre familias de la orden Zingiberales (Strong 1977a). Hay tres especies de Heliconia que viven en la regin de Monteverde por el lado Pacfico: Heliconia monteverdensis H tortuosa y H. vaginalis (Haber, Pers com). Heliconia monteverdensis es una planta que vive arriba de Monteverde en los altitudinales altas. Este planta no vive con H. vaginalis una planta que vive ms bajo en San Luis. Heliconia tortuosa vive en los do s lugares, desde San Luis a la Estacin Biolgica de Monteverde, donde yo hice este proyecto. En este proyecto, yo buscaba por algunos patrones de dao en las hojas de Heliconia entre los tres especies de plantas, la edad de las hojas y el altitud. No enco ntr una diferencia entre los patrones de dao entre especies, pero haba algunas diferencias en cuanto dao haba sobre especies, la edad de las hojas y la altitud. Heliconia vaginalis 0.0001). Heliconia tortuosa y H. monteverdensis Probablemente, estas hojas fueron hechos ms cerca del invierno. Haba ms dao en las hojas viejas en los altitudes altas con H. tortuosa (r egresin simple, p < 0.0001). Estos patrones son explicados mejor con diferencias entre la temperatura y lluvia que l a s diferentes altitudes tienen 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 herbiv ores 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 abun dance and high plant species ric hness 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 nectarines 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 r eciprocally drive herbivores towards specializa tion (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. Hig h 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 speci alized 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 1977 a). Plant family host spec ificity 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 speciali zed 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 br acts. Flowers extend out of the bracts when mature and are pollinated by hummingbirds. News 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 propa gate by rhizomes and some species form large clumps this way (Stiles 1975). Hispine beetles are the major herbivore s 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 geographical ly (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 1 984). 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). B that they feed on the leaf surface by dragging their mandib les across plant surf ace while c rawling 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 elevationa l 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 forests yet we lack even the most basic distribution, and natural hi story 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 22 nd to May 9 th at the end of the dry season at the Estacin Biol gica de Monteverde, the Ecolodge in San Luis and trail to the Catarata in San Luis, and along the trail leading from In vu San Luis to Monteverde. This spanned from 1000m to 1815m in altitude and included the Premontane Moist, Premontane Wet, and Lower Mont ane 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 often have a greenish tint It also has musoid vegetation meaning leaves are oriented vertically on long petioles (Berry et al.
199 1). H. tortuosa overlaps in geographic distribution with both H. monteverdensis and H. vaginalis, which are separated by elevation. H. tortuosa grows five to ten feet tall, has red bracts that may have a yellow base, deep yellow sepals, green ovaries, and musoid vegetation (Berry et al. 1991). H. vaginalis is a lower elevation sp. (700 1300m), three to fifteen feet tall with cannoid vegetation meaning leaves are held obliquely. The leaves are the smallest of the three species. It has red to reddish orange bracts that may have a green keel. Flowers are yellow, and the ovaries are usually green on the distal third (Berry et al. 1991). Patterns of Herbivory I noted hispine herbivory in 671 leaves from 231 individuals. For each plant, I collected data on the t hree newest leaves, labeling the newest leaf 1 and the oldest leaf 3. The length and width of each leaf were recorded with a tape measure. I used a 0.5cm A2 grid to record the area of herbivory by counting the number of squares of damaged leaf tissue and converting that into damage (cm ^ 2 ). This amount of damage (cm ^ 2 ) will be referred to as absolute herbivory. I used an altimeter from a Casio Forester watch to record the altitude at each plant. I drew the patterns of herbivory for each leaf and also made a code to record the patterns. Hispine herbivory was from damage types, based on Strong (1977b). I used length width) to calculate the area of each leaf and used 100 (area of herbivory) / (leaf area) to calculate the perce nt herbivory for each leaf. Patterns of Herbivory I ran a 2 way ANOVA to compare, percent herbivory between species, and lea f age. I also used this test to compare absolute herbivory between species. I ran simple regressions for percent herbivory and alti tude for each species. I also ran a simple regression for the oldest leaves of H. tortuosa to compare percent herbivory with altitude. I used chi square analyses and Morisita Horn Indices to determine the overlap of herbivory patterns between species. A di stribution of the percent of individuals in each Heliconia spp. that showed each type of herbivory was also graphed. Results Statistical Analysis Species differed significantly in the herbivory they suffered. H. monteverdensis had significantly higher percent herbivory than H. vaginalis (Fisher's PLSD, p <. 0.0001) and H. tortuosa (Fisher's PLSD, p < 0.0001). H. tortuosa had significantly higher percent herbivory than H. vaginalis (Fisher's PLSD, p = 0.0117). Oldest leaves suffe red a significantly higher percent herbivory than the youngest leaves when data from all three species were analyzed (Fisher's PLSD, p = 0.0119). H. vaginalis did not show this trend (Average percent herbivory leaf 1:0.145, leaf 3:0.076) (figure 3). Absolute herbivory was not significant between H. monteverdensis and H. tortuosa (Fisher's PLSD, p = 0.2451) but was significant between H. monteverdensis and H. vaginalis (Fisher's PLSD, p < 0.0001). Absolute herbivory also differed significantly between H. tortuosa and H. vaginalis (Fisher's PLSD, p < 0.0001) (figure 2). The simple regression between altitude and percent herbivory was not significant
for H. monteverdensis (simple regressio n, p = 0.6663) (figure 5). H. tortuosa did demonstrate a positive relationship between altitude and percent herbivory (simple regression, p = 0.0272) (figures 6). Percent herbivory in H. vaginalis did not show a significant relationship with altitude (simp le regression, p = 0.6445) (figure 7). Altitude and percent herbivory in the oldest leaves of H. tortuosa were positively correlated (simple regression, p < 0.0001) (figure 8). The chi square analyses did not show significant differences between the patterns of herbivory between species. There was only one pattern of herbivory (wcl, see table 1 and figure 1) that had a significant critical value (X 2 critical value = 9.32805). The Morisita Horn Indices, also showed a wide range of overlap between herb ivory patterns for all species where their altitudinal ranges overlapped (Morisita Horn, H. monteverdensis: H. tortuosa C MH = 0.98551616; H. tortuosa: H. vaginalis C MH = 0.96339667; H. monteverdensis: H. vaginalis C MH = 1.51854594). A graph of the percent of individuals in each species affected by the different patterns of herbivory (figure 7) showed that H. monteverdensis and H. tortuosa demonstrated similar types of herbivory with similar frequencies. H. vaginalis su ffered such little herbivory that all patterns occurred infrequently. Discussion The Cordillera de Tilarn contributes to the cool, misty climate of Monteverde. Descending into San Luis the climate becomes drier and hotter (Haber 2000). Higher elevations thus suffer less desiccation during the dry season than the lower lying valley of San Luis, which begins earlier at lower elevations. Hispine beetle populations are greater during the wet season when more leaves are produced (Strong 1977a). H. monteverdensis is a high elevation species and may have the highest percent of herbivory because the habitat is wetter for a longer part of the year, making conditions suitable for hispine beetles and their hosts longer. If older leaves were produced close st to or during the wet season in H. monteverdensis and H. tortuosa it could explain why the older leaves in these species suffered higher percent herbivory. This would also explain why the oldest leaves in H. tortuosa had higher percent herbivory at highe r elevations. H. vaginalis did not show the same trend (mean percent herbivory in leaf 1 = 0.413, leaf 3 = 0.299), but it is possible that H. vaginalis would show slightly higher percent herbivory in newest leaves if leaf production increases before the on set of wet season since the increase in food availability could allow hispine populations to increase. Also, if H. vaginalis puts out new leaves more frequently than the other two species, then its oldest two leaves may be dry season leaves. This would dec rease herbivory for the leaves sampled in H. vaginalis. The difference in percent herbivory between H. monteverdensis and H. tortuosa is a factor of overall leaf size. H. tortuosa suffered similar absolute herbivory to H. monteverdensis (mean herbivory in H. tortuosa = 21.699, H. monteverdensis = 25.060) (figure 4). The larger leaves of H. tortuosa compared to H. monteverdensis (Berry et al. 1991) inflate the percent herbivory in H. monteverdensis. This could have important effects on the fitness of H. mont everdensis.
Leaves off H. monteverdensis and H. tortuosa are larger and have different vegetative characteristics than H. vaginalis. If new leaves in H. monteverdensis and H. tortuosa take longer for to unfurl than the small cannoid leaves of H. vaginalis then they would provide edible leaf material longer for the hispine beetles. H. vaginalis may be an acceptable host plant for hispines in terms of palatability, but not provide domatia long enough to be inhabited by and be host to hispines. This vegetati ve characteristic may or may not have evolved as a response to herbivory. Although leaves that unfurl quickly would suffer less damage, there are certainly many other factors that could have played the dominant role in the evolution of cannoid vegetation. Heliconia vaginalis occurs at the lowest elevations sampled. These plants are subject to longer dry season conditions, which could mean lower hispine populations and explain the low herbivory in this species. Besides smaller leaves and cannoid vegetation, another possible explanation for low levels of herbivory could be differences in leaf chemistry such as even lower nitrogen content or secondary chemicals that limit the hispine herbivory. This is unlikely since hispines feed on many species i n Heliconiaceae and other families in Zingiberales (Strong 1977a). I expect that the lower herbivory is more a function of time as a rolled leaf and differences in climate. Leaves produced in all species of Heliconia during the dry season probably suffer l ess herbivory than wet season leaves due to a lower population of hispines. Wet season comparisons could determine whether climate or leaf phenology is the major contributor to herbivory of this species. Based on observations in the field (no data collecte d), I did not find that leaves o lder than the three collected in H. vaginalis had higher herbivory. Instead, these leaves also appeared to have similar herbivory to the leaves sampled. This leads me to believe that leaf phenology or other non climatic fact ors are responsible for the low herbivory in this species. Studies could easily be done to determine how leaves are produced in these Heliconia species, which would help determine if leaves remain rolled for significantly different amounts of times between species. Some of the trends seen in herbivory in this study are likely due to smaller population sizes of hispines during the dry season. I would expect herbivory in all species of Heliconia to increase during wet season months when populations of hispine s are high. I only found two hispine beetles during the collection period and did not find turnover between patterns of herbivory between the three species of Heliconia, but significantly lower amounts of herbivory in H. vaginalis. This indicates that hisp ine beetles are not specializing between H. tortuosa and H. monteverdensis, but may or may not be avoiding H. vaginalis. Strong (1977a, b) reports three hispine species for the Pacific north of Costa Rica (Cephalol eia vicina, Chephaloleia puncticollis, and Chelobasis bicolor), although exhaustive sampling was not done. I saw evidence of herbivory by all three of these species. I also found some patterns that did not match those described by Strong (1977a, b). These patterns appeared to be hispine "strip mining" and could be other species of hispine. Johnson (2000) found five different morphospecies of hispines in the San Luis valley when examining hispine herbivory between Marantaceae, Costaceae, and Heliconiaceae. I believe there are several species of h ispines that have not been identified in this area. Further research could determine the population and distribution of hispines in the Monteverde area and their patterns of
herbivory. Specialized herbivores like hispines play important ecological roles in tropical forests yet are very poorly known. There is ample opportunity for future research in hispine beetles. A better knowledge of species present in this area and the patterns that each species leaves would be a helpful base for other research projects Following year long trends of herbivory between Heliconiaceae and other families hi the Zingiberales Order would also provide a better understanding of the ecological role these beetles play in the Monteverde area. Acknowledgements I would like to thank Alan Masters and Mauricio Garcia for their help developing and completing this project, Bill Haber and Willow Zuchowski for their help with species identification, Karen Masters, Andrew Rodstrom, and Rick Smith for all of their help a nd support with statistics and completing this paper. I would also like to tha nk the Ecolodge and Manuel Leit n in San Luis for the use of their property as well as the Estacin Biolgica de Monteverde for the use of their facilities and property. Literat ure Cited AuerBach, MJ. And Strong, D.R. 1981. Nutritional Ecology of Heliconia Herbivores: Experiments with Plant Fertilization and Alternate Hosts. Ecological Monographs 51:63 84. Berrd, Fred and Kress, John. 1991. Heliconia, an Identification Guide. Smi thsonian Institution Press. Coley, P.D. and Barone, J.A. 1996. Herbivory and Plant Defenses in Tropical Forests. Ann. Rev. Ecol. Syst. 27:305 335. Haber, William A. 1990. Lista Provisional de las Plantas de Monteverde, Costa Rica. Brenesia34:63 120. Haber, William A. 2000. Chapter 3 Pp 42 43. In Nalini M. Na dkarni and Nathan T. Wheelwright (Ed). Monteverde Ecology and Conservation of a Tropical Cloud Forest. Oxford University Press, New York. Futuyma Douglas J. 1997. In: Meffe, G. and C. Ronald Corr oll (Eds.). Principles of Conservation Biology, 2 nd Ed. Sinauer Press: Mass. Janzen, Daniel H. 1983. Chapter 11 Pp 163 182. Food Webs: Who Eats What, Why, How, and with What Effects in a Tropical Forest? In D J Futuyma and M. Slatkin (Eds), Coevolution. Sinauer Associates, Sunderland, MA Johnson, Alissa. 2000. Hispinae Rolled leaf Herbivory in Marantaceae, Costaceae, and Heliconiaceae in Monteverde, Costa Rica. CIEE Student Research. McCoy, Earl. 1984. Colonization by Herbivores of Heliconia spp. Plants ( Zingiberales: Heliconiacae). Biotropica 16(1): 10 13.
Stiles, F.G. 1975. Ecology, Flowering Phenology, and Hummingbird Pollination of Some Costa Rican Heliconia Species. Ecology 60(3): 285 301. Seifert, R.P. Neotropical Heliconia Insect Communities. Quarte rly Review of Biology. 57 (1): 1 28. Strong, D.R. 1977. Insect Species Richness: Hispine Beetles of Heliconia Latispatha. Ecology 58(3): 573 582. B Strong, D.R. 1977. Rolled Leaf Hispine Beetles (Chrysomelidae) and their Zingiberales Host Plants in Middle America. Biotropica 9(3): 156 169.
Table 1. Description of the patterns of herbivory found in H. monteverdensis H. tortuosa and H. vaginalis from San Luis valley to the continental divide behind the Estacin Biolgica de Monteverde. Items in bold refer to patterns left by hispine beetles, other patterns may be caused by non hispine herbivores (Based on Strong 1977 a, b). Pattern (see Figure 1 ) Description of Herbivory Pattern Probable Hispine Species wb mark Light brown scars not on leaf veins. Left from Chelobasis bicolor (larvae) *Chelobasis perplexa (larvae) sp. reported only for Cephaloleia vicina (larvae ) wb scar Area of leaf surface with a burned appearance. In some cases caused by dying leaf tissue around areas of herbivory. Could result from damage from several spp. wcl Thin rectangular lines often several between major veins or stacked on top of each other. Left Chelobasis bicolor (adult) c veins scars running in shortsegments on veins. Chelobasis bicolor (adult) r holes Round holes found anywhere on the leaf. h holes/m Horizontal rows of holes or marks across the leaf surface. sq holes Square or rectangular holes. wb sharp Similar to wb marks but smaller small and scratch like. Cephaloleia puncticollis (adult) vert lines Vertical lines of scars along leaf edges. Chelobasis bicolor (larvae) *Chelobasis perplexa (larvae) sp. reported only for Carribean coast pinholes Tiny dots running in parallel lines along the leaf surface. Adult hispine many spp. c margin Chewed marks and holes along the leaf margin. T ypically only one margin for each leaf. Chelobasis vicina (adult) Cephaloleia vicina (adult) c m vein Light brown scars along the midvein of a leaf. Unidentified sm veins Long smooth light brown streaks along veins that were not always in stacks. Unidentified
Figure 1. Visual demonstration of the patterns of herbivory seen in the field among H. tortuosa and H. monteverdensis and H. vaginalis between the San Luis valley (1000m elevation) and Continental Divide behind the Estacin Biolgica de Monteverde (1815m).
Figure 2. Drawing of the two forms of vegetative characteristics. The first is musoid vegetation seen in H. tortuosa and H. monteverdensis The second is cannoid vegetation seen in H. vaginalis Figure 3. Herbivory on three species of Pacific slope Heliconia from Monteverde, Costa Rica split by leaf age. Percent herbivory is measured as the (area of leaf missing) / (leaf area) 100. Oldest leaves in H. monteverdensis and H. tortuosa had significantly high er herbivory than H. monteverdensis had higher percent herbivory than H. tortuosa H. vaginalis H. tortuosa had higher herbivory than H. vaginalis (Fis H. tortuosa H.m = H. monteverdensis and H.v = H. vaginalis 1 = newest leaf, 2 = second leaf, 3 =
oldest leaf. Std. Dev. H.T (1) = 0.049, mean = 0.423. Std. Dev. H.T (2) = 0.067 mean = 0.575. Std. Dev. H.t (3) = 0.100 me an = 0.728. Std. Dev. H.m (3) = 0.277 mean = 3.277. Std. Dev. H.v (1) = 0.145 mean = 0.413. Std. Dev. H.v (2) = 0.079 mean = 0.248. Std.Dev. H.v (3) = 0.076 mean = 0.299. Figure 4. Herbivory on three species of Pacific slope Heliconia from Monteverde, Costa Rica. Herbivory is measured as the absolute area of leaf damaged (cm^ 8 ). H.t = H. tortuosa H.m = H. monteverdensis and H.v = H. vaginalis H. monteverdensis did not have significantly higher herbivory than H. tortuosa H monteverdensis and H. tortuosa had significantly higher herbivory than H. vaginalis 34.8, mean = 25.060. Std. Dev. H.t = 33.4, mean = 21.649. Std. Dev. H.v = 4.30, mean = 1.998.