Slide 1

Clinal Study of Heliconia caribaea L. (Heliconiaceae) Floral-Bract Phytotelms: pH and Biosurvey, Including Bioassays for Watermolds and Inquiline-feeding Experiments Ruth Short Bull Fort Berthold Community College New Town, North Dakota Abstract: Clinal-patterns in pH and species occurrence and abundance were detected in Heliconia caribaea phytotelmic floral bracts: (1) The soil in which the plants was growing and the fluid both in the stalk of the inflorescence and closed apical bracts all had a pH of 6. Thereafter, bract- fluid pH increased progressively to 8 in open-subtending bracts, decreasing to 7.6 in the bottom-most ones. (2) The greatest number of mosquito larvae occurred in the second opened distally-placed bract. Thereafter, numbers decreased progressively. The oldest, proximal bracts had no mosquito larvae. This progressively declining-distribution in mosquito larvae suggests that site-recruitment for egg deposition and, or larval survivorship decreased with increasing bract age (senescence). (3) Copepod densities increased progressively down the inflorescence with basal bracts having estimates in excess of 200 individuals/ mL of bract-liquid. The converse clinal-distribution in mosquitoes and copepods suggests that the later may be feeding on the former. And (4) chironomid midge larvae were detected in the middle bracts. No algae were observed in any of the bract water-samples and radish-seed bioassays for watermolds and aquatic fungi yielded few positives - 16 out of 225 bract samples. The same watermold was detected in all positive-assays - Saprolegnia sp. Controlled in vitro experiments revealed that both chironomid midge larvae and the copepods fed on Saprolegnia mycelia and oospores. Based on their sheer numbers and results of in vitro experiments, it is suggested that copepods play an important, if not pivotal, role in controlling watermold growth in the floral bract of H. caribaea and, as such, copepods may be determining the species-structure and ecology of the H. caribaea phytotelmic community. I. Background: Heliconias are native to Central and South America. The floral-bracts of many Heliconia are phytotelms (Fig. 1 and 2), that is they hold water and serve as habitats for a varied-community of aquatic organism. Bracts open sequentially and basipetally from the bottom of the inflorescence to the top. II.Initial Observations Mosquito larvae and copepods (Figs. 3 and 4) appear to predominate in the phytotelmic-bracts of Heliconia caribaea. Cursory inspection of the floral-bracts indicates the apparent absence of algae, aquatic fungi and watermolds. Fig. 1. Inflorescence of Heliconia caribaea floral bracts. (Note: unopened apical- bracts.) Fig. 2. Floral-bract/ phytotelm of Heliconia caribea. (Note: Liquid, spent deliquescent florets, and recently bloomed, white floret. Fig. 3. Mosquito larva common inquiline of Heliconia caribaea floral-bract. III.Research Questions: What are the inquiline-associates of Heliconia caribaea and what is the relative abundance of each particularly in regard to diptera larvae and copepods? Does the phytotelmic-biodiversity (species richness) and abundance vary as a function of bract-age? And, if so, what physiochemical parameters are contributing to this? If aquatic fungi, and watermolds are absence from the Heliconia caribaea phytotelmic community, why is this so? IV.Hypotheses: The species diversity and abundance of Heliconia caribaea bracts varies as a function of age. pH of the fluid of the bracts varies with age. Invertebrate-associates of Heliconia caribaea bracts feed on aquatic fungi and watermolds. V.Experimental Design: pH of bract-fluid Biodiversity survey of Heliconia caribaea: a.Samples from 4 colonies, 34 inflorescences, and 225 bracts (n = 225). b. Numbers or estimates of taxa (e.g., mosquito, and chronomid midge larvae, and copepods) fungi. Radish-seed bioassays of bract-liquid for watermolds in vitro-feeding experiments with chironomid midge larvae and copepods. VI.Results (cont.) - Biodiversity survey. Of the macro- invertebrates assessed from 225 Heliconia caribaea bract the greatest number of individuals were mosquitoes, including larvae and pupae (1075 individuals), followed by chironomid midge larvae (142), nematodes (91), and rat-tail maggots (37) (Fig. 5.). However, when micro-invertebrates are included, by far the greatest numbers were from copepods, at times having estimated-densities in excess of 200 individuals/mL. Fig. 6. Heliconia caribaea pH of floral bracts (n = 10; s.e). Note: Zero (0) on the X-axis indicates the pH was 6 for each of the following: (1) fluid in unopened apical bracts, (2) internal fluid of the inflorescence stalk, and (3) the soil. X-axis values 1-10 are for subtending opened bracts in sequence descending the inflorescence. Fig. 5. Biodiversity survey of macroinvertebrates of 225 Heliconia caribaea floral bracts. Note: Data is given as total number of individual encountered. Fig. 4. Copepod with attached eggs abundant inquiline of Heliconia caribaea floral-bract. VI. Results (cont.) - Clinal variations. Clinal variations in pH, mosquito larval number, and copepod density moving down the Heliconia caribeae inflorescence were detected: The internal pH of the Heliconia caribaea inflorescence stalk, as well as that of the fluid in unopened, apical bracts, was 6.0. Soil pH was also 6. Thereafter, the pH increased progressively to plateau at 8.0 in subtending, opened bracts, only to decline to 7.6 in the oldest basal bracts (Fig. 6). VI. Results (cont.) - Watermold and aquatic fungi bioassays. Radish-seed bioassays of 225 bract-water samples yielded 16 positives (i.e., 7%) all for the watermold Saprolegnia sp. (Fig. 8). No aquatic fungi were detected. After the first apically placed opened bract, the average number of mosquito larvae, including pupae, decreased progressively to 0 moving down the inflorescence (Fig. 6). This was in contrast to copepod-densities which increased descending the inflorescence (Fig. 7). Fig. 7. Clinal variations in Heliconia caribaea floral bracts: mosquito larvae number and copepod density as a function of bract placement/maturation. VI. Results (cont.) - Watermold feeding experiments. Both chironomid midge larvae and copepods obtained from H. caribaea bracts fed on in vitro cultures of Saprolegnia sp. (Fig. 9a ). Fig. 8a and b. The watermold Saprolegnia sp. detected in radish seed bioassays of Heliconia caribaea bract water samples. (Note: A. hyphae growing from radish seed and B. zoosporangia at the tips of most hyphae). Fig. 9a and b. Sporlegnia colony before (A) and after (B) being exposed to copepods. VII. Discussion - VIII. Literature Cited Bronstein, J.L. 1986. The origin of bract liquid in a neotropical Heliconia species. Biotropica 18: 111-114. Naeem, R.L. 1988. Predator-prey interactions and community structure: Chironomids, mosquitoes and copepods in Heliconia imbricata (Musaceae). Oecologia 77: 202-209. Richardson, B.A. and G.A. Hull. 2000. Insect colonisation in bracts of Heliconia caribaea in Puerto Rico. Ecological Entomology 25: 460-466. Richardson, B.A., C. Rogers, and M.J. Richardson. 2000. Nutrients, diversity, and community structure of two phytotelm systems in a lower montane forest, Puerto Rica. 2000. Ecological Entomology 25: 348-356. Schaper, S. 1999. Evaluation of Costa Rican copepods (Crustacea: Eudecapoda) for larval Aedes aegypti control with special reference to Mesocyclops thermocyclopoides. Journal of the American Mosquito Control Association 15: 510-559. Seifert, R.P. 1982. Neotropical Heliconia insect communities. Quarterly Review of Biology 57:1-28. IX.Acknowledgments NSF Research Experience for Faculty (REF) Program and the Wilson Botanical Garden and OTS Field Station at Las Cruces, Costa Rica. Special thanks to: Sofia Olivero-Lora, Universidad de Puerto Rico en Humacao, Alejandro Lopez-Araujo and Javier Lopez-Araujo, University of Miami at Coral Gables for their diligence and fellowship in contributing to this research. AB A B The findings reported herein collaborate in part and amplify on those of Richardson (see, following). Richardson et al. (2000) found that recently opened bracts of H. caribaea had a pH of 7.9 and that for lower bracts pH declined to 5.2. In the present study unopened bracts had a pH of 6 which gradually rose to pH 8 by the fourth subtending opened bract. Only to decline to 7.6 in the lowest basal bracts (Fig.6). Why bract pH rises to 8 and why these findings differ from Richardsons is not known. Bronstein (1986) found that water in the bracts of Heliconia imbricata is generated by internal active transport by plant. Preliminary findings indicate this is occurring in H. caribaea (Short Bull & Petersen, unpublished data). The inverse-clinal relationship between mosquito and copepod abundance along the inflorescence (Fig. 7), where one increases while the other decreases potential has interesting and testable implications for the community ecology of H. caribaea. This is because copepods have been demonstrated to be predators of mosquito larvae (e.g., Schaper, 1999). Copepods were not reported in the bracts of populations of H. caribaea in Puerto Rico (Richardson & Hull, 2000). Naeem (1988) reported on the predation of mosquito larvae by the larvae of a chironomid midge in H. imbicata. In this study chironomid midge larvae midges comprised a significant component of the H. caribaea inquiline fauna (Figure 5). The presence of both copepods and chironomid midge larvae in the phytotelms of H. caribaea, suggests that a predator-prey community structure may be in operation. Finally, the in vitro experiments demonstrated feeding of both copepods and chironomid midge larvae on the watermold Saprolegnia sp. (Fig. 9), helps to explain both the absence of aquatic fungi and the low occurrence of watermolds in the bracts of H. caribaea. Further, suggesting the potentially important role these invertebrates may be playing in regulating and structuring the phytotemic community ecology of Heliconia caribaea. Further investigation would be necessary to demonstrate whether this is so.