University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Faculty Publications in the Biological Sciences Papers in the Biological Sciences 11-1977 The Extrafloral Nectaries of Ipomoea carnea (Convolvulaceae) Kathleen H. Keeler University of Nebraska-Lincoln, [email protected] Follow this and additional works at: https://digitalcommons.unl.edu/bioscifacpub Part of the Botany Commons Keeler, Kathleen H., "The Extrafloral Nectaries of Ipomoea carnea (Convolvulaceae)" (1977). Faculty Publications in the Biological Sciences. 275. https://digitalcommons.unl.edu/bioscifacpub/275 This Article is brought to you for free and open access by the Papers in the Biological Sciences at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Faculty Publications in the Biological Sciences by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Keeler in American Journal of Botany (November-Decemeber 1977) 64(10). Copyright 1977, Botanical Society of America. Used by permission. Amer. J. Bot. 64(10): 1182-1188. 1977. THE EXTRAFLORAL NECTARIES OF IPOMOEA CARNEA (CONVOLVULACEAE)l KATHLEEN H. KEELER School of Life Sciences, University of Nebraska, Lincoln 685~8 A B S T R A C T lpomoea carnea (Convolvulaceae) possesses two types of extrafloral nectaries, located on the petiole and on the pedicel. These secrete a complex nectar containing sugars and amino acids. The insects attracted to the extrafloral nectaries are predominantly ants and they are relatively abundant throughout the year. A number of incidents of plant defense as a result of the presence of extrafloral nectary visitors at the extrafloral nectaries of I. carnea were observed and are consistent with the ant-guard theory of the function of extrafloral nectaries. RECENTLY, increased attention has been given to Elias, 1972; Carroll, 1974; Keeler, 1975b). Re- the question of the function of extrafloral nec- cent work has for the most part supported the taries and particularly to the hypothesis that the idea that the function of extrafloral nectaries is ecological function of these nectaries is to attract to attract insects, especially ants, which defend ants which protect the plant (Elias, 1972; Elias the plant from herbivores. Elias' morphological and Gelband, 1975; Elias, Rozich, and New- work on Pithecellobium macradenium (Legu- combe, 1975; Bentley, 1976; 1977). In this minosae) (1972) and Turnera ulmifolia (Tur- paper the activity of the extrafloral nectaries of neraceae) (Elias et al., 1975) indicated that the a tropical dry forest vine, Ipomoea carnea (Con- extrafloral nectaries of these two plants are very volvulaceae), is described and evidence is given complex structures with nectar production cycles that supports the contention that extrafloral nec- correlated with the times herbivores are expected taries function to attract insects which are pro- to be the most active, which would support their tective to the plant. role in an ant-plant association. Extrafloral nectaries are glands which secrete Elias and Gelband (1975) also found that the an aqueous solution of sugar and other chemicals four extrafloral nectary systems of Campsis rad- (Baker and Baker, 1973) that can be found on icans (Bignoniaceae) are responsible for attract- aboveground parts of plants outside the flower. ing ants and that in the presence of abundant ants, They occur in a variety of monocotyledonous and there is a decrease in the frequency of flower rob- dicotyledonous families (Zimmermann, 1932; bing.2 Bentley (1976) found that a significant Schnell, Cusset, and Quenum, 1963). The mor- amount of the variance in the percentage of buds phology and chemical composition of extrafloral that matured on Bixa oreliana (Bixaceae) was nectaries have been analysed in a number of cases. explained by a linear regression of the abundance Nevertheless, the function of extrafloral nectar- of ants at the site. She (1977) also showed that ies is not well established. when artificial extrafloral nectaries were created In the case of ant-inhabited acacias, extrafloral on common bean seedlings (Phaseolus vulgaris), nectaries have been shown to provide the major by placing karo syrup on the leaves, the treated source of sugar for the resident ant population plants weighed significantly more at the end of (Janzen, 1966, 1967; Brown, 1960). However, the experiment than did the control plants in the where the insects which visit extrafloral nectaries rainy season. On the other hand, Lukefahr and do not reside on the plant, the story is less clear others (1960; 1965; 1966) have shown that and has been debated for over a century (see strains of nectariless cotton, derived from crosses of Gossypium tomentosum, had significantly 1 Received for publication 10 February 1977; revision lower infestations of a number of important pest accepted 8 April 1977. species, under a range of field and cage condi- I wish to thank H. G. Baker, I. Baker, P. A. Opler than did and Y. B. Linhart for their advice and encouragement. I tions, extrafloral nectary-bearing cotton am grateful to the help of the Costa Rican staff of the strains. Organization for Tropical Studies (O.T.S.), especially J. In this paper observations and experiments on Campabadal. T. S. Elias, R. B. Kaul and R. W. Shuel the extrafloral nectaries of Ipomoea carnea Jacq. made helpful comments on the manuscript. This research in Costa Rica was funded in part by NSF GB-237256, NSF GB- (Convolvulaceae) are reported 255924, NIH GM-367 and an O.T.S. student subsistence grant. This work was done in partial fulfillment of the 2Van der Pijl (1954) observed the presence of ants to Ph.D. degree, Department of Genetics, University of disturb and displace flower-robbing Xylocopa spp. bees California, Berkeley. in Java. 1182 November-December, 1977] KEELER-EXTRAFLORAL NECTARlES OF IPOMOEA 1183 I S .: r # _ 'Gi, : ,~~~~~~~~~~~~~~~~~ _-g .....r 3if Fig.~~*_1, 2. .:Cmoou bretes takin exrfoa neta fro eioanetr of Ipomoea.........cre. X 1.....;|S 2~~.Acuulto of neca at peiela exrfoa netre of I. carnea. .X. which support the work of Bentley, Elias, and season, because, as the dry season proceeds,Ipo- their predecessorsin suggesting that the extra- moea carnea loses its leaves. Flowering is con- floralnectaries attract protective ants to the plant. fined to the dry season, so the pedicellar ex- trafloral nectaries function only at that time. MATERIALS AND METHODS-Ipomoea carnea Consequently,there is little overlap between the Jacq. [syn. I. fistulosa, (Austin, in press)] is a period of petiolar and pedicellarextrafloral nec- twining woody vine which is sufficiently robust tary activity. to supportitself to a height of two meters. It is The function of floral nectaries is well estab- found on both the Atlantic and Pacific coasts of lished to be part of the process of pollination,so Mexico south to Argentina (Matuda, 1964; the activityof the floral nectariesof I. carnea will O'Donell, 1952). The populationstudied was in not be considered here. However, it should be GuanacasteProvince, Costa Rica, near the Or- pointed out that althoughthe plant is a melitto- ganizationfor Tropical Studies'Palo Verde field philous obligate outcrosser (Keeler, 1975a, b), station. This area is in the tropical dry forest the flower-visitinginsects are entirely different zone of Holdridge (1967), receiving 1,800 mm from the insects which visit the extrafloralnec- of rainfall a year, but having a distinct dry sea- taries. son betweenDecember and May. The chemical constitutentsof the nectars were determinedby Irene Baker using spot tests and Ipomoea carnea was chosen for study because chromatography(Keeler, 1975b). The frequency of the abundant nectar it produced. It was and distributionof the extrafloralnectary visitors thought that the function of nectaries would be were studied in a series of surveysin which were more easily demonstratedin a plant which pro- recordedthe insects visiting the nectaries of 500 duced copious quantitiesof nectar. In addition, or 1,000 branches. Two different branches per 1. carnea was abundantnear the Palo Verde field plant were observed whenever possible. Two station and consequently more accessible than such surveys were made in the rainy season many other extrafloralnectar producing plants. (October and November, 1973) and one in the I. carnea has two extrafloralnectary systems. dry season (January,1974), in the pasturestudy An extrafloralnectary is located on either side of areaat Palo Verde. the distal end of the petiole. A ring of five Insect specimens were identified as follows: extrafloralnectaries occurs at the base of each pseudomyrmecineants by D. H. Janzen, Dept. flower around the pedicel. The petiolar extra- of Zoology, University of Michigan; other ants floral nectaries are most active during the rainy by R. R. Snelling,Los Angeles County Museum; 1184 AMERICAN JOURNAL OF BOTANY [Vol. 64 TABLE 1. Free sugars in Ipomoea carnea nectarsa TABLE 2. Amino acids in Ipomoea carnea nectarsa Nectar Extrafloral Floral Nectar Petiolar Pedicellar Extrafloral Floral Amino acid Petiolar Pedicellar Sucrose 33 8b 35.8 54.8 Glucose 32.9 33.1 29.1 Alanine 0.0062a 0 0.076 Fructose 24.2 29.1 16.1 Arginine 0.0291 0.0342 0.131 Melibiose 3.9 trace 0 Asparagine 0.0012 0.0616 0.057 Raffinose 5.9 0 0 Glutamic acid 0.0029 0.0027 0.001 a Determined by chromatography using solvent of Glycine 0 0 0.006 Smith (1969), 316 and stain of Saini (1966). Isoleucine 0.0069 0 0 Serine 0.0518 0.0383 0 b Percent of total sugar. a Determined by chromatography of dansylated amino acids and fluorometry. Method of I. Baker (unpubl.). larval lepidoptera by T. Davies, California Acad- Determined by I. Baker. emy of Sciences, San Francisco; and other in- b ,m/ml. sects by P. A. Opler, Office of Endangered Spe- cies, U.S. Fish and Wildlife Service, Washington, D.C. much longer than that of petiolar extrafloral nec- taries, which increased the difference in total nec- RESULTs-Extrafloral nectaries-The petiolar tar production compared to the rainy season.