The Pollination Ecology of Solanum Rostratum (Solanaceae)

The pollination mechanisms and pollen vectors of Solanum rostratum have been examined by greenhouse experiments and field studies. Although the capacity for autogamy exists in this weedy annual, it rarely occurs because of two factors: (1) the morphology of the flower and (2) the foraging behavior of the various species of Bombus, the primary pollen vector in the regions studied. The percentages of geitonogamy and xenogamy are dependent on the flight pattern of the bees and the number of open flowers on a plant. CASUAL OBSERVATIONS made on a population of Solanum rostratum Dunal in early June, 1972, in Marshall County, Oklahoma, near the University of Oklahoma Biological Station, suggested that the plants were bumble bee pollinated. This study was undertaken to determine the vector or vectors of pollen transfer, the mechanism of reproduction, and the roles in reproduction, if any, of the large anther and of the projection of the style from the side of the blossom (enantiostyly). MATERIALS AND METHODS-During the summer of 1972 field studies were conducted on a single population of S. rostratum and its floral visitors in Marshall County, Oklahoma (Table 1). These studies were continued in the summer of 1973 on three populations in Cleveland County, Oklahoma, and on greenhouse transplants from two locations in Cleveland County and one in McClain County, Oklahoma. In addition, limited observations were made on two populations in Texas and one in Iowa as comparisons. Floral phenology and morphology were observed and related to pollination and reproduction of the plants. Data collected include time of floral opening and closing, time of anthesis, region of stigmatic receptivity, relative size and position of stamens, and position of the style. Two sets of experiments were conducted to determine the mode of reproduction: (1) Bags were placed over flowers that had been emasculated in bud, over single nontreated flowers, and 'Received for publication 17 July 1974. Acknowledgments: The author wishes to thank J. R. Estes for his valuable assistance throughout the course of this study and especially for his critical reading and suggestions on the manuscript. Sincere appreciation is also expressed to R. W. Thorp for his identifications of the insect visitors and Kathy Kaputska for her illustrations. Submitted in partial fulfillment of the requirements for the degree of Master of Science. 2 Present address: Department of Entomology, Kansas State University, Manhattan, Kansas 66506. over entire inflorescences; seed-set among the treatments was compared. (2) Hand-pollination experiments were undertaken in the greenhouse to examine possible differential fertility of the dimorphic anthers and to test the capability for autogamy, geitonogamy, and xenogamy. Pollen was transferred within a flower, between flowers of one plant, and between flowers of different plants. The results of pollination using the two types of anthers were maintained separately. Seed-set was determined from mature fruits and results compared with that obtained in the field. Pollen from both types of anthers was stained with lactophenol-analine blue and examined for fertility. Over 100 hr were spent observing and recording the frequency, periodicity, and behavior of insect visitation. Insect behavior was observed and recorded with a Mamiya-Sekor 35 mm camera or a Pentax 35 mm camera with a macro lens and with a Cinekodak Special 16 mm movie camera. The movie film was analyzed frame-by-frame with a Vanguard motion analyzer. Insects were collected, identified, and the position, quantity, and composition of pollen loads examined. Insects were tracked in the field (South Base, Lindsey Street, and Lake Thunderbird) over five days to estimate the potential for xenogamy and geitonogamy. Several experiments with fluorescent powder (d -3-5 pm) as a marker were conducted to monitor pollen dispersal: (1) The apices of the small anthers of ten open flowers of one plant (South Base) were marked at 0630 hr CDT; all open flowers in the population were collected in the evening and examined under a ChromatoVue UV viewing cabinet. (2) The apices of the large anthers of 11 open flowers on a greenhousegrown plant were also marked and the plant was placed within the Lake Thunderbird population and observed. All flowers visited by bees subseauent to visitation of the test Dlant were imme-