FLOWERING PLANT REPRODUCTIVE BIOLOGY Contributed by: Brenda L. Young, Department of Natural Sciences, Daemen College, Amherst, NY 14226 Read before lab: the appropriate text chapter or lab manual section. Preparation for Lab * What does a pollen grain contain? Is "pollen" just another word for "sperm cell"? What is the role of pollen in reproduction? * In what flower parts is pollen produced? How do the sperm and egg nuclei get together in flowering plants? * What is pollination? How does it differ from fertilization? * Why is pollination usually necessary for successful reproduction of flowering plants? * Flowering plants, of course, are sessile (fixed in one place). Unlike animals and some lower plants, they cannot seek out mates to transfer gametes. What are some specific ways by which pollen is transferred from one plant to another? Most flowers have male and female parts in close proximity. This suggests that sexual reproduction is probably a pretty simple matter, and that most plants would probably reproduce primarily by self-fertilization. Although selfing does happen in some species, most flowering plants have adaptations that help to ensure that they are ontcrossed, or fertilized by other individuals. * What are some of the possible advantages of selfing? of outcrossing? Research goals for each Lab group 1. Study the flower structure of your assigned species. (Identify petals, sepals, stamens, pistil(s).) Summarize this as a drawing. What features of the flowers (e.g. color, size, odor, food rewards) might be important in attracting potential pollinators? Would these characteristics tend to promote outcrossing? 2. Identify the flower visitors by at least an hour of observation under favorable conditions (i.e. reasonably sunny, warm weather). Be quantitative - count the number of pollinators per hour, and determine the percentage of each type. Use the drawings and descriptions at the end of the lab to identify major types of visitor. Insect collecting materials will be available if you need a closer look at any of them. 3. Decide which flower visitors really could be pollinators - which types would probably carry pollen from the stamens to the pistil? 4. Test one hypothesis about a factor affecting the rate of flower visitation. (Remember, a hypothesis is what you think will happen, and why.) Possible factors to examine are: cloudy vs. sunny weather; warm vs. cool (don't forget to check temperature); edge of forest vs. interior; clumped plants vs. individuals; many open flowers per plant vs. few; presence vs. absence of other flowering species; flower color (some species have variations in color) Data collection Watch a known number of flowers for a known amount of time (15 or 20 min). Record the number of insect visitors of each type. Repeat at least 5 times. Calculate the visitation rate in number of insects per flower per hour. For item 4 above, repeat the 15-min observation period at least 5 times for each set of conditions. Do a statistical test (Which one? If you're not sure, consult with the instructor or TA.) to determine whether visitation rates really do differ significantly. Presentation of results Present these results as a group poster. There will be some time in next week's lab to organize this, but decide on who will do what (making drawing, doing statistics, etc.) in advance. Your poster should include the following information: names of authors, descriptive title, your hypothesis (indicate why you thought that it was likely to be correct), methods used to test the hypothesis, results (include: drawing of the flower, description of characteristics attracting visitors, list of visitors with probable pollinators indicated, table or figure showing number of visitors or pollinators under contrasting conditions, and results of the statistical test), and your conclusion. NOTE: Descriptions and illustrations of common pollinators follow.