SEEING RED: Daphnia and Hemoglobin A MIDDLE SCHOOL CURRICULUM UNIT MODELING ECOLOGICAL INTERACTIONS AND THE SIGNIFIGANCE OF ADAPTATIONS Anne Deken Ste. Genevieve du Bois School Warson Woods, Missouri 2005 Summer Research Fellowship for Science Teachers Sponsored by Howard Hughes Medical Institute Washington University Science Outreach SEEING RED: DAPHNIA AND HEMOGLOBIN Teacher Manual INTRODUCTION The freshwater zooplankton Daphnia plays an important role in aquatic food chains and has been used as an ecological model for many years. Daphnia is also used in other scientific disciplines including chemistry, physiology, and genetics. Daphnia is useful in many disciplines because of its physical characteristics, such as a transparent outer covering, sensitivity to toxins, and quick development of adaptations. Through this unit, middle school students are able to study this ecological model organism from a variety of different perspectives. They will examine this organism’s phenotypic characteristics, observe Daphnia’s response to an environmental stress (low oxygen), and investigate the complex role of an invasive Daphnia species in an aquatic food chain. CURRICULUM OVERVIEW The activities in this unit are separated into the following three sections: Part 1 – Observing Daphnia Characteristics and Behavior (teacher manual p. 8-11, student manual p. 1-6) Part 2 – Seeing Red: Daphnia and Hemoglobin (teacher manual p. 12-13, student manual p. 7-13) Part 3 – An Invasive Species of Daphnia (teacher manual p. 14-15, student manual p. 14-15) Students begin by looking at the physical features of Daphnia and understand how these characteristics allow them to survive in their environment. They will then investigate Daphnia’s ecological interactions and begin to understand why they are useful for scientific study. Students will see how Daphnia turn red under low oxygen conditions through an increased production of hemoglobin, and thus serves as an ideal model to study the physiological effects of environmental stress. They will also discuss how an invasive species is able to populate a foreign area. Using the invasive species Daphnia lumholtzi, students will predict the type of adaptation that has allowed it to invade North America. Finally, students will also discuss what impacts an invasive species can have on an ecosystem. Through the study of Daphnia, students will understand how adaptations allow an organism to be successful in a particular environment and the importance of balance between organisms in an aquatic ecosystem. Seeing Red: Daphnia and Hemoglobin – Teacher Manual 1 FIT TO STANDARDS Based on the National Science Education Standards for middle school life science students, this unit focuses on the content areas of population and ecology along with diversity and adaptations. This unit will meet the following National Science Content Standards: o Populations of organisms can be categorized by the function they serve in an ecosystem. Plants and some microorganisms are producers--they make their own food. All animals, including humans, are consumers, which obtain food by eating other organisms. Decomposers, primarily bacteria and fungi, are consumers that use waste materials and dead organisms for food. Food webs identify the relationships among producers, consumers, and decomposers in an ecosystem. o The number of organisms an ecosystem can support depends on the resources available and abiotic factors, such as quantity of light and water, range of temperatures, and soil composition. Given adequate biotic and abiotic resources and no disease or predators, populations (including humans) increase at rapid rates. Lack of resources and other factors, such as predation and climate, limit the growth of populations in specific niches in the ecosystem. o Biological evolution accounts for the diversity of species developed through gradual processes over many generations. Species acquire many of their unique characteristics through biological adaptation, which involves the selection of naturally occurring variations in populations. Biological adaptations include changes in structures, behaviors, or physiology that enhance survival and reproductive success in a particular environment. It will also meet the following Missouri Assessment Program learning objectives: o Identify populations within a community that are in competition with one another for resources. o Predict the possible effects of changes in the number and types of organisms in an ecosystem on the population of other organisms within that ecosystem. o Relate examples of adaptations within a species to its ability to survive in a specific environment. o Predict how certain adaptations may offer a survival advantage to an organism in a particular environment. Seeing Red: Daphnia and Hemoglobin – Teacher Manual 2 BACKGROUND INFORMATION ON DAPHNIA Physical description Daphnia, commonly called water fleas, are a freshwater zooplankton found in ponds and lakes all over the world. Daphnia received the name water flea due to their jerky swimming motions. Some types of Daphnia can be seen with the human eye, while others must be identified with a microscope. Depending on the species they can range in size from 0.5mm to 1cm. Their outer covering, or carapace, is transparent, so many internal organs can be seen, especially the beating heart. On the head there is a compound eye and a pair of antennae, which are used for swimming. Females are usually larger than males and have a brood chamber under their outer carapace where eggs are carried. Food chain relationships Daphnia are an extremely important part of aquatic food chains. They eat primary producers such as algae, yeast, and bacteria. Daphnia are the prey of tadpoles, salamanders, newts, aquatic insects, and many types of small fish. Fluctuations in Daphnia populations can cause algae overgrowth or even a drastic drop in fish populations. Through the food chain, larger animals caught or eaten by humans can be affected by large changes in Daphnia populations. Reproduction The Daphnia lifespan is approximately eight weeks. Daphnia reach maturity quickly, within five to ten days, and produce multiple offspring each cycle. Daphnia can reproduce both asexually and sexually. During times of plentiful food, females reproduce asexually to produce clones. When food is scarce, Daphnia reproduce sexually in order to produce genetic variation and increase the chance of species survival. During harsh weather conditions, resting eggs are produced. These eggs have a tough outer coating, which can withstand time, heat, drying, and cold temperatures. Reactions to environmental stress Daphnia have a number of natural responses to environmental stress, and due to these qualities are often used as an indicator of watershed health. The term “watershed” refers to all the land and water within a drainage area. Daphnia can detect the presence of kairomones, chemicals released by predators. In response to these chemicals Daphnia can grow larger head and tail spines or develop through a shorter gestation period. They are extremely sensitive to changes in water toxicity. This can be monitored through changes in heartbeat or Daphnia death. When Daphnia are exposed to hypoxic (low oxygen) conditions, they can increase hemoglobin production. Due to their clear outer carapace, they will appear red when hemoglobin production has increased. Species Three species of Daphnia will be used in this unit. Daphnia magna is very rarely found in the wild and is often sold in pet stores as a food source. They can become as large as 1/5 inch and are often less tolerant of environmental changes. Daphnia pulex is very similar to D. magna, but is usually smaller. They are the most common species found across temperate North America. Daphnia lumholtzi is an invasive species originally from Seeing Red: Daphnia and Hemoglobin – Teacher Manual 3 Africa and Asia, which have extremely large head and tail spines. D. lumholtzi is currently invading watersheds in the United States. Daphnia magna Daphnia pulex Daphnia lumholtzi Classroom advantages Daphnia can be found in most freshwater lakes and ponds. They are also inexpensive to purchase and cultures are easy to maintain. One culture can easily produce enough individuals for entire class viewing. Organisms can easily be seen through a dissecting or compound microscope. The resting eggs can be kept for months to years. Seeing Red: Daphnia and Hemoglobin – Teacher Manual 4 DAPHNIA CULTURING PROTOCOL 1. Ordering Daphnia Carolina Biological Supply, http://www.carolina.com Daphnia magna • Catalog #14-2326 Daphnia magna Culture Kit (live) $31.50- includes culture water, plastic aquarium, dried algae powder, and live Daphnia • Catalog #14-2330 Daphnia magna (live) $6.95- Culture for 30 students Daphnia pulex • Catalog #14-2304 Daphnia pulex Culture Kit (live) $26.95- includes culture water, plastic aquarium, food, and live Daphnia • Catalog #14-2314 Daphnia pulex (live) $6.75- Culture for 30 students • Catalog #14-2302 Daphnia pulex (resting eggs) $5.50 • Catalog #14-2316 Daphnia food $5.30 2. Preparing culture water Regardless of the type of culture water used, allow at least 24 hours for water to settle and temperature to stabilize before introducing live Daphnia. • Carolina Biological Supply kits - culture water is provided. Follow directions included in culture kit. • Pond water - Pond water should contain algae, but should not be too thick for organisms to move and obtain oxygen. • Spring water - Fill container and add food or nutrients.