Lab Section: Name: Pre-lab Homework Lab 8: Community Interactions

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1 Lab Section: Name: Pre-lab Homework This lab deals with how different organisms interact within an area (community interactions). Prior to lab, answer the following questions to help you prepare for lab. It will be expect that you have read through the textbook s topic on Community Interactions. 1. The community of PCC includes all the people and all their interactions (students, staff, instructors, etc.). These interactions would concern social science. How does this differ from the biological definition of a community of organisms? Relate your answer to the number of species involved and the types of interactions (see question 2 below) Community of people Number of species Types of interactions Give a specific example of an interaction you recently had with another person in your community Community of organisms Give a specific example of an interaction you ve had with a different species in your community 2. Biologists use the following to help describe the huge number of interactions seen in nature: (Commensalism, Mutualism, Parasitism, Predator/Prey and Competition between different species). Complete the following table: Fill in the blanks to see the general effect on the organisms involved. Type of Community Interaction Commensalism Table 1: The categories of community interaction. Effect on Species A Effect on Species B Benefited (+) Harmed (-) Benefited (+) Benefited (+) Harmed (-) Benefited (+) Competition between different species Harmed (-) 3. In lab, we will examine the 3 symbiotic relationships (3 of these 5 different types of community interactions). In the table below, indicate the 2 interactions we will not be covering. And give a specific example of this type of interaction. (Give the names of the 2 organisms and their interaction). Excluding humans, use an example that you know about or have observed. Interaction type Specific example (remember: these need to be between different species) We will be using lab laptop computers in class this week. Feel free to bring in your own laptop or tablet computer if you prefer. 1

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3 Name: Date/Lab time: LAB SYNOPSIS: This is an observation lab. You will use your observation skills to record (drawings and explanations) several types of interactions seen in communities of living organisms. OBJECTIVES: After successfully completing this lab, a student will be able to: Describe in general terms ways that different species in a community can interact. Explain how interactions can cause changes in the morphology or behavior of a species. Identify types of community interactions from specific examples. Introduction: Community- made up of populations of different species that interact with each other in some way. There are many many ways different species interact. Ecologists categorize interactions based on the effects they have on the species involved (Table 1). Community interactions often have large effects on the populations that are part of the interaction. Close interactions between species leads to coevolution. Coevolution- the interdependent evolution of two or more species having a close ecological relationship. Table 1: General categories of community interactions. In these situations, Benefited/Harmed, can often mean life or death for the organisms involved. These 3 are types of symbiotic relationships Type of Interaction Effect on Species A Effect on Species B Mutualism Benefited (+) Benefited (+) Commensalism Benefited (+) Neutral (0) Parasitism Benefited (+) Harmed (-) Competition (between different Harmed (-) Harmed (-) species) Predator/Prey Harmed (-) Benefited (+) Exercise 1: Mutualism Mutualistic interactions occur when both species receives some benefit from the interaction. This type of interaction can often lead to a very strong association between different species of organisms. In many cases the mutualism becomes so complete that the two organisms are described as living in symbiosis, an association where the two organisms are living together continuously. Symbiosis- A close, prolonged association between two or more different organisms of different species. 3

4 A: Mutualism in Legumes with Nitrogen Fixing Bacteria Nitrogen is an essential plant nutrient often lacking in soils. Gardeners often add nitrogen fertilizer to stimulate plant growth. Although Earth s atmosphere is ~70% nitrogen (N2), plants cannot use this triple bonded nitrogen gas (N N). Some plants, notably legumes (the bean and pea family) form a relationship with a soil bacterium (Rhizobium spp.). These bacteria live in specialized plant structures called root nodules. This is a mutualistic symbiotic relationship, both organisms benefit. The bacteria are fed and housed by the plant and the plant receives nitrogen for growth. Observation of Root Nodules: 1. Examine the living legume roots on display in the lab and draw them in the space below. Be sure to note the number of nodules and their size. 2. Next, use one of the lab laptops to visit Scroll down to the low magnification image of the root nodules (40X total magnification). Note the internal structure of the nodule and the many plant cells within. Each plant cell has one nucleus (stained purple). 3. Now exam the high magnification of the root nodule. Note the many many bacteria within the soybean plant cells. (bacteria are small) The large structure in the middle of the plant cells the nucleus (for a frame of reference). Note the many red stained Rhizobium bacteria cells within the plant cells. Draw and label legume roots with nodules Draw a soybean cell containing many bacteria use 1000X image QUESTIONS on mutualism of legumes and nitrogen fixing bacteria: 1. Examine the living roots with nodules. The nodules on the younger part of the root system (farther away from the base of the plant) are usually smaller than on the older root? Why do you think this is? 4

5 2. Examine the micrograph of bacteria within the plant cells. The shapes vary depending on how they were sectioned. Do you think all the bacteria are the same species (yes / no)? What evidence do you have that supports your answer? 3. A mutualistic relationship is one where both species benefit. Research has shown that Rhizobium bacteria fix nitrogen gas into forms that the plant can use for growth and development. Looking at the nodules and the bacteria inside them, what do you think is the benefit for the bacteria? B: Mutualism in Lichen (fungus and photosynthetic bacteria or algae) Lichens are a common sight in most ecosystems. Actually, lichen isn t a single organism at all but rather two different organisms, a fungus and a photosynthetic organism (algae or cyanobacteria), living in a mutualistic relationship. There are a huge number of different types of lichens and so as is often the case, scientists place lichens into different categories. This time, the categories are based on the physical appearance of the lichens. The three major categories are: Crustose type grow as a tight crust that sticks to rocks, twigs, walls, and almost any surface. Foliose type looks like foliage, meaning it looks like flatten leaf-like structures. Note the color difference between the upper surface vs. the lower surface. Fruticose type forms stringy or hair-like structures. The mutualistic nature of the lichens is really only apparent if you examine microscopy images of them. Then, you can see two distinct types of cells, the long thin cells of the fungus (called hyphae) and the usually smaller and rounder cells of the algae. For this lab, you will examine both the entire lichen and the microscopic structure by viewing an online microscope image. Observation of Lichens: 1. Examine the living lichens on display in the lab and draw or describe them in the spaces below. Be sure to distinguish between the three different types of lichen. Foliose lichen Crustose lichen Fruticose lichen 5

6 2. View the image of a lichen cross-section, Identify the two different organisms present. The fungus is stained purple/pink. The algae are highlighted green. Note where the algae are found within the fungus portion. Are they near the top? Near the bottom? Draw and label the fungi portion and the algae portion Cross-section of lichen thallus (body) at 400x magnification QUESTIONS on mutualism in lichens: 1. Is there a major difference in size and shape of the three different types of lichen? Why do you think this is? How is this related to where they live? 2. A mutualistic relationship is one where both species benefit. A. What is the benefit to the algae? B. What do you think is the benefit to the fungus? (hint: you will need to hypothesize based on your knowledge of the types of organisms present) 3. The cells of the organisms that make up lichen are still distinct and separate from each other. Reproductive spores produced by the fungal portion lack algae! What are the consequences of that for lichen reproduction? 6

7 C: Mutualism in Termites and Gut Symbionts Termites are often thought of as a pest because of the destructive nature of their colonies in homes. However, these social organisms are key decomposers of dead trees in many ecosystems. Wood contains cellulose and lignin, polymers that are indigestible to all animals (including most termites!). Termites are only able to digest wood with the aid of a whole community of mutualistic symbiotic organisms that live inside the termite digestive tract. We will look at this interaction in two different ways. First we will watch a short video that shows living termites and the contents of their digestive tracts. Then we will examine images of termite protist flagellates (many of the internal species move using cellular structures called flagella and so are called flagellates). Observation of Termite Mutualism: 1. Watch the lab video or youtube termite gut symbionts. Note the way organisms inside the termites are adapted to that environment. Note them swimming around gobbling up woody material. Try to identify as many different types of organisms as you can. 2. View the image of termite protist flagellates via the link found at Recall, these flagellated organisms are in the Kingdom Protista. These single celled organisms, like all eukaryotes, have true nuclei and true membrane bound organelles. Sketch these organisms from the video or from the link in the space below. Draw each of the different, common types of termite gut organisms Termite gut organisms at 100x magnification QUESTIONS on mutualism in termites: 1. Concerning the video on termite gut organisms; Many of these species that live in the termite gut cannot live outside their host. Why do you think they cannot live in the environment outside of termites? 7

8 2. When you examined the image/or video of termite gut symbionts, how many different types of organisms did you see? Why do you think that there are this many organisms? 3. A mutualistic symbiotic relationship is one where both species benefit. What is the benefit to the termite? What do you think is the benefit to the organisms inside the termite? (hint: think about the information you learned from the video) 4. In this relationship, the termite actually digests some of the protist flagellates found inside it. In this case, there is some harm to the internal guest of the termites. Why do you think scientists classify this as a mutualistic relationship if some of the organisms are being harmed? Exercise 2: Commensalism Recall that commensalism is an interaction where one species receives some benefit but the other species is unaffected by the interaction. Some ecologists don t think that truly commensalistic relationships exist, arguing that all relationships have either some benefit to the neutral species (and so would be a mutualistic relationship) or some harm (and so would be classified as parasitism). We will use the term since it is common in ecology and will help us to think about the nature of some relationships. 8

9 A: Commensalisms of Epiphytic Lichens Epiphytes are plants that live upon another plant. Recall lichens are a mutualistic symbiotic organism composed of a fungal portion and a photosynthetic organism portion. Lichens themselves are communalistic when they grow upon the limbs of trees. The lichen benefits by being high in the tree, getting more sunlight and other resources. The tree however is unharmed. Note: The branches we have in lab are from dead tree branches. Living braches shed their bark, thus large amounts of lichens rarely accumulate. Observation of Lichen Commensalism: 1. Examine the tree branch covered with lichens. Note the number of different types of lichens (identify them as crustose, foliose, or fruticose). Note their location on the branch, ex. only on one side of the branch, all over, other. QUESTIONS on commensalism: 1. Estimate how many different species of lichen (or moss) are on the branch you observed. 2. What community relationship do you think one species of lichen has with different species of lichen on the same branch? (Which of the categories from table 1 seems most likely? Describe how the different lichen species are interacting in a way that puts them in this category.) 3. What percentage of the branch was covered by these epiphytic lichens? 4. The scientists that claim there is no such thing as commensalism would look for evidence of either mutualism or parasitism in this relationship. a. How might this tree/lichen be a mutualistic relationship? b. How might this tree/lichen be a parasitic relationship? 9

10 Exercise 3: Parasitism A predator-prey relationship is when one organism benefits while another is killed and eaten. Parasitism is a type of symbiosis where the parasite lives on or inside of the host organism. The parasite benefits while the host is harmed (but usually not killed). Many examples of parasitism involve very complex relationships with multiple species serving as hosts during different stages of the life cycle of the parasite. This is especially common in a group of parasites called internal parasites, which complete their life cycles inside the bodies of other organisms. A: Parasitism by Plasmodium on Humans Malaria is a disease that kills over 500,000 people every year. The cause of malaria is a microscopic protist in the genus Plasmodium. Plasmodium infects two hosts during its complex life cycle, mosquito and human. Plasmodium forms sporozoites, specialized cells in the mosquito s salivary glands. When bitten by a mosquito these sporozoites are transferred into a person s blood and make their way to the liver. Asexual reproduction (in humans)- In the person s liver, Plasmodium sporozoites begin to reproduce asexually forming cells called merozoites. After 1-2 weeks some merozoites leave the liver and infect red blood cells where they continue to reproduce asexually spreading throughout the blood. Some merozoites develop into gametocytes (specialized male and female reproductive cells). Sexual reproduction (in mosquitos)- female mosquitos are good mothers and need blood to feed her eggs. When a female mosquito take blood from an infected person, male fertilize female gametocytes and eventually form a oocyst. In the mosquito s salivary glands oocysts burst open releasing 1000s of new sporozoites ready to infect the next person. Observation of Plasmodium: 1. Sketch the images of human red blood cells infected with Plasmodium Note mammal red blood cells lack nuclei. 10 Draw and label a human red blood cell and the plasmodium protist inside. Plasmodium at 400x magnification

11 QUESTIONS on parasitism in Plasmodium: 1. One of the traits of parasitism is that the parasite doesn t kill its host (at least not initially). What advantage is there to a parasite to not kill its host? 2. Using the information on the previous page, fill in the diagram of the life cycle of Plasmodium: Transferred to humans by: Once in human host, cells infect this organ: 1. sporozoites found in: Gametocytes are transferred to: and eventually become: A new cell type, the: migrates to red blood cells and form Gametocytes Red Blood Cell During her lifetime, a single mosquito may feed off many different infected people. Since sexual reproduction of Plasmodium occurs within the mosquito, this increases the chances of cross fertilization. This is an advantage of having the complex life cycle seen in Plasmodium. 3. What are some disadvantage(s) to such a complex life cycle? 11

12 B: Parasitism of Tapeworms with Multiple Hosts Tapeworms (Class Cestoidea) are animals that are parasitic to humans and other animals with backbones. Like Plasmodium, tapeworms also have a complex life cycle with two, and sometimes three separate host species. Primary host- the host in which the parasite undergoes sexual reproduction (within the small intestine of host). Intermediate or secondary host- the host in which a parasite passes its larval and nonsexual stages. Pigs, cows or rabbits are common intermediate hosts for human primary host tapeworm infections. How might you get infected by a tapeworm? By eating undercooked or raw meat that contains cysts (cysticercus). Cysts contain larvae which hatch and develop into tapeworms in the small intestine. Adult tapeworm structure- Scolex- the head of the tapeworm has hooks and suckers that embed into the wall of the small intestine and hold it in place. Just behind the scolex is a short neck region where the tapeworm grows. Proglottids- very thin segments forming the tape, which can growth the length of your small intestine (50 feet (15 meters)) and contain ~5,000 proglottids. Each proglottid is a sexual reproduction structure production both sperm and egg. For cross fertilization, ideally there would be at least 2 separate tapeworms in the intestine. However, they can fertilize themselves. As proglottids mature they fill with s of eggs, break off and are shed your feces. If you poop outside, or your feces gets into the water or food of the intermediate host (ex. pigs, cows), then the tapeworm eggs can hatch and develop into cysts in the muscle tissue of the intermediate host completing the tapeworm life cycle. Humans can also be intermediate hosts and get muscle cysts. So avoid contact with feces containing tapeworm eggs. Note these bold text structures on the tapeworm model (eggs, cysticercus, scolex, proglottids). Within the proglottids; male reproductive structures are colored red, female structures are white. Observation of Tapeworm: 1. Check out the tapeworm model. Each segment of the tapeworm proglottid contain both male and female structures. They are hermaphrodites. Although tapeworms can fertilize themselves, sexual reproduction with another tapeworm leads to more diversity in their offspring. Thus it is always better to have more than one tapeworm in your intestine (at least for the tapeworm). 2. Look over the whole tapeworm imbedded in plastic. Estimate the number of proglottids in the last ~2cm (~1inch) of the tail end. Record this number.. These represent the mature proglottids. You will need the proglottid number to answer a question in questions section. 12

13 3. Using the dissection microscopes, examine the varied tapeworm samples imbedded in plastic. Make three sketches in the space below. The scolex, an immature proglottid high up on the body (near the scolex) and a mature proglottid lower down near the end of the tape. Label an egg within a proglottid Scolex Immature proglottid Gravid (mature) proglottid 3. Note the visible eggs in a mature proglottid. Each proglottid can contain 10s of thousands of eggs. Use this information to answer question 2 below. QUESTIONS on parasitism in tapeworms: 1. Tapeworms have no digestive system (and in fact no way to eat at all since they have no mouth). How are they able to get the nutrients they need? (hint: they are very thin and have a high surface area) 2. How many proglottids did you estimate there were on the tail end of the tapeworm displayed in the lab? The average number of eggs per proglottid is 25,000. Do the math. How many eggs is that? Does this seem like a lot to you? 3. The parasites we have discussed here are usually very specific in their choice of host. For example, Plasmodium vivax is only transmitted by one species of mosquito (Anopheles stephensi), and different species of tapeworms are found only in one species of intermediate host. Other parasites, primarily those that are external like mosquitoes and leeches, are much less picky about their hosts. Why do you think internal parasites are so much choosier about their hosts? 4. Think about the life cycle of these tapeworms and of the Plasmodium parasite. Both organisms have more than one host species (a separate primary host and a separate intermediary host); in fact, this is common with many different groups of parasites. What do you think is an advantage of having more than one host? (hint: look at the advantage mentioned in the Plasmodium section) 13