Reproductive Lottery

Islands in the Stream 2002: Exploring Underwater Oases Reproductive Lottery FOCUS a handout. This activity is very visual and should Reproductive strategies of reef fishes be very easily understood by the students. GRADE LEVEL Suggested Learning Procedure Modifications: 9-12 (Biology) Step #2: Give the class five sheets of typing paper. Have them cut each sheet with scissors into 20 FOCUS QUESTION postage size pieces of paper and place all 100 Why do spawning reef fishes come together in pieces into a bowl or container. such large numbers to spawn, and why do they Step #3: Divide class into two equal groups, of release such large numbers of eggs? which half will represent female fishes and the other half will represent male fishes. LEARNING OBJECTIVES Students will be able to explain that fishes that MATERIALS reproduce externally have to release great numbers Typing paper of eggs and milt (sperm) in order to ensure fertil- 3 sets of red, blue, yellow, orange and green ization. markers Scissors ADDITIONAL INFORMATION FOR TEACHERS OF DEAF STUDENTS 2 large bowls or containers In addition to the words listed as Key Words, the following words should be part of the vocabulary TEACHING TIME list. One 45-minute class period Reproductive Adaptation SEATING ARRANGEMENT Spawning Groups of 10 Fertilization Gametes MAXIMUM NUMBER OF STUDENTS Vulnerable 20 students Aggregation Spawn KEY WORDS External fertilization There are no formal signs in American Sign Fecundity Language for any of the key words and many are Spawning aggregation difficult to lipread. Writing these words on the board to refer to during the lesson will be extreme- ly helpful. They can also be given to the students as 1 Islands in the Stream 2002: Exploring Underwater Oases - Grades 9-12 (Biology) Islands in the Stream 2002: Exploring Underwater Oases - Grades 9-12 (Biology) Focus: Reproductive strategies of reef fishes oceanexplorer.noaa.gov oceanexplorer.noaa.gov Focus: Reproductive strategies of reef fishes BACKGROUND INFORMATION After an egg is fertilized, it still has a limited Though some animals ensure the survival of their chance of survival. The eggs are very vulnerable species by staying with their offspring during the to predators and sudden changes in the environ- beginning of their lives and providing them with ment, such as cold snaps. The eggs of these fishes protection and care, others ensure the survival of do not have large amounts of yolk in them on their species by playing the odds. A 12-year old which the developing zygote can feed, so the fish red snapper will release over nine million eggs in that hatches from the egg emerges as a tiny larva. one spawning because only a very small percent- They, too, are very vulnerable to predators and age of these eggs will result in a fertilized egg and changes in the environment, as well as drifting into resulting larva that will survive to reach adulthood. areas where food is limited. As the young fish con- This is a reproductive strategy, because at least a tinues to grow and develop, the chances of survival few of those millions will survive just by beating the increase, but only a few will survive to adulthood. odds, and the snapper does not have to expend But the reproductive strategy works, because by energy on parental care and instead, can put playing the odds, enough eggs survive to become energy towards her own survival and be ready to members of the spawning community themselves spawn again the next year. and the species continues. Reef fishes of the South Atlantic Bight, such as the LEARNING PROCEDURE gag grouper and red snapper, have high fecundity 1. Discuss with students how reef fishes, such as (large numbers of eggs and sperm per individual); snappers and groupers, come together in large a reproductive adaptation that ensures that at least aggregations to spawn. Tell them that one mature some of the offspring will survive to reach adult- female red snapper may release as many as nine hood. Groupers and snappers are solitary, ter- million eggs at once during a spawning. Ask ritorial fishes that claim a spot on a reef habitat them why they think this would be an advantage and remain there almost the entire year. Though to the species. Write their ideas on the board. living alone in a territory provides these fishes with 2. Divide the class into two groups of ten. Give enough food, it does not provide the opportunity each group five sheets of typing paper. Have for congregating with large numbers of members of them cut each sheet with scissors into 20 postage the same species for reproduction. To address this size pieces of paper and place all 100 pieces of need, snappers and groupers and other territorial paper into a bowl or container. reef fishes will leave their territories at approxi- 3. Divide each group into five students that repre- mately the same time each year to come together sent female fishes and five students that represent in large spawning aggregations. Populations of male fishes. Pair one female fish student with these fishes will meet at the same site each year to one male fish student and give each student pair release eggs and milt into the water for external one of the colored markers, so one pair is the fertilization. These aggregations once numbered blue fish, one pair is the red fish, one pair is the thousands of fishes, because bringing many fishes yellow fish, one pair is the orange fish, and one together, all releasing thousands or even millions of pair is the green fish. Explain to the students that eggs and sperm into the water, ensures the chances each pair has to reproduce through external fer- of successful fertilizations. Scientists are unsure what tilization, but the female only releases one egg brings the eggs and sperm together in the water, at a spawning, and the male only releases one but one factor is just the concentration of these sperm at spawning. Give students another piece gametes in the same area of water, thus ensuring of typing paper, and have each female fish cut that at least some of them will “find” each other and off another postage stamp-sized piece of paper an egg will become successfully fertilized. and put a dot on it with their colored marker. 2 3 Islands in the Stream 2002: Exploring Underwater Oases - Grades 9-12 (Biology) Islands in the Stream 2002: Exploring Underwater Oases - Grades 9-12 (Biology) Focus: Reproductive strategies of reef fishes oceanexplorer.noaa.gov oceanexplorer.noaa.gov Focus: Reproductive strategies of reef fishes Give each male student a data sheet. sized pieces of paper, put colored dots on them 4. Place each of these pieces of paper in the bowl and place them in containers. Female fishes are with the other pieces and mix them up. Have now releasing 20 eggs each. each male fish draw one piece of paper out of 11. Tell males they are now releasing 20 sperm the container without looking. If the paper has cells, so each now gets 20 attempts at a suc- the pair’s colored dot on the paper, they have cessful fertilization. Have all five males draw 20 a successful fertilization. Have them place the pieces of paper each and then record the num- paper back in the bowl, and try another draw- ber of successful fertilizations for trial one of this ing to draw out the correct colored dot. Have section. Replace papers and repeat these steps them repeat these steps for three more trials and for four more trials. record the number of successful fertilizations on 12. Have students compare how the number of suc- their data sheet. cessful fertilizations changed as they became 5. Tell students that all of the fishes in the group more fecund, or as they released more eggs and are now the same species and any colored dot sperm. Have students discuss again why a fish represents an egg. Leave the five pieces of paper may need to release millions of eggs in order to with colored dots in the bowl. Have each male ensure successful fertilizations. fish draw from the bowl for a colored dot, and write the number of times the group of males THE BRIDGE CONNECTION draws a colored dot for a successful fertilization www.vims.edu/bridge on the data sheet next to trial one of this section. Choose “Biology,” then “Fishes” for information on Replace papers and repeat these steps four more life history and reproduction of fishes. trials. 6. Have “female fishes” cut out four more postage- THE “ME” CONNECTION sized pieces of paper, put colored dots on them A reef fish comes together with others of its species and place them in containers. Female fishes are and releases its gametes into the water and then now releasing five eggs each. its part in the regeneration of its species, at least 7. Tell males they are now releasing five sperm cells, for that spawning season, is over. Compare this to so each now gets five attempts at a successful a human parent. What do humans have to do in fertilization. Have all five males draw five pieces order to ensure that their offspring survive to adult- of paper each and then record the number of hood? Discuss this as a class. successful fertilizations for trial one of this section. Replace papers and repeat these steps for CONNECTIONS TO OTHER SUBJECTS four more trials. Mathematics 8. Have “female fishes” cut out five more postage- sized pieces of paper, put colored dots on them EVALUATION and place them in containers.

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