DETERMINING THE EFFECT OF DAPHNIA WHEN EXPOSED TO FISH HORMONES. Siemens Research Report

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1 DETERMINING THE EFFECT OF DAPHNIA WHEN EXPOSED TO FISH HORMONES Siemens Research Report 0

2 Table of Contents Abstract...ii Executive Summary...ii Introduction...1 Materials and Methods.1 Illustration and Discussion...2 Results...7 Conclusion & Future Work...7 References.9 i

3 Abstract Water fleas, Daphnia, are common in lakes and are important components of food webs. They eat phytoplankton and are prey for fish. Fish are known to influence the expression of many traits in Daphnia. Daphnia responds to the presence of fish by growing faster and producing more offspring. They also produce defenses, such as head and tail spines, in the presence of fish. Here I tested the influence of predator cues on rates of population growth in Daphnia. I measured changes in abundance of Daphnia ambigua that either were or were not exposed to fish predators to fish predator s cues over a ten day period. I found that the Daphnia exposed to predators produced more offspring, and as the days passed, the Daphnia not exposed to predators began to produce as much as the other Daphnia. Executive Summary Fish give off hormones that make Daphnia respond by producing offspring more rapidly. To prove this, I poured fish hormones in three jars labeled predators. As the days passed, what was being determined is whether the hormones of fish cause any change to the Daphnia population. This new population was compared to the Daphnia without the fish hormones. After the ten-day period, what was found is that the Daphnia exposed to the hormones did indeed produce more rapidly than the unexposed Daphnia. ii

4 Introduction This experiment will determine whether the hormones of fish will affect the population of Daphnia. It s an interesting study because it involves using real life species and multiple hands-on assignments. The only missing information is whether the hormones affect the population. The way the hormones are inserted is simply just pouring the same amount in three jars. This experiment is being processed in six jars, three with and three without hormones. As the days go by, it will be noticeable whether the Daphnia are producing more offspring or not. My hypothesis assumes that the Daphnia with the predators hormones will not produce any offspring because they will be in shock. Materials and Methods Six jars were used in the process, three with the predators hormones, and three with just the Daphnia combo, which is a liquid substance that is almost like the lake water they live in. As the days passed, it was then determined if the Daphnia produced offspring with fish hormones around. The jars are kept in a warm incubator, which is set to the temperature Daphnia normally live in. It s important to always provide algae for the Daphnia to eat and continue their natural life style. 1

5 Illustration and Discussion Because of this finding, students are able to understand that when daphnia are surrounded by predators, they are more likely going to produce more offspring than Daphnia that aren t surrounded. Nobody thinks about Daphnia, and most don t even know what they are. To do an experiment with living creatures that nobody knows about makes it even more interesting and worth talking about because everyone should want to listen and learn more about Daphnia. Because this observation has been made, other students could determine that, if they feed the fish Daphnia, the hormones left for the next coming group of Daphnia might produce offspring before being eaten. 2

6 Figure 1: Microscopic picture of Daphnia ambigua (mature) Looking at Figure 1, you can tell it s mature by the four eggs located on its back. Daphnia are normally clear, but they turn green when they consume algae. Daphnia eggs could be found in mud at the bottom of a lake in specific places, not including Texas. It is difficult to determine male and female Daphnia. They are basically identical except that males are generally smaller in size, have larger antenules, and the first legs have a stout hook used in clasping the female during mating. 3

7 No. of Daphnia/L Predators Non-Predators Day By looking at this graph you can determine that at the beginning, the predators produced more offspring than the non-predators. As you can tell, the non-predators aren t too far behind. But by the end, the predators still produce more that the nonpredators. This chart covers the ten-day period it took to complete the project. 4

8 Rate of increase of Daphnia (per liter) Non-predator Predator The rates between the predators and non-predators are almost similar, but the information gained was from a sample of 200 ml, which probably isn t very accurate. 5

9 Rate of increase of Daphnia (per liter) Non-predator Predator This chart is basically placing the number of Daphnia from one jar of the predators and non-predators. From all the other charts, it seems as though the predators and non-predators are going at the same pace but, if you were to count all the predator jars and compare them to the non-predators, you would see the huge difference in the numbers. 6

10 Results After five days passed, the jars were checked to determine whether the fish hormones affected the growth population of the Daphnia. Samples were taken from the jar to only get an estimated idea of how much changed over time. When the data was collected, it could be determined that the predator jars were more affected. The predators had produced more offspring than the non-predators. The idea of the nonpredators producing more was wrong because they weren t terrified and didn t need to produce more quickly. The controls present in the experiment were the Daphnia combo and pipette. Two days later, the jars were checked again and this time, the nonpredators produced more. Conclusion & Future work In conclusion, the predators produced more because of their surroundings, but they adapted and began to produce offspring normally, and the non-predators eventually equaled the same amount of offspring once the predators calmed down. What was learned is that when Daphnia is surrounded by predators, they begin to produce faster than usual. The thought was that the predators would be too shocked and afraid to produce, and the non-predators would continue their normal schedule and produce more. An experiment that could refine my conclusion is one that involves somebody trying to determine which population will develop faster. If more time was given, a new experiment might expose the behavioral way of the fish. What is supposed 7

11 is that they might react differently with food. I would thus start preparing everything now because experiments with fish could take up to a year. 8

12 References Walsh, M. R. and D. M. Post. The impact of intraspecific variation in a fish predator on the evolution of phenotypic plasticity and investment in sex in Daphnia. Journal of Evolutionary Biology 25: