Stickleback Lab

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Ricky Vance
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Biology 120 Lab
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February 1, 2013
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Ricky Vance
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Biology 120 Lab
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February 1, 2013
Phenotypic Variation of the Stickleback

Phenotypic Variation of the Stickleback

2013
2013

Abstract:
The purpose of the research was to formulate a question and develop a hypothesis based on the variations observed between two populations of threespine stickleback, in order to gain a better understanding of natural selection and evolution. Measurements were taken of the number of scutes, ventral length and standard length in Population A. Population B data was provided by instructor. Four null hypotheses were formed on each of the measurements taken, the last hypothesis being no difference between populations. Data was collected from classmates and then compiled together into an excel spreadsheet. Using the spreadsheet, determined confidences intervals and looked for overlapping in the populations. From the confidence interval, it was concluded that there was a significant change between the populations. All of the hypotheses were rejected except for one. Thus proving phenotypic variation and natural selection occurred.

Introduction:
Stickleback are most commonly found in the ocean, but can be found in some freshwater lakes. Sticklebacks are noticeable by the presence of isolated spines in the dorsal fin and a number of lateral bony plates known as scutes. Their maximum length is about four inches, but few of them are more than three inches long. They mature sexually at a length of about two inches. All species show a similar mating behavior, which is also unusual among fish. The males construct a nest from vegetation held together by secretions from their kidneys. The males then attract females to the nest, then female will lay their eggs inside the nest where the male can fertilize them. The male then guards the eggs until they hatch. The freshwater species were trapped in freshwater lakes in Europe, Asia and North America after the ice age, and have evolved different features from the ocean variety. Freshwater sticklebacks are among the youngest species known to exist, having a short evolutionary time span of 22,000 years. This allows scientists to easily track and monitor several of their evolutionary changes. Additionally, many differences have been found between the freshwater stickleback and marine species from which they have evolved (Pennisi 2004). Typically, marine fish have a larger number of scutes while freshwater populations show a reduction in the number of these scutes (Lacasse 2012).Therefore, observation of changes in freshwater sticklebacks is considered to be a valuable tool in the study of evolution and natural selection. An experiment was performed with different populations of threespine sticklebacks, Gasterosteus aculeatus, a species of freshwater stickleback obtained from a river system located in California. One population lived in an area with a low population of a major predator, the rainbow trout. While the other population lived in a high density of rainbow trout. This was done in order to formulate a question based on observable phenotypic differences in two populations of threespine sticklebacks from the river system. Four null hypotheses were proposed. The hypotheses were no significant change in the number of scutes, no change in ventral spine length, no difference in overall length, and lastly natural selection and evolution did not occur. Careful measurements were taken including the ventral spine length, number of scutes, and standard body lengths. Upon completion, a note was made of any differences observed. A further comparison of the data with that of classmates...
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