Assignment 8*
Understanding Change in Organisms

 
Prior to this lesson, you have been working with the concepts of Steno's Laws, radiometric dating, and geologic time.  The "Understanding Geologic Time" web site you visited at the end of Assignment 4 briefly introduced the concept of using fossils to study prehistoric Earth and estimate geological time.  This week's activity will focus specifically on changes that occur in living organisms over long periods of time.  You will begin by viewing a short video that explains the significance of fossils to the study of the history of this planet. 


Fossils are generally helpful for understanding macroevolution, during which higher taxa of organisms originate, change, and go extinct.  Obviously much smaller changes occur in organisms over shorter periods of time, such as the evolution of resistance to new antibiotics by bacteria.  You will study these smaller changes that occur in populations of organisms (microevolution) through a simulation of a wild guppy population.

Use the icon below to access the video about whale fossils.  Click on Video 3, "How do we know evolution happens?" when the web page opens.
 
 

Getting Into the Fossil Record

   
It may be difficult, initially, to understand how organisms could possibly change their form and function over time.  Nevertheless, we know that they do change.  If your grandfather happens to be a farmer, ask him if the herbicides he used years ago remained effective.  The answer will probably be 'no'.  It was not the herbicide that changed, however.  It was the genetic make-up of the plant population that changed.  Some plants that he sprayed were resistant to the herbicide due to their unique genetic make-up (just as your genotype is unique to you).  Over the years, plants that were resistant became more common in the population while the non-resistant plants became fewer and fewer.   Other more natural selection pressures act continuously on all organisms, leading to the survival of those who have adaptive genotypes and the loss of individuals with less adaptive genotypes.
 

 
 

To review the basic mechanisms of natural selection, click on the icon below and view the short video about the evolution of hummingbirds.  Select Video 4 once the web page opens.
 
 

How does evolution really work?

 

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Have you ever wondered why many birds and fishes are brightly colored?  Doesn't that make these animals more vulnerable to predators?  You will examine these questions while conducting a simulation of the impacts of predation on a wild guppy population.   The simulation is based on Dr. John Endler's now famous research on the evolution of various characteristics of guppies.   You read a little about Dr. Endler's work in your assigned reading.  If you are interested, the original manuscript of his research on guppy evolution is available at :  Natural Selection on Color Patterns on Poecilia reticulata.

As you work through the simulation, be sure to visit all links.  You will learn more from this activity if you become familiar with the various color morphs that occur in guppies and the different fishes that predate on guppies.  Once you have looked over the guppy, predator, and habitat information then you are ready to conduct the simulation itself.

Before running the simulation, answer questions #1 and #2 on your workheet.  Then click on the icon below.  Select Activity, "Flashy Fish" and run the simulation once using the settings currently in place and become familiar with the program.  Now, go back to your data sheet and write a hypothesis for item #3 and a prediction of the outcome you expect if your hypothesis is supported.  Proceed to complete the work sheet.  Based on the results of your first experiment, state a new hypothesis and prediction for item # 6 (even if your first hypothesis was supported).   Remember, the objective of this activity is to help you understand how selection acts to cause change in populations.  Make sure that you demonstrate your understanding of natural selection when you explain why your hypotheses and prediction(s) were supported or rejected (items #6 and 8). In particular, make sure that your understand of the effects of sexual selection AND selction for cryptic coloration is clear in your explanations.  Turn in your work sheet before leaving class.