This case study examines evolution in guppies as evidenced by color variation in populations.  It is based on an iconic study performed by John Endler where he collected data on guppies by scoring the size, number, and brightness of spots.

Students progress though the slides (lecture and discussion), and examine details of Endler’s study, such as where the pools were located and why natural barriers created different environments for  the native guppies.

The case also examine two predatory fish found in Trinidad,  the killifish (Rivulus hartii)  and the pike (Crenichichla alta).  Students then examine real data gathered in the experiment that showed how the color and number of spots found on guppies was related to the types of predators in the stream.   Students should be able to conclude that in streams with aggressive predators, natural selection favors guppies that do not have bright spots.   Students can also explore a NetLogo simulation on guppies and predators.

This case was based on John Endler’s Research, published in 1980 under the title:  “Natural Selection on Color Patterns in Poecilia reticulata. “

Next Generation Science Standards

HS- LS4-2 Construct an explanation based on evidence that the process of evolution primarily results from four factors: (1) the potential for a species to increase in number, (2) the heritable genetic variation of individuals in a species due to mutation and sexual reproduction, (3) competition for limited resources, and (4) the proliferation of those organisms that are better able to survive and reproduce in the environment

HS-LS4-3 – Apply concepts of statistics and probability to support explanations that organisms with an advantageous heritable trait tend to increase in proportion to organisms lacking this trait.

HS-LS4-4 – Construct an explanation based on evidence for how natural selection leads to adaptation of populations.