Fellow name: Sara Painter
Title of Lesson: Goby Evolution
School: Culver City Middle School
Grade Level: 7th
Subject(s): Evolution and Natural Selection
Summary
In this lesson the students will learn about evolution through a natural selection simulation
using the Catalina Blue Banded Goby as a model organism. The students will be introduced
to goby life history traits and life cycle. The students will be asked to make hypotheses
about what traits might be under natural selection in gobies. Students will learn about sex
change in gobies and how the size at which a goby changes sex from female to male can
greatly alter its lifetime reproductive success.
The class of students will then be lead through a natural selection activity that will consist
of several generations of goby recruitment and reproduction. The activity will begin when
each student has a goby “settle” on their desk. Each student will need to count out the
appropriate number and distribution of offspring for their goby to enter the pool for the
next generation. Next the students will randomly reach into the pool of offspring and
choose their parent goby for the following generation. This process will be repeated for 34 generations or until a change in the average population phenotype is observed. During
the activity the students will record the number of gobies of each phenotype in the
population for each generation. The students will use this data to make histograms of the
initial and final populations and draw conclusions about the selective pressure at work in
the population.
In what way is your lesson/activity inquiry-based?
The students will examine evolution in an imaginary population of gobies. The students
will need to take the information presented to them in the introduction to form a
hypothesis about which phenotype will be the most successful. The activity will take the
students through several generations in a goby population and the students will collect
data on the number of each phenotype during each generation. This data will then be used
to make predictions and draw conclusions about what is happening in their population.
Time Required
One class period:
- PowerPoint introduction ~ 20 min
- Student independent work ~ 10 min
- Evolution activity ~ 50 min
- Closure ~ 10 min
Group Size
N/A this activity will be done as a whole class
Cost to implement:
None
Learning Objectives
After this lesson, students should be able to:
- Describe the life cycle of a Catalina goby
- List several traits that are under natural selection in gobies
- Define evolution and natural selection
- Define fitness
- Relate natural selection to sexual selection
- Explain why “survival of the fittest” is not the best definition of evolution by
natural selection
Introduction / Motivation:
Use the Catalina Goby PowerPoint to introduce the students to the material and provide
them with the necessary background information they will need to complete the activity.
Follow the PowerPoint slides to walk through a typical life cycle of a goby. Present this
information in the format of a story about the life of Bubbles the goby. Following the story,
summarize the goby lifecycle and ask the students to brainstorm some goby traits that may
increase success in their environment. Give the students a few minutes to discuss their
ideas with a neighbor before giving them the chance to share their ideas with the rest of the
class.
Most of the student ideas will have to do with traits that increase survival but not
necessarily increasing reproductive success. Use this as a platform to jump into a review
of evolution by natural selection. Define natural selection as “a process by which
individuals that are better adapted to their environment are more likely to survive and
successfully reproduce than other members of the same species.” Emphasize that
reproduction is a critical part of this process. Emphasize that survival is meaningless
without reproduction.
Next discuss how reproductive success varies in gobies. Teach the students about how
reproduction and sex change occurs in gobies. Explain that for both female and male
gobies reproductive success increases with body size, but that it does so for different
reasons. Larger females have the energy reserves and the space to produce more eggs than
smaller females. Males need to be able to successfully guard and defend a nest site in order
to reproduce. A male’s ability to do secure and guard a nest increases with body size.
Explain to the students that the body size at which they change sex can greatly affect their
lifetime reproductive success. Hand out the Goby Reproduction and Evolution worksheet.
Give the students ~10 minutes to use the provided table of reproductive success and goby
size to create a line graph and answer the associated questions. Afterwards review the line
graph and associated questions with the students. Following the discussion give the
students a few minutes to make a hypothesis about the body size at which a goby should
change sex from female to male in order to maximize lifetime reproductive success.
Procedure:
The students will now be introduced to the natural selection activity. Explain to the
students that they are going to test their hypotheses by simulating natural selection and
evolution in gobies. The students will be told that their classroom is the ocean and their
desk will represent a rocky reef where the gobies will live out their lives. The gobies will
be represented by small squares of paper with a picture of a goby and a body size on it.
Each color and size will represent a different sex change strategy which affects the lifetime
reproductive success of the gobies.
During each generation the goby which settles on their reef will grow and reproduce and
change sex during its life. For simplicity tell the students that all gobies begin life as female
and change sex to male at one point during their life. Hand out the first generation of
settling gobies. Explain to the students that the number on the goby indicates the body size
at which they change sex. Use the table in the PowerPoint to help explain to the students
what the different phenotypes are and how many offspring they should count out for their
parent goby.
Two volunteer students will be selected each round to pass out the settling gobies and
collect the newborn juveniles. During each round:
1. Juvenile gobies from the open ocean (a big plastic container) will be selected at
random to settle, one on each student desk. The first generation of gobies will begin
with an even phenotype distribution.
2. After each student in the class has a goby on their desk the remaining individuals in
the open ocean will be discarded to represent the high mortality rate during this
phase of life.
3. After all the settling gobies are passed out take a survey of the class to find out the
distribution of phenotypes. These numbers will be written in a table on the white
board and each student will also need to record this data on their worksheet.
4. Now each goby on the reef will reproduce and each student will need to count out
the correct number and type of offspring according to the reproduction chart to
enter the open ocean. The reproduction chart will be displayed using the projector
so all students can refer to it during the activity:
Reproduction Chart:
5. The open ocean will be shook up and mixed thoroughly to simulate waves and
currents and then steps 1-5 will be repeated.
The activity will continue for 3-4 generations or until a noticeable difference in phenotype
distribution is being observed. After several generations have been completed stop the
activity and discuss the results with the students. Have the students complete the second
half of the worksheet in class if time remains or finish for homework.
Materials List
To share with the entire class:
- 12 Zip lock baggies filled with colored squares with pictures of gobies from
which the students will count out their offspring
-
Large container to use as the open ocean
Safety Issues
none.
Lesson Closure
After the activity is competed and the students have had a chance to construct their
histograms (or this has been assigned as homework) discuss the results with the class.
Take a survey to see how many students thought that evolution occurred and how they
came to this conclusion. Use the next two PowerPoint slides to define evolution as change
in the average trait of a population over time. Explain why “survival of the fittest” is not the
best definition of evolution. Define fitness as reproductive success. Tie this back to the
initial introduction and emphasize that evolution is not dependent on survival as much as
reproductive success. Next show the students some pictures of traits that have evolved
because they are beneficial to reproduction (sexual selection) even though some of these
traits may also be detrimental to survival such as the peacocks beautiful tail.
Is this lesson based upon or modified from existing materials? If yes, please specify
source(s) and explain how related:
n/a
References:
Toothpick fish
Megan Brown and Maureen Munn, The GENETICS Project
Carol Furry, Eckstein Middle School, Seattle, WA
http://chroma.gs.washington.edu/outreach/genetics/download/toothpickfish.pdf
Studying Living Organisms
Beans and Birds: A Natural Selection Simulation
Woodrow Wilson Biology Institute
1995
http://www.accessexcellence.org/AE/AEPC/WWC/1995/beansbirds.php
Attachments
Goby Reproduction and Evolution Handout
List CA Science Standards addressed:
2.b. Students know sexual reproduction produces offspring that inherit half their genes from each
parent.
3.b. Students know the reasoning used by Charles Darwin in reaching his conclusion that natural
selection is the mechanism of evolution.
7.c. Communicate the logical connection among hypotheses, science concepts, tests conducted,
data collected, and conclusions drawn from the scientific evidence.
Lesson Implementation Comments
Overall the lesson went very smoothly and most aspects of the lesson went according to my
plan. The students enjoyed the PowerPoint presentation especially the story about
Bubbles. The students asked many thoughtful questions and were especially fascinated by
the idea of sex changing gobies. The overall lesson did a good job of capturing the interest
of the students and engaging them in the activity.
When I designed this lesson I knew it was slightly more advanced than some of the other
lessons and activities the students have done in class thus far this year. However, I thought
that some of the students were ready for a higher level of thinking and I estimate that 2030% of the students understood the sex change aspect of the lesson. Even though I
accurately predicted that the majority of students would not fully understand the sex
change component of the lesson I do think that every student had a chance to grasp the
main points of the lesson. The main points I wanted to get across were that evolution
happens in populations and not to individuals and that reproduction is just as important as
survival.
One change that may improve the lesson is to alter the phenotype under selection (since
how size at sex change can affect reproductive success is a difficult concept for 7th grade
students.) However, if I chose another phenotype it might not be very realistic to the
Catalina Goby.
Another thing I may do differently in the future is to plan to have the students do simple
activities to increase their table reading and graphing skills before the lesson is
implemented. Many students had difficulty reading the table (to find out how many and
what type of offspring their parent goby produced) and required a lot of individual help
with this. Also, all but a few students had difficulty creating a line graph from the table on
their worksheet, and needed a lot of explicit direction for this part.