Cross-Dressing Salmon
By Tom Horvath
CQ#1: Which statement best describes
natural selection?
A. Survival of the fittest.
B. The strongest individuals get to reproduce.
C. The best adapted individuals survive and
reproduce.
D. Survival and reproduction is a matter of luck.
Typical Salmon Life Cycle
•
Female salmon dig the redd (gravel nest) with tail.
•
Male protects redd from other potential spawners & attracts females.
•
Females deposit eggs while male fertilizes eggs (external fertilization).
•
Embryos hatch and develop into alevins.
•
Alevins emerge as fry from the redd and start actively searching for food.
•
After a period of growth in fresh water, anadromous species will start
their downstream migration to the sea.
•
Silvery smolts undergo a series of physiological and morphological
changes that acclimate them to the salt water conditions.
•
Smolts feed and grow to fully developed adult salmon.
•
Adult salmon return to their natal stream to spawn (reproduce).
•
Most salmon spawn only once during their lifetime (semelparous).
•
The majority of salmon species die within a week of spawning.
Movie Clip
CQ#2: Out of all the eggs a female lays,
how many hatchlings (or smolts) do you
think will survive to spawn?
A. 50% (50 out of 100)
B. 10% (10 out of 100)
C. 1% (1 out of 100)
D. 0.1% (1 out of 1000)
E. Less than 0.1 %
6
Which are the lucky few who
make it to reproduce?
Charles Darwin’s Theory of Natural
Selection
It is not just random luck.
Some individuals have a better
chance of surviving and
CQ#3: Are all these smolts ABSOLUTELY identical?
A: Yes B: No
Theory of Evolution
by Natural Selection
•
More offspring produced than survive to
adulthood (OVERPRODUCTION).
•
Variation among individuals of a species.
What good is variation?
ADAPTATION
•
Any characteristic that improves the survival
or reproductive success of an organism.
•
Often the result of natural selection.
•
Organisms match closely with their
environment.
Survival is only half the story –
you have to reproduce to pass
on those good traits that aided
Theory of Evolution
by Natural Selection
•
More offspring produced than survive to adulthood
(
OVERPRODUCTION
).
•
Inheritable variation among individuals of a species.
•
Best adapted individuals survive and reproduce
(UNEQUAL REPRODUCTIVE SUCCESS).
Movie Clip
18
The most dominant males (usually largest and most
aggressive) successfully defend their redds and
inseminate the eggs. Smaller males that also have
the kype lose out in head-to-head competition with
larger males.
CQ#4: Are we seeing “survival of the fittest” in
action here?
•
Lack dominant male characteristics (e.g., no kype).
•
Appear more female-like.
Disadvantage: They can’t compete head-to-head with
dominant males either, but….
A Different Type of Male
Female Mimic
Why do these non-dominant
males persist in the population
over time?
Why don’t female mimics get
weeded out through natural
CQ#5: Why are female mimics still found
in each generation?
A. Some outcompete the dominant males in the redds.
B. They appear from mutations randomly each
generation.
C. They have a different reproductive strategy from
dominant males and it works.
D. Some females change into males under stressful
environmental conditions.
Female mimics can stay near the redds because dominant
males don’t see them as competition; they think they are
females.
These fish get a brief chance to inseminate a few eggs before
being ultimately bumped out by dominant males.
CQ#6: Even though female mimics are not
dominant, are they fit?
A. Yes
B. No
Survival of the Fittest?
Fitness can be compared with relative
values (values from 1 to 0)
•
A fitness value of 1 is assigned to the
phenotype with the highest representation.
•
All other phenotypes are assigned based on
their reproductive success relative to the
dominant type.
Fitness Value Example
•
Dominant male phenotype produces 300
male offspring in the next generation.
•
Female mimic phenotype produces 50 male
offspring in the next generation.
•
Small male phenotype produce only 5 male
offspring.
Natural Selection
•
Analyzing change in frequency of traits in a
population:
•
Three patterns emerge:
–
Directional selection
–
Stabilizing selection
–
Disruptive selection
Natural Selection
Directional Selection
-Individuals of one
extreme phenotype
favored.
29
Stabilizing Selection -
Individuals with
intermediate phenotype
favored;
Extreme phenotypes
selected against.
Disruptive Selection -
Both extreme phenotypes
favored; intermediate
Directional Selection
30
Population with
no natural selection
Population under
directional selection
Body Size of Salmon
F
re
q
u
en
cy
Stabilizing Selection
31
Population with
no natural selection
Population under
stabilizing selection
Body Size of Salmon
F
re
q
u
en
cy
Disruptive Selection
32
Population with
no natural selection
Population under
disruptive selection
Body Size of Salmon
F
re
q
u
en
cy
CQ#7: Given our fitness value from the
example, which pattern of selection would
we expect in the salmon population?
CQ#8: Do individuals have to be the
“strongest” to be fit?
A. Yes
B. No
CQ#9: Which of these traits might confer
fitness upon an individual?
A. Being sneaky and tricking the dominant males into
letting you hang around the spawning females.
B. Having an awesome hook on your jaw and large
body size.
C. Having sperm that are extra good at finding and
fertilizing eggs.
Slide Credits
Slide 1 , Slide 19 , and Slide 24
Description: Spawning salmon.
Author: Andrew Holland, Timberwolf Photography, [email protected] Source: The Adams River Salmon Society
Link: http://www.salmonsociety.com/2006_Photo/AH6s.jpg Clearance: ©Andrew Holland, used with permission.
Slide 3
Description: Diagram of the salmon life cycle.
Source: USDA Forest Service—Tongass National Forest
Link: http://www.fs.fed.us/r10/tongass/districts/mendenhall/fishcam/lifecycle.shtml
Clearance: Public domain, a work of the United States Federal Government under the terms of Title 17, Chapter 1, Section 105 of the US Code.
Slide 6 and Slide 8
Description: Mass of salmon eggs.
Source: Bonneville Power Administration, United States Department of Energy Link: http://www.bpa.gov/corporate/BPANews/Library/images/fish/
Slide 7—Left
Description: Survival chart for an average salmon family. Source: U.S. Fish and Wildlife Service
Link: http://www.fws.gov/r5cneafp/survival.gif
Clearance: Public domain, a work of the United States Federal Government under the terms of Title 17, Chapter 1, Section 105 of the US Code.
Slide 9
Description: Water-colour portrait of Charles Darwin. Author: George Richmond
Source: Wikimedia Commons.
Link: http://en.wikipedia.org/wiki/Image:Charles_Darwin_by_G._Richmond.jpg
Clearance: A faithful reproduction of an original two-dimensional work of art from the late 1830s. The work of art itself is in the public domain and its copyright has expired. This applies to the United States, Australia, the European Union and those countries with a copyright term of life of the author plus 100 years or fewer.
Slide 10 and Slide 13
Description: Salmon smolts.
Source: Bonneville Power Administration, United States Department of Energy Link: http://www.bpa.gov/corporate/BPANews/Library/images/fish/
Clearance: Public domain, courtesy of BPA.
Slide 11
Description: Mass of salmon.
Source: Bonneville Power Administration, United States Department of Energy Link: http://www.bpa.gov/corporate/BPANews/Library/images/fish/
Slide 17
Description: Male salmon showing hook nose (kype). Source: U.S. Fish and Wildlife Service
Link: http://www.fws.gov/r5cneafp/hookjaw.jpg
Clearance: Public domain, a work of the United States Federal Government under the terms of Title 17, Chapter 1, Section 105 of the US Code.
Slide 20 and Slide 33
Description: Male and Female sockeye salmon. Source: Fisheries and Oceans Canada
Link: http://www.pac.dfo-mpo.gc.ca/recfish/Species/sockeye_e.htm
Clearance: Permissible non-commercial reproduction in accordance with Fisheries and Oceans Canada.
Slide 22
Description: Illustration of single salmon.
Source: USDA Forest Service—Tongass National Forest
Link: http://www.fs.fed.us/r10/tongass/districts/mendenhall/fishcam/images/sockeye_female.jpg
Clearance: Public domain, a work of the United States Federal Government under the terms of Title 17, Chapter 1, Section 105 of the US Code.
Slide 23
Description: Sockeye salmon spawning in an Alaskan stream. Author: Wyatt Rivard
Source: Dreamstime.com, ID 8063677
Clearance: Copyrighted, licensed, royalty free.
Slide 25
Description: .
Source: USDA Forest Service—Tongass National Forest
Link: http://www.fs.fed.us/r10/tongass/districts/mendenhall/fishcam/lifecycle.shtml
