Evolution of Armor
Plating in Three-spined
Sticklebacks
EEB 440: Biology of Fish
Isaac Fine, Allie Leitch, Karen Baweja, Meagan
Crofoot
Three Spined Stickleback
Gasterosteus aculeatus
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Frequent the Northern Hemisphere
Typically 4-6cm long
Have at least 3 dorsal spines
Known for their unique trait of Armor Plating
Armor Plating
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Bony Plating in place of scales
Existence of the armor plating is dependent on if the fish
are marine or freshwater dwellers
Marine sticklebacks are typically fully-armored (about 30
bony plates)
Freshwater sticklebacks are typically low-armored
(about 10 bony plates)
(Smith 2009)
Evolutionary Benefits
Armor Loss
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When a stickleback gives up body armor, it gains
agility and speed
o More beneficial in an environment such as a lake
o Freshwater environments lack an abundance
diversity of predators compared to marine (Smith
2009)
Evolutionary Benefits
Armor Loss
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Marine three-spined sticklebacks rely on their full
armor plating to protect them from predators
It is not uncommon for freshwater sticklebacks to
have fewer spines because of the decreased amount
of predators (Smith 2009).
Life history
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Many sticklebacks are anadromous, and the low-armored
individuals tend to survive more in the freshwater
environments
The rate at which this transition occurs is surprising and
uncommon: the change can be seen in as little as 1-3
generations
Review
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Amount of Lateral plate armor is heritable and
under selection
(Bell 2001)
Major Locus
o Ectodysplasin-Eda
(Colosimo et al. 2005)
Minor Loci
o 5
o unnamed
o Semi-Additive
(Colosimo et al. 2005)
Review Continued
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Additional selection on Eda (Low Armor
Allele)
o Due to the correlation between decreased
armor and increased growth rate
 Differences between marine and
freshwater sticklebacks
(Barrett 2010)
Flexible-Stem model of Evolution
(Wund et al. 2008)
Applications
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Model Organism: an extensively studied species
used to help understand the biological processes
of other species.
quick generation time
rapid evolution
ability to adapt to new environments
well studied
Lake Washington
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Reverse Evolution: evolving back to a more
primitive form resulting in a loss of diversity over
time.
o Involves the collapse of a phenotypically diverse
population into a single form.
(Kitano et al. 2008)
The Great Lakes!
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By the 1960s several Lake Michigan herring
species had disappeared, most catches were of a
single form.
Lake Huron was dominated by 2 herring species in
the past, recent data indicate they have become
a single hybrid form.
Seehausen 2006
Conservation Genetics
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Humans are playing a huge role in the loss of
fish biodiversity
Turning natural systems into managed systems
leading to homogenous environments
o invasive species, overfishing, pollution
By using the threespine stickleback to come to
a better understanding of these processes we
can promote new diversity and prevent future
loss in species throughout the world
Future Work
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Speciation
o Sexual Selection
 Imprinted/Learned Behavior
 Reproductive Isolation
o Ecological Factors
Model Generation
Future Work
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Sexual Imprinting
o Learning mate choice early in life
 Paternal Nest Gluing
o Know it happens but not the mechanism
o If tied to ecologically divergent traits,
sexual isolation
Future Work
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Stickleback examples
o Body Size
 Foraging niche dependant
o Nuptial Color
 Adaptation to signaling and sensory
systems in different light environments
o Odor Difference
 Diet difference, habitat, and immune
system genes determined by local
parasites
Kozak, Head and Boughman 2011
Questions?