Evolution of Armor Plating in Three-

spined Sticklebacks

EEB 440: Biology of Fish Isaac Fine, Allie Leitch, Karen Baweja,

Meagan Crofoot

Three Spined SticklebackGasterosteus aculeatus

• Frequent the Northern Hemisphere• Typically 4-6cm long• Have at least 3 dorsal spines• Known for their unique trait of Armor

Plating

Armor Plating

• 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 Benefitsof Armor Loss

• 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 Benefitsof Armor Loss

• 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).

• 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

Life history

Review

• Amount of Lateral plate armor is heritable and under selection

(Bell 2001)

• Major Locus o Ectodysplasin-Eda

(Colosimo et al. 2005)

• Minor Locio 5o unnamed o Semi-Additive

(Colosimo et al. 2005)

Review Continued

• 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)

• 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

Applications

• 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)

Lake Washington

• 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

The Great Lakes!

• 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

Conservation Genetics

Future Work

• Speciationo Sexual Selection

Imprinted/Learned Behavior Reproductive Isolation

o Ecological Factors• Model Generation

Future Work

• Sexual Imprintingo Learning mate choice early in life

Paternal Nest Gluingo Know it happens but not the

mechanismo If tied to ecologically divergent traits,

sexual isolation

Future Work

• Stickleback exampleso Body Size

Foraging niche dependanto 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?