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?