Genetic and morphometric divergence in threespine stickleback in the Chignik catchment, Alaska

Area of Science:

• Evolutionary biology
• Ecology
• Genetics

Background:

• Divergent selection pressures drive adaptation and speciation.
• Threespine stickleback (Gasterosteus aculeatus) repeatedly invade freshwater, showing rapid diversification.
• Reproductive isolation is key to maintaining divergence.

Purpose of the Study:

• Investigate genetic and morphometric differentiation in sticklebacks across diverse environments.
• Identify population structure and gene flow.
• Determine factors maintaining divergence.

Main Methods:

• Microsatellite markers to assess genetic relationships.
• Morphometric analysis to quantify body shape and size.
• Analysis of individuals from brackish and freshwater habitats.

Main Results:

• Two distinct genetic populations identified: brackish and freshwater.
• Brackish sticklebacks were larger with different body shape.
• Evidence of upstream migration from brackish to freshwater, but limited hybridization.

Conclusions:

• Genetic and morphometric divergence is driven by selection in different environments.
• Pre- and/or postzygotic barriers, not geographic distance, maintain reproductive isolation.
• Stickleback populations show adaptation and divergence in novel environments.