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Related Experiment Video

Updated: Dec 28, 2025

Dissection and Flat-mounting of the Threespine Stickleback Branchial Skeleton

Dissection and Flat-mounting of the Threespine Stickleback Branchial Skeleton

Published on: May 7, 2016

Microhabitat contributes to microgeographic divergence in threespine stickleback.

Meghan F Maciejewski¹, Cynthia Jiang^2,3, Yoel E Stuart^2,4

¹Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, Connecticut, 06269.

Evolution; International Journal of Organic Evolution

|February 15, 2020

Summary

Microgeographic variation in threespine stickleback (Gasterosteus aculeatus) challenges migration-selection balance theory. Morphological differences within populations suggest habitat-specific selection, not just gene flow, drives divergence.

Keywords:

Gasterosteus aculeatus dispersal neighborhood migration-selection balance

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Last Updated: Dec 28, 2025

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Area of Science:

Evolutionary Biology
Ecology
Genetics

Background:

Migration-selection balance theory predicts limited divergence at small spatial scales due to gene flow.
Classic examples suggest divergence can occur under strong selection, plasticity, or nonrandom dispersal.
Microgeographic variation is often assumed absent in well-mixed populations.

Purpose of the Study:

To investigate microgeographic morphological variation in threespine stickleback (Gasterosteus aculeatus) within lake and stream populations.
To test the assumption of well-mixed populations and identify factors contributing to within-population divergence.
To explore the role of microhabitat and genetic factors in microgeographic variation.

Main Methods:

Examined trap-to-trap morphological variation in 34 traits across 16 lake and 16 stream stickleback populations.
Assessed the influence of between-trap distance and microhabitat characteristics (depth, substrate) on morphological variance.
Investigated the association between microhabitat, genotype at specific loci, and genetic isolation by distance.

Main Results:

Significant morphological variation was observed among traps within populations for most traits.
Microhabitat characteristics and between-trap distance explained some of the within-population morphological variance.
Microhabitat was associated with genotype, but no genetic isolation by distance was detected, suggesting heritable habitat preferences.

Conclusions:

The assumption of well-mixed populations is untenable for threespine stickleback.
Microgeographic divergence can occur over small spatial scales despite strong gene flow.
Heritable habitat preferences may be a key mechanism driving microgeographic variation in stickleback populations.