Three-spined stickleback – Gasterosteus acutealus
Two-spined stickleback – Gasterosteus wheatlandi
Four-spined sticlkleback – Apeltes quadracus
[These images have been copied from several web sources]
The first two species were observed by Linnaeus in 1758. Their fossil records date back to the upper Tertiary and Miocene eras. Lake-dwelling stickleback species have developed from marine ones as a result of the formation of lakes due to the recession of glaciers after the last Ice Age some 10,000 years ago.
A study published in the journal Current Biology in May 08 (report found here) concerns the three-spined stickleback. This is one of the most variable of fishes. Most American authors have recognised an American species as well as a European one, the former with longer dorsal spines than the latter. But the long-spined as well as the short-spined one is known to occur on the other side of the Atlantic with every possible gradation between the two.
According to the Current Biology report, when Lake Washington, which was terribly polluted in 1955 was cleaned up, the three-spined stickleback population adjusted the change in environment by reverting to an ancestral armour-plated form.
The fish is equally at home in sea water as in fresh water. As can be seen in the photograph above, it builds nests with bits of grass, weed, and other vegetation.
A discussion of the evolution of the three-spined stickleback in lakes is found in a page by Susan Foster. The author points out that two different varieties of lake-dwelling sticklebacks — limnetic and benthic — have developed, and the same pattern of evolution has taken place in three different regions. A map from Susan Foster’s page, showing the range of stickleback population is reproduced below: