Threespine Stickleback - Gasterosteus aculeatus

The three-spined stickleback, Gasterosteus aculeatus is native to northern Europe, northern Asia and Northern North America. But has been introduced to areas of southern and central Europe.

The Threespine Stickleback can be seperated into two distinct groups, the freshwater group and the saltwater group which only returns to freshwater to breed. Although the same species there is a wide range of differences between different freshwater populations. There is one difference between that fresh and saltwater groups that is universal. The freshwater grouping has between 0 and 12 lateral armour plates, and shorter dorsal and pelvic spines.

As noted the freshwater varieties of this single species are very variable from lake to lake. So varied that there are at time two populations of the same species that do not interbreed with each other because their habits are so different. That is something you don't see everyday.

You might think it best to conclude that there diverse populations are in fact different species but as has been shown pheno type doesn't neccessarily convey a different genotype. For example a heavily armored population of saltwater threespine sticklebacks became land locked and in only a couple of decades had largely taken on the armor and appearance of there historically landlocked forms.

Just as there are many physical traits that vary feeding traits vary greatly as well as maturity dates and how long they live. Pretty unique compared to what we would call normal variations.

In spring the males build nests on the bottom where mating takes place. Territorial males develop a red throat and belly coloration. After the eggs are deposited the female leaves and the male tends the nest. Males build the nests from vegetation, sand, pebbles and other debris, adhering the material together with a glue-like substance.

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