We’ve discussed how environmental cues can be just as important as direct sexual signals. What happens when the environment is altered in such a way that sexual signals take on a whole new meaning?

Phosphate pollution in near shore areas of the Baltic Sea has caused eutrophication – massive overgrowth of filamentous algae – in areas that were once clear with high visibility.

These waters are prime breeding grounds for stickleback fish (Gasterosteus aculeatus). In a normal habitat, the males build nests, with the healthiest obtaining the most desirable territories. They wait for females to come and inspect them before deciding where to deposit their eggs.

In a polluted environment, however, all bets are off.

Eutrophication makes it difficult for females to find any nest, regardless of the male’s territory or social status. In this thick algal overgrowth, weak and parasitized males can build their nests right alongside those of strong males and not be detected or chased away.

Moreover, females tend to mate with the first male that they find.

This is another (unfortunate) example where the strongest, fittest males will not necessarily have the greatest reproductive success. Whereas in the case of fiddler crabs such interference maintains genetic diversity, for sticklebacks eutrophication has the potential to direct “natural” selection in entirely the wrong way.

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This post is an adapted excerpt from my book “Wild Sex: The Science Behind Mating In The Animal Kingdom“