In the mating season, round goby males can adopt either of two behaviors. They can either become territorial males, which guard a nest, court females, and care for their eggs, or they remain non-territorial.

This behaviour can be identified in many goby species. However, it is to date unclear whether the choice taken reflects earlier life experiences or is a on-the-spot decision reflecting nest site availablity.

To identify whether males before the mating season are pre-destined for one or the other behaviour, we investigate DNA methylation patterns in the hypothalamus of non-territorial, territorial, and pre-mating-season males.