These little fish swap their gender roles every season

Generally speaking, it's the males of a species that take the active role in finding mates. And that's true of Norway's goby fish...at least in the beginning. Every year, males and females gradually swap their roles in the mating process.

Gobies are incredibly common throughout the waters of northern Europe, and they fit a lot of life into their one-year existence. Crucially, it's the males that focus on looking after their young, and the male population in general tends to drop precipitously over the course of the year. Those two factors combine to repeatedly shift the ways in which the two goby genders view reproduction, as researchers at the Norwegian University of Science and Technology recently discovered. Researcher Lise Cats Myhre explains:

Their need to breed is obvious. They only have the one season to give birth. We saw up close how goby girls grew progressively more desperate, and less shy, as summer approached and the number of possible mates dropped. [The males] may have a hard time defending their territory and at the same time caring for the eggs. Doing so may both exhaust them and make them more exposed to predators than the females which live a much more relaxed social life in flocks. By mid-summer the mating game just changed completely. Males were often surrounded by harems of willing females showing off their bellies nearly bursting of eggs. I never saw that early in the season."

Because so many males are no longer available for breeding towards the end of the mating season - either because they were busy raising children or because they were, well, dead - the sudden scarcity reverses which gender can afford to be picky in choosing a mate. Research leader Professor Trond Amundsen points out this is a good example of how the sexual dynamics in other species can be just as fluid and complex as those among humans, and that reproductive behaviors are hardly fixed. For more, check out the NTNU website.

Via The American Naturalist. Image by scot6eus.