Female Fish Judge Males on DIY and Nest-Building Skills—Before Dumping Them

Sticklebacks can answer many profound human questions, like: What does a truly gender equal society look like? How should couples share the burden of childcare? How best to allocate menial domestic chores?

Truly, these little fishes have the answer.

Commonly found in coastal or freshwater bodies in the Northern Hemisphere, sticklebacks powerfully challenge our conventional expectations of male-female gender roles in the natural world. Female sticklebacks—preferring to hang out with their girlfriends—leave the burden of childcare entirely to the male fish. And according to new research, the female fish pick their male sexual partners based on their DIY skills.

"We're very used to thinking about females providing care all the time," explains Dr. Iain Barber of the University of Leicester. "But in fish, where there is parental care, it's often the males who do provide it."

As the eggs are externally fertilized, females need to dump them with the males so they can deposit their sperm. "And the female is gone by that point, so the male gets left 'holding the baby,' if you like."

After they've dumped the baby, flighty female fish like nothing better than to hang out with their girlfriends. "During the breeding season the females live in shoals with their other female sticklebacks. They're quite social and swim around in groups, develop their eggs in clutches, find males to spawn with, then return back to the female group."

While the females are hanging out, the males are busy building the nests in which they'll raise their stickleback offspring. While scientists already knew that males put an inordinate amount of effort into building their nests along the edges of rivers and lakes—and fighting other males for space—Dr. Barber and his colleagues made an important new discovery.

"We put males in tanks and gave them materials and let them build nests under one of two conditions: with fully oxygenated water, or slightly reduced oxygen levels," Barber explains. "When in reduced oxygen conditions, the males built nests that were more open and less compact, enabling them to fan more oxygen over the baby fish." Conversely, when oxygen levels were higher the males build tighter, more compact nests—showing that male sticklebacks are very responsive to oxygen conditions in the tank.

"What was really cool," Barber goes on, "was that when we put the females in the tank, they decided whether or not to spawn with the males based on the conditions they were experiencing and how the nest reflected that." The female fish would select looser nests in tanks with reduced oxygen, and tighter nests in high-oxygen environments.

I ask what other factors female sticklebacks use when determining a mate. "They always choose the most brightly colored, strongest, fittest males," Barber responds. He explains these are fixed preferences that don't change. "But when it comes to the behavior of the female stickleback, they were changing what they preferred based on current conditions."

What can we learn from these fish? "They have these cool abilities to change their behavior and preferences depending on the conditions they're in," Barber argues. "These are only little fish that people don't care too much about. Everyone's much more excited about salmon, or cod, or whatever. But what it indicates to me is that all of these fish are severely affected by changing climates and environmental conditions. By studying them in the lab, we can get a feel for the sort of things that might be going on in natural environments."

Male sticklebacks: the heroes we deserve, and the heroes we need.