Scientists let swordtail fish choose their mates for nine generations; males kept picking larger females while female preferences varied |

Green swordtail fish have taken part in a digital dating game to help scientists understand how animals choose their mates. Researchers from the University of Exeter placed individual fish in tanks with screens showing virtual partners. The fish could then spend time near the partner they preferred.Those choices were used to create new virtual fish for the next generation, allowing the researchers to track preferences across nine generations. Males repeatedly chose larger females, while females showed more varied preferences, including longer tails and brighter colours. According to the University of Exeter, they used genetic algorithms to create new virtual partners based on the fish’s choices.

How did researchers track fish preferences across generations

University of Exeter scientists tested 11 females and 12 males individually in tanks with a moving image of a possible mate displayed at either side. Each fish could swim freely for three minutes while researchers observed its movement.The tank was divided into three zones: a neutral centre and an area near each virtual mate. If a fish spent longer near one option, that virtual mate was declared the winner. Two new virtual fish were then created using the winning mate’s characteristics and those of another randomly selected winner.The process was repeated across nine generations. The experiment allowed researchers to see which traits became more common as fish selected their preferred partners, creating a digital version of selection.

Male swordtails consistently chose larger females

Male green swordtails showed a consistent preference for larger females throughout the experiment. As this choice was repeated across generations, the virtual female fish became larger. The final generation was more than 24% larger on average than the first generation.The study notes that this preference probably reflects the fact that larger females can produce more offspring. Female preferences were less consistent overall. Different females favoured different traits in potential mates, including longer tails and brighter colours. One female increasingly chose mates that looked more like females, although the reason for this preference remains unclear.

Digital fish allowed researchers to track changing mate preferences

The experiment used digital fish rather than real animals as potential mates in the trials. Genetic algorithms created new sets of virtual fish based on the characteristics selected by the participants. This gave the researchers a way to let the fish refine their preferences over successive generations.Kathryn Bullough from the Centre for Ecology and Conservation at Exeter’s Penryn Campus in Cornwall said, “Studying mate choices in animals is difficult because experiments can only present animals with a limited range of potential mates”.The new approach allowed fish to design their ideal partner by repeatedly selecting from newly generated options. The researchers could then track how preferences changed as generations progressed.

Why green swordtails were chosen for the dating experiment

Green swordtails are native to Central America and are named for the distinctive sword-like tail found on males. The species was considered suitable for the experiment because the fish respond to videos of other fish and provide no parental care for their young.Dr Laura Kelley said this makes their mate choice relatively straightforward, because the fish are primarily looking for good genes to pass to their offspring. The researchers said a similar study using real fish would take years. Their digital method provides a tool for examining how wild animals choose mates while allowing potential partners and their traits to change through successive generations.