This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Fish have "designed" their perfect partners in a new experiment—revealing simple male preferences and more complex female tastes. University of Exeter scientists put green swordtail fish in tanks with a screen at either end displaying different virtual mates.
The findings are published in the journal Royal Society Open Science. Each time a fish chose a favorite (measured by time spent near each option), the winning virtual fish "survived" and was paired with a winner from another trial. Together, they produced a new "generation" of offspring tested in the next round of trials.
This allowed fish to home in on their ideal mate over nine generations. Males consistently chose larger females, while females showed much more individual variation—favoring, for example, longer tails or brighter colors. "Studying mate choices in animals is difficult because experiments can only present animals with a limited range of potential mates," said Kathryn Bullough, from the Centre for Ecology and Conservation at Exeter's Penryn Campus in Cornwall.
"Our new approach allowed fish to 'design' their ideal partner, with genetic algorithms creating new sets of options for fish to choose from, allowing them to refine their preferences." In the experiments, 11 females and 12 males were tested individually, with a moving image of a possible mate displayed on each side of their tank. The green swordtails were free to swim for three minutes, and their movement was observed in three "zones"—the neutral center and a zone near each virtual mate. If a fish spent longer near one virtual mate than the other, that mate "won," and two more virtual fish were created based on its characteristics and those of another random winning mate.
This mimics sexual selection, the idea that certain attractive traits make an individual more likely to be chosen and reproduce, so these traits reappear and become stronger over generations. Because males preferred larger females, virtual females in the final generation were more than 24% larger on average than those in the first generation. This preference probably reflects the fact that larger females can produce more offspring.
One female chose mates that looked increasingly like females. The reasons for this are unclear, but it's possible that this female avoided threatening male characteristics and moved away from them—and therefore toward more female traits. Native to Central America, green swordtails get their name from the males' distinctive swordlike tail fin.
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