The Beatles said it best: Love is all you need. And according to new research from The Australian National University (ANU), the same is true in the animal kingdom. Well, at least for mosquitofish – a matchstick-sized fish endemic to Central America and now found globally.
According to the ANU scientists, male mosquitofish possess impressive problem-solving skills and can successfully navigate mazes and other tests. Males that perform better have a higher chance of mating.
Lead author Dr Ivan Vinogradov said male mosquitofish likely evolved better cognitive abilities over time because of the advantage it gave them in finding females and producing offspring – a phenomenon known as "sexual selection".
"Evolution of intelligence in animals has long been thought to have been driven by natural selection. Animals that were better at problem solving were more adept at gathering food, finding shelter, and avoiding predators and hence lived longer," Dr Vinogradov said.
"They then passed on these genes to their offspring, helping future generations become smarter over time.
"But there is another explanation for the evolution of intelligence: braininess is an attractive quality to the opposite sex. A better brain might help an animal find more mates, have more sex, and eventually have more babies.
"This suggests that intelligence in mosquitofish partly evolved through sexual selection, where traits that boost mating and fertilisation success become more common over generations. Sexual selection is usually stronger in males than females because in most species there are more males seeking mates than females ready to mate and breed.
"Our study suggests that intelligence in mosquitofish isn't only driven by their need to find food or avoid predators, but also by the complex challenges of finding love. This shows that, much like humans, love conquers all."
The researchers measured intelligence of the male mosquitofish by putting them through a series of underwater tests – including navigating mazes, detouring around transparent barriers and learning to remember different coloured spots – offering a reward for the fish that were able to complete the tests.
The team then tracked, over a two-month period, how many offspring each male produced when competing against other males for a female partner to mate with.
After performing more than 2,000 paternity tests, the scientists found that smarter males who successfully navigated the underwater tests mated with more females and produced more offspring than less-intelligent fish that failed the tests.
"Our findings imply that the evolution of cognitive abilities may have been driven by sexual selection for males who gained more mating opportunities," study co-author Professor Michael Jennions said.
"Something about these males seemingly gave them an edge in securing mating opportunities. Perhaps females recognised and preferred smarter males, or maybe smarter males were better at chasing the females and forcing them to mate, a common, if unpleasant, practice in mosquitofish.
"Future research is needed to observe the males more closely and see how the mating behaviour of smarter and dumber males differs."
The research is published in Nature Ecology and Evolution . The research team involved scientists from Australia, Germany and South Africa.
