The Eastern Mosquitofish, scientifically known as Gambusia holbrooki, is native to the southern United States, but its global reach is remarkable.
Initially introduced as a biological agent to combat mosquitoes carrying malaria, this species has spread to numerous countries, leaving a significant ecological footprint.
According to the International Union for Conservation of Nature (IUCN), the mosquitofish is among the 100 most harmful invasive exotic species on the planet due to its impact on local fauna.
Intelligence and sexual selection in the mosquitofish
Recent research from the National University of Australia has revealed that male Gambusia affinis, a species closely related to G. holbrooki, possess remarkable cognitive abilities.
These small fish, barely the size of a matchstick, can navigate efficiently through mazes and overcome challenges underwater. According to the study’s author, Ivan Vinogradov, these skills likely evolved due to the reproductive advantage they provided to the smarter males. This process is known as sexual selection.
The researchers highlight that, in addition to natural selection, which drives survival through problem-solving and predator evasion, intelligence can evolve as an attractive trait for mating.
The cleverest males tend to have greater opportunities to reproduce, either because females prefer them or because they manage to outcompete their rivals.
Experiments and findings
To explore the relationship between intelligence and reproductive success, scientists subjected the mosquitofish males to a series of underwater tests. These included mazes, detours around transparent obstacles, and learning color patterns. Fish that successfully completed the tests were rewarded.
During a two-month follow-up, the offspring produced by each competing male for mates were tracked.
The results were revealing. Males who excelled in cognitive tests mated with more females and produced more offspring compared to their less intelligent counterparts. This study suggests that cognitive abilities have evolved, in part, thanks to sexual selection.
Implications for cognitive evolution
Michael Jennions, co-author of the study, emphasizes that these findings highlight how traits associated with mating can shape the evolution of intelligence. “Perhaps females recognized and chose the smarter males, or maybe these males were simply more effective in pursuing females and forcing encounters, something common in this species,” Jennions points out.
The researchers conclude that a deeper analysis of male mating behavior is needed to better understand the dynamics between intelligence, courtship, and reproduction in mosquitofish.
The case of the mosquitofish demonstrates how the interaction between natural and sexual selection can lead to complex traits like intelligence while raising fascinating questions about evolution in the animal kingdom.
Cover photo: Stuart Hay (ANU)
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