When selecting a mate, looks don’t matter to female guppies

A new study led by the University College London (UCL) has found that while female guppies with smaller brains can recognize attractive males, they do not consider them to be more appealing or choose to mate with them.

Judith Mank is one of the study’s senior authors and a UCL professor of Genetics, Evolution, and Environment.

“One of the biggest decisions a female guppy has to make in its life is choosing who to mate with,” said Professor Mank. “It is very important, so you might think they would all prefer a single most attractive male. But we found that it takes a certain amount of brain-power to size up an attractive mate.”

The research was focused on female Trinidadian guppies that were separated into two groups based on brain size and mating preferences. The fish were exposed to males that were either colorful with long tails, which are thought to be the most attractive to females, or males that were less colorful.

The fish were kept in separate tanks so that exposure was only visual, and the female fish were allowed to evaluate the males. The researchers measured gene expression in the brain tissue of the females. This allowed them to identify genes that were being actively expressed in two relevant brain regions involved in processing visual signals and in the integration of those signals for complex decision-making.

All of the females were found to exhibit similar patterns of activity in the sensory processing areas when they saw an attractive male, which suggests that they can all distinguish between attractive and average males. On the other hand, only the fish with larger brains showed a variation in decision-making signals when they saw attractive or unattractive males.

“Guppies are an excellent example of ecological adaptation, and this raises questions about potential trade-offs with increasing intelligence,” said study first author Dr Natasha Bloch.

“Brighter colors could attract predators, so there’s an assumption that fish in environments with many predators would evolve to be less colourful, but there may be a more complex relationship involving predation pressure, female choice and cognitive ability.”

Study co-author Dr. Alberto Corral-Lopez added: “While the exact mechanisms behind female preferences in guppies require further investigation, we know that not choosing colorful and long-tailed males would be disadvantageous, as their sons would not inherit the optimal genes for appearance, and would thus have a harder time finding a mate.”

“By clarifying what happens in the earliest stage of female mate preference behavior in animals with different cognitive abilities, we have shed light on the structure of the genetic networks underlying female mate preferences, adding to our understanding of how animals evolve different mating patterns,” said study co-senior author Professor Niclas Kolm.

The research is published in the journal Nature Ecology & Evolution.

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By Chrissy Sexton, Earth.com Staff Writer