Guppies teach us why evolution happens

Places, not predators, are evolution catalysts

Date: September 18, 2019

Source: University of California - Riverside

Guppies, a perennial pet store favorite, have helped a UC Riverside scientist unlock a key question about evolution:

Do animals evolve in response to the risk of being eaten, or to the environment that they create in the absence of predators? Turns out, it's the latter.

David Reznick, a professor of biology at UC Riverside, explained that in the wild, guppies can migrate over waterfalls and rapids to places where most predators can't follow them. Once they arrive in safer terrain, Reznick's previous research shows they evolve rapidly, becoming genetically distinct from their ancestors.

"We already knew that they evolved quickly, but what we didn't yet understand was why," Reznick said. In a new paper published in American Naturalist, Reznick and his co-authors explain the reason the tiny fish evolve so quickly in safer waters.

To answer their questions, the scientists traveled to Trinidad, guppies' native habitat, and conducted an experiment. They moved guppies from areas in streams where predators were plentiful to areas where predators were mostly absent. Over the course of four years, they studied how the introduced guppies changed in comparison to ones from where they originated.

"If guppies evolve because they aren't at risk of becoming food for other fish, then evolution should be visible right away," Reznick said. "However, if in the absence of predators they become abundant and deplete the environment of food, then there will be a lag in detectable changes."

Guppies from all four streams were marked so they could be tracked over the course of four years. The scientists tracked the males, which tend to live about five months. They looked at the fishes' age and size at maturity, which are key traits affecting population growth.

continued

Male guppies grow larger brains in response to predator exposure—but not females

June 4, 2018, British Ecological Society

Male guppies exposed to predators in the wild or in captivity have heavier brains than those living in relatively predator-free conditions, according to new research published in the journal Functional Ecology.

Behavioural ecologists from Liverpool John Moores University, UK and McGill University, Canada sampled guppies from two rivers in northern Trinidad. In each river, guppies live above a waterfall, a location that only guppies and a few other small species of fish have managed to colonize, and below the fall, where many predators including pike cichlids live.

"Guppies offer an excellent model for evolutionary research because they have colonized multiple independent rivers in Trinidad where they are exposed to a variety of different conditions", said Dr. Adam Reddon, now at Liverpool John Moores University's School of Natural Sciences and Psychology. "We were particularly interested in finding out how the brains of these widely-distributed fish have evolved for dealing with the challenges of living under predation threat."

The researchers looked at whether there are differences in relative brain mass between wild guppies collected from high and low predation populations and found that, for their body size, males collected from high predation sites had on average 17% heavier brains compared to males from low predation sites in the same river. Female guppies, by contrast, did not show this pattern.

To test the origins of these findings, the ecologists conducted a laboratory experiment in which they exposed young guppies to cues of predation risk.

Read more at: 

Guppies change their eye color to deter rivals

June 4, 2018, University of Exeter

Tiny fish called Trinidadian guppies turn their eyes black to warn other fish when they are feeling aggressive, new research shows.

A study led by the University of Exeter, in collaboration with the University of the West Indies, found that when facing a rival, guppiesrapidly turn their irises from silver to black before attacking their adversary.

This makes their eyes more conspicuous and is an "honest" signal of aggression—larger guppies do it to smaller ones whom they can beat in a fight, but smaller ones do not return the gesture.

As part of the study, the researchers made visually realistic robotic guppies to see what would happen if smaller fish displayed their aggressive motivation—and larger fish flocked in to compete with the small imposters for food.

Dr. Robert Heathcote, lead author of the study and from the University of Exeter, said: "Trinidadian guppies can change their iris colour within a few seconds, and our research shows they do this to honestly communicate their aggressive motivation to other guppies.

"Experimentally showing that animals use their eye colouration to communicate with each other can be very difficult, so we made realistic-looking robotic fish with differing eye colours and observed the reaction of real fish."

Guppies rapidly turn their irises from silver to black before attacking smaller rivals. Credit: Robert Heathcote, University of Exeter

Professor Darren Croft, also from the University of Exeter and an author of the study, added: "Eyes are one of the most easily recognised structures in the natural world and many species go to great lengths to conceal and camouflage their eyes to avoid unwanted attention from predators or rivals.

Read more at: 

Guppies: Study sorts the maths whizzes from the dunces

Heightened sense of mathematical concepts enhances 'survival of the fittest' among fish Date: December 5, 2016
Source: Springer

Some guppies have a better sense of maths than others. It allows some to find the biggest shoal possible in which to be protected against predators, while others are better at choosing fruitful foraging ground. This is according to research conducted by Tyrone Lucon-Xiccato and Marco Dadda of the University of Padova in Italy in Springer's journal Behavioral Ecology and Sociobiology.

It is well known that some people and animals such as chimpanzees and African grey parrots are simply better at solving mathematical and numerical problems than others. It helps them compare and distinguish between quantities, and to make decisions accordingly to adapt to their surroundings. Because very little work has so far been done to establish whether individual animals belonging to different species also possess such enhanced mental abilities, Lucon-Xiccato and Dadda turned to guppies (Poecilia reticulata). Theirs is the first study of its kind on fish. Three quantity discrimination tests were set to 26 guppies kept under laboratory conditions.

For guppies, safety in numbers is important. Living together in shoals provides them with better protection against predators. To find out if these fish can distinguish between bigger and smaller shoals, individual guppies were introduced to a new tank that provided no cover or refuge, but in which shoals of either four or six others swam. Two foraging tasks were also set. In the one, the fish had to choose between four or six food items, and in the other between different-sized bites.



Continued

Researchers find that some guppies can count

October 28, 2015

The humble guppy may not look like the smartest fish in the school, but research conducted by Associate Professor Culum Brown, from the Department of Biological Sciences at Macquarie University, and colleagues from the University of Padova, has shown that they are far smarter than we thought. Their research, published in Frontiers in Behavioural Neuroscience, examined the ability of guppies to count.

"We found that guppies that have very strongly lateralised brains are better at counting than those that have non-lateralised brains," said Professor Brown.

Scientists have often wondered why humans and other animals have lateralised brains, where the two halves of their brain execute different functions. In humans, for example, the left hemisphere is often associated with language and maths, while the right hemisphere is more artistic. One theory suggests that having strongly lateralised brains allows each hemisphere to analyse information separately.

Read more at: 

No Blue Skies for Mice: Scientist Study Differential Distribution of Photoreceptors in Retina of Mice

Dec. 4, 2013 — Guppies, hyenas and mice share one particular retinal specialization in their eye: Photoreceptors ("cones") sensitive to 'green' light are largely located in the top half of the eye, whereas cones sensitive to 'blue' light dominate the bottom half. Since the lens inverts the image as it enters the eye this arrangement seems to make intuitive sense: blue light from the sky is detected by the blue cones, while the greenish light from the ground falls onto the green cones.

Scientists led by Thomas Euler at the Werner Reichardt Centre for Integrative Neuroscience at the University of Tübingen have investigated this retinal specialization in mice. In their study, just published in the journal Neuron, they show that this arrangement is not an adaptation to the predominating 'colors' of the sky and the ground, as was previously thought. Their experiments showed that the apparent match between 'color' and differential cone distribution brings the animals no advantage. "The green cones would 'see' the light in the sky just like the blue cones," explains Thomas Euler. Instead, this specialized distribution of cones appears to subserve a much more fundamental aspect of vision: the detection of dark-light contrasts.

Read more

Why Do Guppies Jump?

Apr. 25, 2013 — If you've owned a pet guppy, you know they often jump out of their tanks. Many a child has asked why the guppy jumped; many a parent has been stumped for an answer. Now a study by UMD biologist Daphne De Freitas Soares reveals how guppies are able to jump so far, and suggests why they do it.

Soares, an expert in the brain circuitry that controls animal behavior, decided to study jumping guppies while researching unrelated evolutionary changes in the brainstems of Poecilia reticulata, a wild guppy species from the island of Trinidad and the forebear to the familiar pet shop fish. During that 2011 project, a guppy jumped out of a laboratory tank and into Soares' cup of chai. 

"Fortunately it was iced chai and it had a lid on, so he stayed alive," Soares said. "That was enough for me. I had to use a high speed camera to film what was going on."

Soares, an assistant professor of biology, and UMD biology lecturer Hilary S. Bierman used high speed videography and digital imaging to analyze the jumping behavior of nine guppies from the wild Trinidadian species.

In a research paper published April 16 in the online peer-reviewed journal PLOS One, Soares and Bierman reported the jumping guppies started from a still position, swam backwards slowly, then changed direction and hurtled into the air. By preparing for the jump -- a behavior never reported before in fish, according to the two biologists -- the guppies were able to jump up to eight times their body length, at speeds of more than four feet per second.

Soares and Bierman concluded that guppies jump on purpose, and apparently not for the reasons other fish do -- to escape from predators, to catch prey, or to get past obstacles on seasonal migrations.

The biologists hypothesize that jumping serves an important evolutionary purpose, allowing guppies to reach all the available habitat in Trinidad's mountain streams. By dispersing, they move away from areas of heavy predation, minimize competition with one another, and keep the species' genetic variability high, the researchers believe.

"Evolution is truly amazing," said Soares, who spent her own money on fish food, but otherwise conducted the study at no cost.

Video of jumping guppy: http://www.youtube.com/watch?v=Fryho0sIp3E

http://www.sciencedaily.com/releases/2013/04/130425132814.htm

Big Brains Are Pricey, Guppy Study Shows

Jan. 3, 2013 — Bigger brains can make animals, well, brainier, but that boost in brain size and ability comes at a price. That's according to new evidence reported on January 3rd in Current Biology, a Cell Press publication, in which researchers artificially selected guppies for large and small brain sizes.

The findings lend support to the notion that bigger brains and increased cognitive ability do go together, a topic that has been a matter of considerable debate in recent years, said Niclas Kolm of Uppsala University in Sweden. They also represent some of the first convincing evidence that large brains are expensive, evolutionarily speaking.

"We provide the first experimental evidence that evolving a larger brain really is costly in terms of both gut investment and, more importantly, reproductive output," Kolm said.

Together, the findings strongly support the idea that relative brain sizes among species are shaped through a balance between selection for increased cognitive ability and the costs of a big brain.

The results in guppies have important implications for us humans. After all, one of the most distinctive features of the human brain is its large size relative to the rest of the body.

"The human brain only makes up 2 percent of our total body mass but stands for 20 percent of our total energy demand," Kolm said. "It is a remarkably costly organ energetically."

Continued:  http://www.sciencedaily.com/releases/2013/01/130103131110.htm

They Call It 'Guppy Love': Biologists Solve an Evolution Mystery

ScienceDaily (Nov. 23, 2011) — Guppies in the wild have evolved over at least half-a-million years -- long enough for the males' coloration to have changed dramatically. Yet a characteristic orange patch on male guppies has remained remarkably stable, though it could have become redder or more yellow. Why has it stayed the same hue of orange over such a long period of time?

Because that's the color female guppies prefer.

"Sometimes populations have to evolve just to stay the same," said Greg Grether, a UCLA professor of ecology and evolutionary biology and co-author of a study published Nov. 23 in the online edition of the journal Proceedings of the Royal Society B: Biological Sciences, a major journal for research in evolutionary biology.

"In this case, the males have evolved back over and over again to the color that females prefer," said Grether, who noted that there are many examples in which there is less variation among populations of a species than life scientists would expect.

The new study, funded by the National Science Foundation, "provides a neat solution to a mystery that has puzzled me for years," he said.

The orange patches on male guppies are made up of two pigments: carotenoids (which they ingest in their diets and are yellow) and drosopterins (which are red and which their bodies produce).

Carotenoids are the same pigments that provide color to vegetables and fruits. Plants produce carotenoids, but animals generally cannot; guppies obtain most of their carotenoids from algae.

UCLA's Kerry Deere, the lead author of the study, conducted experiments in which she presented female guppies (Poecilia reticulata) with a choice of males with low, medium and high levels of drosopterin to see which males they preferred. In her experiments, the females were given a wider range of pigment choices than they would find in the wild. Deere, who was a graduate student of ecology and evolutionary biology in Grether's laboratory at the time and is currently a UCLA postdoctoral scholar in human genetics, conducted more than 100 mate-choice trials.

The females strongly preferred the intermediate males, those whose patches, or spots, were the right hue of orange -- not too red and not too yellow.

"The females preferred the males with an intermediate drosopterin level by a highly significant margin," Deere said.

"Males that are closer to this preferred hue probably have more offspring," Grether said.

If guppies were dependent only on carotenoids for their orange coloration, one would expect to find large changes in the color of their orange patches because the availability of algae varies by location. Guppies are native to Trinidad and Venezuela; the ones in this study were from Trinidad.

(Unlike the colorful guppies sold in pet stores, female guppies in the wild do not have bright coloration like the orange patches. Males are not as ornate, or as large, as the pet-store variety either.)

"A pattern I discovered 10 years ago, which was mysterious at first, is that in locations where more
carotenoids are available in their diet, guppies produce more of the drosopterins," Grether said. "There is a very strong pattern of the ratio of these two kinds of pigments staying about the same.

Read more here ...

Less attractive fish have 'better sperm'

In a study of tropical guppies, scientists have found that the less attractive males have "better sperm".


The research revealed that colourful flamboyant-looking males "invest" in their appearance at the expense of their sperm quality.

This suggests, the scientists say, that there is a trade-off between different characteristics that help the male to reproduce.

The findings are described in the Royal Society journal Proceedings B.

Professor Jonathan Evans from the Centre for Evolutionary Biology at the University of Western Australia carried out the study.

He described how his findings supported "sperm competition theory", whereby females mate with several males and the quality and swimming speed of the sperm determine which male fathers the offspring.

Guppies are a particularly useful species in which to study this, because the males engage in two types of reproductive behaviour - courtship displays and non-consensual or "sneak" mating.

"Males that predominantly performed sneak matings were less ornamented but had faster swimming sperm than those that predominantly used courtship," explained Professor Evans.

He continued in the journal article: "The reproductive advantage enjoyed by attractive males might potentially be offset by the poor performance of their ejaculates during sperm competition."