Across the animal kingdom, males and females of the same species are often locked in a battle of the sexes. The instigator is evolution itself. It drives them to develop weapons, tactical tricks and defensive maneuvers that aid in an animal's fight to pass its genes on to a new generation.
Research by scientists in the University of Texas at Austin's Department of Integrative Biology have been featured in two magazine cover articles recently. Both call attention to groundbreaking work by leaders in the country's sixth-ranked ecology, evolution and behavior program.
First, in January, The New York Times Magazine explored how animals' extravagant beauty is leading scientists to rethink core questions pertaining to evolution. The magazine spoke with two professors of integrative biology Molly Cummings and Michael Ryan:
Cummings found that Mexican swordtails occupying the upper layers of rivers, where the clear water strongly polarized incoming sunlight, had ornaments that were specialized to reflect polarized light — like a stripe of iridescent blue. These findings parallel similar studies suggesting that female guppies in Trinidad prefer males with orange patches because they first evolved a taste for nutritious orange tree fruits that occasionally fell into the water. "Some people think female preferences just somehow emerge," Cummings says, "but what has been overlooked is that in many cases, it's a result of environmental constraints. It's not always random." ...
Like the glistening scales on the surfperch and swordtails that Cummings studied, the túngara [frog's] costly mating call [studied by Michael Ryan] did not evolve to convey any pragmatic information about health or fitness. But that doesn't mean that these traits were arbitrary. They were the result of specific, discernible aspects of the animals' environments, anatomy and evolutionary legacy. "I took a real beating when I suggested this idea in 1990," Ryan says. "It was very widely criticized. But now sensory bias is considered an important part of the evolution of these preferences."
Animals' process of sexual conflict can lead to a wide range of complex behaviors and traits, according also to the cover story in the 2019 edition of the College of Natural Sciences' award-winning magazine The Texas Scientist. "As males and females engage in a tug of war over control that's never completely won or lost, more than mating happens. Animals may grow smarter, more beautiful and perhaps even better at parenting," the article explains.
The article describes work by Cummings, Ryan and Steven Phelps, another professor of integrative biology, noting that he, "began studying the brains of male prairie voles to see if he could determine what made them monogamous. He was surprised to find that, within the same species, some males are more faithful and some are less faithful, and that the difference comes down to a subtle genetic variation in their brains. ... Both the monogamous and the philandering males continued to flourish in the wild. But why would monogamy evolve in the first place if males generally benefit from having more partners to help them spread their genes? Wouldn't the less faithful trait be favored?"
This Valentine's Week, Cummings, Ryan and Phelps will give public-friendly talks about sexual selection, forming bonds and finding mates at this week's Austin Nerd Nite. The event, to be held at The North Door (502 Brushy Street) will be held on Wednesday, Feb. 13. Doors open at 7:30 and talks begin at 8 p.m.
Catch the coverage of Cummings, Ryan and Phelps' research:
How Beauty is Making Scientists Rethink Evolution in The New York Times Magazine
The Mating Game in The Texas Scientist (excerpt below)
When it comes to reproductive traits, life often imitates an old country-western duet where the guy sings, "I'm going to wear the pants," and the gal fires back, "But I'll tell you which pair to wear." It's the female brain that tends to dictate what is attractive.
In an effort to understand why males do things that can be dangerous to them – like display flashy colors and sing noisy tunes – Mike Ryan, professor of integrative biology, studies an inch-long native of Central America called the túngara frog. Lonely males crouching along the shores of puddles call out in the night, hoping to attract females, while also hoping to avoid attention from nearby frog-eating bats. Males start their calls with a low-pitched whine and then sometimes tack on a series of higher pitched sounds called chucks. The females are attracted to calls with more chucks, but the bats are attracted to the sound, too.
Ryan and his colleagues discovered that female túngara frogs have two hearing organs—one that best hears low-pitched whines and the other that best hears high-pitched chucks. The team found females evolved these organs before the males started making the sounds.
"Thus, females are the biological puppeteers, making the males sing exactly what their brains desire," Ryan wrote in his 2018 book A Taste for the Beautiful.
That male traits are driven to evolve by the way the female brain processes information—in other words, by what females find beautiful—is a big idea in evolutionary biology. It's why peacocks produce dazzling tail feather fans and why male nightingales sing their intricate and endlessly creative songs.
Ryan has gone on to uncover some surprising quirks of the female frog's brain. For example, when he and his graduate student Amanda Lea played for female túngara frogs the calls of two males, females would reliably choose the one with the most attractive calls (i.e., chocked full of chucks and with just the right pitches and timing). But then if a third, much-less-attractive call is added to the mix, about a third of the time, females would switch to the one with the second-most-attractive calls. This "decoy effect" works in humans, too—it's exploited by retailers to get us to buy more expensive cars and by online advertisers to get us to click on ads.
Ultimately, the female brain, which evolved to do many other things besides finding mates, has its own limitations and quirks, and it conjures up an aesthetic that males strive to match.
"I argue that beauty only exists because it pleases the eyes, ears, or noses of the beholder," Ryan wrote. "More generally, that beauty is in the brain of the beholder."
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