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How climate change is affecting how animals and people date and mate – The Washington Post

Leave it to climate change to teach us that looks aren’t everything

(Video: Dan Woodger for The Washington Post)

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This article is the first installment of the new Hidden Planet column, which explores wondrous, unexpected and sometimes funny science of our planet and beyond.

Dating and mating have never been hotter — and that’s not always a good thing.

Take the male dragonfly, which tries to impress a lady with striking yellow, red, brown and black wing designs like a flittering Pablo Picasso. But some males are finding that looking that attractive in darker pigments isn’t worth the energy in a warming world. Now many are losing the bling in their wing to help stay cool — even if it could disappoint the ladies.

Leave it to climate change to teach us that looks aren’t everything.

Animals and humans are shifting how they select mates as greenhouse emissions raise global temperatures and warm our world. (Video: Brian Monroe, John Farrell/The Washington Post)

In the animal world, the selection of certain traits has long been the biggest driver in how some sexual species will evolve. If a trait, behavior or dance will help attract or compete for a mate, they’ll do it even if it’s not that useful otherwise. But as our planet warms to unthinkable temperatures, some are forced to rethink their dating habits.

Those adjustments come in many forms. A lot of animals are giving up attractive traits, while others are keeping those characteristics and finding different ways to conserve energy. Some animals are adjusting by altogether shifting the attributes they value in a mate. And although the research is very limited, there is even some evidence suggesting that human mating habits are changing in a warming world too.

Currently, animals are not adapting fast enough to keep up with changes in the climate. But in the long run, changes in sexual selection could be an important component for some animal species to adapt faster and more efficiently to a rapidly warming climate — and it’s something that will be critical as climate change could drive as many as 1 in 6 animal and plant species to extinction.

“We’re all realizing, ‘Oh, we need to be studying reproduction in addition to survival if we’re going to understand how organisms are going to respond to the climate over the next 20 to 50 years,’ ” said Michael Moore, an evolutionary biologist at the University of Colorado at Denver.

Here are a few animals adapting their mating behavior in high heat.

I like big phenotypes and cannot lie

The male lion with the greatest, darkest mane. The male peacock with the longest and most colorful feathers. The “Bachelor” or “Bachelorette” contestant with prettier or more handsome looks (we’ll get to human mating momentarily).

Typically, many sexual animals find a mate based on observable characteristics, known as a phenotype. The animal with grander, flashier or more flamboyant features than its competitors is preferred. These traits are usually focused in males, but not always (shout-out to my sea horse ladies).

Evolutionary biologists say those eye-catching displays are usually indicators of good genes, which females want to pass along to their offspring. In some animal communities, such as lion prides, the most preferred males will mate with many females, and those traits will be passed down the most often.

“The males that can grow these very big ornaments or signals or make really loud calls or beat all the other males out, they are in some way genetically superior,” said Rob Knell, an evolutionary ecologist at Queen Mary University of London. “For good-quality males, in strongly sexually selected systems, you should see more rapid adaptation to changing environments.”

But many of those flashy traits are energy-draining. For example, high amounts of dark pigmentation in a dragonfly’s wings can heat up the insect by as much as 3.5 degrees (about 2 degrees Celsius). That’s just too much for a dragonfly in today’s climate. The same can be said for the stress on any number of species.

“There’s definitely evidence that as our climate warms and as our environment becomes more stressful in a bunch of different ways, it’s becoming increasingly difficult for these organisms to produce these traits that are really important for attracting mates and intimidating reproductive rivals,” Moore said.

In studying more than 3,000 dragonfly observations, Moore and his colleagues found that males have now opted for less pigmentation in recent decades. During Earth’s hottest years, males displayed the least amount of color.

“The best evidence that we have so far is either that natural selection is killing off the really ornamented males in the warmest years,” said Moore, who is further studying how females are responding to the shift toward less colorful males. Or the males with a lot of coloration “are unable to ever even make it to the places where they engage in these courtship behaviors and where they fight other males for territories.”

But losing the flashy trait isn’t the only option. Craig Packer, who has studied lions for decades, said animals could keep their ostentatious display and opt to develop other traits to balance out the extra energy load.

For instance, lions with dark, heat-absorbing manes could develop better panting skills, seek shade more often or take longer breaks after sex (during which males with lighter manes could swoop in on the lionesses). Research shows that darker-maned males also drink more water, presumably helping the lions to cool off.

Dark manes are a basically a male telling the world, “Look at me, I can handle the heat,” said Packer, an ecologist at the University of Minnesota. “As long as some males are better able to cope, they will still manifest a little bit more conspicuous coloration and the females can still use that” to select mates.

Females are becoming less choosy

When females are feeling the (literal) heat, they can appear less picky in whom they select.

Under higher temperatures, Moore said, some females alter what they value or even their number of lovers. Scientists are still studying such adjustments in the wild, but they have observed changes in a female’s taste in lab studies.

One lab study found that female European corn borer moths became less selective of a particular seductive pheromone in males, or “perfume” as researcher Genevieve Kozak called it, at higher temperatures. She reasoned that the females may be stressed out at higher temperatures or even struggle to survive, so they are “putting everything into this mating because it might be their last one.”

“They might just be getting less choosy. They still have the preferences but are not expressing them,” said Kozak, an evolutionary biologist at the University of Massachusetts at Dartmouth.

Another lab study found that female fruit flies, who typically mate with only one male, expanded the number of mates at higher temperatures. In short, female fruit flies became more promiscuous — although Saint Louis University researcher Noah Leith prefers to say they are “more receptive to more mates under climate change.”

Leith, who published a review of animal mating habits under warmer temperatures, explained that females altered their behavior to ensure reproductive success. Under warmer temperatures, some males have trouble producing sperm. So females end up mating with multiple males to ensure they receive enough viable sperm to fertilize all of their eggs.

When human love lives heat up

So what about people? Researchers say it would probably be impossible to disentangle the effect of climate change on our dating lives given many other societal influences. Even so, some research shows that people get hot and bothered in the heat.

Like in fruit flies, reproductive health in people can also be influenced by high temperatures. One study, which focused on people in the United States, showed that eight to 10 months after days above 80 degrees Fahrenheit, the birthrate decreased by 0.4 percent. The researchers found a slight rebound in births over the next few months, though, suggesting that people can avoid heat-induced birth lulls by shifting the month they have sex.

Separate research suggested that birthrates were likely lower because higher temperatures lower reproductive health, not necessarily because people procreated less on hotter days.

It’s hard to say how human mating will evolve in a warming world because so much more goes into whom we want to date and mate with.

“I try and stay out of human mating systems evolution stuff because people are so weird,” Knell said. “People are weak-to-moderately sexually selected, and so these effects aren’t going to be strong in humans anyway. Then we have huge overwhelming influences of things like culture on top of that.”

Culturally, climate change may be having an impact on one aspect of romantics: online dating. OkCupid data shows users, especially millennials and Gen Z daters, have increased mentions of environmental and climate-related terms on their profiles. Analyzing profiles from more than 385,000 OkCupid users from August to November this year, daters who said they believe climate change is real received 43 percent more likes. They also received 28.5 percent more messages.

This, however, is probably just an issue for humans. Lions probably aren’t asking potential mates their opinions on global warming.

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