Why Would an Animal Trade One Body for Another?

Most species undergo metamorphosis, but scientists aren’t sure why the process evolved. One new theory: Metamorphosis gives animals greater access to food.

By Carl Zimmer NY Times 25 March 2019

“As a child growing up in the Netherlands, Hanna ten Brink spent many days lingering by a pond in her family’s garden, fascinated by metamorphosis.

Tadpoles hatched from eggs in the pond and swam about, sucking tiny particles of food into their mouths. After a few weeks, the tadpoles lost their tails, sprouted legs and hopped onto land, where they could catch insects with their new tongues.

Eventually Dr. ten Brink became an evolutionary biologist. Now science has brought her back to that childhood fascination.

Eighty percent of all animal species experience metamorphosis — from frogs to flatfish to butterflies to jellyfish. Scientists are deeply puzzled as to how it became so common.

What evolutionary path could lead to a caterpillar — an admirably adapted leaf-eating machine — to tear down its body and rebuild it as a butterfly?

In the May issue of American Naturalist, Dr. ten Brink, now a postdoctoral researcher at the University of Zurich, and her colleagues lay out a road map for the evolution of metamorphosis. It has appeared, they argue, as a way for a species to eat more food.

The path to that feast is hard to travel, and metamorphosis has only arisen a few times in history. But once it does, the scientists also find, it rarely disappears.

Dr. ten Brink, Andre M. de Roos of the University of Amsterdam, and Ulf Dieckmann of the International Institute for Applied Systems Analysis in Austria created complex mathematical equations that captured some of the fundamentals of animal life — how much food they eat, how fast they grow, how many offspring they had and so on.

The researchers began by considering animals that didn’t go through metamorphosis. Keeping the same body through their lives, they are well adapted to one kind of food.

But what if their environment contained a second food, one that they could consume as adults if they evolved a different anatomy? Natural selection would prevent the animals from adding the second food to their diet, the researchers found.

In this case, evolution favors specialists: If animals evolve to eat the second food, their offspring will become worse at consuming the original diet when they’re young. More of them will die before they can mature.

“The obvious solution to the problem is to evolve metamorphosis,” said Dr. ten Brink. Young animals stay well adapted to the original food, while adults switch to the new food with a rebuilt body.

But animals pay a steep price to go through metamorphosis. They burn a lot of calories to tear apart the old anatomy and develop a new one. There’s a chance that this complicated process will go awry, leaving them with defects.

Metamorphosis also takes time, leaving animals vulnerable to predators and parasites. In many cases, Dr. ten Brink and her colleagues found, the cost of metamorphosis is too high for it to be favored by natural selection.

“You have to get back something really good,” she said.

Natural selection will favor metamorphosis if adult animals are rewarded with an abundant supply of food — enough to make up for the cost and to allow them to have lots of offspring.

In early stages of this shift, the adults will start out poorly adapted to the new food. But there’s so much for them to eat that they still get a decent meal.

“I like the concept — I like that they tried to look for the ultimate cause,” said Joanna Wolfe, a postdoctoral researcher at Harvard. But she wondered if food is the only reward that can help drive the evolution of metamorphosis.

Some species might benefit in other ways. Adults might take on bodies that allowed them to find mates more successfully, for instance. Larvae in the ocean might change their forms in order to be carried far away by the currents, expanding their range.

“I would like to see some things added to their model,” she said.

Dr. ten Brink agreed that the new study is a foundation for more detailed ones. “This paper is really the start of something,” she said.

If animals so rarely evolve metamorphosis, why is it so common? One reason may be that once metamorphosis arises, it’s very hard for a species to lose it.

It’s easy enough to imagine a situation where giving up metamorphosis would be a benefit. Imagine an outbreak wiping out the food that adults eat. For the species, it would be advantageous for individuals to remain larval and survive on what food remains.

But in most situations, Dr. ten Brink’s study suggests, evolution works against our expectations. If the adult food gets harder to find, natural selection will favor adults that do a better job of finding what little food is left.

“It’s an evolutionary trap,” said Dr. ten Brink. “If conditions get really bad, you go extinct.”

Vincent Laudet, a biologist at Pierre and Marie Curie University in Paris, said his own research on vertebrates supported Dr. ten Brink’s findings.

The first fish species went through metamorphosis, he noted, and it has largely endured for over half a billion years.

“In some vertebrates, metamorphosis is camouflaged, but it is never lost,” Dr. Laudet said.

When Dr. Laudet speaks of “some vertebrates,” he includes us. When babies leave the womb, their tissues undergo important changes, governed by some of the same hormones that spark metamorphosis in frogs and other animals.

“Our birth, biologically speaking, is a metamorphosis,” Dr. Laudet said.

Song Birds & Extinction

This Songbird Is Nearly Extinct in the Wild. An International Treaty Could Help Save It — but Won’t.

Over a quarter of the species threatened by commercial trade are not protected by Cites, the global agreement intended to save them.

By Rachel Nuwer - 15 March 2019

“Fewer than 500 black-winged mynas remain in the wild in Indonesia, but each year more of the songbirds are captured and sold as pets.

Banteng — “the most beautiful and graceful of all wild cattle,” according to the World Wide Fund for Nature — were listed as endangered in 1996, but their horns still are sold in markets across Southeast Asia.

And the critically endangered giant carp, a Mekong River native that can weigh up to 600 pounds, recently began turning up on restaurant menus in Vietnam. Experts warn that the fish might soon be pushed into extinction.

International trade poses a threat to all of these species, yet not one is subject to key regulations that would help protect it. They are not listed under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (Cites), a treaty meant to ensure that trade does not imperil the survival of threatened and endangered species.

These are not isolated cases: Cites oversights are all too common for many of the world’s endangered species, conservationists warn. “There’s a backlog of species that are being over-exploited and traded internationally, but lack protection,” said David Wilcove, an ecologist at Princeton University.

“Wildlife trade is a threat equal to or greater than habitat destruction for many species, and it’s not going to get any better unless countries step up,” added Dr. Wilcove, co-author of research into the problem published recently in the journal Science.

Cites protects thousands of animal and plant species by barring trade of the most highly endangered and by sustainably regulating the others. But as conservationists have repeatedly pointed out, the treaty neglects entire classes of animals, including 92 percent of the world’s 10,700 reptile species, most amphibians, songbirds and fish, as well as invertebrates and small mammals.

In their study, Dr. Wilcove and Eyal Frank, an environmental economist at the University of Chicago, sought to detail the disconnect between scientific data and action taken to protect plants and animals threatened by international trade.

The researchers first consulted the International Union for Conservation of Nature’s Red List, the authority on the conservation status of the world’s species. The scientists zeroed in on those listed between 1994 and 2013 as threatened with extinction, and then narrowed their focus to species jeopardized by the international wildlife trade.”

Flower Men of Saudi Arabia

Eric Lafforgue - Al Jazeera 12 March 2019

“Saudi Arabia - In Jizan and Asir, Saudi Arabia's southern provinces, live the reclusive Flower Men.
For centuries, these descendants of the ancient Tihama and Asir tribes have been known for wearing colourful flower garlands on their head.
They lived completely isolated until 20 years ago; their villages had no electricity or paved roads and they lived according to traditional tribal law.
Even today, the Flower Men were reluctant to have their photos taken or even meet strangers.
They enjoy their peaceful way of life and the margin of autonomy they are given.
They are the only tribes in Saudi Arabia who are allowed to grow and consume khat, a stimulant drug. Possession of drugs is punishable by the death penalty in the kingdom.
The Flower Men also hold strongly to their tradition of floral decorations as a peaceful way of setting them apart.
The community spreads across the border into Yemen, a country the Saudi-led coalition is targeting in air raids.'

Do Any Animals Know Their Grandparents?

By Mara Grunbaum, Live Science Contributor | March 9, 2019

“Grandparents are revered in many human societies. But telling stories about old times and overfeeding grandchildren seem like distinctly human traits. Are these classic grandparent behaviors really limited to Homo sapiens? Do any animals know their grandparents the way people do?

For most species on Earth, the answer is an unequivocal no. "Usually, there just aren't grandparents living anymore" when an animal is born, said Mirkka Lahdenperä, a biologist at the University of Turku in Finland. Even if an animal's life span does overlap with its grandparents', most species spread out to avoid competing for resources, so the odds of running into a grandparent are slim.

But there are a few notable exceptions, primarily among mammals that live in close-knit social groups. In her book "The Social Behavior of Older Animals" (Johns Hopkins University Press, 2009), Canadian zoologist Anne Innis Dagg described troops of langur monkeys in India in which older females commingled with their daughters and grandchildren.

The grandmother langurs have a particular job: They aggressively defend the group's infants against attacks from humans, dogs and rival monkeys. Some female langurs even give their own grandchildren special treatment, grooming them and stepping in when they play too roughly with other young.

Many whale species, too, travel in family pods that include both grandmothers and grandcalves. In groups of sperm whales, according to Dagg, old females help babysit the group's young while their mothers dive for food.

Orca grandmothers often lead their pods and can live for decades after they stop reproducing. (The oldest known orca, nicknamed "Granny," died in 2016 at over 100.) In 2015, scientists writing in the journal Current Biology suggested that these elder orcas help their descendants survive during hard times, because they remember all the best places to find food.

Elephant herds are also famously matriarchal. Calves are typically born into groups led by their grandmothers, who can live to around 80 years old. The females in a herd form close bonds, said Lahdenperä, and collaborate to raise their young.

In a 2016 study in the journal Scientific Reports, Lahdenperä tried to determine if being an elephant grandmother has evolutionary benefits. She analyzed records from a semi-captive population of Asian elephants working for the timber industry in Myanmar. Some adult females still lived in groups with their mothers, while others had been moved to different areas.

Lahdenperä found that the calves of young mothers were eight times more likely to survive if their grandmothers lived near them than if they didn't. When the calves' mothers were older and more experienced at raising babies, this beneficial "grandmother effect" disappeared even if the actual grandmothers were still around, she found.

It isn't entirely clear how elephant grandmothers help their inexperienced daughters, said Lahdenperä. There's anecdotal evidence that they may help nurse their grandcalves, thereby giving them a nutritional boost. But Lahdenperä thinks that the more likely advantage is the wisdom a grandmother elephant has amassed during her long lifetime. If a calf gets stuck in a mud pit, for example, its grandmother might be more successful at helping the calf than its mother would be, because she's seen similar situations.

Indeed, most evidence for the benefits of grandparenting comes from mammals. But in 2010, researchers reported in Current Biology that in colonies of insects called gall-forming aphids (Quadrartus yoshinomiyai), older females defend their relatives after they've ceased to reproduce. And a 2007 study in the journal Evolution found that older female Seychelles warblers (Acrocephalus sechellensis) sometimes help their offspring raise chicks.

And what about grandfathers? Studies of humans in recent decades have shown that a living grandfather can improve a person's mental health and other indicators of well-being, said Lahdenperä. But there's no evidence of that in the animal kingdom, she said. Male animals rarely socialize with their own progeny, let alone any further descendants. "Males are usually focusing on producing [more of] their own offspring, and aren't providing so much care," Lahdenperä said.”

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