13 NATURE’S WEIRDEST LIFE CYCLES

Rogue Queens, Sex-Changing Fish, and Rain-Making Bacteria: Nature’s Weirdest Life Cycles
By Brandon Keim, Wired, 29 May 2013.

The word 'unnatural' is often used to describe what's considered weird or unusual. But is anything weirder than nature?

Just look at 17-year cicadas, poised to flood the U.S. East Coast after having stayed underground since Bill Clinton was President. And cicadas are just the start: Biology abounds with creatures that change shape, change sex, change locations and in some cases cause other creatures to do these things.

It's a strange, marvellous world out there. On the following pages are gathered some of life's oddest, most extraordinary journeys.

1. A Long Wait

Image: Dan Century/Flickr/Cicadamania.com

Everyone's wondered what it would be like to step outside time for a while, to disappear one day and return, years later, to the same spot in a changed world. That's what cicadas of the Magicada genus have evolved to do.

The Magicada species are known as 13-year and 17-year cicadas, the latter of which will in coming weeks emerge from East Coast soils. In keeping with their name, they last visited 17 years ago, when they hatched from eggs laid on trees and plants and burrowed into the soil below.

Since then they've lived underground, drinking tree sap and slowly assuming adult form. After emerging, they'll live for just one more month, devoting their final days to finding mates. In a few months, the next generation will hatch and begin the cycle anew.

Except for their 13-year cousins, it's a life cycle unprecedented in the natural world. Scientists think it evolved as a defense mechanism: The time lag makes it difficult for predators to specialize in eating them, and when they do emerge, their overwhelming numbers make any losses insignificant.

2. Parasites and Rogue Wasps

Parasites alter host behaviour in all sorts of bizarre, self-serving ways, the most infamous example being Toxoplasma gondii that alter rodent brains - by, say, making them attracted to cat urine - so as to increase their chances of being eaten, thus transferring T. gondii to the predator intestines where they reproduce. Perhaps the strangest of all parasite-induced life cycles, though, is that produced by Xenos sparum fly larvae that each spring infects European paper wasps.

A parasitized wasp worker becomes withdrawn and selfish, shirking its colony duties, a behaviour unknown in the society-first, caste-programmed world of wasps. Eventually the worker leaves its colony and flies to some predetermined gathering place for parasitized wasps. At this point male X. sparum wriggle out from their hosts and mate with females, which remain inside.

Wasps originally infected by males die shortly after this morbid bacchanal, but wasps infected by females survive, gathering food and fattening themselves - an indulgence typically experienced only by queens. Come autumn, fattened and strong, the rogue wasps fly to places where queens gather to hibernate through winter. They don't engage in any queen-like reproductive behaviour; they're just living the life.

When next spring arrives, infected wasps wander through the countryside, depositing X. sparum eggs under leaves as traps for the next generation of unwary victims. They even sneak back into wasp colonies, where soldier wasps haven't yet matured, and in one final act of rebellion, spread X. sparum inside them.

3. When Nemo Grows Up

Image: Joshua Nguyen/Flickr

Clownfish are far from the only sequential hermaphrodites, but they're one of the few species in which males change into females, rather than vice versa. (They're also the most adorable.)

Each anemone-dwelling clownfish colony contains one dominant female, several adult males, and adolescents of both sexes. If if the dominant female dies, one of the adult males will undergo hormonal changes that transform it into the colony's new matriarch.

4. Eels Go the Other Way

Migratory fish the world over follow a single rule: They're born in fresh water, swim to the sea, and return as adults to spawn. Migratory eels do the opposite. They hatch at sea, thousands of miles from the nearest shore, and are carried by currents to land. Just a finger-length long and still sexually indeterminate, they swim up streams and rivers, along the way becoming male or female and eventually reaching the waters where they'll spend their adult lives. Years later, they swim back to sea, gathering thousands of miles away to mate.

How do they find their way back? What determines if an eel becomes male or female? Nobody knows. In fact, there's a whole lot that's not known about eels.

5. The Symbiotic Salamander

Each of our cells contain structures descended from organisms that, billions of years ago, found a mutually beneficial niche inside primeval multicellular organisms. We're also full of bacteria, to the point where the microbes in our bodies vastly outnumber human cells. But these symbioses don't involve organisms that can actually be seen by the naked eye and would on their own be considered high-level forms of life, as is the case with spotted salamanders and algae.

After spotted salamanders lay their eggs, algae drift inside, thriving in the nitrogen-rich environment. As the embryo develops, algae actually migrate inside its cells, where they may nourish development by processing key nutrients. If that salamander turns out to be a female, she may pass on the algae to her own offspring.

6. Small Fish, Big Fish, Flatworm

Prosorhynchoides borealis flatworms hatch inside clams buried in seafloor mud off the coast of Iceland. When the larvae finish eating the clams, they wriggle outside, drifting in currents until landing on the scales of a passing cod. Into the cod they burrow, passing through its body and congregating in its nervous system, where they reach the next stage of their lives.

The flukes still aren't ready to reproduce, though. That requires the intestines of monkfish, a large, toothy predator of cod. Only after a cod is eaten - something that, if other parasites are a guide, Prosorhynchoides might encourage by altering the cod's behaviour - do the flatworms finish their life cycle, laying eggs that are excreted in faeces and come eventually to rest on the seafloor, infecting the next generation of clams.

7. Tricking the Trickster

It's an ecological dance so complicated that it deserves a flow chart. Alcon blue butterfly caterpillars secrete ant pheromone-mimicking chemicals that trick local ants into picking up their eggs. The ants raise the larvae (above), feeding and protecting them while ignoring their own offspring. Meanwhile, Ichneumon eumerus wasps have evolved to exploit this deceit: when they detect an Alcon caterpillar inside an ant colony, they rush inside, spray a chemical that makes the ants attack each other, and amidst the confusion lay eggs inside the Alcon. When it forms a chrysalis, the larvae hatch and eat it. [More here and here]

8. A Very Singular Purpose

Adactylidium are a genus of parasitic mites that live on the eggs of tiny, fringe-winged insects and were once objects of puzzlement to scientists, who noticed that male Adactylidium inevitably died within a few hours of emerging from their mothers' bodies. They accomplished nothing, not even reproduction, in that brief time.

What was going on with the males? Microscope studies showed that, inside each impregnated female, her own eggs hatch a brood consisting of some half-dozen sisters and a single male. As the brood develops, the lone male copulates with his sisters; by this time, mom has died. By the time the sisters are old enough to chew through her body and reproduce anew, the male's job is done, and he dies soon afterwards. Sometimes he never even crawls outside, spending the entirety of life inside mom.

9. Duck-Billed Oddness

Image: Alan Couch/Flickr

The only mammal on the list, duck-billed platypi are one of just five mammal species to lay eggs. (The others are spiny anteaters.) This is thought to be an ancient trait, something that was common hundreds of millions of years ago in ancestral mammals but has been almost entirely lost to evolutionary time.

In a trait that's simultaneously endearing and icky, female platypi secrete milk that is licked off their stomachs by their offspring. Since platypi wriggle belly-down on land, the offspring get generous serving of dirt, too, which may help strengthen their immune systems.

10. Slime Mould

Is a slime mould an animal? Or not? The answer is: sometimes.

When you encounter a slug-like slime mould under a forest log or rock, it actually contains millions of formerly single-celled protists gathered in one giant protoplasmic broth. If you watch the mould long enough, or make a film and watch it sped up, you'll see it wander in search of food. After finding food, it forms a stalk topped by a spore-filled sac. The spores contain a fortunate few of the original single-celled protists' nuclei; when the sac bursts, the rest are left behind.

The spores land and again become single-celled organisms. When they're done eating, they converge, forming a slug with a fresh appetite.

11. Ant Berry Surprise

Berry-loving birds abound in the South and Central American forest homes of giant Cephalotes atracus ants, offering possibilities that Myrmeconema neotropicum roundworms neatly exploit. They make the giant Cephalotes atracus ants they parasitize physically resemble berries, with swollen, bright-red abdomens that the ants feel an urge to shake in the air, drawing the attention of those berry-eating birds in whose droppings M. neotropicum will spread. [More here and here]

12. Bacteria Make it Rain

The only bacteria on this list, Pseudomonas syringae are sheathed in proteins that allow ice crystals to form around them at above-freezing temperatures. (In the image above, P. syringae bacterium are seen in a cross-section of ice.) When this happens on the surface of leaves, the plants wither, giving P. syringae something to eat. Then, after the plant has decomposed, they're swept by winds into the atmosphere, where they once again seed an ice crystal that falls as rain onto the next leaf.

13. Who Needs Men?

Female-only, self-cloning species were once considered evolutionary oddities, reproductive dead-ends doomed to early extinctions. There's dozens of them, though, and there are benefits to reproducing parthenogenetically, as the ability to hatch an unfertilized egg is technically known. To continue your lineage, you don't need any help.

The whiptail lizard above is actually a member of a newly-created parthenogenetic species that arose from the hybridization of two sexually-reproducing lizard species. Though their parents had sex, these lizards never will.

[Source: Wired. Edited. Some links added.]