Tag Archives: nature

Sympathy for the Devils

This work by Mike Lehmann is licensed under a Creative Commons Attribution 3.0 Unported License.

Tasmanian devil, a marsupial native to the Australian island of Tasmania
[This work by Mike Lehmann is licensed under a Creative Commons Attribution-Share Alike 3.0 Unported License.]

Last week, I was lucky enough to attend the TedX DeExtinction event in Washington, DC. The event, hosted by National Geographic and Revive & Restore, was a day long series of short talks about the science and ethics of “de-extinction.” De-extinction is the idea that you can use new reproductive and stem cell biology techniques to revive extinct species, from the recently disappeared (e.g. bucardos and gastric brooding frogs) to the long lost (e.g. wooly mammoths  and giant ground sloths). The event raised quite a few questions on the ramifications of bringing species back from the dead: would de-extinction take funding away from conservation efforts? Would a de-extinct mammoth really be a mammoth? Would there even be a place for these new old species in our changing world? Is de-extinction, like the moon landing, a vehicle to inspire scientific wonder and progress?

We can (and should) argue about the ethics and reasons for reviving lost species, but we should also explore how to use synthetic biology to save dwindling species from imminent extinction. Take for example, the Tasmanian devil. Though these large marsupials were once common across Tasmania, their population has been devastated by a strange form of contagious facial cancer.

In the late 1990’s, facial tumors were spotted on devils in northeastern Tasmania. The cancer was deadly, killing the animals it infected within six months. More importantly, the cancer jumped from devil to devil with ease by taking advantage of the species’ aggressive nature: when Tasmanian devils fight (which they often do), cancer cells can be transferred from the teeth of an infected devil to the face of their uninfected sparring partner. The facial cancer has caused a 90% drop in devil population since it appeared, and total extinction of the species within 30 years is a distinct possibility.

This work by Menna Jones is licensed under a Creative Commons Attribution 2.5 Generic License.

Tasmanian devil face tumors
[This work by Menna Jones is licensed under a Creative Commons Attribution 2.5 Generic License.]

Transmissible cancer isn’t unheard of. Dogs can pass on a form of venereal cancer, and there’s a contagious sarcoma that affects Syrian hamsters. Cancer transmission has also been known to happen in humans after organ transplants or by passing between mother and fetus. However, in most animals, the immune system recognizes and destroys foreign cells (cancerous or otherwise). In fact, this is one of the main hurdles with organ transplants. Recipients have to take immunosuppressive drugs and in some instances immune system reactivity leads to organ rejection. In the case of Tasmanian devils, however, this immune hurdle doesn’t exist.

Immune system recognition of “self” and “other” relies on molecules on the surface of the cell called major histocompatibility complexes (MHCs). MHCs act as signaling flags to the immune system, telling your immune cells whether a cell is normal, infected with a pathogen, cancerous, or an invader. There are two main classes of these molecules, and each one has regions that vary among members of the population. Variation in MHC molecules allow immune cell to differentiate your cells from other cells, kind of like knowing members of your sports team because you all wear the same jersey. Human MHC class I molecules have six sites where they can vary, and hundreds of variations available for most sites.

Tasmanian devils, on the other hand, have very little population diversity in MHCs. At some point in the past, the devils experienced what’s known a genetic bottleneck. A large portion of the population was killed (cause unknown), leaving only a small gene pool, and thus a small sampling of MHC variations.

Tasmanian devil MHC complexes are so similar that their bodies can’t  tell the difference between their own cells and those of other devils. Every team’s jersey is so similar that it’s hard to know who’s on the home team and who’s the visitor. So when cancer cells from an infected devil latch onto an uninfected devil, they go undetected by the immune system and spread unhindered. Genetic studies of the cancer have shown that the DNA of tumor cells is extraordinarily similar across the infected devil population. Furthermore, the tumor DNA is significantly different from the infected devil’s DNA. These facts point to a tumor that arose in one devil and spread as a tissue graft to other devils through bites. Because of their lack of immune diversity, the Tasmanian devil population is being wiped out by one giant tumor run amok.

What can we do to stop the eradication of Tasmanian devils? Synthetic biology may have the answers. Developing technology may allow scientists to create Tasmanian devils with more MHC diversity, devils with immune systems that would spot and destroy the invading cancer cells before they took root. In my next blog post, I’ll talk about the discoveries and technology that could save the Tasmanian devil, and other species that are near (or already) extinct.

716px-Tasmanian_devil_head_on

How can we save these guys? Tune in next time to see!
[This work by KeresH is licensed under a Creative Commons Attribution-Share Alike 3.0 Unported License.]

Sources:

O’Neill, Iain. “Tasmanian devil facial tumor disease: Insights into reduced tumor surveillance from an unusual malignancy.” International Journal of Cancer. 127.7 (2010): 1637-1642.

 Siddle, Hannah et al. “Transmission of a fatal clonal tumor by biting occurs due to depleted MHC diversity in a threatened carnivorous marsupial.” PNAS. 104.41 (2007): 16221-16226.

Siddle, Hannah et al. “MHC gene copy number variation in Tasmanian devils: implications for the spread of a contagious cancer.” Proceedings of the Royal Society: Biology. 277.1690 (2010): 2001-2006.

Woods, Gregory et al. “The Immune Response of the Tasmanian Devil & Devil Facial Tumour Disease.” EcoHealth. 4.3 (2007): 338-345.

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Sequestration: Much Better in Nature Than in Congress

“You are what you eat” has become a cliché spouted by parents and diet gurus alike. Of course, while most of us might feel a bit sick after eating all the leftover Halloween candy, we’re not going to turn the yellow of Lemon Heads or start oozing chocolate out of our skin glands. For some members the animal world, however, diet is important for more than nutrients and energy. In fact, many species depend on their food to give them the colors, poison, and unearthly glow for which we know them best. Here are four animals for which “you are what you eat” is a fact of life:

 

The golden poison dart frog. The size of a paper-clip but toxic enough that one frog has enough poison to kill 2 elephants. [image source]

The golden poison dart frog is only as big as a jumbo paper-clip, but so deadly that one frog contains enough poison to kill two elephants. [image source]

1.  The golden poison dart frog goes by the scientific name P. terriblis with good reason. It may be the most poisonous animal in the world – terrible indeed for would-be predators. Despite their diminutive size (up to 55 millimeters long, about two US quarters placed side by side), golden poison dart frogs pack quite a punch. One frog carries enough poison to kill ten to twenty humans. However, unlike many other poisonous animals, golden poison dart frogs outsource their poison production. The frogs isolate and concentrate alkaloid batrachotoxins from the bugs that they eat, a process called sequestration. During digestion, batrachotoxin is shuttled from the frogs’ gut to special skin glands, where it becomes a key ingredient in the deadly slime that coats their skin. Concentrating the poisonous chemicals in their food is a common thread with all poison dart frogs, but P. terriblis’s use of batrachotoxin in particular is what makes it especially deadly. Frogs kept in captivity will lose their toxicity, since their new diet doesn’t usually include the alkaloid-rich bugs crucial to toxin production.

Frogs aren’t the only animal that uses the capture-and-concentrate tactic for making poisons. For example, the monarch caterpillar is also poisonous because of an alkaloid-rich diet (in this case, the leaves of the milkweed plant). Some of this toxin carries over to the adult butterfly, making it an unpleasant meal for predators.  There are even several species of birds in Papua New Guinea that use the same strategy, appropriating insect alkaloid toxin and storing it in their skin and feathers.

 

 

Flamingos and many other birds get bright colors by sequestering pigments from their food [image source]

Flamingos and many other birds get bright colors by sequestering pigments from their food [image source]

2. Sometimes an animal’s signature color comes from what it eats – flamingos owe their lovely pink-red hue to a class of pigments called carotenoids. Carotenoids are first produced by plants (beta-carotene is what gives carrots their orange color). Flamingos get their carotenoids from the plankton, algae, and brine shrimp they eat. In fact, a lot of the color variation across flamingo species comes from their food source. Flamingos that feed on carotenoid-producing algae directly are a darker hue than those that get their carotenoids through a second-hand source (like eating shrimp that eat algae). Without this dietary infusion of color, flamingos would be a dull gray or white. Flamingo coloring is a big concern in zoos and aquaria, where the birds don’t get all the carotenoids they would in the wild. To keep their animals more naturally colored (and attractive to visitors), zookeepers may feed them extra prawns or sprinkle their food with a concentrated carotenoid additive.

Scarlet tanager males and females are both colored by carotenoids [image source: male female]

Scarlet tanager males and females are both colored by carotenoids [image source: male female]

Carotenoid-derived coloring is not uncommon, especially among birds. The red plumage of scarlet ibises and cardinals and the pink bellies of salmon all owe their distinctive color to a diet high in the pigment. Scarlet tanager males are turned (you guessed it) scarlet by a high-carotenoid diet, while the females are an olive-green from the interaction of carotene and another pigment, melanin.

 

 

Nudibranch sea slugs steal both color and poison from their food [image source]

Nudibranch sea slugs steal both color and poison from their food [image source]

3. Members of the nudibranch sea slug family scavenge both color and toxins from their prey. Among the family are some of the most brightly colored denizens of the ocean – and that’s saying a lot for since nudibranchs make their home in the kaleidoscopic world of coral reefs. These slugs dine on other invertebrates like baby jellyfish, coral polyps, anenomes, and even other sea slugs. Nudibranchs can sequester pigments from their prey and then display them on their own skin, creating a colorful pattern well matched to their environment. Among the brilliant background of a coral reef, the nudibranchs’ rainbow hues are the perfect camouflage.

Considering the fact that many nudibranchs can also recycle more active defense mechanisms, their bright skin is also warning to predators. Nudibranchs that feed on jellyfish can steal their prey’s special stinging cells (nematocysts). The nematocysts travel harmlessly through the slug’s digestive tract and are transported to their back, where the nematocysts begin their new life as a slug defense mechanism. And like poisonous dart frogs, certain nudibranchs concentrate toxins from the sponges they eat to make their own poisonous brew. 

 

 

Aequorea Victoria jellies need to eat fluorescent food to flow [image source]

Aequorea Victoria jellies need to eat fluorescent food to flow [image source]

4. Aequorea victoria jellyfish, like many other bioluminescent animals, glow a soft fluorescent blue and green thanks to a chemical cascade taking place inside their clear flesh. This species of jellyfish holds a special place in the hearts of many biologists, who use the jelly’s green fluorescent protein (GFP) in everything from imaging to genetic engineering. In fact, the discovery and development of GFP as a tool won several scientists a Nobel Prize in 2008.

For all the glory given to GFP, it’s not actually the piece of the cascade that supplies the jellyfish their glow. GFP simply takes the light from another molecule, coelenterazine, and shifts it from blue to green. Coelenterazine is a type of luciferin, a light-emitting molecule. During the light-producing chemical cascade, coelenterazine is energized to an excited state by the enzyme luciferase. Coelenterazine then returns to an unexcited state by releasing energy in the form of light.

coelenterazine2

A simplified version of the light-producing cascade in A. victoria jellies

Scientists in the lab have to externally supply coelenterazine to their specimens for them to glow; as it turns out, the A. victoria jellies have to import coelenterazine as well. A. victoria at the Monterey Bay aquarium slowly lost their ability to glow, but when the jellies were fed a diet of bioluminescent plankton, they lit right back up. The luciferase enzyme part of the bioluminescence cascade is coded into the jellyfishes’ DNA. However, they need to scavenge the actual light source from already glowing prey – like having to steal a bulb from a neighbor every time you wanted to turn on your lamp.

The Whistling Ducks of Pointe-a-Pierre

Black-Bellied Whistling Tree Ducks at the Point-a-Pierre Wildfowl Trust

Black-Bellied Whistling Tree Ducks at the Point-a-Pierre Wildfowl Trust

My family hails from the Trinidad, the southernmost island in the Caribbean.  We still go back every few years to visit, and I always look forward to good food and time with my extended family. I also try to squeeze in as much jungle and beach visiting as I can. When my family planned a trip for this past Christmas, I vowed to myself that I would drag them on some eco-adventures by whatever means necessary. The means turned out to be whining (and a lot of it). But, on our second to last day on the island, we made it out to the Pointe-a-Pierre Wildfowl Trust.

Pointe-a-Pierre Wildfowl Trust is a bird sanctuary and breeding center tucked away inside the grounds of the Petrotrin Oil Refinery. The friendly guards at the refinery gates waved us in once we’d explained why we were there (they don’t want people to just come wander around the refinery for no good reason). We followed their directions down winding roads through the refinery grounds. When we finally made it to the Wildfowl Trust, we were greeted by a different sort of guard – a curious but wary Indian Peacock, who was seemingly unaware that his bedraggled tail was more sympathy-inducing than impressive. He strutted around our car, fanning that molting tail if we got too close and letting out some extraordinarily strident cries. He eventually seemed satisfied that we weren’t a threat (or he’d figured out that we weren’t going to feed him) and left us alone after we started down the gravel path to the visitor center of the Trust.

Indian Peacock that greeted us

The Indian Peacock that greeted us in the parking lot

Pointe-a-Pierre’s main visitor building, the Learning Centre, serves as a staging area for tourists and students, souvenir shop, and tiny museum. It’s filled with preserved animal and insect specimens in varying states of disrepair and yellowing educational posters. You don’t come to the Trust for the Leaning Centre, however – you come for the gardens and birds surrounding it.

On the porch outside the building, Frankie the Blue-and-Gold Macaw gives guests a much friendlier greeting than the peacocks in the parking lot. A victim of the illegal pet trade, Frankie was confined at a young age, disrupting proper wing growth. He’ll never be able to fly and is kept separate from the other macaws at the Trust (a small breeding population) due to his special needs. He is now used to educate visitors and students about conservation and animal treatment. In a scratchy voice, Frankie tells visitors “Hello” as they pass by.

Frankie, the Blue-and-Gold Macaw, having a snack.

Frankie, the Blue-and-Gold Macaw

The Learning Centre is also surrounded by a tropical garden, filled with bright flowering trees and plants. More peacocks, including alabaster White Peacocks, strut through the garden, occasionally followed by a group of peahens (female peafowl, peacocks are the male of the species); the ladies seemed much less interested in the humans wandering around their home.

A White Peacock and some peahens enjoying food that Frankie dropped out of his cage. A Muscovy Duck joined in the feast.

A White Peacock and some peahens enjoying food that Frankie dropped out of his cage. A Muscovy Duck (left) joined in the feast.

Our official tour starts with one of Pointe-a-Pierre’s lakes. The Trust serves two main purposes – to educate the public about environmental issues and to breed and release several species of endangered or threatened birds.

The commitment of the Trust to breeding native wildfowl is evident as soon as we reach the lake. The shore is covered in ducks. Many of them rest standing on one leg on a nearby tree and nesting boxes. The vast majority of the birds are small waterfowl with bright coral-orange beaks and feet. Their bodies are mostly a soft brown fading to grey on their heads, with black-edged white wings, black bellies, and black tails. And though these are definitely ducks, they don’t quack. When we first approached the lake, I thought we were hearing the cries of native songbirds, but the whistling “pichichi” sound that filled the air was coming from the collection of ducks on the lake shore. These are the Black-Bellied Whistling Tree Ducks for which the Trust was founded.

Black-Bellied Whistling Tree Ducks resting on one of their nesting boxes. In the wild, they nest in hollow trees.

Black-Bellied Whistling Tree Ducks resting on one of their nesting boxes. In the wild, they nest in hollow trees.

It was actually a hunter who took the first steps to preserve the Black-Bellied Ducks. He noticed that there were fewer ducks around each year, and decided that something had to be done to preserve the island population. Black-Bellied Whistling Tree Ducks weigh only 1.5-2 pounds; each duck provides very little meat, so hunters must kill more of them to get the same amount of meat that fewer larger ducks would provide. The Black-Bellied Ducks are also docile and easy to catch. While the bird isn’t endangered worldwide, they are threatened by over-hunting in Trinidad. Since 1962, the Wildfowl Trust has released over 1300 Black-Bellied Whistling Tree ducks alone and over 1400 other ducks of various species.

Black-Bellied Whistling Tree Duck in flight. Source: http://americans4birds.ipower.com/waterfowl.html

Black-Bellied Whistling Tree Duck in flight.   (Source)

The wild Trinidadian population of Black-Bellied Ducks lived in the island swamps, feeding at night. They can also be found along the coast of Mexico and northern South America. Whistling tree ducks live in family groups, which they protect aggressively against outsiders (including other Black-Bellied Ducks). They huddle in groups on the shore and swim in neat rows among the lily pads, like something out of a children’s book.

Black-Bellied Whistling Tree Ducks swimming in a row

Black-Bellied Whistling Tree Ducks swimming in a row

Duck mating pairs are monogamous and will stay together for years raising and taking care of their young. Some of the ducks at the Trust are still young enough to have a grey beak instead of the orange beak of an adult (placing them at under 8 months old). 

Juvenile Black-Bellied Duck. In addition to a grey instead of orange beak, their plumage is also less bright than adults. Source: http://www.pbase.com/nsxbirder/image/117423122

Juvenile Black-Bellied Duck. In addition to a grey instead of orange beak, their plumage is also less bright than adults. (Source)

Birds like the whistling tree duck aren’t as flashy as macaws or peacocks, but they’re an important part of the ecosystem all the same. The ducks eat mosquito larva, keeping down the insect population. They also disperse plant seeds in their scat; water lilies in particular rely on species like ducks to spread their seeds. The Trust aims to educate school kids and visitors alike on links between humans and the environment, by immersing visitors in the natural world around them and through educational signs posted around the Trust grounds.

Our tour takes us past several signs detailing the rain cycle, feeding chain, and climate change. We also pass breeding cages of Blue-and-Gold Macaws (like Frankie), who had been driven to extinction on the island by the illegal pet trade. These birds had been imported from Venezuela in an effort to re-establish a native population. There are more ducks too – White-Faced Whistling Ducks, Fulvous Whistling Ducks, White Cheeked Pintails, and Muscovy Ducks (easy to pick out by the red patches on their faces).

A Muscovy Duck (with some Black-Bellies in the background). Muscovy's are much larger than the Black-Bellied ducks. Females like the one pictured here can weigh up to 7 pounds, and males  can weigh up to 15

Muscovy Ducks like the one in the foreground are much larger than Black-Bellied Ducks. Females (like the one pictured here) can weigh up to 7 pounds, and males can weigh up to 15

The trust even breeds Scarlet Ibis, a bright pinkish-red bird with a long curving bill that lives in the same swampy habitat as the Black-Bellied Whistling Tree Ducks. Ibises are hard to breed and require a very particular diet of shrimp and insects to maintain their vibrant color. The Scarlet Ibises in the Trust are the brightest I’ve ever seen, and the Trust has successfully released almost 100 specimens into the wild.

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Scarlet Ibis breeding enclosure. Juvenile ibises are grey and their scarlet feathers come in as they mature

It’s fitting that we leave the Trust the same way we came in, escorted by a curious (and probably hungry) group of peacocks. They’re still swaggering around like we humans are but lowly peasants in their kingdom. From the loving treatment and reverence I’ve seen given to the birds here, I think they’re right.

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Further reading:
Pointe-a-Pierre WildFowl Trust webiste
Listen to the calls of the Whistling Tree Duck