Life in Slow Motion: the Three-Toed Sloth

(Via: Wikimedia Commons)

Common Name: Three-Toed Sloth

A.K.A.: Genus Bradypus

Vital Stats:

  • There are four species of three-toed sloth: brown-throated, pale-throated, maned, and pygmy
  • Critically endangered pygmy sloths are thought to number only around 300
  • Average body length of around 45cm (18”)
  • Two-toed sloths have a similar arboreal lifestyle, but belong to a different family entirely

Found: Rainforests of Central and northern South America

It Does What?!

Evolution, we’re sometimes led to believe, is an ongoing pressure to produce the fastest, strongest, and most cunning creatures possible, in an effort to improve each species’ fitness in its environment. But what if a niche existed in which being well-adapted simply meant holding very still and taking it easy?

Oh, to be a sloth.

Three-toed sloths are small-dog-sized mammals which live in the rainforest canopy and survive on a diet of leaves. Rather than sitting atop the branches and risking a fall if they lose their balance, sloths use their large claws to cling to branches from below, even sleeping in this position. Leaves aren’t exactly the most nutritious food, calorie-wise, so they conserve energy by moving  v e r y   s l o w l y,  reaching top speeds of around 240m (787’) per hour. Over the course of an entire day, this works out to only 3 or 4 different trees, at most. And this is in their natural environment of the canopy; on the ground, sloths are practically helpless. Unable to even stand due to their minimal musculature, they must simply pull themselves along the earth if a break in the canopy necessitates a ground crossing. [Check out this video of a sloth crossing a road in Costa Rica with the help of some protective humans… your heart will break for the poor thing.]

When vegetation starts growing on you, it’s time to get some exercise.
(By: Maureen Sokolovsky, Via: travelhotnews.com)

This same natural… well, sloth, is what helps them to avoid their main predators, which include jaguars, anacondas, and birds of prey. Hanging motionless upside down, sloths can appear to be just another bunch of leaves. Aiding this illusion is the fact that many sloths are, in fact, somewhat green. This is due to a thin layer of algae which grows over their fur, each hair of which is specially shaped to encourage microbe growth. And the algae aren’t the only ones treating sloths as if they were inanimate objects; a species of moth known as the “sloth moth” also lives in their fur, while a small bird, the yellow-headed caracara, forages for its food there. Basically, other animals consider these guys to be just another piece of the landscape.

The energy-saving ways of the sloth really can’t be overstated- they don’t even maintain a normal mammalian body temperature, but one several degrees lower, necessitating a lot of basking in warm places to keep them comfortable. And the insides don’t go any faster than the outside; sloths only go to the bathroom around once per week, laboriously making their way down to ground level to use a special pit they’ve dug for themselves there. [Here’s another great video of Sir David Attenborough telling us about sloth toilet habits.]

The Zen-like smile of the world’s most chilled-out creature.
(By: Karla Aparicio, Via: Smithsonian Tropical Research Institute)

But surely the pace of things picks up a bit when it’s time to make baby sloths, right? Apparently not. Reports by researchers indicate that mating in sloths involves about twenty minutes of hanging nearly motionless in a tree together, followed by several days of hanging out a few metres apart, doing nothing and probably avoiding eye contact, before both decide it’s time to take off. Baby sloths are born singly, or occasionally as twins, and spend the first nine months of their life clinging to their mothers’ front, first nursing, and then licking chewed leaves from her mouth, before finally setting out on their own.

And that’s pretty much the life of a sloth. With a lifespan as long as thirty years, it’s a good thing they don’t get bored. Or maybe they do… giving us the answer to the question, ‘Why did the sloth cross the road?’

[Fun Fact: With nine cervical vertebrae, compared to only seven in most mammals, sloths have a huge amount of flexibility in their necks, with a rotation similar to that of owls.]

Says Who?

  • Bezerra et al. (2008) Journal of Ethology 26: 175-178
  • Dias et al. (2009) Journal of Ethology 27: 97-103
  • Raines (2005) Zoo Biology 24: 557-568
  • Taube et al. (2001) Mammal Review 31(3):173-188

    Bye!
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Randomly Assembled and Surprisingly Dangerous: The Platypus

(Via: National Geographic)

Common Name: The Duck-Billed Platypus

A.K.A.: Ornithorhynchus anatinus

Vital Stats:

  • Only species of Family Ornithorhynchidae
  • Males average 50cm (20”) long, females 43cm (17”)
  • Weigh between 0.7 and 2.4kg (1.5 – 5.3lbs.)
  • Body temperature of 32 degrees Celcius; five degrees lower than placental mammals
  • Live up to 17 years in captivity
  • Eat freshwater crustaceans, worms, and insect larvae

Found: Eastern Australia and Tasmania

It Does What?!

Besides looking like it was assembled from spare parts? We’ve all seen pictures of platypuses (yes, “platypuses”, not “platypi”) before, and everyone knows what total oddities they are: the duck-like bill, the beaver-esque tail, the fact that they lay eggs, despite being mammals; but behind these weird traits lie… even more weird traits! So let’s take a moment to appreciate the lesser-known eccentricities of the platypus, shall we?

First off, these cuddly looking freaks are actually dangerous. Male platypuses have a spur on each hind foot which is filled with a venom powerful enough to kill a large dog. While it isn’t enough to take out a human, it does cause severe, incapacitating pain whose after-effects can last for months. One of only a very few venomous mammals, the male’s venom production increases during the breeding season, suggesting its purpose may lie in competition with other males.

Why your dog and your platypus shouldn’t play together.
(By Jason Edwards, via: How Stuff Works)

And speaking of breeding, reproduction in platypuses isn’t exactly ‘mammal standard’, either. Unlike all other mammals, which have two sex chromosomes (X and Y; XX for females, XY for males, with rare exceptions), the platypus has ten. Talk about evolutionary overkill. A male platypus has the pattern XYXYXYXYXY, while a female has ten Xs. Researchers have found that the actual genetic structure of these sex chromosomes is actually more similar to birds than mammals, although 80% of platypus genes are common to other mammals.

After this alphabet soup of chromosomes arranges itself, up to three fertilised eggs mature in utero for about four weeks; much longer than in most other egg-laying species (in birds, this may be only a day or two). Once laid, the eggs are only about the size of a thumbnail, and hatch in around ten days. While platypuses produce milk, they don’t actually have proper teats to suckle their babies- the fluid is released from pores in the skin. A small channel on the mother’s abdomen collects the milk, which is then lapped up by the young. Strangely, the babies are actually born with teeth, but lose them before adulthood. Such is the impracticality of platypus design…

Adorably impractical.
(Via: noahbrier.com)

Finally, let’s explore platypus hunting methods. Platypuses are the only mammals with the sixth sense of electroreception. Those leathery duck bills of theirs are actually precision receptors that can detect the electric fields created in the water by the contractions of muscles in their prey. Considering the prey in question is largely worms and insect larvae, we’re talking big-time sensitivity here. The bill is also very receptive to changes in pressure, so a movement in still water can be picked up in this way as well. Researchers have suggested that by interpreting the difference in arrival time of the pressure and electrical signals, the hunter may even be able to determine the distance of the prey. This would be especially useful, given that platypuses close both their eyes and ears when hunting. In fact, they won’t even eat underwater; captured food is stored in cheek pouches and brought to land to be consumed.

So there you have it. The platypus: even weirder than you thought.

[Fun Fact:The female platypus has two ovaries, but only the left one works.]

Intelligent Design’s Worst Nightmare
(Via: Animal Planet)

Says Who?

  • Brown (2008) Nature 453: 138-139
  • Grant & Fanning (2007) Platypus. CSIRO Publishing.
  • Graves (2008) Annual Review of Genetics 42: 565-586
  • Moyal (2002) Platypus: The Extraordinary Story of How a Curious Creature Baffled the World. Smithsonian Press.

Death from Below! (The Purse-Web Spider)

(Via: Wikimedia Commons)

Common Name: Purse-Web Spiders

A.K.A.: Family Atypidae

Vital Stats:

  • The family contains three genera; Atypus, Calommata, and Sphodros
  • Females reach up to 30mm (1.2”) in length
  • Fangs can measure up to half the spider’s body length
  • Prey includes crickets, beetles, millipedes, ants, wasps, and other spiders
  • Web tubes measure up to half a metre (20”) from top to bottom

Found: Africa, temperate regions of North America, Europe, and Asia

It Does What?!

Imagine you’re a beetle, peacefully strolling along the forest floor, minding your own business, when suddenly, two enormous black spikes drive up out of the earth and impale you through the abdomen. As everything fades to black, your last beetle-ly thought is, “What the hell was that?!

You have just become a tasty lunch for the purse-web spider.

So how does this work? Well, unlike most of the spiders we’re familiar with – those with small, pincer-like mouths that sit in webs all day – purse-webs are a type of primitive spider called a mygalomorph. In this group, the fangs are like a pair of large (relative to the spider) tusks that only move up and down; they don’t pinch, and this feature lends itself to some rather creative hunting methods.

Rather than constructing a flat, aerial web designed to have something fall into it, the purse-web spider spins what is essentially a silken tube-sock. The ‘foot’ of this sock lies along a slight depression in the ground, while the upper part lies vertically against a tree or rock (or, in some species, angles downward into the earth). The spider will then place bits of bark and lichen onto both parts of the web as camouflage. Over time, moss will actually begin to grow on the web, completing the disguise. All the spider needs to do now is wait, suspended from the ceiling of her underground lair, for some unwitting creature to walk over it. When this happens, she rushes to the source of the disturbance and spears her prey from below with her fangs before they realise what hit them (like this).

Invisible by spider standards, anyway.
(Via: Wikimedia Commons)

The spider will be vulnerable to larger predators if she ventures out into the open, so she simply cuts a slit in the web, drags her impaled prey inside, and seals up the hole again. Having sucked out their delicious insides, she then drops the dead husks out of the top of her sock like so much household garbage. In fact, researchers determined the diet of the purse-web spider by noting the various exoskeletons hanging from the outside of the web, having gotten caught on their way down. Apparently, all the dead bodies seemingly stuck to the side of a nearby tree aren’t much of a deterrent to other passersby.

So, since these spiders never leave their burrows, and kill anything that approaches, mating must be tricky, right? Right. The male is attracted to the female’s web by means of pheromones, and ventures out to find it. Once he locates the web, he must be very careful, tapping at the outside of the tube in a way that indicates he isn’t prey. Ultimately, though, whether he’s prey or not will be up to her. If the female inside isn’t yet mature or is already pregnant, she won’t hesitate to eat him when he attempts to enter the burrow. Researchers experimenting with placing male spiders in or near the webs of unreceptive females noted, essentially, that they run like hell as soon as they figure out what’s what. Research is amusing sometimes.

A male purse-web spider on what will be either the best or worst day of his life.
(Via: Florida Backyard Spiders)

But in the happy instances where the female is willing to mate, the male enters safely, and in fact continues to live with her for several months of domestic bliss before he dies naturally. And then she eats him anyway. Spiders are not sentimental creatures. Her eggs will take almost a year to hatch, and the young will stay with her for nearly another year after that, before striking out in the world to spin their own tube-sock of death.

Says Who?

  • Beatty (1986) Journal of Arachnology 14(1): 130-132
  • Coyle & Shear (1981) Journal of Arachnology 9: 317-326
  • Piper (2007) Extraordinary Animals: an encyclopedia of curious and unusual animals. Greenwood Press, Westport CT.
  • Schwendinger (1990) Zoologica Scripta 19(3): 353-366

What’s the matter, louse got your tongue? (Cymothoa exigua)

Via: Parasite of the Day

Common Name: The Tongue-Eating Louse

A.K.A.: Cymothoa exigua

Vital Stats:

  • Females are 8-29mm long by 4-14mm wide (0.3”-1.1” x 0.16”-0.55”)
  • Males are 7.5-15mm long by 3-7mm wide (0.3-0.6” x 0.12”-0.28”)
  • Preys on 8 species of fish from 4 different families

Found: In the Eastern Pacific, between the Southern U.S. and Ecuador

It Does What?!

With a name like “Tongue-Eating Louse”, you know this is going to be viscerally horrible, but bear with me… it’s also pretty neat. Despite the name, these aren’t actually lice, but parasitic crustaceans known as isopods. While there are dozens of species in the genus Cymothoa, most are parasites which live in the gills of fish and are, relatively speaking, unremarkable. But Cymothoa exigua is something special. While the male of the species (and this is a slippery term, as they can change sex when necessary) lives in fish gills, the female has developed an altogether original strategy.

Try to enjoy a tuna sandwich now.
Via: Smithsonian.com

Entering through the gills, the female takes up a position at the back of the fish’s mouth and attaches herself to the base of its tongue. She then pierces the tongue with her front appendages and begins to consume the blood inside it. Over time, the lack of bloodflow causes the tongue to slowly wither up and fall off. What’s left is a stump consisting of about 10% of the original tongue (yes, someone measured this). The parasite can now attach herself to the stump using her seven pairs of hook-like pereopods (read: ‘feet’) and actually begin to function as the fish’s tongue.

What’s really amazing is how well this seems to work. The parasite has evolved a body shape which closely matches the curves of the inside of the host’s mouth. Unlike our tongues, a fish tongue has no real musculature or flexibility; its only real function is to hold food against the fish’s teeth. With the parasite in place, the host is able to use its body to do exactly that. While the isopod is thought to feed on the fish’s blood, researchers have found that infected hosts have normal body weights and typical amounts of food in their digestive tract when caught. This is, to date, the only known case of a parasite functionally replacing an organ in its animal host.

Once it’s in there, this thing’s not coming out without a fight.
Via: This Site

Because edible snapper fish are amongst the host species of C. exigua, there have been cases of the parasite showing up in people’s supermarket purchases, including one person who thought they had been poisoned after eating one. So are they dangerous? Not to eat, no, but researchers tell us they can give a nasty little bite, given the opportunity. So the moral of this story is: if you bring home a fish for dinner and see an evil-looking parasite posing as its tongue… don’t stick your finger in its mouth.

.

Says Who?

  • Brusca & Gilligan (1983) Copeia 3: 813-816
  • Brusca (1981) Zoological Journal of the Linnean Society 73(2): 117-199
  • Williams & Bunkly-Williams (2003) Noticias de Galapagos 62: 21-23
See you in your nightmares.

Sea Cucumbers, or, How to Really Lose Weight Fast

Via: www.starfish.ch

Common Name: Sea Cucumbers, Holothurians

A.K.A.: Class Holothuroidea

Vital Stats:

  • Approximately 1250 species
  • Size: 2-200cm (¾” to 6.5’)
  • Lifespan: 5-10 years in the wild

Found: Throughout the oceans, in both shallow and very deep regions

It Does What?!

Where to begin? This is an odd one… To start, despite the name sea cucumber, this isn’t a plant but an animal; a relative of starfish and sea urchins. One could be forgiven for mistaking the holothurians for plants, however. Most spend their lives lying on the ocean floor, looking like a sunken vegetable, and covering a distance of a couple metres or less per day in their search for food. The creatures feed on small particles, like algae and plankton. There is a tiny mouth at one end of their body, surrounded by between eight and thirty tentacle-like feet with which they grab their food and which can actually be retracted into their mouth. But that’s not really the interesting end of a sea cucumber, as we’ll see.

Via: www.answers.com

Lacking both eyes and any rapid means of locomotion, holothurians are tempting prey for crabs, fish, and other large sea creatures. When threatened, they have the single most bizarre and seemingly impractical defence mechanism ever evolved: self-evisceration. As a predator approaches, the sea cucumber violently contracts the muscles around its body wall and actually expels its own internal organs via its anus (demurely labelled as the ‘aboral pole’ in the diagram). Yes, really. In some species, these organs include most of the creature’s respiratory system, which takes the form of sticky threads that blanket and ensnare the predator. And just to add genuine injury to the insult, this discharge is accompanied by a toxic chemical known as holothurin, which kills whatever’s nearby. Disgusting, but effective. Once expelled, the missing organs can be regenerated in 1-5 weeks, depending on the species. Some researchers speculate that this ability may even be used as a means of ridding the organism of accumulated waste or parasites. The ultimate detox regime, if you will.

Are those your lungs, or are you just happy to see me?
Via: Wikimedia Commons

One such parasite is the pearl fish. You see, holothurians actually breathe through their rear end as well, so when one of them, umm… opens up… to take in some fresh, oxygenated water, in goes the fish, which then feeds on the sea cucumber’s internal organs. You can see why they might want to rid themselves of this visitor.

Strange as it all seems, the sea cucumber’s strategy is quite a successful one. At depths below five and a half miles (8.8km), they make up fully 90% of the mass of all macrofauna (i.e. any animal that’s not microscopic). Among the species that live at shallower depths, populations can reach a density of 1000 cucumbers per square metre. And it’s a good thing, because they’ve got one predator with whom spewing out their guts won’t work: humans. Sea cucumbers are a popular ingredient in Chinese and other Southeast Asian cuisines, although only about ten species are used for this purpose. These species are farmed commercially in artificial ponds, and are also used in traditional Chinese medicine. Perhaps not surprisingly, they are considered to improve male sexual health.

Does a Body Good.
Via: www.theworlds50best.com

[Fun fact: Sea cucumbers have a body wall made up of collagen fibres which they can ‘unhook’ at will, essentially liquefying their interiors and allowing them to squeeze into very small cavities as a means of hiding from predators. Once inside the cavity, they re-solidify themselves, making the creature very difficult to extract from its hideout.]

Says Who?

If the Eyes are the Window to the Soul, this Fish has a Sunroof

Things are lookin’ up

Common Name: Barreleye Fish

A.K.A.: Macropinna microstoma  (and related species)

Vital Stats:

  • Size: 15cm (6″) long
  • Depth: 600-800m (2000′-2600′) below sea level
  • Discovered: 1939
  • First Photographed: 2008

Found: Subarctic and Temperate regions of the North Pacific

It Does What?!

As you have likely already noticed, fish don’t have necks. At least not in the sense that they are able to look upward. So for a bottom-dweller lurking about in the cold depths of the ocean, being able to see that tasty bit of food floating by above is something of a problem. Some species get around this issue by floating vertically in the water so their whole bodies are pointing upwards. Simple enough. But in the spirit of meeting every challenge with an impossibly bizarre solution, nature has also produced a fish with eyes directly on the top of its head. After all, why re-orient the entire fish when you can just shift a couple of parts?

Those things on the front that look like eye sockets?
That would be its nose.

But the strangeness of the Barreleye Fish goes a little further than that. These aren’t just normal fish eyes in an unusual location. This species’ main prey are jellyfish and their relatives, which frequently come equipped with stingers that could damage the eyes of most predators. So rather than a normal spherical eye perched on top of its head, Macropinna has a tubular structure with the lens buried deep within its head (the dark green areas in the images). Overlying the tubular eyes is a tough, fluid-filled, transparent shield which the fish can look through. That’s right, it looks through the top of its own head. This way, stings from jellyfish will never damage the delicate ocular tissue.

What’s more, the fish’s unique tubular eyes are supremely adapted for the dark depths of the ocean. They allow unusually accurate depth perception (due to a large overlap of the two visual fields) and enhanced light gathering compared the spheroid eyes. In an environment up to 2600 feet (800m) down, where little daylight penetrates and everything appears in monochrome, these adaptations enable the barreleye to distinguish even faint shadows and silhouettes moving above it, and to precisely gauge how far up they are.

The Barreleye Fish, failing to look at the camera.

Researchers had long been puzzled as to how the barreleye eats, since, with its eyes on top of its head, its visual field didn’t include the area around its mouth. The species has been known since 1939, but only as small mangled bodies caught up in deep-sea fishing nets (adults are only about six inches long). In each case, the transparent casing of the fish’s head had been destroyed by the nets and the rapid changes in pressure as the nets were pulled up, making its anatomy difficult to study. In 2008, however, scientists from the Monterey Bay Aquarium Research Institute sent remote operated vehicles with cameras down to try, for the very first time, to snap some photos of these oddballs in action. What they learned was that, when it spots prey, the barreleye can actually rotate its entire tubular eye downward, like moving the telescope in an observatory. This way, it can turn and look at its target straight on as it pursues. Most of the time, though, the fish was seen to use its large, flat fins to hold itself nearly motionless, looking up through its personal sunroof, just waiting for some unlucky jellyfish to float on by.

Says Who?

  • Robison & Reisenbichler (2008) Copeia 4: 780-784.
  • Monterey Bay Aquarium Research Institute

All images taken by the Monterey Bay Aquarium Research Institute (MBARI)

Every Day is a Crappy Day for the Bird-Dropping Spider (Celaenia excavata)

Celaenia excavata
(via: http://commons.wikimedia.org/wiki)

Common Name: The Bird-dropping Spider

A.K.A.: Celaenia excavata

Found: Eastern and Southern Coastal Australia

It Does What?!

Quick, what’s the first thing that comes to your mind when someone says “disgustingly inedible” ?

If you said “Why, poop, of course!”… congratulations, you think just like Celaenia excavata. And if the thing you’re trying to look inedible to is a bird, naturally, you go with bird poop. Such is the evolutionary reasoning behind the politely-named Bird-Dropping Spider. And while remaining motionless is a must, looking the way it does allows the spider to sit comfortably atop a leaf all day, secure in the knowledge that spiders’ main predators, birds and wasps (who apparently aren’t into eating bird poop either), won’t take an interest.

“Nobody here but us droppings.”
(Thanks to Ron Atkinson at http://www.findaspider.org.au)

But the mimicry doesn’t end there for this sneaky little guy- by day it sits inactive and gross-looking, but by night, it hangs upside down from a leaf and releases the mating pheromones of a female moth. When some unlucky male moth comes looking for a good time, the spider snatches it right out of the air with its powerful front legs and wraps it up for dinner. The moth may be eaten right away or, if its capturer isn’t feeling hungry quite yet, be hung under a leaf next to the spider’s egg sacs, which, oddly enough, look like nuts (see top photo).

Believe it or not, Celaenia excavata isn’t the only spider out there masquerading as merde. Another such trickster is Mastophora cornigera, a North American species which is part of a group known as the Bolas Spiders, or Fishing Spiders. Not content to hope their prey wanders into arm’s reach, bolas spiders release pheromones to attract male moths, then dangle a line of silk with a sticky blob on the end. Once a moth gets close enough, the spider swings its line and –yoink– rips the poor thing right out of mid-air. Whoever thought up Spiderman’s web-slinger clearly had a bolas spider in mind.

So there you have it, the leisurely lifestyle of a successful spider: pile of poo by day, upside-down fisherman by night.

Says Who?