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The Cost of Colour

Sobo_1906_324Try to imagine a colour you’ve never seen. Or a scent you’ve never smelled. Try to picture the mental image produced when a bat uses echolocation, or a dolphin uses electrolocation. It’s nearly impossible to do without referring to a previous experience, or one of our other senses. We tend to tacitly assume that what we perceive of the world is more or less all there is to perceive. It would be closer to the truth to say that what we perceive is what we need to perceive. Humans don’t require the extraordinary sense of smell that wild dogs do in order to get by in the world. But it wasn’t always this way.

Scent molecules are picked up and recognized in our noses by olfactory receptors. Each type of receptor recognizes a few related types of molecules, and each type of receptor is written into our DNA as an olfactory receptor (OR) gene. In mammals, OR genes make up the largest gene family in our genome. There are over a thousand of them. Sadly for us, over 60% of these genes have deteriorated to the point of being nonfunctional. Why? In what must be a hard piece of news for X-Men fans, extra evolutionary features tend not to hang around unless they’re actively helping us to survive longer and breed more. If a gene can develop a fault that makes it useless without causing its host a major competitive disadvantage, it’ll eventually do so, and an incredible number of these broken genes – called “pseudogenes” – have built up and continue to sit in our genome. This isn’t specific to humans; cows, dogs, rats, and mice all have about 20% of their OR genes nonfunctional. But that still works out to a difference of hundreds of different types of scents that we can’t detect. Even compared to our closest relatives, the apes and old world monkeys, we have twice as many OR pseudogenes, and are accumulating random mutations (the cause of pseudogenes) at a rate four times faster than they are. This is all quite logical, of course; humans have evolved in such a way that being able to smell prey or potential mates from a distance just isn’t key to our survival.

Phylo tree image
From: Gilad et al. (2004) PLoS Biology 2(1): 0120

What’s more interesting is that when scientists looked at the OR genes of apes and old world monkeys (OWMs), they found elevated rates of deterioration there, too… about 32%, compared to only 17% in our next closest group of relatives, the new world monkeys (NWMs). So what happened between the divergence of one group of primates and the next that made an acute sense of smell so much less crucial? The answer came with the one exception among the NWMs. The howler monkey, unlike the rest of its cohort, had a degree of OR gene deterioration similar to the apes and OWMs. The two groups had one other thing in common: full trichromatic vision. Nearly all other placental mammals, including the NWMs, are dichromats, or in common parlance, are colourblind. Using molecular methods that look at rates of change in genes over time to determine when a particular shift happened, scientists determined that in both instances of full colour vision evolving, the OR genes began to deteriorate at about the same time. It was an evolutionary trade-off; once our vision improved, our sense of smell lost its crucial role in survival and slowly faded away. In apes and monkeys, this deterioration process seems to have come to a halt – at a certain point, what remains is still necessary for survival – but in humans, it is ongoing. We know this because of the high number of OR genes for which some individuals carry functional copies, and some carry broken copies. This variability in a population, called polymorphism, amounts to a snapshot of genes in the process of decay, since the broken copies are not, presumably, causing premature death or an inability to breed amongst their carriers. So as we continue to pay the evolutionary price for the dazzling array of colours we are able to perceive in the world, our distant descendants may live in an even poorer scentscape than our current, relatively impoverished one. There may be scents we enjoy today that will be as unimaginable to them as the feel of a magnetic field is to us.

As a quick final point, it turns out humans aren’t the only animal group to have undergone a widescale loss of OR genes. Just as full colour vision made those genes unnecessary for us, so moving into the ocean made them unnecessary for marine mammals. In an even more severe deterioration than that seen in humans, some whales and porpoises have nearly 80% OR pseudogenes. As you may already know, whales, dolphins, and other marine mammals evolved from land-dwelling, or terrestrial mammals (want to know more about it? Read my post here). Using methods similar to those mentioned above for primates, researchers found that at about the same time they were adapting anew to life in the ocean, their scent repertoire was beginning to crumble. And since anatomical studies show that the actual physical structures used to perceive scent, such as the olfactory bulb in the brain, are becoming vestigial in whales, it’s likely the loss isn’t finished yet. Interestingly, the researchers behind this study also looked at a couple of semi-marine animals, the sea lion and the sea turtle, which spend part of their time on land, and found that they have a sense of smell comparable to fully terrestrial animals, with no increased gene loss.

The widescale and ongoing loss of the sense of smell in certain animals, particularly ourselves, is a nice illustration of an evolutionary principle which can be summarized as “use it or lose it”, or more accurately, “need it or lose it.” We tend to think of evolution as allowing us to accrue abilities and features that are useful to us. But unless they’re keeping us and our offspring alive, they’re not going to stick around in the long term. Which makes you wonder, with humans’ incredible success in survival and proliferation on this planet, which relies overwhelmingly on our cognitive, rather than physical abilities, what other senses or abilities could we eventually lose?

Sources

*The image at the top of the page comes from Sobotta’s Atlas and Text-book of Human Anatomy (1906 edition), now in the public domain.

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Back to the Deep, Part 2

(Via: Best-Diving.org)
(Via: Best-Diving.org)

Common Name: Whales, Dolphins, and Porpoises

A.K.A.:  Order Cetacea

Vital Stats:

  • While the lifespan of most whale species is unknown, evidence indicates bowhead whales can reach ages of around 200 years.
  • Sexual maturity in whales occurs at around 7-10 years of age.

Found: Throughout the world’s oceans, save the very northernmost regions

WhaleMap

It Does What?!

Last time, we looked at how whales evolved from a deer-like creature the size of a housecat into the aquatic behemoths they are today. This week, we’ll cover a couple of the odds and ends of whale weirdness.

One important thing to understand about evolution – particularly in cases of a major habitat shift, as we see in whales – is that it’s not an orderly or “well-thought out” process. A good analogy is to think of an old building that’s being renovated and rewired. New additions may be built onto old structures and new wiring overlaid on old plans, creating a product very different, and often much less efficient, from what would have been created were a new building made from scratch. Because you have to work with what’s already there.

Whale respiration is an excellent example of this point. When the ancestors of modern cetaceans took to the water, developing gills and breathing like fish wasn’t an option, because the machinery wasn’t intact… they were already much too far down the evolutionary path of a terrestrial mammal. What they could develop were more efficient lungs and greater control over how they used them. For humans, breathing is an unconscious and largely involuntary act – it just happens, whether we think about it or not, and we can’t choose to stop doing it for very long. Even if you were to hold your breath until you passed out, you’d just start breathing again the moment you lost control (take note, parents of tantrum-prone toddlers). For whales on the other hand, respiration has become voluntary; they breathe because they choose to do so. Life underwater and the need to hunt without distraction made this ability more valuable than the safety of an involuntary mechanism.

caption (Via:)
Whale-snoring.
(Via: The Telegraph)

There is, of course, a major drawback. For whales, control over respiration came at the price of ever being able to fully fall asleep. If a cetacean were to sleep as we do, it would stop breathing and drown. As a result, they’ve evolved the ability to sleep with one brain hemisphere at a time. So while one hemisphere rests, the other is awake, one eye is open, and the whale is in motion, surfacing periodically. In fact, they appear not to experience REM sleep at all, meaning that these creatures gained their mastery of the oceans, very literally, at the cost of their dreams.

Another interesting problem during whale evolution was that of temperature regulation. Anybody who’s been swimming knows that even relatively warm water can start to give you the chills after a while, especially if you’re not expending a lot of energy. This is because water is an excellent conductor of heat, and will constantly draw warmth away from the skin’s surface. Now once you get into the sunless depths of the ocean, to say nothing of the polar oceans that many whales live in, things get very chilly very fast. To counteract this, whales have developed a thick, insulating layer of fat that holds in the heat and keeps their core body temperature from plummeting. Easy peasy, right?

But what happens when the whale expends a lot of energy, say, on an intense feeding session, and builds up too much heat? Ever shovel snow in a heavy winter coat? After a few minutes, you’re ready to tear the coat off because you’re sweating so much. Not so easy when the coat’s under your skin. Well, researchers have recently discovered what they think may be the answer to this problem.

caption (Via: National Geographic)
That’s 144 inches, in case you were wondering.
(By: Craig George, Via: National Geographic)

In the bowhead whale, which lives exclusively in frigid arctic and sub-arctic waters (and therefore has a great deal of insulation), biologists found a mysterious, twelve foot long organ positioned along the roof of the mouth, made out of what is, essentially, the same tissue found inside penises. That is to say, spongy tissue filled with a lot of blood vessels which can expand as it fills with blood. So how does a giant mouth-penis help a whale cool off? It’s quite clever, really. The brain being the major point of concern for overheating, the organ, called the corpus cavernosum maxillaris, lies directly beneath it. Hot blood is pumped into the organ, filling the spongy tissue, as the whale opens its mouth, letting in a great volume of icy water which surrounds the engorged tissue, quickly drawing off much of the heat. The cetacean equivalent of a cold shower. This cooled blood then drains from the organ and lowers the temperature around the brain.

And if this extra-penis-as-thermoregulator wasn’t cool enough, it seems to have a secondary function as well. The organ is also packed with sensitive nerve endings (naturally…), which the researchers believe the whales may use to determine the prey density in a given area (bowheads are filter feeders), helping them to decide whether to remain in a location and feed, or move on in search of better pickings.

Fun Facts:

  • The ability to “sleep” with one eye open was likely also highly valuable to the much smaller ancestors of the cetaceans, for whom predation was a bigger problem.
  • Whales have fleshy nasal plugs with which they can plug their blowholes while diving.
  • Oceanic dolphins have the highest relative brain size among extant cetaceans.

Says Who?

  • Ford et al. (2013) The Anatomical Record 296: 701-708
  • Gatesy & O’Leary (2001) Trends in Ecology and Evolution 16(10): 562-570
  • Gatesy et al. (2013) Molecular Phylogenetics and Evolution 66: 479-506
  • Lyamin et al. (2008) Neuroscience and Behavioral Reviews 32: 1451-1484
  • Uhen (2010) Annual Review of Earth and Planetary Sciences 38: 189-219
  • Zimmer (2013) The Loom, March 4th.
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Back to the Deep, Part 1

(Via: Wikimedia Commons)
(Via: Wikimedia Commons)

Common Name: Whales, Dolphins, and Porpoises

A.K.A.:  Order Cetacea of Class Mammalia

Vital Stats:

  • Consists of 88 living species
  • Order is divided into Odontoceti, the toothed whales (73 sp.), and Mysticeti, the baleen whales (15 sp.)
  • Odontoceti includes both dolphins and porpoises
  • The largest whale, a blue whale, can grow up to 30m (98’) in length and weigh as much as 20 elephants

Found: Throughout the world’s oceans, save the very northernmost regions

WhaleMap

It Does What?!

caption (By: Nobu Tamura, via: Wikimedia Commons)
The twenty pound vermin that went on to rule the oceans.
(By: Nobu Tamura, via: Wikimedia Commons)

Picture it: the time is just over 50 million years before the present – the early Eocene – the climate is much warmer than today, undergoing a period of rapid global warming… it is the Age of Mammals. On the shores of the tropical Tethys Sea, in what would eventually become India, a small, deer-like animal, not much larger than a housecat, wades into the water and dives briefly to retrieve a fish before returning to dry land. This has become a successful strategy for its species, avoiding competition from other mammals by eating marine life. Well-fed, the creatures reproduce rapidly, creating competition amongst themselves. Those individuals with greater lung capacity and better swimming ability catch more food, outcompeting those who don’t. Over great stretches of time, characteristics enabling speed and skill under water become more important than those enabling life on land, and selection tilts in favour of a longer, more lithe body, smaller hindlimbs, stronger forelimbs for paddling, and less fur.

caption (Via: AccessScience)
Swimming: great for a slim figure.
(Via: AccessScience)

Millions of years pass as our small hunter’s descendants eventually lose the ability to ever return to land. They have no fur now… it isn’t useful for retaining heat beneath the waves. Fat is, though, and this begins to accumulate in thicker layers under their bare skin. Their front legs are nearly inflexible at the joints, trading range of movement for strength and widening into precision rudders to control direction as they swim. In concert, the tail becomes more muscular and widens into flukes at the tip, propelling them forward powerfully with each stroke. Their back legs – unneeded – atrophy, gradually losing both size and bone structure, until the foot is completely gone. A small stub lingers for a time before the last vestigial bones simply remain inside the smooth body wall, evidence of a distant terrestrial past. The nasal opening has migrated to the top of the head for ease in surface breathing. Ten million years have passed since the scene on the shore, and we now have our first fully aquatic whale.

Of course, much still had to happen before we arrived at the whales of today. In the time since aquatic mammals first arose, a major division took place within the Cetacea. One group, the toothed whales, or Odontoceti, continued to hunt and eat fish and large marine fauna, including squid and even other whales. To aid in finding their prey, these whales developed echolocation, the use of projected sound to create an image of the surrounding area, thereby becoming the loudest mammal, with vocalisations of more than 180 decibels (a jackhammer tops out at about 120dB). The large bulge we see on the forehead of dolphins and other toothed cetaceans is an organ called a ‘melon’ (because they couldn’t think of anything more science-y sounding just then), which is thought to help direct and focus these sounds.

caption (Via: Wikimedia Commons)
Who needs teeth when you can have a broom in your mouth?
(Via: Wikimedia Commons)

Being a top-level predator isn’t very energetically efficient, though, and there isn’t always enough prey to go around. So at some point, one group of whales began to move toward a different strategy. The origins of the Mysticeti, the baleen whales, are still a bit unclear, but these animals switched from hunting large fauna to eating colossal numbers of tiny sea creatures such as krill. In order to do this, the whales lost their teeth and developed baleen in their place. Baleen is essentially a fine-toothed comb that filters small animals from the water as it passes. The whale takes a giant mouthful of water and pushes it out against the combs until only food remains. While this may seem less efficient than just grabbing a big fish and eating it, filter feeding is what allowed the largest whales to evolve to their present size. The blue whale, Balaenoptera musculus, is believed to be the largest animal which has ever existed on Earth, and it got that way eating mostly shrimp the size of your thumbnail. Amazing, isn’t it?

Now that we’ve covered how they got that way, tune in next time for part two, where we’ll explore the many weird and wonderful aspects of life as a modern whale.

Fun Facts:

  • Baleen whales still have teeth during the embryonic stage of their development, much as human fetuses briefly develop tails.
  • Toothed whales do not chew their food; it is eaten whole or torn into large pieces and swallowed. This may be related to the fact that, unlike most mammals, they have only one set of teeth.

Says Who?

  • Gatesy & O’Leary (2001) Trends in Ecology and Evolution 16(10): 562-570
  • Gatesy et al. (2013) Molecular Phylogenetics and Evolution 66: 479-506
  • Lyamin et al. (2008) Neuroscience and Behavioral Reviews 32: 1451-1484
  • Uhen (2010) Annual Review of Earth and Planetary Sciences 38: 189-219
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The Devil You Know, the Devil You Don’t

(Via: Wikimedia Commons)
(Via: Wikimedia Commons)

Common Name: The Tasmanian Devil

A.K.A.:  Sarcophilus harrisii (Family Dasyuridae)

Vital Stats:

  • Latin name translates to “Harris’s Meat Lover” after naturalist George Harris
  • Weigh 6-13kg (13-29lbs.), around the size of a small dog
  • Largest carnivorous marsupials in the world after the extinction of the thylacine in 1936
  • Live up to five years in the wild; fully grown at two years of age

Found: On the Australian island-state of Tasmania

Devil Map

It Does What?!

Spins around in circles and chases talking rabbits, if the cartoons are to be believed. But Tasmanian devils have suffered from some bad press over the years. While they’re often portrayed as incurably vicious, dangerous creatures, this isn’t really the whole truth. Yes, they can scream like a person getting dismembered. And yes, they’re good little hunters that can take down prey larger than themselves, partly thanks to having the strongest bite per unit body mass of any living mammal. (Crunching through large bones is not a tall order for a Tasmanian devil.) But they just as often scavenge carrion killed by other causes, frequently in the form of roadkill. They don’t tend to attack humans, either (unless that human happens to be dead already). Faced with live humans, devils will usually just hold still and hope you don’t see them, sometimes trembling nervously as they do so. Doesn’t exactly strike fear into your heart, does it?

caption(Via:)
How many newborn devils CAN you fit on a 20 cent piece?
(Via: 500 Questions)

In fact, more than anything, devils deserve a bit of sympathy (just ask the ‘Stones)… life is tough for them right from the word ‘go.’ You see, Tasmanian devils are marsupial, meaning the young are born very under-developed and must crawl from the birth canal into their mother’s pouch to find a nipple to latch onto while they finish baking. The problem here is, devils give birth to between twenty and thirty babies, but possess only four nipples, which aren’t shared. In fact, they’re effectively stuck in the infant’s mouth from the time they latch on, preventing them from falling out of the mother’s pouch. So as newborn babies, fresh from the womb, they already have as much as an 87% chance of immediate death. That is some harsh selection right there. Somewhat tellingly, the babies can’t open their eyes until three months after their birth, yet come out of the womb with a full (if small) set of claws. You can see where evolution’s priorities were here.

But it doesn’t get much easier for the four that win the nipple race. Tasmanian devils are already working with a rather restricted range, having been hunted to local extinction on mainland Australia around 3000 years ago (probably by dingoes, which aren’t found in Tasmania). Nevertheless, they were doing pretty well in keeping their numbers up and had a healthy population until the mid-90s, when disaster struck.

caption(Via: Wikimedia Commons)
Don’t image-search this disease… it gets so much worse.
(Via: Wikimedia Commons)

Because the entire Tasmanian population of devils was originally based on only a few individuals, they’ve experienced a ‘Founder Effect,’ which basically means that the genetic diversity from one animal to the next is quite low. In terms of disease, they’re all susceptible to the same things. So when a form of transmissible cancer known as Devil Facial Tumour Disease (DFTD) suddenly popped up in 1996, it spread like wildfire from one devil to the next, mostly via their tendency to bite one another during sex and mealtimes.

An infected devil quickly develops tumours on its face and inside its mouth. This eventually makes it difficult to eat, leading to starvation within a year of contracting the disease. DFTD is estimated to have already killed up to 50% of all devils, rushing them from a healthy population to an endangered species in record time. While the government has taken the step of building up a healthy, captive population which will be isolated from the disease, in the long term, this will have the effect of reducing the species genetic diversity even further. As a small glimmer of hope, researchers are now reported to have found a few individuals with at least partial immunity to the disease, and hope to try to build a cure based on their physiology.

caption(Via:)
Bitey the Devil picks a fight.
(Via: TravelerFolio)

Fun Facts:

  • Tasmanian devils store fat reserves in their tails… a fat-tailed devil is a healthy devil.
  • See the white spots on the devil pictured above? All bite marks. Each scar leaves a patch of white fur. The natural white streak on the devil’s thick-skinned chest is thought to draw attacks away from more sensitive areas.
  • Unlike most other marsupials, the devil’s pouch opens to the rear of her body rather than the front (like a kangaroo), making it impossible for her to interact with her babies while they’re nursing there.
  • Devils tend to try to eat whatever’s available when they’re hungry. The following have been found in their droppings: steel wool pot scrapers, tea towels, parts of leather shoes, blue jeans, plastic fragments, dog collars (minus the unfortunate dog that had been in it), and echidna spines.
  • The only other known form of non-viral, transmissible cancer is a type of venereal disease that occurs in dogs.

Says Who?

  • Attard et al. (2011) Journal of Zoology 285: 292-300
  • Coghlan (2012) “’Immortal’ Tasmanian devil brings vaccine hope” New Scientist, 17 February
  • Grzelewski (2002) Smithsonian 68: February
  • Hamede et al. (2013) Journal of Animal Ecology 82: 182-190
  • Hesterman et al. (2008) Journal of Zoology 275: 130-138
  • Marshall (2011) “Tasmanian devils were sitting ducks for deadly cancer” New Scientist, 27 June
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The Old Girls’ Club

(Photo by the Author)
(Photo by the Author)

Common Name: African Elephants, Asian Elephants

A.K.A.: Loxodonta africana, Elephas maximus

Vital Stats:

  • Comprise the entirety of Family Elephantidae and Order Proboscidea
  • African elephants are thought by some to be two species; the African Forest Elephant, and the African Bush Elephant
  • Can live for up to 70 years in the wild
  • The largest living terrestrial animals, reaching heights of up to 4m (13’) and weights of up to 7000kg (15,000lbs.)
  • Consume up to 150kg (330lbs.) of food daily

Found: Savannahs, bushlands, and forests in sub-Saharan Africa and Southeast Asia (but sparsely across these regions)

Elephant Map

It Does What?!

Everyone knows elephants are cool. And weird looking. What they don’t tend to get a lot of credit for is just what complex lives they live, and how well-adapted they are to their surroundings. Far from being the dim, bovine, eating machines they’re often depicted as, elephants have been found to have an intelligence and self-awareness ranking up around that of primates and cetaceans, with comparably nuanced societies.

caption(Via:)
Jumbo renounces vegetarianism.
(Via: One Big Photo)

Elephant herds are matriarchal, being led by the oldest female and consisting of her close female relatives and their young offspring. Males are given the boot around the time they reach sexual maturity during their teens (because even the most intelligent animals find teenage boys a trial) and live the rest of their lives either alone or with a small pack of other exiled males.

Good parenting and discipline (delivered by mom with a swat of the trunk) seem to be extremely important for young male elephants; when orphaned males were introduced to a game reserve in South Africa in the late ‘90s, they immediately began going on killing sprees, hunting down and violently killing over 30 (endangered) rhinos, a completely abnormal behaviour for an elephant. As soon as well-adjusted adult males were introduced, the aggression stopped. Everybody needs a good role-model, I guess.

You may have heard stories about so-called “elephant graveyards,” where elephants go to die and leave remains near those of their relatives. While these have now been found to be a myth, appearing due to large die-offs happening suddenly in times of drought, it’s true that elephants show an inordinate amount of interest in the carcasses and bones of other elephants. Presented with a set of bones, elephants will become highly agitated and touch the bones repeatedly with their trunks, especially the dead animal’s tusks. Researchers speculate that this is because the tusks feel the same as they did in life, and touching is such an important aspect of elephant society. They are the only known animal outside of humans to take a particular interest in the bones of their species.

caption(Via:)
Probably not what evolution intended.
(Via: The Road to Anywhere)

And what about their most obviously bizarre feature? How did a prehensile nose develop?! It’s hard to say for sure, but one interesting theory comes from the fact that elephants use their trunks as snorkels while swimming, sometimes crossing shallow lakes by simply walking across the bottom with only their noses above water. Given that manatees are one of elephants’ closest relatives, some scientists have speculated that elephants evolved from aquatic mammals, slowly becoming terrestrial, but never losing their once-important snorkel. (Or their internal testicles, another trait associated with an aquatic lifestyle.) Other scientists think those guys don’t know what they’re talking about and lack evidence to support this theory. So it goes in science.

Whatever their origin, elephants’ trunks have become enormously important in their lives, and are used in everything from eating to fighting to bonding with family members. Actually a fusion of the nose and upper lip, trunks have over 100,000 muscles and are sensitive enough to crack open a peanut shell and retrieve the seed from it. The ability to grasp comes from one or two (in Asian and African elephants, respectively) finger-like extensions at the trunk’s tip. These “fingers,” combined with the elephants’ high degree of intelligence, have allowed them to learn the use of several tools, including tree-branch fly-swatters, which they probably invented millions of years before we came up with the idea. Different priorities…

caption(Via: Wikimedia Commons)
Yeah, we definitely need a few more of these.
(Via: Wikimedia Commons)

And finally, let’s not forget the dearly departed cousins. While African and Asian elephants are the only remaining species of Proboscidea, the order containing both mammoths and mastodons, there were once over 160 of them, inhabiting every continent except Australia and Antarctica. Most of these persisted until the most recent ice age killed off nearly all of the largest mammals. Some systematists believe that Asian elephants are in fact more closely related to woolly mammoths than they are to African elephants, and it’s even been speculated that a cloned mammoth could some day be gestated in the womb of an Asian elephant. ‘Cause if we learned anything from Jurassic Park, it’s that reanimating extinct megafauna is a great idea.

Fun Facts:

  • Elephants use ‘seismic communication,’ transmitting messages via a low-pitched rumble, which is detected by distant elephants using the pads of their feet.
  • While they can move surprisingly quickly, elephants don’t technically “run,” due to the fact that their legs never all leave the ground simultaneously.
  • It’s a common myth that elephants get drunk eating fermented marula fruits which have fallen to the ground. Given the low level of alcohol which accumulates in rotting fruit, an animal the size of an elephant would have to eat an unrealistically huge amount in a short time to reach a high enough blood alcohol level. But they do seem to enjoy them as a snack.

Says Who?

  • Choi (2011) “Woolly Mammoths Could Be Cloned Someday, Scientist Says”. Live Science.
  • McComb et al. (2006) Biology Letters 2: 26-28
  • Morris et al. (2006) Physiological and Biochemical Zoology 79(2): 363-369
  • Shoshani (1998) TREE 13(12): 480-487
  • Shoshani & Tassy (2005) Quaternary International 126-128: 5-20
  • Shoshani et al. (2006) Brain Research Bulletin 70: 124-157
  • West (2002) Physiology 17: 47-50
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The Life and Times of the Last Earthpig

(Via:)
(Via: National Geographic)

Common Name: The Aardvark

A.K.A.: Orycteropus afer, Family Orycteropodidae

Vital Stats:

  • Also referred to as the “antbear” or “earthpig”
  • Common name derives from Afrikaans words meaning ‘earth’ and ‘pig’
  • Habitats include savannas, grasslands, and woodlands
  • Weighs 40-65kg (88-140lbs.) and can grow up to 2.2m (7’3”) long
  • Can live up to 24 years in captivity
  • Nocturnal, feeding only during the evening and at night

Found: Sub-Saharan Africa

Aardvark Map

It Does What?!

Like the platypus and several other creatures we’ve looked at, aardvarks are considered “living fossils,” organisms which have changed little from the way they looked millions of years ago (around 20 million, in this case).

Aardvarks don’t look much like most mammals of today, other than a passing similarity to the South American anteater, to which it isn’t closely related. In fact, aardvarks aren’t particularly closely related to anything. Not only are they the sole species in their genus, but they have their own family and order as well. This is because everything else that used to inhabit these ranks has since become extinct. At one time, there were at least 14 different species in the aardvark family, spread over parts of Africa, Europe, and Asia; but today, there’s just our friend the earthpig. Strangely, among the aardvark’s closest living relatives are manatees and elephants (all part of the motley superorder, Afrotheria), which suggests just what distant cousins they must be.

Okay, so aside from having outlived its family members, what’s so interesting about these things? Well, one look at them will tell you they must have evolved to fit some unusual lifestyle. Aardvarks are myrmecophagous, meaning they specialise in eating ants and termites, and nearly everything about that odd little body is geared to this task. First, finding their insect food means digging into large anthills and termite mounds, so aardvarks have become prodigious diggers, tunnelling at rates of up to two feet in 15 seconds with their heavily clawed feet. They use this skill in creating their underground burrows as well, excavating tunnels up to 13m (43’) long and even changing their home’s layout from time to time. Because, you know, you get tired of the same old thing…

caption(Via:)
Clark the Aardvark, fresh from finishing his new ensuite bathroom with walk-in closet.
(By: Frans Lanting, Via: Posterlouge)

Moving further up, the aardvark’s narrow, elongated head and long, snake-like tongue are perfect for dipping into the minute passages made by ants and termites. They even have a special sticky saliva that adheres to ants at a touch. In a single night of feeding sessions lasting from five seconds to two minutes per stop, an aardvark can attack 200 hills, consuming as many as 50,000 insects. The ants and termites try to fight back, of course, but the aardvark has thick, tough skin and can seal its nostrils shut, making bites and stings ineffective.

There’s just one feature of the aardvark that doesn’t make a lot of sense for its insect-eating lifestyle, and that’s a set of back teeth. (In fact, they’re are born with front teeth as well, but lose them at maturity.) No other myrmecophage on Earth has a functional set of teeth… you just don’t need ‘em to eat ants. So why do aardvarks have them? A little thing called the Aardvark Cucumber!

In a bonus piece of evolutionary weirdness, aardvarks supplement their diet with a single type of fruit, a cucumber which has now become entirely reliant on hungry aardvarks for its continued existence. The plant flowers above ground – as plants do – but then pushes itself into the earth as it sets fruit, resulting in a subterranean fruit. These cucumbers are dug up by aardvarks and eaten as a source of moisture, while the seeds go undigested and are conveniently deposited elsewhere with a ready source of fertiliser for germination. Without the aardvark, seed dispersal would be impossible, and new plants would be unable to obtain enough water and nutrients to survive.

So there you have the life of the lonely aardvark… enemy of the ants, saviour of the cucumber, brother to no one.

caption(Via:)
“I laugh in the face of probable extinction… and nail clippers.”
(Via: Zooborns)

[Fun Fact: If pursued into its burrow, an aardvark will protect itself by sealing off the tunnel behind itself and digging further into the ground in the other direction.]

[Also… On their front feet, aardvarks have lost their equivalent to our thumb, retaining only four digits.]

Says Who?

  • Endo et al. (2003) Annals of Anatomy 185: 367-372
  • Lehmann et al. (2004) Journal of African Earth Sciences 40: 201-217
  • Lehmann (2008) Fossil Record 11(2): 67-81
  • Taylor et al. (2002) Journal of Arid Environments 50: 135-152
  • Taylor & Skinner (2003) Journal of the Zoological Society of London 261: 291-297
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Charity Among Vampires

(Via: National Geographic)

Common Name: The Vampire Bat

A.K.A.: Subfamily Desmodontinae

Vital Stats:

  • Subfamily contains three species; the common vampire bat (Desmodus rotundus), the hairy-legged vampire bat (Diphylla ecaudata), and the white-winged vampire bat (Diaemus youngi)
  • All three feed only on blood, a phenomenon known as hematophagy
  • The common vampire bat feeds primarily on mammals, while the other two species prefer avian blood
  • Can live up to 20 years in captivity

Found: Throughout Mexico, Central America, and all but the most southern reaches of South America

It Does What?!

Several years ago while on a botanical expedition in the rainforests of South America, I woke one morning to find that one of the other team members, still fast asleep in his hammock, had – apparently – been stabbed in the shoulder during the night. A surprising amount of blood had run down his arm, and yet he snored peacefully away. What the hell had happened to this guy, and was he the world’s deepest sleeper, or what?

Nope. Turns out he had just unwittingly provided a good meal for Desmodus rotundus… the common vampire bat.

As horrifying as it may seem to have flying vermin drinking your blood whilst you sleep, it’s really not as bad as pop culture would have us believe. The bats are more scavenger than predator. To begin with, they prefer stealth and guile to any kind of open attack. Sleeping animals are best, and victims are never approached from the air, Caped Crusader-style. Instead, the bat will land nearby and walk on all-fours over to its prey. From there, it uses heat sensors in its nose (similar to some snakes) to detect where blood vessels pass close to the surface of the skin. In cows, another favourite blood donor of Desmodus, bites are usually just above the hooves or around the ears.

Breakfast of Champions
(Via: National Geographic)

Also contrary to popular belief, the bites are never violent; they’re more like a tiny nick from a very sharp razor- painless, but they tend to bleed a lot. In this case, they’re bleeding a lot because the bat’s saliva contains anticoagulents, preventing the blood from clotting. The bat will lap at the cut with its tongue (no blood-sucking here), transferring saliva into the wound, which will sometimes continue to bleed for hours afterward.

An entire feeding session takes the bat only about 20 minutes, during which time it can consume up to half its own weight in blood. How is this possible? Vampire bats have an amazingly efficient excretory system; the plasma (liquid) portion of the blood is immediately absorbed and passed through the kidneys. Within minutes of beginning to feed, the vampire starts to pee at the same time, and continues to do so until its meal has been reduced to a manageable volume. (Did they leave this part out of the Twilight movies?)

Creepy as these little beasts may seem, they have a surprisingly enlightened social structure. Vampire bats have been cited by animal behaviourists as one of the few examples of reciprocal altruism (“tit for tat”) in nature. You see, the vampire lifestyle is a bit precarious- a bat will die if it fails to feed for two successive nights. As a lifesaving measure, a bat in such dire straits will actually beg another bat for food. The other bat will then regurgitate some of its meal – just enough to make do – into its hungry neighbour’s mouth. Impressively, the bats even keep score. A hungry animal will turn preferentially to a bat it has helped out in the past, and cheaters are recognised and allowed to starve.

“Okay, what do we learn to imitate next?”
(Via: conservationcentre.org)

Far from being mindless, aggressive little monsters, vampire bats are altruistic, intelligent creatures. How intelligent? Researchers who housed a vampire bat with a hen observed the bat to mimic the behaviour of a chick so effectively that the hen settled down on top of the bat as she would to keep a baby warm. The bat then nicked her on the stomach and drank her blood while she tried to mother it.

Now that’s just creepy.

[Fun Fact: Vampire bats listen to the rhythm of an animal’s breathing to determine whether or not it’s asleep. They prefer to return to a victim they’ve had previous success with, and evidence suggests that they can identify individual humans by their breathing noises in the same way that we recognise individuals by their voices.]

[Also: The common vampire bat can jump up to three feet off the ground to reach large prey.]

Says Who?

  • Groger & Wiegrebe (2006) BMC Biology 4:18
  • Lee et al. (2012) PloS ONE 7(8): e42466
  • Schutt (2008) Natural History, November Issue, pg.22
Become a donor today!
(Via: Vampire Legends)
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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.