Blog | Erin Zimmerman

May 19, 2013

Back to the Deep, Part 2

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

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.

April 21, 2013

Back to the Deep, Part 1

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

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

March 14, 2013

Cuckoos: Outsourcing Childcare, Hogging the Bed

Common Name: Parasitic Cuckoos

A.K.A.: Subfamily Cuculinae (Family Cuculidae)

Vital Stats:

Range in length from 15-63cm (6-25”) and weigh between 17g (0.6oz.) and 630g (1.4lbs.)
The majority of cuckoos are not parasites, but around 60sp. are (about 56 in the Old World, and 3 in the New World)
Babies of brood parasites are initially coloured so as to resemble the young of the host species

Found: The cuckoo family is present throughout the temperate and tropical world, with the exceptions of southwest South America and regions of North Africa and the Middle East. Parasitic cuckoos occupy a subset of this range, principally in the Old World.

It Does What?!

Parenting is tough… less sleep, less free time, all those all those hungry mouths to feed. What’s a busy mother to do? You know you need to perpetuate the species, but who has the time? Impressively, cuckoos have come up with the same answer that many humans have: outsourcing! Involuntary outsourcing, in this case.

One of these things is not like the others.(Via: Timothy H. Parker) — One of these things is not like the others.
(Via: Timothy H. Parker)

Once a female cuckoo has mated and is ready to lay the eggs, rather than build a nest and slog her way through childcare, she waits for another female with freshly laid eggs to take off for some food and just lays her egg there, spreading her clutch across several nests. In theory, when the duped female returns, she’ll just settle in and care for the new egg along with her own. Cuckoo eggs have a shorter incubation period than that of their host, so the foreign egg usually hatches first, at which point the baby cuckoo just gives the other eggs (or chicks, if the timing didn’t quite work out) a good shove, and enjoys having both a nest and a doting mother to itself. The cuckoo chick will tend to grow faster than its host species, so it keeps its adoptive parent busy with constant begging for food, having eliminated the competition.

But this wouldn’t be a fun evolutionary arms race if the host species just took it on the chin. Birds plagued by cuckoo eggs have worked out several ways to try to cope with the problem. First off, and not surprisingly, they’ve developed a burning hatred of cuckoos. Adult cuckoos seen in the area of the hosts’ nests will immediately be mobbed and run off by a group of angry mothers. The cuckoos, however, have learned to use this to their advantage by having the male of a pair tease and lure the angry mob away while the female lays her eggs in peace. Advantage: cuckoos.

And this, kids, is how you deal with those annoying younger siblings.(Via: M. Bán, PLoS ONE) — And this, kids, is how you deal with those annoying younger siblings.
(By: M. Bán, PLoS ONE)

A second strategy used by the parasitised birds is to learn to recognise foreign eggs and pre-emptively toss them out of the nest. Cuckoos responded to this in two ways. First, they slowly evolved eggs to match those of their host bird in colour and size (or, in the case of covered nests, very dark eggs which aren’t easily seen at all). Bird species with higher levels of egg rejection just end up with cuckoo eggs which look more and more similar to their own. Second, if a host does reject the foreign egg, the cuckoo who laid it will sometimes come and just destroy the entire nest, killing anything left inside it in an act of motherly vengeance. Advantage: cuckoos.

A third strategy, developed by the Superb Fairy Wren (not to be confused with the equally floridly named Splendid Fairy Wren) is a bit more clever. As soon as the host mother lays her eggs, she begins to sing to them in a very specific pattern. Now, in this case, the cuckoo egg will hatch around the same time as her own eggs, but was deposited there several days later than her own. This means that her own chicks have been sitting there, unborn, learning her song for a longer period of time than the cuckoo has. Once the eggs are hatched, only her own chicks will be able to properly replicate her calls. Can’t sing the song? No food for you. And if, prior to starving to death, the parasite chick does manage to push her chicks out of the nest, the mother will fail to hear the proper response at all and know to simply abandon the nest entirely. Advantage: Fairy Wren. Superb indeed.

Shrikes: don't try to outsmart a bird that kills mammals for sport.(Via: Arkive.org) — Shrikes… don’t try to outsmart a bird that kills mammals for sport.
(Via: Arkive.org)

There is at least one known case of a former host species throwing off the yoke of cuckoo parasitism entirely. The red-backed shrike, aside from being particularly murderously aggressive toward adult cuckoos (and many other things), became very good at identifying cuckoo eggs, very quickly. So quickly, in fact, that researchers believe the cuckoos simply didn’t have time to adapt. In laboratory experiments, the shrikes correctly identified and rejected 93.3% of all cuckoo eggs placed in their nests. Pretty good pattern recognition for a brain the size of a pea. While cuckoo-red shrike parasitism has been known historically for some time, it hasn’t been seen in nature for the last 30-40 years.

Shrikes for the win.

Fun Facts:

Even typically non-parasitic cuckoos will sometimes lay their eggs in the nests of their own or other species, but will still help to feed the chicks (parental guilt, perhaps?).
The eggshells of parasitic cuckoos are unusually thick, helping prevent them from cracking as their mother drops them from above into the host nest.
Striped cuckoos, not content to just shove their adoptive siblings out of the nest, actually peck them to death with their beaks.
A few birds deal with homicidal cuckoo chicks by building steep-sided nests, making it difficult for any chick to be pushed out (and raising them as one big, happy family, I guess).

Says Who?

Colombelli-Négrel et al. (2012) Current Biology 22: 2155-2160
Feeney et al. (2012) Animal Behaviour 84: 3-12
Lovaszi & Moskat (2004) Behaviour 141(2): 245-262
Spottiswoode & Stevens (2012) American Naturalist 179(5): 633-648
Wang & Kimball (2012) Journal of Ornithology 153: 825-831

March 1, 2013

The Devil You Know, the Devil You Don’t

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

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?

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.

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.

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

February 21, 2013

Axolotls in Never Never Land

Common Name: Axolotls

A.K.A.: Ambystoma mexicanum

Vital Stats:

Grow to a length of 15-45cm (6-18”)
Can live up to 15 years
Have no eyelids
Usually black or brown in colour, but mutation occasionally produces pink skin
Eat insects, worms, and small aquatic animals
Commonly kept as pets and, in parts of Mexico, food

Found: In the Xochimilco lake system, near Mexico City

It Does What?!

Axolotls are the Lost Boys of the amphibian world… they never grow up. These bizarre little salamanders are found only in a single lake system near Mexico City and, if the city’s pollution gets much worse, may soon not be found there, either.

First, a little background on salamanders in general. These amphibious, lizard-like creatures begin life in a larval stage. While adult salamanders have lungs and spend much of their time out of the water, larvae have only gills and are completely aquatic. They commonly undergo a metamorphosis in which the gills are lost and the body changes shape, thinning out and losing its ‘tadpole with legs’ appearance. Many salamanders have displayed the ability to occasionally forego metamorphosis, remaining in their larval stage for life. This phenomenon of looking like a juvenile even during adulthood is called “neoteny.”

What makes axolotls special is that they’re what’s called “obligate neotenes,” meaning they simply never go through metamorphosis… every adult axolotl looks like the larval stage of other salamander species. At some point in their evolution, it became either more beneficial or downright necessary for them to remain aquatic. Biologists have speculated that this is because their smaller larval form requires less food, and because the lakes where they live are low in iodine, an element required for their transformation.

Interestingly, while axolotls almost never go through metamorphosis in the wild, in a certain percentage of them, the genetic instructions for doing so seem to still be intact. If you have a larval axolotl and you want an adult form, you can either give it an injection of iodine, or, for the more deranged among you, gradually deprive it of its pool of water. Either method of forced metamorphosis has a high mortality rate and, at best, causes a hugely decreased lifespan, but it does show they haven’t entirely lost that capacity.

caption(From:) — The future of multi-tasking.
(From: McCusker & Gardiner (2011) Gerontology 57: 565)

An eternally youthful appearance isn’t even the axolotls’ only superpower. The creatures also possess a Wolverine-like ability to heal themselves. Not only can they – and other salamanders – regrow lost limbs, they can actually regenerate parts of vital organs, including sections of the brain, spinal cord, and, in one study, up to 50% of the heart ventricle. Axolotls can also receive organ transplants from other individuals without rejection or problems with lack of function in the new tissue. Obviously, these traits have made them of intense interest to a certain species which doesn’t regrow limbs, hearts, or spinal cords. Researchers hope that by studying the genetic and biochemical basis of these heightened healing abilities, they can create their own army of X-Men help amputees and victims of spinal cord injuries. But this research is still in its early stages. In the meantime, it would probably be in our best interests not to drive them to extinction.

Fun Facts:

Axolotls have tiny vestigial teeth, which in other salamanders only grow during metamorphosis.
Sometimes, an axolotl with a heavily damaged limb will both repair the old limb and regrow a new one, ending up with an extra leg (see above).
Forced metamorphosis can be only half-successful, producing adult forms with juvenile characteristics, such as a thickened neck.
Obligate neotenes like axolotls end up with a lot of extra “junk” DNA [biologists: via duplications of the pseudogenes created when their life history changed], which has actually resulted in their having larger cells than other salamanders.
It’s hard not to look crazy when you have no eyelids.
(Via: Aquadisiac News)

Says Who?

Chernoff (1996) International Journal of Developmental Biology 40: 823-831
Martin & Gordon (1995) Journal of Evolutionary Biology 8: 339-354
Neff et al. (1996) International Journal of Developmental Biology 40: 719-725
Rosenkilde & Ussing (1996) International Journal of Developmental Biology 40: 665-673

February 14, 2013

The Old Girls’ Club

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)

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.

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.

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…

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

February 6, 2013

The Life and Times of the Last Earthpig

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

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…

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.

[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

January 30, 2013

Living in Filth and Looking Up at the Stars

Common Name: Dung Beetles

A.K.A.: Subfamily Scarabaeinae

Vital Stats:

Many subsist entirely on faeces, while others also consume fungi and decaying plant matter
Found in extremely diverse habitats, on all inhabited continents
Grow up to 6cm (2.4”) long, and can live for up to three years

Found: Across the temperate and tropical regions of the world

It Does What?!

Dung beetles… if you believe in reincarnation, these are why you try to stay on the straight and narrow. Otherwise, you might end up coming back as a creature whose life quite literally revolves around excrement. Dung beetles owe their entire existence to the fact that larger animals have inefficient digestive systems, consuming manure for its remaining nutrients and even laying their eggs inside it as food for their future young. Gross, yes, but once you get past the “ick” factor, it’s a pretty practical system.

Dung beetles come in three main varieties: rollers, tunnellers, and dwellers. Rollers, which are the type most people are familiar with, roll faeces into small balls which they roll away with them to consume and bury elsewhere. Tunnellers dig under the dung, burying it on site as an underground food source. Dwellers, the slackers of the dung beetle world, don’t bother with burying their treasure, preferring to simply live in it where it falls. I’ll focus on the rollers from here on in, as they’re the most bizarrely specialised of the bunch.

Dung beetles find their warm, fresh meals either through their excellent sense of smell or, in the case of some species, by simply riding around on their chosen food provider until the right time comes. Studies have shown that the beetles prefer omnivore or herbivore droppings to those of carnivores, perhaps for the more easily-digestible plant matter. One particularly intrepid group of researchers even determined that human faeces are favoured above those of most other large mammals. Good job, guys. Your funding agency must be proud.

It's a hot commodity... so to speak.(Via: Wikimedia Commons) — It’s a hot commodity… so to speak.
(Via: Wikimedia Commons)

Rollers immediately set to work on a new pile of droppings by shaping a dense little ball of up to ten times their weight (about TimBit sized, for you Canadians out there. Mmm!). Before rolling the ball away to be eaten/buried for later, the beetle will climb up on it and do a sort of dance, rotating around its top. Researchers also observed the beetles doing this dance if their rolling path was disturbed, or if another beetle stopped them to try to steal their ball.

So why the dance? As you might guess, it’s a means of getting their bearings, but what’s really fascinating is how they’re doing it. Dung beetles always roll their balls in a straight line directly away from its origin, probably as a means of reducing competition from other nearby beetles as quickly as possible. And they do this despite facing the ground as they roll the ball with their hind legs. During the day, this was fairly obviously accomplished by positioning themselves according to the direction of the sun, using their dorsal vision. However, they can also do it on a clear, moonless night. How?

Using a planetarium and a series of experiments which, hilariously, involved fitting the dung beetles with little cardboard hats to block their overhead vision, a South African researcher has determined that the beetles are actually using the light from the Milky Way to navigate. This is the only known instance of animals using an entire galaxy to orient themselves. Birds and seals have been known to use stars for positioning, but never the Milky Way itself. This from a tiny creature that cleans up piles of poop for a living… there’s probably an inspiring metaphor here somewhere.

Goes great with coffee!(Via: Wikimedia Commons) — Goes great with coffee!
(Via: Wikimedia Commons)

In the “But what does it do for me?” department, dung beetles are actually immensely useful to humans. Beyond restoring important soil nutrients, in areas of intense cattle-grazing, the beetles cart off and bury literally tonnes of manure that would otherwise host dangerous parasites and disease-carrying flies. Australia has intentionally introduced African dung beetles for this express purpose. Results have been much better than certain other introductions there.

The value of dung beetles has apparently been recognised for a very long time. Ever heard of the sacred scarab beetles of ancient Egypt? Yep… they’re dung beetles. One and the same. The beetles represented transformation and were linked with the god of the rising sun, who was believed to remake the sun and roll it across the sky each day, like the beetle with its ball. Something to think about next time you’re watching a beautiful sunrise.

[Fun Fact: Dung beetles in the African savanna use their dung balls as thermal refuges, periodically climbing up on them to moisten and cool their feet, which can increase in temperature by as much as ten degrees as they travel over the hot ground.]

Says Who?

Baird et al. (2012) PLoS ONE 7(1): e30211
Chamorro-Florescano (2011) Evolutionary Ecology 25: 277-289
Dacke et al. (2013) Current Biology 23: in press
Smolka et al. (2012) Current Biology 22(20): R863-R864
Whipple & Hoback (2012) Environmental Entomology 41(2): 238-244

December 19, 2012

Happy Holidays!

Time for a much-needed break, ladies and gentlemen! I’m heading to the farm on vacation for a couple of weeks, then taking off to South Africa for a few weeks after that. I’ll be speaking at the 6th International Legume Conference in Johannesburg, followed by a trip to Kruger National Park in the northeast of the country for a week of botanizing and gaping at large animals. I’ll see if I can’t find some questionable evolution going on there to tell you guys about when I get back. In the meantime, have a happy holiday and a great start to 2013, and I’ll see you back here on January 30th.

December 12, 2012

Hidden Kingdom, Part Two

Common Name: Leafcutter Ants

A.K.A.: Genera Atta and Acromyrmex of Tribe Attini

Vital Stats:

Fungi grown by leafcutter ants come from the family Agaricaceae
Ant species can maintain their association with a specific fungal cultivar for millennia
Neither the ants nor the fungal cultivars can survive outside of the symbiosis
Some ant species are capable of completely defoliating a small tree in under a day

Found: Humid forests of Central and South America

It Does What?!

Last week, we looked at leafcutter colonies, their various castes, and the impressively long lives of ant sperm. But obviously, leafcutter ants are known principally for one thing- cutting leaves. This they do on a grand scale, forming lines of thousands upon thousands of ants, dutifully toting chucks of foliage back to their colony. Why? To fertilize their fungus, of course! Much as we like to think of agriculture as one of the crowning achievements of mankind, the fact is, ants came up with it much earlier than we did. About 50 million years earlier, actually. (But they haven’t figured out how to deep-fry anything yet, so there’s that, I guess.)

caption (Via: Wikimedia.org) — The fungus is hungry.
(Via: Wikimedia.org)

When a young queen leaves her original colony to found a new one, she carries in her mouth a small piece of fungus to use as a starter culture (think yogurt or sourdough bread) for the colony’s gardens. Initially, she will care for this culture alone, but once the first generation of workers is born, they will take over the task from that point on. Since fungi don’t photosynthesize, they’re perfectly happy in a pitch-black underground garden, but they still need nutrients with which to grow, and dead vegetation is their food of choice. As the larger worker castes return with leaf (and flower) fragments up to three times their own mass, the minima gardeners clean away any outside fungal spores and chew the vegetation into smaller and smaller pieces. They then mix the shredded leaves with fungus and add the mixture to the garden. And, just for an extra fertiliser kick, they mix in their own faeces. Waste not, want not, right?

With all the workers coming and going, and so much foreign vegetation entering the colony, infections of the garden by competing fungal spores are inevitable, despite the ants’ best efforts. One such invader is the fungus Escovopsis, a parasite of other fungi, which can decimate a colony’s food supply and, in the case of young and vulnerable colonies, sometimes cause them to fail entirely.

But the ants have a secret weapon: bacteria. These adaptive little farmers actually carry around a ready supply of antimicrobial compounds right on their bodies. The bacterium in question, Pseudonocardia, grows directly on the ants’ exoskeletons and, researchers suspect, is nourished by a substance excreted through the ant’s glands. In return, Pseudonocardia produces a compound that the farmers can spread on invading fungus, killing it without damaging their food source. Symbioses within symbioses… and these are just the ones we know about.

Meanwhile, outside the colony, another fascinating parasite threatens the workers. Known as phorid flies, or ant-decapitating flies, you can probably guess why these things are a problem. Female phorid flies land on the backs of the larger worker ants as they travel to and from their leaf harvesting sites, laying eggs on the worker’s thorax. Once the eggs hatch, the larvae work their way into the ant’s head and start to eat the tissue surrounding the brain, eventually moving on to the brain itself (causing aimless wandering behaviour similar to that caused by the zombie ant fungus). Finally, the young parasites secrete an enzyme which causes the ant’s head to fall off completely, leaving them a convenient vessel in which to finish their development into adults.

Not to be outsmarted (by anything, apparently), leafcutter ants instituted a policy of defensive piggyback rides. Workers on the foraging path carry tiny minima ants on their backs as they travel. The minimae are too small to be useful hosts for the phorid fly, and so are able to fearlessly attack the flies as they approach, keeping the foragers safe. And not to lose an opportunity for increased efficiency, the little passenger will also begin cleaning the leaf fragment as the larger worker carries it home.

So there you have it. Leafcutter ants form colonies of millions, assign specialised tasks to different classes of citizens, grow their own crops, excel at problem-solving, and know how to use antibiotics. Next to humans, they form the largest and most complex societies on Earth. Forget robots and computers, people- if anything’s going to gain sentience and overthrow humanity, my money’s on the ants.

[Fun Fact: They compost, too. At least one leafcutter species maintains ‘outdoor’ waste heaps of discarded leaves and fungus. Special disposal workers (often old or unhealthy ants) turn the heap regularly to speed up decomposition.]

Says Who?

www.antweb.org
Marietta College Leafcutter Ant Page
Dijkstra & Boomsma (2006) Insectes Sociaux 53: 136-140
Evison & Hughes (2011) Naturwissenschaften 98: 643-649
Evison & Ratnieks (2007) Ecological Entomology 32: 451-454
Holman et al. (2011) Molecular Ecology 20: 5092-5102
Mueller et al. (2008) Evolution 62(11): 2894-2912