South America | Erin Zimmerman

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

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 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.

caption (Via:) — I use the term “garden” loosely…
(Via: Marietta College)

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

December 5, 2012

Hidden Kingdom, Part One

(Via:) — (By: Tobias Gerlach & Jenny Theobald, Via: deepgreenphoto.com)

Common Name: Leafcutter Ants

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

Vital Stats:

47 species; 15 in Atta, 36 in Acromyrmex
Atta ants have three dorsal spines and a smooth exoskeleton, while Acromyrmex ants have four spines and a rough exoskeleton
Less than 5% of new queens are able to build a successful colony
A maxima may have a head width of up to 7mm (0.28”), while a minima reaches less than 1mm (0.04”); mediae fall somewhere in between

Found: Humid forests of Central and South America

It Does What?!

Once in a while, I come across a species that’s just so strange and interesting, a single post doesn’t seem to do it justice. With that in mind, welcome to part one of the wonderous life of the leafcutter ant.

Let’s begin at the start of it all – a new colony being founded. This happens when a fertile, winged female and several fertile, winged male ants (called drones) are born and grow to maturity. One day, the winged crew will fly away together and engage in what’s called a nuptual flight, where the female mates with several different males (up to seven in some species) while in mid-air. Having accomplished what is literally their only purpose in a short, glorious life, the drones promptly die, while the new queen scouts out a good place to start her colony. Finding it, she yanks off her own wings, never to fly again, as her body starts to break down her flight muscles, using the energy to produce eggs.

Ant reproduction is remarkable in that actual mating occurs only once in the queen’s life. The males of her nuptual flight together provide hundreds of millions of sperm that will be the basis for the entire colony to come. At the risk of sounding like a weirdo, ants have amazing sperm. A human sperm cell, under ideal conditions, can survive for up to five days. If they don’t get the job done in that time, they’re finished. The sperm of leafcutter ants, having been collected by the queen, can live for up to thirty years. That’s probably older than a lot of the people reading this. They can spend decades just waiting around in storage for the egg with their name on it. And that’s not all- they come armed. As in, chemical warfare. The seminal fluid of ants contains compounds that can lower the survival of rival sperm (from other drones) while not harming those of the ant they came from. Weaker sperm are thereby killed off early in the game. Of course, this kind of thing doesn’t go on for a long time. The storage organs of the queen contain their own fluid that will neutralize chemical weapons on the way in. Think of it as the metal detector at the door.

Right. So the queen has her new place picked out and the on-site sperm bank is up and running. Time to make a colony. What she needs first are workers. In a small chamber she’s excavated underground, she begins to lay large numbers of eggs. These serve two purposes, because the early hatchers will eat the late hatchers until the food supply gets built up. It pays to be a bit premature when you’re an ant.

Nearly every worker born to the queen over the life of the colony will be a sterile female, and each will belong to one of three major castes- minimae, mediae, and maximae. These castes will dictate both their size and function in life. Sensing the needs of the colony, the queen can actually control which type of worker she is producing. First come the minimae, which are the smallest caste and will principally tend the underground gardens which are the colony’s food source (more on ant agriculture in part two), as well as acting as nurse-maids for growing larvae. Next are the mediae, which are larger and act as the colony’s foragers, bringing plant material with which to fertilize the gardens, and defending against minor threats or obstacles in the troop’s path. Finally, once the colony has reached a population of several thousand, come the maximae, or soldier ants. These big brutes are up to thirty times the mass of a minima and do all the heavy lifting, carrying bulky items, moving big obstacles, and cutting tough pieces of vegetation. They’re also the last line of defence when something serious threatens the colony or the foraging parties. And because ants are all about organisation, within each caste, there are numerous sub-castes which are responsible for specific duties, depending on which species we’re talking about.

Over time, leafcutter colonies can become impressively large, comprising over 5 million residents- the population of a major human city. It’s amazing to consider that these are kept running smoothly without central authority, technology, or the aid of written or spoken language. Not to mention opposable thumbs.

Tune in next week for a look at leafcutter agriculture, their interesting relationships with symbiotic fungi and bacteria, and why ants give each other piggyback rides to work.

[Fun Fact: The largest leafcutter ant colony on record required the excavation of approximately 40 tonnes (44 tons) of earth and contained thousands of different chambers.]

Says Who?

www.antweb.org
Marietta College Leafcutter Ant Page
den Boer et al. (2010) Science 327: 1506-1509
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

November 28, 2012

Charity Among Vampires

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)

October 31, 2012

Nights of the Living Dead… Further Horrors of the Insect World

TarantulaHawk-large3-550x420 — (By: Paul Nylander Via: The Tucson Citizen)

Common Name: The Tarantula Hawk

A.K.A.: Genera Pepsis and Hemipepsis

Vital Stats:

The two genera make up Tribe Pepsini in Family Pompilidae
Grow up to 5cm (2”) long
Stingers are up to 7mm (1/3”) long
Quite long lived for wasps, with lifespans of more than a year
Adults feed primarily on milkweed nectar

Found: Across much of the tropics and southern hemisphere

It Does What?!

Happy Halloween, readers! Today’s the day when we’re surrounded by images of zombies, witches, ghosts, and spiders- all creatures meant to scare us on some level. Of course, only one of these things is real. And spiders truly are a scary thing for many people. For all you arachnophobes out there who are feeling vaguely uncomfortable about the preponderance of fake spiders out there today, did you ever wonder what the spiders fear? What keeps tarantulas, the biggest, scariest arachnids of them all, awake at night? Tarantula hawks, that’s what. If spiders had Halloween, this is what they would dress up as.

Like any good mother, the female tarantula hawk wants to ensure that her baby has all the food it requires to grow up into a healthy adult wasp. Rather than bag a large piece of prey and have it spoil by the time her egg hatches, she has developed an ingenious system of keeping meat fresh.

Spying a tarantula from the air, she will attack, injecting the spider with her venom as it struggles to bite her. A particularly hard and slippery exoskeleton renders this counterattack ineffective; the fangs simply slip off her. Before long, the tarantula has succumbed to her venom and is alive, but completely paralysed. Once the prey has been neutralised, she sets out over land, dragging the spider up to 100m (quite a long way, considering the scale involved) back to the site of a burrow she has dug out. Here, our mom-to-be lays a single egg on the helpless spider’s abdomen, then proceeds to immure it in the burrow.

Guyana Photo — A hundred metres starts to look like a very long trip.
(By: Erin Zimmerman, taken during my field work in Guyana)

But this is only the beginning of the horror for the paralysed spider. Soon after, the egg hatches, and the hungry larva tunnels directly into the spider’s flesh, eating as it goes. The larva instinctively knows to avoid the tarantula’s vital organs as it eats, thereby keeping the prey alive for as long as possible. After several weeks of chowing down, the larva finishes off the job and emerges from the spider’s body, having now matured into a wasp. It then simply unseals the burrow and flies away, leaving the late tarantula in its ready-made grave.

Wondering what happens when a person gets stung by one of these? It’s an interesting question, because the answer is both “a lot” and “not much”. You see, the paralytic agent in the venom only works on invertebrates, and won’t actually do any real damage to human tissue. Before you go trying to catch one, though, know that, in terms of immediate reaction, tarantula hawks are considered to have the single most painful insect sting in the world. It’s best described by an entomologist who has actually experienced such a sting:

“Advice I have given in speaking engagements was to ‘lay down and scream’. The reasoning being that the pain is so debilitating and excruciating that the victim is at risk of further injury by tripping in a hole or over an object in the path and falling onto a cactus or into a barbed wire fence. Such is the pain, that few, if any, can maintain normal coordination or cognitive control to prevent accidental injury. Screaming is a satisfying expression that helps reduce attention to the pain of the sting itself.” [Schmidt 2004]

In short… don’t touch these.

A few words now on just how frighteningly well-adapted this wasp is. Not only is it covered in armour and full of incredibly painful venom, but at roughly the size of your little finger, it’s one of the largest wasps out there, and more of a fight than most insectivores want to deal with. It is essentially without predators. And lest any potential enemies forget why they’re not touching it, the tarantula hawk has both a distinct colour and a characteristic odour, meant to remind aggressors of the pain associated with any previous run-ins. Researchers have described tarantula hawks as being “among the best defended animals on earth” [Schmidt 2004]. And because success always spawns imitation, there are now several other creatures mimicking the appearance of the female tarantula hawk as a form of protection, including the more-or-less defenceless males of the same species.

So the next time you shudder at the thought of a tarantula stalking you in the wild, stop and remember what might be stalking it.

[Fun Fact: Despite its phenomenal pain-inducing qualities, tarantula hawk venom is only about 5% as lethal as honeybee venom, based on studies by people who inject white mice with horrible things for a living.]

Says Who?

Alcock & Kemp (2006) Ethology 112: 691-698
Kurczewski (2010) Northeastern Naturalist 17(1): 115-124
Schmidt (2004) Journal of the Kansas Entomological Society 77(4): 402-413
Schoeters et al. (1997) Canadian Journal of Zoology 75: 1014-1019

October 24, 2012

Life in Slow Motion: the Three-Toed Sloth

MC_Drei-Finger-Faultier — (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.]

9gbn1d94yyb72eqlyt — 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.]

three-toed-sloth-with-child — 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!

August 15, 2012

Killing Me Softly, or, The Fatal Embrace of the Strangler Fig

Ficus_watkinsiana_on_Syzygium_hemilampra-Iluka — (Via: Wikimedia Commons)

Common Name: Strangler Figs

A.K.A.: Ficus species

Vital Stats:

There are around 800 sp. of figs, over half of which are hemi-epiphytes, like stranglers
Around 10% of all vascular plants are epiphytes (about 25,000 species)
The trees which produce the figs we eat are terrestrial, and do not grow in other trees

Found: Tropical forests of Latin America, Southeast Asia, and Australia

It Does What?!

What does it take to squeeze the life out of a full-grown tree? A lot of time and some very long roots, apparently. Many parasites eventually bring about the untimely death of their hosts, but few do it as slowly and as insidiously as the strangler fig.

Stranglers begin life as a tiny seed that leaves the back end of a bird and happens to land on a tree branch high in the rainforest canopy. The seed germinates, and the young fig begins to grow as an aerial plant, or epiphyte, taking its moisture from the air and its nutrients from the leaf litter on its branch. Thousands of plant species, including most orchids, grow in this manner. But then an odd thing begins to happen. The seedling produces a single long root. Very long. From tens of metres up in the canopy, this root grows all the way down to the ground. Many young stranglers will die before their questing root reaches the earth, but for those that make it, a connection is formed with the soil through which water and nutrients can be extracted. From this point on the great, towering giant which holds this tiny little interloper is in mortal danger.

Fig1 — The strangler fig, playing “harmless epiphyte.”
(Screenshot from The Private Life of Plants, BBC)

A secure connection to the soil allows the fig to speed up its growth and to begin sending more and more roots earthward. Rather than dropping straight down, like the initial root, these later organs will twine around the bark of the host tree. At first, the roots are tiny, like mere vines crawling over the host trunk. Over time, however, they thicken, covering more and more of the trunk’s surface. Where they touch or overlap, the roots actually fuse together, forming a mesh over the surface of the bark. Up above, the stem of the strangler is growing as well. It rises through and above the host branches, soaking up the light and leaving the other tree shaded and starved for energy.

In fact, this is a war fought on two fronts. As the starving host tree struggles to gather light energy to send downward from the leaves, it is also increasingly unable to bring water up from its roots. This is because the tree’s trunk continues to expand even as the strangler’s grip grows tighter around it. These opposing forces effectively girdle the tree, crushing the vascular tissues that carry moisture from the soil. Eventually, the battle is lost and the tree dies. Fortunately for the fig, its major investments in root growth have paid off – the dead host tree does not fall, taking the strangler with it. Instead, it simply rots where it stands. Finally, many years after its arrival on the scene, the strangler fig has achieved independence. It is now a free-standing tree, completely hollow and supported by its interwoven lattice of aerial roots.

Fig2 — The first root finds the ground.
(Screenshot from The Private Life of Plants, BBC)

So what happens when more than one strangler fig seed lands on a particular tree? Something quite unique… the roots of the different individuals fuse and form an organism which is indistinguishable from a single tree, except by molecular testing. These are what biologists refer to as ‘genetic mosaics.’ What’s more, the individuals actually begin to act like a single tree. You see, figs typically have staggered flowering times, such that it is unlikely for numerous trees in a small area to be in bloom at the same time. This helps in keeping their wasp symbionts well nourished. Once trees fuse, however, they seem to become physiologically linked as well, with researchers reporting that they bloom as a single individual.

Fig3 — The most hurricane-proof tree ever.
(Screenshot from The Private Life of Plants, BBC)

[Fun Fact: Some strangler fig species have very high growth rates, and huge individuals have actually been found engulfing abandoned buildings in the tropics.]

Says Who?

Harrison (2006) Journal of Tropical Ecology 22(4): 477-480
Perry & Merschel (1987) Smithsonian 17: 72-79
Schmidt & Tracey (2006) Functional Plant Biology 33: 465-475
Thomson et al. (1991) Science 254: 1214-1216

2437448440_6a44fea919 — Don’t meditate under strangler figs.
(Via: Flickr, by vincenzooli)

August 8, 2012

The Zombie Apocalypse: Already Underway

Common Name: The Zombie-Ant Fungus

A.K.A.: Ophiocordyceps unilateralis

Vital Stats:

Whole “graveyards” of 20-30 ants may be found within a single square metre
Telltale bitemarks on fossil plants suggest this fungus, or a related species, may have been in operation for the last 48 million years
Host species is the carpenter ant Camponotus leonardi

Found: Tropical forests throughout the world

It Does What?!

Despite all the advances of modern neuroscience, the fact is, human understanding of brain chemistry and its manipulation still has a long way to go. Much to the chagrin of those plotting world domination, we won’t be chemically controlling each other’s minds any time soon. How embarrassing then, that a mere fungus seems to have perfected this technique. Almost fifty million years ago. Scooped again, humanity.

It begins with an ant walking along the ground, deep in a tropical forest somewhere. This ant, Camponotus leonardi, lives high in the trees, but must occasionally come down to cross from one tree to another when there is a break in the canopy. As it walks, a minute fungal spore drifts down from above and lands in its back, unnoticed. The unseen spore springs into action, producing an enzyme which breaks down the ant’s exoskeleton just enough to allow a fungal hypha, like a tiny root, to enter. The host’s fate is now sealed.

Fungus1 — This is your brain on ‘shrooms.
(Via: Flickr, by Alextkt)

While the ant climbs back up into the canopy and goes about its business, the fungus grows through its insides, breaking down and consuming the non-vital soft tissues as it goes, keeping the animal alive even as it is being eaten. Soon, the fungal tendrils reach the brain and begin to produce chemicals which affect the host’s behaviour in very specific ways. First, it will experience convulsions that cause it to fall out of its tree. These will continue periodically, preventing it from returning to its colony. Over a period of hours, the ant will then wander, erratically and aimlessly, over the ground and low-growing plants.

This is where the precision of the fungus’ mind control becomes truly impressive. At solar noon, when the sun is highest in the sky, the infected ant will abruptly climb the stem of a small plant and find a leaf pointing north by northwest at a height of 20-30cm above the ground. Yes, really. No one knows how this jaw-dropping specificity is accomplished, but it’s what the fungus wants, providing a temperature of 20-30 degrees Celcius (68-86F) and a relative humidity of around 95%. In cases where ants were experimentally moved to different heights or orientations, the fungus was unable to reproduce properly.

Fungus3 — What the fungus wants, the fungus gets.
(Via: Wikimedia Commons)

Having found the perfect leaf, the zombified ant will go to its underside, find a major leaf vein, and just bite down on it as hard as it can. The fungus has already destroyed the muscles required to release this grip, and so there the ant stays, slowly dying over the course of the afternoon. Once its victim has been dispatched, the fungus grows toward the leaf, further anchoring itself to the plant. Around a week later, the parasite completes its horrifying circle of life by growing a fruiting body, similar to a mushroom, from the back of the dead ant’s head. This will open to release thousands of tiny spores, raining down over any potential hosts which may be walking below.

While the fungus is able to infect other, closely related, species of carpenter ant, it has less precise control over these hosts and isn’t always successful in getting the ant to do its bidding, suggesting that even minor variations in brain structure can stump it. So we’re probably safe from the fungal zombie apocalypse. At least for the time being…

Says Who?

Andersen et al. (2009) American Naturalist 174(3): 424-433
Hughes et al. (2011) Biology Letters 7: 67-70
Hughes et al. (2011) BMC Ecology 11: 13
Pontoppidan et al. (2009) PloS ONE 4(3): e4835

July 25, 2012

The Bloodhounds of the Plant World (Cuscuta sp.)

Common Names: Dodder, Goldthread, Witch’s Shoelaces

A.K.A.: Genus Cuscuta

Vital Stats:

Approximately 200 species
Part of the Convolvulaceae family, which includes morning glory and sweet potato
Only 15-20 species are considered to be problematic crop parasites

Found: Throughout temperate and tropical parts of the world

It Does What?!

We’ve discussed a few parasites on this blog already, and they’ve all been pretty typical of what comes to mind when we think of parasitic organisms- tiny, malignant little creatures that invade the host’s body, steal its resources, and, in some cases, eat its tongue. But when we think ‘parasite,’ we don’t usually think ‘plant.’ As it turns out, there are an estimated 4500 parasitic species just among the angiosperms, or flowering plants. Among them, dodders have to be one of the strangest.

Found nearly throughout the world, these vine-like plants begin as tiny seeds that germinate late in the spring or summer, after their potential host plants have established themselves. The young seedling has no functional roots and little or no ability to photosynthesize, so initially, it must make do with what little nutrition was stored in its seed. This isn’t much, so the plant has only a few days to a week to reach a host before it dies. To better its chances, the dodder stem swings around in a helicopter-like fashion as it grows, trying to hit something useful.

Much more impressive is the plant’s other method of finding suitable hosts- a sense of smell. Recent research has found that, uniquely among plants, the dodder can actually detect odours given off by surrounding plants and grow towards them. In experiments, the seedlings were found to grow toward the scent of a tomato, even if no actual plant was present. What’s more, they are capable of showing a preference among hosts. Presented with both tomato plants, which make excellent hosts, and wheat plants, which make poor hosts, seedlings were found to grow toward the aroma of tomatoes much more often. Like herbivores, they can use scent to forage amongst a variety of species for their preferred prey.

800px-Tomato_scanned — Smells like lunch… even to other plants.
(Via: Wikimedia Commons)

Once a host plant is found, the dodder begins to twine itself around the stem and to form haustoria (singular: haustorium). These are like tiny tap roots that pierce the host’s stem and actually push between the living cells inside until they reach the vascular system. Once there, the haustoria enter both the xylem (where water and minerals move upward from the roots) and the phloem (where sugars from photosynthesis move around the plant). From these two sources, the dodder receives all its nutrients and water, freeing it from any need for a root system, or even a connection to the soil. And since it doesn’t need to capture solar energy, all green pigment fades from the parasite, and it turns a distinctive yellow or red colour. Leaves aren’t necessary either, which is why the plant is essentially nothing but stem, explaining its common name of “witch’s shoelaces.”

Click for Higher Resolution — Not what you want to see when you head out to weed the garden.
(Via: County of Los Angeles)

Once it gets comfortable on its new host, the dodder can grow at a rate of several centimetres a day (impressive for a plant) and produce stems of a kilometre or more in length, quickly overrunning an area. It can also attach itself to additional hosts – hundreds, in fact – which is problematic, because at this point it becomes the plant equivalent of a dirty shared needle. Since the vasculature of the hosts is connected, any virus present in one host can be freely transferred to any other. This ability, coupled with its affinity for potatoes, tomatoes, tobacco, and several other important crops, makes dodder a major nuisance for many farmers. And since it’s able to regenerate from just a single, tiny haustorium left in a host plant, it’s really hard to get rid of. There’s always a flip side, though; in some ecosystems, dodder can actually maintain biodiversity by preferentially parasitising the more competitive plants, allowing the weaker ones to survive. It seems dodder may also be the Robin Hood of the plant world.

[Extra Credit: Here’s a video showing how dodder can completely take over a group of nettle plants, complete with ominous soundtrack. Narrated by the fantastic Sir David Attenborough.]

Says Who?

Costea (2007-2012) Digital Atlas of Cuscuta (Convolvulaceae). Wilfred Laurier University Herbarium, Ontario, Canada
Furuhashi et al. (2011) Journal of Plant Interactions 6(4): 207-219
Hosford (1967) Botanical Review 33(4): 387-406
Pennisi (2006) Science 313: 1867
Runyon et al. (2006) Science 313:1964-1967
Cuscuta: 1, Acacia: 0
(Via: Wikimedia Commons)