Defenses

Recap: Ok, so last month I gave some general information about different foxes, in the hopes to exemplify their extreme adaptability. It’s rare to find a terrestrial carnivore that is so widely dispersed, simply because it’s capable of adapting to so many different environments (You certainly won’t find wolves, or many other fair sized carnivores surviving in urban environments!). The broad niche of foxes makes them highly important ecologically, and of course, they’re adorable, too! But, enough about foxes! =P

This month I will be giving some examples of really cool adaptations that allow an organism to defend against predators. I’ll be giving examples of chemical, behavioral, physical, and “other” defense mechanisms. I’ll start each off with some well-known and obvious examples, but I will be giving and discussing my favorite examples which I’ve studied in class, or through reading. I will try to incorporate a plant example each week, but at the moment I basically know nothing about botany and don't have a lot of time to research, lol.This Sunday will be chemical defenses, and I have three very interesting examples! So stay tuned… ;)

Chemical defenses are quite common in animals, and are generally very effective. We all know of some chemical defenses: venoms in spiders, snakes, etc., squid ink, a skunk’s musk spray, and so on. But I want to give three interesting and less obvious examples:

1) Horned lizards (Phrynosomatidae – bottom right photo) have a haunting chemical defense called autohaemorrhaging. Basically “autohaemorrhaging” means that they can intentionally make themselves seep, or in the case of the horned lizards, squirt blood. This defense is extremely rare, but is also seen in a few insects and snakes.

Here is a video that shows a horned lizard putting its chemical defense to the use. It’s not as disgusting as it sounds; it’s actually really cool!

                                            


2) Bombardier beetles (Stenaptinus insignis – top right photo) can be found in Africa, Australia, and other subtropical locations. Their defense involves expelling boiling chemicals from its abdomen:

- enzymes and chemicals are contained within a specialized chamber located in the beetle’s abdomen.

- reaction takes place just before expelling – the beetle doesn’t want to have boiling chemicals inside it continuously… So enzymes catalyze the reaction as it leaves the beetle’s abdomen.

Reacton: Hydrogen peroxide is broken down by an enzyme called “catalase”, and 
hydroquinones are then oxidized by an enzyme called “peroxidase”. Reaction is exothermic (generates heat), producing chemicals at temperatures as high as 100˚C!

More info, and the beetle in action in the following link:

3) Chemical defense in plants:

- because plants are sessile (rooted in place and unable to move), defenses are necessary to prevent the organism from being more than just a “free-lunch”. Plant populations would be wiped out very easily, were it not for their defenses (allows only specific herbivores to eat them).

- toxins, irritants, pheromones, and other compounds provide chemical defenses. Pheromones are particularly fascinating because in some species of plants, they attract the natural predators of the organisms feeding on the plants. In other words, say a caterpillar is happily nibbling away on a plant… the plant will expel pheromones to attract a bird or some other animal that normally eats the caterpillar! =P

- common examples of chemical defense in plants include: poison ivy (irritant), milkweed (bad tasting chemicals), and believe it or not, tobacco (shown in picture on left).

The nicotine in tobacco may help to drive a human’s addiction, but to most insects, it’s a deadly neurotoxin potent enough to cause paralysis and even death! Just something interesting to think about next time you smoke a cigarette, lol.

You’ve probably heard of “playing possum” – well that comes from a behavioral defense in the Opossum, which plays dead when threatened. Behavioral defenses are highly unique, and are BY FAR my favorite type of anti-predator adaptation. Some common, well-known examples include: fish that puff up, color changes, and threatening stances intended to ward of predators. Here are a few interesting examples, which I quite like:


There are some extraordinary evasive defenses in lizards. We’ve all heard of flying squirrels, well, how about a flying lizard?! Draco volans, the “Flying Dragon”, (or “Flugdrachen”, in German) can be seen in the top-right photo. It looks like a lizard from prehistoric times, except downsized. Large, loose, and beautifully colored flaps of skin on each side of its body act as temporary wings, and are supported by
long ribs. The ribs can move and be stretched out sideways to help control flight. Here's a video of Draco volans in action:

Another extraordinary evasive defense is exhibited by Sailfin Lizards and Basilisks… (seen in the left photo). Some of these Hydrosaurus species can miraculously sprint across water to escape predation! If you want to check it out here is a video:

There are three steps to the lizard’s sprint; the “slap”, the “stroke”, and the “recovery”. During the “slap” phase, the lizard’s foot goes straight down, displacing water and creating a pocket of air around the foot; the upward force generated by the slap is enough to keep the lizard’s body above the surface while it kicks its leg backwards. This is the stroke phase, and generates the forward momentum. Finally, the recovery phase occurs when the foot is pulled up and out of the water ready for the next “slap” phase. As long as it runs fast enough, the lizard stays upright by pushing sideways with its feet (when necessary). The same idea generally applies when you’re swimming; you have to keep moving to remain buoyant. Also, if you doubt the validity of the “slap” phase, then try “slapping” the water next time your at a lake (you should be able to feel the upward force being generated).


The last example I have is a bird called a water dikkop (Burhinus vermiculatus – bottom-right photo). It nests on the riverbank, at sites where female Nile Crocodiles also have territory. This may seem like a bad idea, but this behavior actually helps the dikkop out! The crocodiles provide the dikkop, and their eggs, with protection from other large reptiles that steal from the dikkop’s nest. (It’s important to note that these thieving lizards are also common prey for the crocodiles). The water dikkop is generally nocturnal, so when it is active at night, and danger is imminent, the bird will send out a “burglar alarm” to that is believed to alert the crocodile of the trespassers. When in danger, the dikkop also lowers its head, spreads its wings, and charges the attacker (can be seen in the photo). Whatever it lacks in size, is compensated for by this birds immense courage. =P

I wanted to just mention that there are a lot of other behavioral defenses, including predator satiation and very elaborate ones in plants… I’ll explain these more in-depth another time (with examples), but that’s all that I have for you this week. =)

Physical Defenses come in all sorts of varieties:

1) Shells that act like body armor. Very common in mollusks (snails, crabs, etc), insects, and reptiles like turtles. Even some plants such as coconuts, and some nuts. (Picture on far left shows an Alaskan King crab hobbling amongst a “bed” of developing polyps - black). 

2) Protrusions extending from the body are another common defense. Examples include porcupines (see the little guy on the top right - contrary to popular belief porcupines cannot "shoot" their quills), sea urchins, tusks, and the spines/thorns on plants such as hazelnuts (see top right photo), acacia trees, cacti and so on.

3) This is the only example that I will actually go into detail this week, just because I don’t have time for three. But this one is really cool, so I had to do it. There’s a group of fish called “Parrotfish”, and some species have an interesting physical defense. First of all, they’re called “parrotfish”, because their teeth have fused into beak-like structures that are specialized for feeding on filamentous algae. Now onto the defense:

Species such as Chlorurus bleekeri, the Bleeker’s Parrotfish, secrete a “cocoon of mucus” around themselves when they go to sleep. (The Bleeker’s Parrotfish can be seen snoozing in a mucus bubble in the bottom right photo). The mucus is secreted from special glands in the fish’s opercular cavity (chamber containing the gills), and becomes gelatinous after coming in contact with the water. It can take up to 30 minutes, but once the cocoon has been secreted, the fish is protected from predation in a few ways… First, many nighttime predators hunt by smell, so the cocoon prevents these predators from detecting the parrotfish’s scent. In addition, the mucus cocoon is an excellent deterrence against predators who hunt with echolocation (emitting sound waves, then interpreting the surrounding environment by analyzing the rebounding echoes). When incoming echoes hit the mucus bubble, they bounce off in unpredictable directions, causing them to either be ignored by the predator, or to just confuse the hell out of the predator.





This week I want to give a few examples of "complex" defenses. Not that they're difficult to understand, it's just that they can't really be stringently classified into just being a "physical", "chemical" or "behavioral" defense mechanism. Anyways, here are two really interesting examples:

The first one is an interesting defense exhibited by anemonefish (also called clownfish; if you’ve seen Finding Nemo!) Here’s a video that explains it better than I can:

(Coleman's shrimp (protected by a shell, instead of mucus), and some other fish are beginning to develop this defence as well, which is interesting because these symbioses are still quite baffling).


The second is one of my favorite plant examples, Mimosa pudica (bottom-right photo)!

This plant is more sensitive than the one in the next video:

Close-up shot of less sensitive plant:

It isn’t rare to see plants that close up at night, because it makes sense (if photosynthesis minimal or not occurring, why not take a break?). But in the case of this plant, it also closes up in response to physical contact, as well as heat. There is an advantage to this; this phenomenon is a defense mechanism. When herbivores brush are eating a plant, and brush up against surrounding parts that they aren’t eating, the leaves will close up. This results in a “wilted” appearance, and the plant is no longer desirable to the herbivore, and so, the herbivore will move on to another plant. Apparently these plants are very inexpensive to have in your garden; however they are not at all easy to find.


Hopefully you found these defenses as interesting as I did, and have learned from and/or enjoyed this month’s “theme” of defenses. It is important to note that there is a plethora of really cool examples out there, and in nearly all cases predators have developed ways to overcome their prey’s defenses. There are also other types of defensive mechanisms that I did not mention (mostly because I know nothing about them… yet…) For instance, some animals use auditory defenses sounds that warn their friends, or their enemies (examples: rattlesnakes, and some birds). Others animals simply just prevent themselves from being detected (I’ll do camouflage and mimicry at some time in the future).