What comes to your mind when you first think of the word “immunity”? Most people probably think of having protection from something; in the case of reality TV, immunity means that you won’t get kicked off the show for a week or two. The word immunity stems from the latin word immunis, meaning free or exempt from taxes or public service (would you prefer to have immunity from taxes or immunity from disease might be an interesting question?). Modern definitions of immunity are centered around protection from or resistance to an obligation, or in the case of health, it means resistance to disease.
Now back to your definition of immunity. Did you immediately think of your immune system and how it protects you from flesh-eating bacteria or getting the flu? If so, your thoughts are in line with the majority. However, if we define immunity as being protected from disease or death, then I would argue that behavior might actually be the most important part of the immune system. Behavior can allow an organism to avoid getting sick in the first place, or even more importantly from getting killed directly by something that wants to eat you!
This brings us to the giant Australia cuttlefish (Sepia apama) < http://eol.org/pages/593213/overview >. These amazing beasts are masters of deception. First, cuttlefish have an extraordinary ability to almost instantly change their color, shape, size, and even the texture of their skin to hide from predators. This ability to morph their appearance is particularly useful when they are trying to secure mating opportunities (aka have sex), and a lurking seal might be hiding around the corner waiting to ambush the unsuspecting cuttlefish. The ability of cuttlefish to change their appearance is so highly evolved that they can actually make themselves look just like a rock on the ocean floor! No they don’t actually change into a rock, but unless you have seen this behaviour before, I think you might have a hard time picking out the cuttlefish in a police line-up of rocks and cuttlefish. I have witnessed a cuttlefish drop to the sea floor and “turn into a rock.” After my initial “where the hell did that thing go” response, I looked around and saw a large New Zealand fur seal (Arctocephalus forsteri) < http://eol.org/pages/328621/overview > approaching! The defenses of the cuttlefish were way ahead of my own.
Cuttlefish videos shot by @WildImmunity
Another amazing behavioral defense of cuttlefish is the ability to produce an ink-like substance to help hide from would-be attackers, sort of like James Bond’s Aston Martin DB5 in Goldfinger spewing an oil slick to escape from one of his perilous chases scenes. I have been lucky enough to go snorkelling on more than one occasion near Whyalla, South Australia, during the cuttlefish breeding season. Whyalla is the largest known site for cuttlefish breeding, and just a few meters from the shore I was able to shoot these amazing videos and photos. In addition to the amazing live cuttlefish, there were a few dead cuttlefish on the beach, and I was able to poke them with a stick, as any good biologist would do. On a side note, cuttlefish usually die soon after mating. Hope it was worth it!
“Can you believe this little thing was the same species that you just saw alive in the video?
So back to our question of “what is immunity?” An organism that gets eaten by a predator is a dead animal, and thus it is not immune to anything of use. Note that some of the dead organisms physiological immune defences may still be in operation (i.e. the complement system and other antibacterial proteins), but they are of no use if the organism is already dead! Since a dead animal isn’t really immune to anything, a behavior that allows you to avoid being eaten is an important part of immunity. Second, attacks by predators can disrupt an organism’s normal physiology and make the organism more susceptible to infection. For example, if a Komodo dragon bites you, you will likely get a severe infection and will probably die without proper treatment, but a smart person can usually avoid being bitten by a Komodo dragon. Again, I would argue that avoiding being bitten by a dragon is better than getting antibiotics after you were bitten, so score another point for behavioral defenses.
Look out for a future post about the festering wounds caused by a bite from a Komodo dragon, and why the dragons themselves don’t die from the bacteria in their own mouth (think compartmentalization).