Today's video is sponsored by Wondrium.
To survive in the oceans,
marine organisms have had to adapt in a number of weird and wonderful ways.
As we explored in the previous video, many have done so by dramatically altering their anatomy,
behaviours and physiologies in order to cope with the challenges they face,
developing survival techniques over millions of years.
Methods ranging from changing colour, developing stingers,
or migrating long distances can help them stay hidden from predators, find a mate or access food.
But some animals have taken a different approach to survival.
Rather than evolve these complex characteristics for themselves, they instead simply disguise
themselves, altering their colouration or anatomy not to serve a function,
but in order to resemble another organism.
In this film, we’ll explore the different kinds of mimicry,
and take a look at how survival through deception can be a key to life in the oceans.
Camouflage is abundant in the marine world.
The best way to survive is to remain un-noticed, to conceal yourself and blend in.
In deep waters, this often comes in the form of taking on darker body colours, while in some
cases, animals take on no body colour at all, blending in through the use of transparency.
They become ghosts amidst the abyss.
But the one method of camouflage that breaks this rule is mimicry. It involves an organism
imitating something that is meant to be seen, not hidden.
In the case of Batesian mimicry, this describes a specific sort of biological resemblance in which a
harmless organism (known as the mimic) imitates a dangerous organism (known as the model).
In many examples, the mimic alters its colouration in order to take
on the often bright, striking colours seen in dangerous animals.
The banded snake eel has taken on the black and white stripes of the banded sea krait -
a dangerous marine reptile with lethal neurotoxic venom.
So, despite being harmless, the eel will be avoided by predators.
Take a look also at the mimic octopus.
Found in the Indo-Pacific shallows, this unassuming cephalopod is a master of
impersonation. A contortionist, able to take on the appearance and behaviour of not one,
but many dangerous creatures.
To imitate the poisonous sole fish,
the octopus uses jet propulsion to build up speed while drawing its arms up into a flattened wedge.
Incredibly, the mimic octopus is able to understand which
creature to impersonate that’s most likely to deter specific predators.
This is demonstrated by the fact that the octopus only seems to mimic sea snakes
when being bothered by damselfishes - a species regularly preyed upon by sea snakes.
For mimicry to be successful, the habitat must contain a large number of ‘model’ animals
with unpalatable characteristics. This isn’t a problem for the multi-talented
mimic octopus with its ability to pick and choose which model to copy.
But in deeper waters, it’s a different story. Food is scarce. Predators are less likely to
be deterred by an animal’s morphology, and bright warning colours will only make you stand out more.
Here, it’s the cnidarians that tend to stay off the menu, like Nanomia bijuga for example.
A siphonophore with incredibly low nutrient density, and armed with numerous stinging cells.
For most predators, they’re simply not worth the effort. So, it’s no surprise
that one small squid species has evolved to resemble these cnidarian neighbours.
Juveniles of the swordtail squid display a long textured tail, primarily used for buoyancy.
But scientists from Monterey Bay Aquarium Research Institute observed that, when in the presence of
Nanomia bijuga, the squid seem to position and colour their tails to imitate the siphonophores.
A clever trick, keeping them from becoming an easy meal for predators. This is a passive example of
mimicry, for the squid intends neither to resemble or conceal danger. Only to appear unsavoury.
While many prey species benefit from imitating predators,
the same is true of some predators that imitate prey. This is known as aggressive mimicry,
a mechanism by which one animal pretends to be something it’s not in order to take advantage of
another. And unlike Batesian mimicry, this variety is MORE common in deeper waters.
The reason for this is that it’s easier to conceal parts of yourself in the all-consuming dark.
In many cases, predators use their bioluminescence to deceive prey.
By controlling the position and intensity of their lights,
anglerfish dangle a luminous orb called an esca. A lure to attract unsuspecting prey.
The bearded scorpionfish is another ambush predator. Instead of using bioluminescence,
it changes its colour and texture to blend in with corals and algae,
then opens its mouth to engulf nearby prey.
Batesian and Aggressive mimicry are both attempts to deceive other organisms. The
mimics are concealing their true nature by pretending to be either dangerous or harmless.
Mullerian mimicry, however, is the only honest form of mimicry. It describes the phenomenon
whereby different harmful or unpalatable species tend to mimic each other’s warning signals.
Think of wasps and bees, two stinging insects, both displaying black and yellow stripes.
As a marine example, consider the nudibranchs.
Molluscs that evolved to lose their shells in favour other forms of protection,
such as the use of poison, while displaying bright colours to alert predators not to eat them.
By resembling each other, these different sea slug species are protected because predators that have
learned to avoid one organism due to its specific warning system, will avoid all similar organisms.
The protective mechanism of Mullerian mimicry
therefore follows the same basic principle as Batesian mimicry.
Their evolutionary contexts are also similar. The convergence between organisms developing
similar appearances is driven by the signal receiver’s behaviour.
Predators that hunt by sight will avoid distasteful animals like sponges.
Via random genetic mutations, some frogfish developed paler colours and bumpy skin;
they resembled sponges, so were avoided by predators,
and thus were more likely to survive and pass on their genes to their offspring.
Over time, the selective action of the predator drove a change in the population of frogfish
that favoured the survival of sponge-like individuals, thus making the sponge the model,
and the frogfish the mimic. The same process can be used to explain the evolution of all mimics.
Overall, mimicry represents an alternative method of adaptation for marine life.
Instead of developing new physiological methods of enhancing survival,
organisms can reap the benefits from the success of others simply through imitation.
Alongside predation and symbiosis, mimicry serves as a vital ecological interaction in an ecosystem;
it drives speciation and biodiversity by opening up a world of opportunity for
animals to take advantage of, leading to the evolution of some weird and wonderful species.
Typically, animals in separate ecosystems come to resemble one another by adapting
to similar lifestyles - a process known as convergent evolution. But the phenomenon of
mimicry challenges our understanding of convergent evolution by demonstrating that different species
in close proximity can come to resemble each other and yet retain completely different lifestyles.
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