What is Adaptive Value?
Adaptive value is the characterization of the evolutionary advantage endowed by the behavior which has evolved in an organism. It is an attempt to understand why the animal behavior is “well designed” and how it increases survival, reproduction and subsequently fitness of an organism or species, the adaptive value is studied.
• Cephalopods are generally thought to use their camouflage to avoid predation. A recent study investigated this hypothesis in octopuses.
• Disguises are probably more efficient than escape mechanisms.
• Some species of cephalopods such as Sepioteuthis sepioide disguise themselves as herbivores in order to get closer to prey.
• Cephalopods respond to predatory stimuli by changing color, which probably confers an adaptive benefit.
• Cephalopods also use their flexible coloration to signal sexual information to one another although this information is not always sincere.
By disguising themselves as flatfish, and sea snakes while in motion and at rest respectively octopuses appear to be a much less attractive prey to a potential predator. The flatfish position allows the legs to assume a flat position, which is thought to generate lift. Similarly bipedal walking behavior in octopuses (A. aculeatus) is just as fast,if not faster, than jet propulsion making it a stealthy method of predator avoidance(Huffard 2006). The following videos demonstrate the speed and discretion of a walking octopus.
Octopus video: Octopus marginatus
Octopus video: Octopus aculeatus
We can infer that the camouflage is adaptive to blending into the environment as the ability to blend in varies across species. A normal octopus has about 230 chromatophores per millimeter squared whereas Luligo plei, a species of squid, only has about 8 per millimeter squared. The density of chromatophores in a cephalopod may reflect the importance of crypsis to survival. In general, species that are active at daytime and live in habitats with complex features, such as coral reefs, rock reefs and kelp forests have very rich patterning repertoires that allow them to easily blend into their surroundings. The opposite is true of nocturnal species that live in simpler habitats (Hanlon and Messenger, 1996).
A recent study testing the concealment from predators hypothesis.
A direct test of camouflage as an anti-predation mechanism showed that in one of the two locations studied octopuses were more often conspicuous than camouflaged while foraging. The authors suggested that octopuses use their camouflage to avoid a consistent visual profile in the ocean rather than maintaining a camouflaged state. This was supported by their observations that the octopuses changed color 177 times/ hour and mimic fish when swimming (Hanlon, 1999). These conclusions may not be warranted for all cephalopods as Cuttlefish display different behavior during hunting and foraging (Hanlon, 1996).
Efficiency of crypsis versus fast escape
The energy cost of disguise is probably a smart investment as predator avoidance which entails ink secretion, and jet propulsion are incredibly energy inefficient mechanisms. Jet propulsion quickly leads to hypoxic conditions and requires internal mantle pressure high enough to stop the octopus' heart (Huffard 2006).
Sepioteuthis sepioide, a species of squid, has been observed mimicking parrot fish. In order to do so, it swims in reverse and creates a display of two false eye spots. It holds its arms and tentacles held together and waves from side to side imitating a fish’s fin. The parrot fish is herbivorous, and mimicking them allows the squid to get closer to potential prey species that do not consider parrot fish to be their predators (Hanlon & Messenger, 1996).This sort of behavior aids most cephalopods in their hunting.
Many species of cephalopods (especially adults) respond to predatory stimuli (either in the natural environment or in a lab) by changing colors and displaying eye spots (Hanlon 1996, Adamo 2006). This response is called a deimatic display and it changes over the course of the cephalopods' life. Cuttlefish also displayed a marked increase in camouflage behavior during the night, suggesting that there are nocturnal pedators which provide selective pressures on the population (Hanlon, 2007).
Deimatic Display of a cuttlefish (Kingand, 2006).
Signal sexual information
Cephalopods use their ability to change colors to communicate with members of their species regarding sexual situations. For example female cuttlefish display a splotched pattern when they see another female (or their mirror image). The splotched pattern does not appear in any of their normal behavior suggesting that it is a form of female to female comunication which could reduce female antagonism (Palmer, 2006). Similarly males display specifc patterns during conflicts with one another. These patterns called the intense zebra display are shown during male - male conflicts. The darkness of the males' faces is highly predictive of whether the fight will escalate with lighter faced males retreating peacefully more often than dark faced males. Cephalopods used their skin tone to determine the victor ouint sexual conflicts without actual violence which could leave both animals injured and less fit (Helly, 1996).
Insincere sexual signalling
Cuttlefish have been observed displaying female markings in order to fool the guarding male and fertilize his female. This strategy is called the sneaker-male strategy and confers higher rates of fertilization than normal courtship. Normal females are continually guarded by a dominant male cuttlefish in addition to rejecting roughly 70% of the mating attempts that are made. This ability to mimic the female form confers a clear adaptive value although it is still unknownwhether the increased mating results in increased progeny. (Hanlon, 2005).
A) Unpaired male (m) assuming female coloration and approaching a paired female (f) while her consort (c) displays to another male (top right). The male then gets to finish mating without disturbance from the consort (B, C)(Hanlon, 2005).