What is protective resemblance?

Answer:

Protective resemblance is believed by biologists to be a product of natural selection and may range from organisms having evolved the appropriate coloration and behavior to obtain protection from predation, all the way to promoting active avoidance by predators. Examples would thus include organisms using crypsis (<Gk kryptos=hidden) such as thorn, leaf, twig and stone mimics among insects (although this is not mimicry in the true sense of mimetic resemblance, i.e. resemblance to a prey species that prior learning has shown to be dangerous), or simply having coloration that makes the organism difficult to distinguish from the background it is most often associated with, for example, anglerfishes or stonefish. In the case of the latter, the protective resemblance permits prey to approach so they can be eaten and would more properly be termed aggressive mimicry.

However, coloration is only a part of the suite of adaptations and to be effective, coloration and form (i.e. leaf or stick shape) must be accompanied by the appropriate behavior. For example, Breder was a fisheries scientist who collected stories of protective resemblance and wrote of the tripletail (Lobotes surinamensis) which as juveniles, rear in areas where mangrove trees are abundant. Not only do the juveniles have a similar shape and coloration to the mangrove leaves complete with spots similar to the leaves of the trees, but they float with one side up on the water's surface. If startled, they sink and drift to the bottom in a manner resembling a leaf moving from side to side. Upon reaching the bottom, they lie motionless for a time and then return to the surface.

Back to mimicry, Batesian Mimicry describes the protective function of an harmless species resembling one that is toxic with viceroy and monarch butterflies respectively the best known examples of mimics and models. Monarch butterfly eggs are deposited on milkweed plants and caterpillars feed on the leaves which contain a cardiac glycoside. For vertebrate predators capable of learning, a single meal of a monarch butterfly is sufficient to cause heart palpatations and retching. Lincoln Brower reported that a bluejay presented with a monarch butterfly two years after its initial exposure, retched and would not even approach the possible prey. For palatable viceroys to obtain protection from their resemblance to monarch butterflies, they must have a similar geographic distribution.

Some bird species such as cuckoos and cowbirds lay their eggs in the nests of other birds and have the host species perform the majority of parental care following their own selection of a suitable nest to deposit a single egg into. The brood parasitic species itself has reared with the host and therefore knows what species to parasitize, their eggs have similar coloration to the host species and the parasite may even push its nestmates out of the nest to obtain the majority of parental care.

Of the three examples given, all are examples of protective resemblance but the first is an example of crypsis, anglerfishes and stonefishes are examples of aggressive mimicry to facilitate predation, and cuckoos and cowbirds use the resemblance of their eggs in size and coloration to permit brood parasitism. Aposematism is closely related and is defined as possessing coloration which is highly visible and provides a warning to predators to avoid the possible prey. Arrow poison frogs are brightly colored and possess behaviors which facilitate predators sampling them and learning avoidance. Because many vertebrate species have extended parental care, parents may teach their offspring to both avoid prey that are noxious and recognize prey that are camouflaged.