User:Ethologyisfun31/Supernormal Stimulus

Supernormal stimulus
Supernormal stimuli are present in areas of biology and psychology, but are also studied within other fields like sociology and art.

For example, when it comes to bird eggs, they can evolve to prefer the artificial versions to their own, particularly evident in brood parasitism, and humans can be similarly exploited by junk food.

A variety of organisms that display or are susceptible to supernormal stimuli include insects, birds, and humans.

Causation
Animals exhibiting, or responding to, characteristics that represent a supernormal stimulus usually display them as a result of selective pressures. Co-evolution between animals displaying supernormal stimuli, and the organisms responding to the supernormal stimuli, rely on evolution and propagation of genetics, behavioral patterns, and other biological factors. Supernormal stimuli such as emphasized color, size, patterns, or shapes, are often successful because an organism that exhibits them will often be selected by an organism that favors it. This will ensure survival and increased reproductive fitness of current and latter generations.

In biology
Niko Tinbergen coined this term through his research, which discovered that experimenters could display an alternate target that attract an organism's attention more so than the naturally occurring target.

Herring gull chicks peck at the red spot located on their parent's bill. The offspring targets the red spot due to the contrast of color (stimulus). They do this in order to receive food through regurgitation from the parent. Tinbergen and colleagues developed an experiment that presented different models to chicks and determined their pecking rates. They used different models including an adult herring gull's natural head, a standard wooden model of its head, the bill only, and a red stick with smaller white markings on it. The pecking rate of the chicks were consistent with the natural head, standard head model, and the bill only model. The pecking rate of the chicks increased when presented with the stick model. This suggests that the chicks preferred the dramatic contrast of the red stick with the yellow markings, therefore the artificial stimulus of the stick model was favored over the basic herring gull head and bill models, proving that the artificial stimuli was favored over the naturally occurring stimuli.

Insects
Pollinators, like butterflies, show behavioral response(s) to supernormal stimuli through intersexual communication. Butterflies use olfactory cues, but primarily rely on visual forms of communication, due to wind and temperature affecting their sense of smell. Sexually active butterflies will perch and wait for a mate. Once an object is detected, the butterfly can determine if the color and movement patterns are of a sexually receptive butterfly. In certain species, like the silver-washed fritillary butterfly (Argynnis paphia), the male butterfly will exhibit high contrast sensitivity and well-developed visual acuity. A more dramatic contrast of color (or movement pattern) resembling, but further emphasizing the traits of the female butterfly, could alter this usual behavior in males. Studies show that the male silver-washed fritillary butterfly select a monochromatic orange paper model, over receptive female butterflies who portrayed their usual coloration/markings.

Manipulation by parasites
Supernormal stimuli can be exhibited by brood parasites, for example, the parasitic cuckoo chick and parental care by reed warblers. Brood parasites have evolved more dramatic colors, sizes, patterns, and/or shapes that lead to the parasite being interpreted as healthier or more preferable, in contrast to neighboring offspring. Cuckoo chicks are often successful because their begging calls, the supernormal stimulus, are representative of an entire reed warbler brood. Due to the host parent's evolutionary instinct, elicited by selective pressures, they will select this exaggerated form of the stimulus. These calls will cause the host parent to primarily invest energy into the parasitic chick and provide it with additional food resources. Studies show that the supernormal stimuli in cuckoo chicks alter the foraging behavior in parental reed warblers.

Maladaptive behavior
Maladaptive behaviors are shown by organisms that display a preference for supernormal stimuli over naturally occurring stimuli. This is often based on instinct to gather as many resources as possible in a resource-sparse environment. It can also be instinctual for certain species to select the supernormal stimuli that will suggest the best energy investment of the individual, often parental investment. The selection of the supernormal stimuli must also simultaneously outweigh the cost of the behavior in order for it to evolve. This is shown in the cuckoo chick and the effects on host reed warblers. These parasitic chicks exhibit irresistible begging calls toward the parental host. This occurs as a result of selective pressures. The reed warbler increases foraging efforts to feed the parasitic chick and its own offspring. As a result, this shows a maladaptive behaviour of the host reed warbler as it is investing into a chick that is not biologically related, which does not provide reproductive fitness gain.

Biodiversity concerns
The significance of supernormal stimuli and brood parasitism or in various other species susceptible to environmental manipulation, is that this can drastically reduce the population numbers of the respective species. Brood parasitism can cause host parents to ignore their own offspring or display a higher parental investment into the parasite. Animals that are at risk of extinction, extirpation, or vulnerability will be impacted by supernormal stimuli present in brood parasites.