Species-typical behavior

The ethological concept of species-typical behavior is based on the premise that certain behavioral similarities are shared by almost all members of a species. Some of these behaviors are unique to certain species, but to be 'species-typical,' they do not have to be unique - they simply have to be characteristic of that species. To understand the importance of species-typical behavior, think about an animal that looks exactly like a dog, but meows, refuses to play fetch, and climbs trees. It's not surprising that humans would find this animal confusing; we expect an animal that looks a certain way to act a certain way, and we associate those behaviors with that animal (e.g. we associate the practice of meowing with cats). The ethological concept of species-typical behavior is based on the premise that certain behavioral similarities are shared by almost all members of a species. Some of these behaviors are unique to certain species, but to be 'species-typical,' they do not have to be unique - they simply have to be characteristic of that species. To understand the importance of species-typical behavior, think about an animal that looks exactly like a dog, but meows, refuses to play fetch, and climbs trees. It's not surprising that humans would find this animal confusing; we expect an animal that looks a certain way to act a certain way, and we associate those behaviors with that animal (e.g. we associate the practice of meowing with cats). Species-typical behaviors are almost always a product of nervous systems, meaning that they're created and influenced by species' genetic code and social and natural environment; this implies that they are strongly influenced by evolution. The phenomenon of the breast crawl is a classic example of this: the vast majority of human newborns, when placed on a reclined mother’s abdomen, will find and begin to suckle on one of the mother’s breasts without any assistance. Such species-typical behaviors can be tied to certain structures of the brain. To prove this point, Murphy, MacLean, and Hamilton (1981) gave hamsters brain lesions at birth, which destroy certain brain structures. They discovered that, while hamsters still expressed species-typical behavior without a brain structure called a neocortex, they lost much of their species-typical play and maternal behaviors when deprived of brain structures called midline limbic convolutions. Likewise, if squirrel monkeys lose the medial segment of a brain structure called the globus pallidus, their ability to engage in certain sexual behavior (e.g. thigh-spreading, groin-thrusting) is either eliminated or impaired. Lesions aren't the only way to discover the role of a structure in species-typical behavior; scientists also use stimulation. In a 1957 experiment, physiologist Walter Hess used an electrode to stimulate a certain part of a resting cat's brainstem; immediately after the stimulation, the cat stood up and arched its back with erect hair - a species-typical behavior in which cats engage when frightened. The behavior lasted as long as the stimulation lasted, and ended as soon as the stimulation ended. Later experiments revealed that even if the same part of the brain is stimulated with the same amount of energy for the same period of time, the intensity of the elicited behavior changes depending on the context. In 1973, behavioral physiologist Erich von Holst attached an electrode to one part of a chicken's brainstem, and recorded the (admittedly somewhat subjective) data. When briefly stimulated without any unusual environmental factors, the chicken was restless. When briefly stimulated in the presence of a human fist, the chicken reacted with a slightly threatening posture, and in the presence of a weasel, the chicken took a very threatening pose, with feathers bristling. In short, the brainstem elicits species-typical behavior that is appropriate to the surrounding environment. Oftentimes the presence or density of certain chemical receptors on cranial structures like the brainstem determine their importance in one species-typical behavior or another. Consider voles. prairie voles are monogamous; they also have a high density of oxytocin receptors (OTRs) in a brain structure called the nucleus accumbens. Non-monogamous meadow voles, on the other hand, do not. Likewise, monogamous pine voles have a high-density of OTRs; non-monogamous meadow voles do not. The way in which hormones alter these receptors is an important behavioral regulator. Consider the ways in which gonads affect OTRs in different rodents. In female rats, gonadal estrogen increases the level of OTR binding and, when the ovarian cycle maximizes the amount of estrogen in the bloodstream, causes OTRs to appear in ventrolateral regions of the structure called the ventromedial nucleus. This, in turn, increases the likelihood that a female rat will engage in certain species-typical sexual activity by increasing her sexual receptivity. But the effect of this regulatory mechanism differs between species; though a gonadectomy would decrease (and gonadal steroids would increase) sexual receptivity in the female rat, these things would have the opposite impacts on female mice. While some species-typical behavior is learned from parents, it's also sometimes the product of a fixed action pattern, also known as an innate releasing mechanism (IRM). In these instances, a neural network is 'programmed' to create a hard-wired, instinctive behavior in response to an external stimulus. When a blind child hears news that makes her happy, she's likely to smile in response; she never had to be taught to smile, and she never learned this behavior by seeing others do it. Similarly, when kittens are shown a picture of a cat in a threatening posture, most of them arch their backs, bear their teeth, and sometimes even hiss, even though they've never seen another cat do this. Many IRMs can be explained by the theory of evolution - if an adaptive behavior helps a species survive long enough to be fruitful and multiply (such as a cat hissing in order to discourage an attack from another creature), the genes that coded for those brain circuits are more likely to be passed on. A heavily studied example of a fixed action pattern is the feeding behavior of the Helisoma trivolvis (pulmonata), a type of snail. A study has shown that the intricate connections within the buccal ganglia (see nervous system of gastropods) form a central system whereby sensory information stimulates feeding in the helisoma. More specifically, a unique system of communication between three classes of neurons in the buccal ganglia are responsible for forming the neural network that influences feeding. A species-typical behavior can be altered by experience, as shown by experiments on Aplysia californica, a sea snail. When its gills are stimulated in a novel manner, it withdraws them into its shell for the sake of protection. This is a species-typical behavior. But after a stimuli that was once novel (e.g. a weak jet of water) has been applied repeatedly to the gills, aplysia no longer withdraws them. It has gone through habituation, a process by which the response to a stimulus becomes weaker with more exposure. This occurs because of changes in the nervous system. Neurons communicate with one another at synapses, which consist of the tip of the communicating cell (the presynpatic membrane), the tip of the receiving cell (the postsynaptic membrane), and the space in between the two (the synaptic cleft). When the presynaptic membrane is stimulated by the influx of calcium ions, it releases a chemical called a neurotransmitter, which travels over the synaptic cleft in order to bind to the postsynaptic membrane and thereby stimulate the receiving cell. During habituation, fewer calcium ions are brought into the presynaptic membrane, meaning less neurotransmitter is released, meaning that the stimulation of the receiving cell is not as strong, meaning that the action that it is supposed to stimulate will be weaker. Likewise, the number of synapses related to a certain behavior decreases as a creature habituates, also resulting in weaker reactions. And the structure of the synapse itself can be altered in any number of ways that weaken communication (e.g. decreased number of neurotransmitter receptors on the postsynaptic membrane). It is because of these processes that the species-typical behavior of aplysia was altered.