Behavioral plasticity

Behavioral plasticity refers an animal’s ability to produce more than one alternative form of behavioral phenotype from a single genotype in response to changing environmental conditions. Behavior is among the most variable phenotypic traits and can be impacted by a multitude of factors originating from internal and external stimuli.

Background

The concept of behavioral plasticity began to gain prominence in the 1970’s under the guise of behavioral flexibility (West-Ebberhard). Flexibility in this sense referred to an organism’s ability to alter their behavior in response to the environment. Although, behavioral plasticity has become a more widely used hypothesis over the last decade, demonstrating true plasticity without assuming genetic variance remains controversial and difficult in many studies.

Types

Behavioral plasticity can be broadly classified into two types: exogenous and endogenous plasticities. These classifications can also be defined further into the subcategories of exogenous plasticity refers to the changes in behavioral phenotypes caused by external stimuli, experiences and environments. This type of behavioral response has two major subgroupings as well. When an external stimuli causes or ‘activates’ an immediate plastic response, then the organism is demonstrating activational plasticity. Whereas if an organisms current behavior is altered by past experiences then the animal is said to be exhibiting developmental plasticity. Endogenous plasticity encompasses plastic responses that result from changes in internal cues (circadian rhythm, menstruation, etc.)

These broad classifications also encompasses two subgroupings: contextual and developmental plasticity. Contextual (or activational) plasticity occurs when there is an immediate effect on behavior by an external stimuli. This form of plasticity highlights the assertion that external stimuli in a given environmental context initiate neural and hormonal mechanisms which developed as responses to stimuli and experiences earlier in an organism’s life. Developmental or ‘innate’ behavioral plasticity covers the effects of past experiences and stimuli on an organism’s current behavior.

Distinguishing between developmental and contextual

Developmental behavioral plasticity corresponds to the commonly used of definition of plasticity: a single genotype can expresses more than one behavioral phenotype as a result of different developmental routes triggered by differences in environments. Developmental plasticity thus envelops what is referred to as ‘learning’, or any change in the neuronal pathways as a result of an experience. However, developmental behavioral plasticity also includes developmental changes in morphology and physiology relevant to a particular behavior, such as changes in muscles, limbs or bones that influence foraging or locomotion.

Potential vs. realized plasticity

A useful distinction to make when looking at behavioral plasticity is between potential and realized plasticity. Potential plasticity refers to the ability of a given phenotypic trait to vary in its response to variation in stimuli, experiences, or environmental conditions. Thus, potential plasticity is the theoretical range in behavioral plasticity that could be expressed. This value is never truly known but serves more as a baseline in plasticity models. Realized plasticity, on the other hand, refers to the extent to which a given phenotype actually varies in response to changes in a specific stimulus, experience, or environmental condition. Realized plasticity is the range in which plasticity is actually exhibited. This is value that researchers can observe in studies. Animals that have a high potential behavioral plasticity may pay equally high costs of maintaining the machinery and mechanisms that allow them to detect and respond to different stimuli in their environment. However, the cost of maintaining this potential must be paid even if the animal never needs to express the plasticity. Conversely, having a lower ability of expressing plasticity may have equally high costs in terms of survivorship.

Evolutionary Causes and Consequences

Behavioral plasticity can have major impacts on the evolutionary fitness of an individual. Both developmental and contextual plasticity influence the fitness of an animal in a novel environment by increasing the probability that the animal will survive in that environment. Developmental plasticity is particularly important in terms of survival in novel environments because trial-and-error processes such as learning (which encompass both phenotype sampling and environmental feedback) have the ability to immediately shift an entire population close to a new adaptive norm. As such, the ability to express some level of behavioral plasticity can be very advantageous. In fluctuating environments, animals that can change how they respond to differences in stimuli would have a leg up over animals that were set in a rigid phenotype. However, this would only be the case if the costs of maintaining the ability to change phenotype was lesser than the benefit conferred to the individual.