Phenotypic plasticity

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Phenotypic plasticity refers to some of the changes in an organism's behavior, morphology and physiology in response to a unique environment. [1] Fundamental to the way in which organisms cope with environmental variation, phenotypic plasticity encompasses all types of environmentally induced changes (e.g. morphological, physiological, behavioural, phenological) that may or may not be permanent throughout an individual's lifespan. The term was originally used to describe developmental effects on morphological characters, but is now more broadly used to describe all phenotypic responses to environmental change, such as acclimation (acclimatization), as well as learning. [2] The special case when differences in environment induce discrete phenotypes is termed polyphenism.

Contents

Phenotypic plasticity is the ability of one genotype to produce more than one phenotype when exposed to different environments. Each line here represents a genotype. Horizontal lines show that the phenotype is the same in different environments; slanted lines show that there are different phenotypes in different environments, and thus indicate plasticity. Phenotypic Plasticity Genotypes to Phenotypes.jpg
Phenotypic plasticity is the ability of one genotype to produce more than one phenotype when exposed to different environments. Each line here represents a genotype. Horizontal lines show that the phenotype is the same in different environments; slanted lines show that there are different phenotypes in different environments, and thus indicate plasticity.

Generally, phenotypic plasticity is more important for immobile organisms (e.g. plants) than mobile organisms (e.g. most animals), as mobile organisms can often move away from unfavourable environments. [3] Nevertheless, mobile organisms also have at least some degree of plasticity in at least some aspects of the phenotype. One mobile organism with substantial phenotypic plasticity is Acyrthosiphon pisum of the aphid family, which exhibits the ability to interchange between asexual and sexual reproduction, as well as growing wings between generations when plants become too populated. [4]

Examples

Plants

Phenotypic plasticity of sorghum flowering time evaluated from seven environments. The identified photothermal time, a performance-independent index, quantifies the relevant environmental input and enables a systematic framework for modelling, explaining, and predicting phenotypic values under natural conditions. Phenotypic plasticity.tiff
Phenotypic plasticity of sorghum flowering time evaluated from seven environments. The identified photothermal time, a performance-independent index, quantifies the relevant environmental input and enables a systematic framework for modelling, explaining, and predicting phenotypic values under natural conditions.

Phenotypic plasticity in plants includes the timing of transition from vegetative to reproductive growth stage, the allocation of more resources to the roots in soils that contain low concentrations of nutrients, the size of the seeds an individual produces depending on the environment, [6] and the alteration of leaf shape, size, and thickness. [7] Leaves are particularly plastic, and their growth may be altered by light levels. Leaves grown in the light tend to be thicker, which maximizes photosynthesis in direct light; and have a smaller area, which cools the leaf more rapidly (due to a thinner boundary layer). Conversely, leaves grown in the shade tend to be thinner, with a greater surface area to capture more of the limited light. [8] [9] Dandelion are well known for exhibiting considerable plasticity in form when growing in sunny versus shaded environments. The transport proteins present in roots also change depending on the concentration of the nutrient and the salinity of the soil. [10] Some plants, Mesembryanthemum crystallinum for example, are able to alter their photosynthetic pathways to use less water when they become water- or salt-stressed. [11]

Because of phenotypic plasticity, it is hard to explain and predict the traits when plants are grown in natural conditions unless an explicit environment index can be obtained to quantify environments. Identification of such explicit environment indices from a critical growth periods being highly correlated with sorghum and rice flowering time enables such predictions. [5] [12]

Phytohormones and leaf plasticity

Leaves are very important to a plant in that they create an avenue where photosynthesis and thermoregulation can occur. Evolutionarily, the environmental contribution to leaf shape allowed for a myriad of different types of leaves to be created. [13] Leaf shape can be determined by both genetics and the environment. [14] Environmental factors, such as light and humidity, have been shown to affect leaf morphology, [15] giving rise to the question of how this shape change is controlled at the molecular level. This means that different leaves could have the same gene but present a different form based on environmental factors. Plants are sessile, so this phenotypic plasticity allows the plant to take in information from its environment and respond without changing its location.

In order to understand how leaf morphology works, the anatomy of a leaf must be understood. The main part of the leaf, the blade or lamina, consists of the epidermis, mesophyll, and vascular tissue. The epidermis contains stomata which allows for gas exchange and controls perspiration of the plant. The mesophyll contains most of the chloroplast where photosynthesis can occur. Developing a wide blade/lamina can maximize the amount of light hitting the leaf, thereby increasing photosynthesis, however too much sunlight can damage the plant. Wide lamina can also catch wind easily which can cause stress to the plant, so finding a happy medium is imperative to the plants’ fitness. The Genetic Regulatory Network is responsible for creating this phenotypic plasticity and involves a variety of genes and proteins regulating leaf morphology. Phytohormones have been shown to play a key role in signaling throughout the plant, and changes in concentration of the phytohormones can cause a change in development. [16]

Studies on the aquatic plant species Ludwigia arcuata have been done to look at the role of abscisic acid (ABA), as L. arcuata is known to exhibit phenotypic plasticity and has two different types of leaves, the aerial type (leaves that touch the air) and the submerged type (leaves that are underwater). [17] When adding ABA to the underwater shoots of L. arcuata, the plant was able to produce aerial type leaves underwater, suggesting that increased concentrations of ABA in the shoots, likely caused by air contact or a lack of water, triggers the change from the submerged type of leaf to the aerial type. This suggests ABA's role in leaf phenotypic change and its importance in regulating stress through environmental change (such as adapting from being underwater to above water). In the same study, another phytohormone, ethylene, was shown to induce the submerged leaf phenotype unlike ABA, which induced aerial leaf phenotype. Because ethylene is a gas, it tends to stay endogenously within the plant when underwater – this growth in concentration of ethylene induces a change from aerial to submerged leaves and has also been shown to inhibit ABA production, further increasing the growth of submerged type leaves. These factors (temperature, water availability, and phytohormones) contribute to changes in leaf morphology throughout a plants lifetime and are vital to maximize plant fitness.

Animals

The developmental effects of nutrition and temperature have been demonstrated. [18] The gray wolf (Canis lupus) has wide phenotypic plasticity. [19] [20] Additionally, male speckled wood butterflies have two morphs: one with three dots on its hindwing, and one with four dots on its hindwings. The development of the fourth dot is dependent on environmental conditions – more specifically, location and the time of year. [21] In amphibians, Pristimantis mutabilis has remarkable phenotypic plasticity. [22] Another example is the southern rockhopper penguin. [23] Rockhopper penguins are present at a variety of climates and locations; Amsterdam Island's subtropical waters, Kerguelen Archipelago's subarctic coastal waters, and Crozet Archipelago's subantarctic coastal waters. [23] Due to the species plasticity they are able to express different strategies and foraging behaviors depending on the climate and environment. [23] A main factor that has influenced the species' behavior is where food is located. [23]

Temperature

Plastic responses to temperature are essential among ectothermic organisms, as all aspects of their physiology are directly dependent on their thermal environment. As such, thermal acclimation entails phenotypic adjustments that are found commonly across taxa, such as changes in the lipid composition of cell membranes. Temperature change influences the fluidity of cell membranes by affecting the motion of the fatty acyl chains of glycerophospholipids. Because maintaining membrane fluidity is critical for cell function, ectotherms adjust the phospholipid composition of their cell membranes such that the strength of van der Waals forces within the membrane is changed, thereby maintaining fluidity across temperatures. [24]

Diet

Phenotypic plasticity of the digestive system allows some animals to respond to changes in dietary nutrient composition, [25] [26] diet quality, [27] [28] and energy requirements. [29] [30] [31]

Changes in the nutrient composition of the diet (the proportion of lipids, proteins and carbohydrates) may occur during development (e.g. weaning) or with seasonal changes in the abundance of different food types. These diet changes can elicit plasticity in the activity of particular digestive enzymes on the brush border of the small intestine. For example, in the first few days after hatching, nestling house sparrows (Passer domesticus) transition from an insect diet, high in protein and lipids, to a seed based diet that contains mostly carbohydrates; this diet change is accompanied by two-fold increase in the activity of the enzyme maltase, which digests carbohydrates. [25] Acclimatizing animals to high protein diets can increase the activity of aminopeptidase-N, which digests proteins. [26] [32]

Poor quality diets (those that contain a large amount of non-digestible material) have lower concentrations of nutrients, so animals must process a greater total volume of poor-quality food to extract the same amount of energy as they would from a high-quality diet. Many species respond to poor quality diets by increasing their food intake, enlarging digestive organs, and increasing the capacity of the digestive tract (e.g. prairie voles, [31] Mongolian gerbils, [28] Japanese quail, [27] wood ducks, [33] mallards [34] ). Poor quality diets also result in lower concentrations of nutrients in the lumen of the intestine, which can cause a decrease in the activity of several digestive enzymes. [28]

Animals often consume more food during periods of high energy demand (e.g. lactation or cold exposure in endotherms), this is facilitated by an increase in digestive organ size and capacity, which is similar to the phenotype produced by poor quality diets. During lactation, common degus (Octodon degus) increase the mass of their liver, small intestine, large intestine and cecum by 15–35%. [29] Increases in food intake do not cause changes in the activity of digestive enzymes because nutrient concentrations in the intestinal lumen are determined by food quality and remain unaffected. [29] Intermittent feeding also represents a temporal increase in food intake and can induce dramatic changes in the size of the gut; the Burmese python (Python molurus bivittatus) can triple the size of its small intestine just a few days after feeding. [35]

AMY2B (Alpha-Amylase 2B) is a gene that codes a protein that assists with the first step in the digestion of dietary starch and glycogen. An expansion of this gene in dogs would enable early dogs to exploit a starch-rich diet as they fed on refuse from agriculture. Data indicated that the wolves and dingo had just two copies of the gene and the Siberian Husky that is associated with hunter-gatherers had just three or four copies, whereas the Saluki that is associated with the Fertile Crescent where agriculture originated had 29 copies. The results show that on average, modern dogs have a high copy number of the gene, whereas wolves and dingoes do not. The high copy number of AMY2B variants likely already existed as a standing variation in early domestic dogs, but expanded more recently with the development of large agriculturally based civilizations. [36]

Parasitism

Infection with parasites can induce phenotypic plasticity as a means to compensate for the detrimental effects caused by parasitism. Commonly, invertebrates respond to parasitic castration or increased parasite virulence with fecundity compensation in order to increase their reproductive output, or fitness. For example, water fleas ( Daphnia magna ), exposed to microsporidian parasites produce more offspring in the early stages of exposure to compensate for future loss of reproductive success. [37] A reduction in fecundity may also occur as a means of re-directing nutrients to an immune response, [38] or to increase longevity of the host. [39] This particular form of plasticity has been shown in certain cases to be mediated by host-derived molecules (e.g. schistosomin in snails Lymnaea stagnalis infected with trematodes Trichobilharzia ocellata) that interfere with the action of reproductive hormones on their target organs. [40] Changes in reproductive effort during infection is also thought to be a less costly alternative to mounting resistance or defence against invading parasites, although it can occur in concert with a defence response. [41]

Hosts can also respond to parasitism through plasticity in physiology aside from reproduction. House mice infected with intestinal nematodes experience decreased rates of glucose transport in the intestine. To compensate for this, mice increase the total mass of mucosal cells, cells responsible for glucose transport, in the intestine. This allows infected mice to maintain the same capacity for glucose uptake and body size as uninfected mice. [42]

Phenotypic plasticity can also be observed as changes in behaviour. In response to infection, both vertebrates and invertebrates practice self-medication, which can be considered a form of adaptive plasticity. [43] Various species of non-human primates infected with intestinal worms engage in leaf-swallowing, in which they ingest rough, whole leaves that physically dislodge parasites from the intestine. Additionally, the leaves irritate the gastric mucosa, which promotes the secretion of gastric acid and increases gut motility, effectively flushing parasites from the system. [44] The term "self-induced adaptive plasticity" has been used to describe situations in which a behavior under selection causes changes in subordinate traits that in turn enhance the ability of the organism to perform the behavior. [45] For example, birds that engage in altitudinal migration might make "trial runs" lasting a few hours that would induce physiological changes that would improve their ability to function at high altitude. [45]

Woolly bear caterpillars ( Grammia incorrupta ) infected with tachinid flies increase their survival by ingesting plants containing toxins known as pyrrolizidine alkaloids. The physiological basis for this change in behaviour is unknown; however, it is possible that, when activated, the immune system sends signals to the taste system that trigger plasticity in feeding responses during infection. [43]

Reproduction

Hatch rates for red-eyed tree frog tadpoles depends on predation Hatch rates for red-eyed tree frog tadpoles depends on predation.png
Hatch rates for red-eyed tree frog tadpoles depends on predation

The red-eyed tree frog, Agalychnis callidryas , is an arboreal frog (hylid) that resides in the tropics of Central America. Unlike many frogs, the red-eyed tree frog has arboreal eggs which are laid on leaves hanging over ponds or large puddles and, upon hatching, the tadpoles fall into the water below. One of the most common predators encountered by these arboreal eggs is the cat-eyed snake, Leptodeira septentrionalis. In order to escape predation, the red-eyed tree frogs have developed a form of adaptive plasticity, which can also be considered phenotypic plasticity, when it comes to hatching age; the clutch is able to hatch prematurely and survive outside of the egg five days after oviposition when faced with an immediate threat of predation. The egg clutches take in important information from the vibrations felt around them and use it to determine whether or not they are at risk of predation. In the event of a snake attack, the clutch identifies the threat by the vibrations given off which, in turn, stimulates hatching almost instantaneously. In a controlled experiment conducted by Karen Warkentin, hatching rate and ages of red-eyed tree frogs were observed in clutches that were and were not attacked by the cat-eyed snake. When a clutch was attacked at six days of age, the entire clutch hatched at the same time, almost instantaneously. However, when a clutch is not presented with the threat of predation, the eggs hatch gradually over time with the first few hatching around seven days after oviposition, and the last of the clutch hatching around day ten. Karen Warkentin's study further explores the benefits and trade-offs of hatching plasticity in the red-eyed tree frog. [46]

Evolution

Plasticity is usually thought to be an evolutionary adaptation to environmental variation that is reasonably predictable and occurs within the lifespan of an individual organism, as it allows individuals to 'fit' their phenotype to different environments. [47] [48] If the optimal phenotype in a given environment changes with environmental conditions, then the ability of individuals to express different traits should be advantageous and thus selected for. Hence, phenotypic plasticity can evolve if Darwinian fitness is increased by changing phenotype. [49] [50] A similar logic should apply in artificial evolution attempting to introduce phenotypic plasticity to artificial agents. [51] However, the fitness benefits of plasticity can be limited by the energetic costs of plastic responses (e.g. synthesizing new proteins, adjusting expression ratio of isozyme variants, maintaining sensory machinery to detect changes) as well as the predictability and reliability of environmental cues [52] (see Beneficial acclimation hypothesis).

Freshwater snails (Physa virgata), provide an example of when phenotypic plasticity can be either adaptive or maladaptive. In the presence of a predator, bluegill sunfish, these snails make their shell shape more rotund and reduce growth. This makes them more crush-resistant and better protected from predation. However, these snails cannot tell the difference in chemical cues between the predatory and non-predatory sunfish. Thus, the snails respond inappropriately to non-predatory sunfish by producing an altered shell shape and reducing growth. These changes, in the absence of a predator, make the snails susceptible to other predators and limit fecundity. Therefore, these freshwater snails produce either an adaptive or maladaptive response to the environmental cue depending on whether the predatory sunfish is actually present. [53] [54]

Given the profound ecological importance of temperature and its predictable variability over large spatial and temporal scales, adaptation to thermal variation has been hypothesized to be a key mechanism dictating the capacity of organisms for phenotypic plasticity. [55] The magnitude of thermal variation is thought to be directly proportional to plastic capacity, such that species that have evolved in the warm, constant climate of the tropics have a lower capacity for plasticity compared to those living in variable temperate habitats. Termed the "climatic variability hypothesis", this idea has been supported by several studies of plastic capacity across latitude in both plants and animals. [56] [57] However, recent studies of Drosophila species have failed to detect a clear pattern of plasticity over latitudinal gradients, suggesting this hypothesis may not hold true across all taxa or for all traits. [58] Some researchers propose that direct measures of environmental variability, using factors such as precipitation, are better predictors of phenotypic plasticity than latitude alone. [59]

Selection experiments and experimental evolution approaches have shown that plasticity is a trait that can evolve when under direct selection and also as a correlated response to selection on the average values of particular traits. [60]

Plasticity and climate change

Unprecedented rates of climate change are predicted to occur over the next 100 years as a result of human activity. [61] Phenotypic plasticity is a key mechanism with which organisms can cope with a changing climate, as it allows individuals to respond to change within their lifetime. [62] This is thought to be particularly important for species with long generation times, as evolutionary responses via natural selection may not produce change fast enough to mitigate the effects of a warmer climate.

The North American red squirrel (Tamiasciurus hudsonicus) has experienced an increase in average temperature over this last decade of almost 2 °C. This increase in temperature has caused an increase in abundance of white spruce cones, the main food source for winter and spring reproduction. In response, the mean lifetime parturition date of this species has advanced by 18 days. Food abundance showed a significant effect on the breeding date with individual females, indicating a high amount of phenotypic plasticity in this trait. [63]

See also

Related Research Articles

Phenotype Composite of the organisms observable characteristics or traits

In genetics, the phenotype is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological properties, its behavior, and the products of behavior. An organism's phenotype results from two basic factors: the expression of an organism's genetic code, or its genotype, and the influence of environmental factors. Both factors may interact, further affecting phenotype. When two or more clearly different phenotypes exist in the same population of a species, the species is called polymorphic. A well-documented example of polymorphism is Labrador Retriever coloring; while the coat color depends on many genes, it is clearly seen in the environment as yellow, black, and brown. Richard Dawkins in 1978 and then again in his 1982 book The Extended Phenotype suggested that one can regard bird nests and other built structures such as caddis-fly larvae cases and beaver dams as "extended phenotypes".

Genotype–phenotype distinction

The genotype–phenotype distinction is drawn in genetics. "Genotype" is an organism's full hereditary information. "Phenotype" is an organism's actual observed properties, such as morphology, development, or behavior. This distinction is fundamental in the study of inheritance of traits and their evolution.

A maternal effect is a situation where the phenotype of an organism is determined not only by the environment it experiences and its genotype, but also by the environment and genotype of its mother. In genetics, maternal effects occur when an organism shows the phenotype expected from the genotype of the mother, irrespective of its own genotype, often due to the mother supplying messenger RNA or proteins to the egg. Maternal effects can also be caused by the maternal environment independent of genotype, sometimes controlling the size, sex, or behaviour of the offspring. These adaptive maternal effects lead to phenotypes of offspring that increase their fitness. Further, it introduces the concept of phenotypic plasticity, an important evolutionary concept. It has been proposed that maternal effects are important for the evolution of adaptive responses to environmental heterogeneity.

Acclimatization or acclimatisation is the process in which an individual organism adjusts to a change in its environment, allowing it to maintain fitness across a range of environmental conditions. Acclimatization occurs in a short period of time, and within the organism's lifetime. This may be a discrete occurrence or may instead represent part of a periodic cycle, such as a mammal shedding heavy winter fur in favor of a lighter summer coat. Organisms can adjust their morphological, behavioral, physical, and/or biochemical traits in response to changes in their environment. While the capacity to acclimate to novel environments has been well documented in thousands of species, researchers still know very little about how and why organisms acclimate the way that they do.

The thrifty phenotype hypothesis says that reduced fetal growth is strongly associated with a number of chronic conditions later in life, including coronary heart disease, stroke, diabetes, and hypertension. This increased susceptibility is said to result from adaptations made by the fetus in an environment limited in its supply of nutrients. The thrifty phenotype is a component of the fetal origins hypothesis.

Facilitated variation

The theory of facilitated variation demonstrates how seemingly complex biological systems can arise through a limited number of regulatory genetic changes, through the differential re-use of pre-existing developmental components. The theory was presented in 2005 by Marc W. Kirschner and John C. Gerhart.

Canalisation (genetics)

Canalisation is a measure of the ability of a population to produce the same phenotype regardless of variability of its environment or genotype. It is a form of evolutionary robustness. The term was coined in 1942 by C. H. Waddington to capture the fact that "developmental reactions, as they occur in organisms submitted to natural selection...are adjusted so as to bring about one definite end-result regardless of minor variations in conditions during the course of the reaction". He used this word rather than robustness to take into account that biological systems are not robust in quite the same way as, for example, engineered systems.

Genetic assimilation is a process described by Conrad H. Waddington by which a phenotype originally produced in response to an environmental condition, such as exposure to a teratogen, later becomes genetically encoded via artificial selection or natural selection. Despite superficial appearances, this does not require the (Lamarckian) inheritance of acquired characters, although epigenetic inheritance could potentially influence the result. Waddington stated that genetic assimilation overcomes the barrier to selection imposed by what he called canalization of developmental pathways; he supposed that the organism's genetics evolved to ensure that development proceeded in a certain way regardless of normal environmental variations.

Plant perception (physiology)

Plant perception is the ability of plants to sense and respond to the environment by adjusting their morphology and physiology. Botanical research has revealed that plants are capable of reacting to a broad range of stimuli, including chemicals, gravity, light, moisture, infections, temperature, oxygen and carbon dioxide concentrations, parasite infestation, disease, physical disruption, sound, and touch. The scientific study of plant perception is informed by numerous disciplines, such as plant physiology, ecology, and molecular biology.

Evolutionary physiology Study of changes over time in a populations physiological characteristics in response to natural selection

Evolutionary physiology is the study of the biological evolution of physiological structures and processes; that is, the manner in which the functional characteristics of individuals in a population of organisms have responded to natural selection across multiple generations during the history of the population. It is a sub-discipline of both physiology and evolutionary biology. Practitioners in the field come from a variety of backgrounds, including physiology, evolutionary biology, ecology, and genetics.

<i>Daphnia magna</i> Species of small freshwater animal

Daphnia magna is a small planktonic crustacean that belongs to the subclass Phyllopoda. It inhabits a variety of freshwater environments, ranging from acidic swamps to rivers made of snow runoff, and is broadly distributed throughout the Northern Hemisphere and South Africa.

Transgenerational epigenetic inheritance

Transgenerational epigenetic inheritance is the transmission of epigenetic markers from one organism to the next that affects the traits of offspring without altering the primary structure of DNA —in other words, epigenetically. The less precise term "epigenetic inheritance" may cover both cell–cell and organism–organism information transfer. Although these two levels of epigenetic inheritance are equivalent in unicellular organisms, they may have distinct mechanisms and evolutionary distinctions in multicellular organisms.

Insects have a wide variety of predators, including birds, reptiles, amphibians, mammals, carnivorous plants, and other arthropods. The great majority (80–99.99%) of individuals born do not survive to reproductive age, with perhaps 50% of this mortality rate attributed to predation. In order to deal with this ongoing escapist battle, insects have evolved a wide range of defense mechanisms. The only restraint on these adaptations is that their cost, in terms of time and energy, does not exceed the benefit that they provide to the organism. The further that a feature tips the balance towards beneficial, the more likely that selection will act upon the trait, passing it down to further generations. The opposite also holds true; defenses that are too costly will have a little chance of being passed down. Examples of defenses that have withstood the test of time include hiding, escape by flight or running, and firmly holding ground to fight as well as producing chemicals and social structures that help prevent predation.

Nemoria arizonaria is a species of moth belonging to the family Geometridae. It was first described by Augustus Radcliffe Grote in 1883. It is indigenous to Arizona, New Mexico and the Davis Mountains in Texas.

Escape and radiate coevolution

Escape and radiate coevolution is a hypothesis proposing that a coevolutionary 'arms-race' between primary producers and their consumers contributes to the diversification of species by accelerating speciation rates. The hypothesized process involves the evolution of novel defenses in the host, allowing it to "escape" and then "radiate" into differing species.

Phenotypic integration

Phenotypic Integration is a metric for measuring the correlation of multiple functionally-related traits to each other. Complex phenotypes often require multiple traits working together in order to function properly. Phenotypic integration is significant because it provides an explanation as to how phenotypes are sustained by relationships between traits. Every organism's phenotype is integrated, organized, and a functional whole. Integration is also associated with functional modules. Modules are complex character units that are tightly associated, such as a flower. It is hypothesized that organisms with high correlations between traits in a module have the most efficient functions. The fitness of a particular value for one phenotypic trait frequently depends on the value of the other phenotypic traits, making it important for those traits evolve together. One trait can have a direct effect on fitness, and it has been shown that the correlations among traits can also change fitness, causing these correlations to be adaptive, rather than solely genetic. Integration can be involved in multiple aspects of life, not just at the genetic level, but during development, or simply at a functional level. Integration can be caused by genetic, developmental, environmental, or physiological relationships among characters. Environmental conditions can alter or cause integration, i.e. they may be plastic. Correlational selection, a form of natural selection can also produce integration. At the genetic level, integration can be caused by pleiotropy, close linkage, or linkage disequilibrium among unlinked genes. At the developmental level it can be due to cell-cell signaling such as in the development of the ectopic eyes in Drosophila. It is believed that the patterns of genetic covariance helped distinguish certain species. It can create variation among certain phenotypes, and can facilitate efficiency. This is significant because integration may play a huge role in phenotypic evolution. Phenotypic integration and its evolution can not only create large amounts of variety among phenotypes which can cause variation among species. For example, the color patterns on Garter snakes range widely and are caused by the covariance among multiple phenotypes.

Heteroblasty (botany) Difference in plant characteristics in juveniles vs. adults

Heteroblasty is significant and abrupt change in form and function that occurs over the lifespan of certain plants. Characteristics affected include internode length and stem structure as well as leaf form, size and arrangement. It should not be confused with seasonal heterophylly, where early and late growth in a season are markedly different. This change is different from a homoblastic change which is a gradual change or little change at all so that there is little difference between the juvenile and adult stages. Some characteristics affected by heteroblastic change include internode length and stem structure as well as leaf form, size and arrangement. Heteroblasty is found in many different Families as well as different species within a genus, this random spread of heteroblastic plants across species is believed to be caused by convergent evolution.

Behavioral plasticity refers to a change in an organism's behavior that results from exposure to stimuli, such as changing environmental conditions. Behavior can change more rapidly in response to changes in internal or external stimuli than is the case for most morphological traits and many physiological traits. As a result, when organisms are confronted by new conditions, behavioral changes often occur in advance of physiological or morphological changes. For instance, larval amphibians changed their antipredator behavior within an hour after a change in cues from predators, but morphological changes in body and tail shape in response to the same cues required a week to complete.

In biology, constructive development refers to the hypothesis that organisms shape their own developmental trajectory by constantly responding to, and causing, changes in both their internal state and their external environment. Constructive development can be contrasted with programmed development, the hypothesis that organisms develop according to a genetic program or blueprint. The constructivist perspective is found in philosophy, most notably developmental systems theory, and in the biological and social sciences, including developmental psychobiology and key themes of the extended evolutionary synthesis. Constructive development may be important to evolution because it enables organisms to produce functional phenotypes in response to genetic or environmental perturbation, and thereby contributes to adaptation and diversification.

Temporal plasticity, also known as fine-grained environmental adaptation, is a type of phenotypic plasticity that involves the phenotypic change of organisms in response to changes in the environment over time. Animals can respond to short-term environmental changes with physiological (reversible) and behavioral changes; plants, which are sedentary, respond to short-term environmental changes with both physiological and developmental (non-reversible) changes.

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