**3. The plasticity spectrum**

All terrestrial plants are stationary and adjust phenotypic responses to survive in fluctuating environments [22, 26]. A wide spectrum of adaptive variation occurs

**41**

**Figure 1.**

*three phenotypic responses occurring simultaneously (f).*

*Phenological Plasticity of Wild and Cultivated Plants DOI: http://dx.doi.org/10.5772/intechopen.85070*

plants [29, 30].

represent different genotypes or individuals [13, 22, 27].

mosaic of responses influences genotypic selection [33, 34].

with a specific phenotypic response, and which is defined as phenotypic plasticity [14]. Three recognizable outcomes associated with a phenotypic response, as illustrated in **Figure 1**, are: (1) a neutral response, (2) an adaptive response, or (3) a maladaptive response [13, 22, 27]. Each panel illustrates the relationship between a phenotypic response and a change in environment. Red, green, or blue colored lines

A neutral response occurs when there is no observable change in plant fitness or plasticity after exposure to novel environmental stress (**Figure 1a**). Canalisation and developmental stability are components of neutral responses that create some confusion in understanding and mapping phenotypes [29]. Canalisation describes the occurrence of a constant phenotype in a given population that is not influenced by environmental or genetic regulation [29]. Developmental stability describes the degree to which organisms withstand environmental changes or genetic perturbations during development [29]. Canalisation measures gene rigidity or the resistance of genes to altered function during environmental changes [29, 30]. Canalisation is a useful measure of genetic robustness and is more frequently described than adaptive plasticity in

Adaptive responses occur in new environments and may or may not occur as a direct result of genetic variation [29]. Adaptive responses result in beneficial changes that maximize phenotypic fitness (**Figure 1b–d**) [27]. Not all phenotypic changes occur because of beneficial adaptive responses [27, 29, 30]. Individuals within a population may experience random passive phenotypic changes that are limited to specific phenotypic traits or that act more broadly impacting adaptive performance at all stages of plant development [29, 30]. Plasticity may be controlled by a single gene or many genes [31, 32]. The plasticity threshold of a plant is a function of individual, pleiotropic, and collective responses within a population. This

*Recognition of the different reaction norms. The three major responses; neutral, adaptive, and maladaptive, which occur within the plasticity spectrum [13, 22, 27, 34, 35]. A neutral response (a). An adaptive response without genetic variation (b), or with genetic variation (c, d). A non-plastic or maladaptive response (e). All* 

### *Phenological Plasticity of Wild and Cultivated Plants DOI: http://dx.doi.org/10.5772/intechopen.85070*

*Plant Communities and Their Environment*

All plants have evolved unique life cycle characteristics that enhance survival and adaptation to diverse short and long-term climatic events that limit resources. Phenotypic responses occur at every stage of plant development, and influence overall plasticity from one generation to the next. Understanding and tracking phenotypic plasticity of wild plants in cultivated plants first requires defining biological reaction norms and their alternatives to clearly illustrate the differences between biological plasticity and non-plastic responses. Examples of phenotypic responses include: (1) rapid seedling growth (2) a short vegetative phase, (3) deep root systems, (4) high seed output, (5) discontinuous or extensive seed dormancy, (6) efficient cellular defense machinery, and (7) environmental plasticity. Although all plants exhibit phenotypic responses, the level of response is largely influenced by the degree of cultivation. Several species of trees and weeds are exceptional models for defining and tracking the range of both short and long-term heritable characteristics of wild plasticity [1, 4, 12, 16–21]. Drought response studies in agronomically important, and highly cultivated crops like wheat, add perspective about the contributions of selective breeding programs; how increased cultivation results in gains or losses in adaptive responses and plasticity [7]. Transitional plant models, such as *Chenopodium quinoa* (quinoa) and *Hordeum vulgare* (barley) will be used to

illustrate the evolutionary path from wild plasticity to cultivated plasticity.

Climatic events trigger heterogeneous responses in plants. Plant responses occurring from biotic or abiotic factors drive two distinct adaptation mechanisms, natural selection and phenotypic plasticity. Both mechanisms reveal the full genetic capacity of plants [22, 23]. The genetic makeup or genotype of each plant species determines how a plant will react in new environments [24]. Accumulated exposure to novel environmental stresses over many generations may increase selection toward the frequency of favorable alleles versus a reduction of unfavorable alleles, and results in less genetic diversity [22]. Otherwise, in natural selection, any change in plant phenotype is defined as phenotypic plasticity [25]. Changes in phenotypic plasticity impact individual fitness without changing genetic diversity [22, 26]. Sometimes a novel genotypic response does not deviate from a normal range of reactions, i.e., the reaction norm, and sometimes it does [27]. Thus, plants have a wide array of genotypic responses that impact phenotype. Non-cultivated plant species like trees acquired wild plasticity through the combination of both the long-term accumulation of genetic changes and the conservation of favorable survival strategies through time [24]. Adaptive responses result in phenotypic plasticity [22, 26]. Adaptive responses also maximize phenotypic fitness, or the ability to respond and survive in changing environments [27]. Breeding programs have accelerated the adaptive process to abiotic stresses, like drought, in domesticated plant species by selecting for tolerance to drought or increased resource-use efficiency [28]. This approach has allowed breeders to select for favorable plant responses based on flexibility to varied environmental changes. A broad understanding of wild plasticity in non-domesticated plant species will enhance and extend our current understanding of the range of plasticity

All terrestrial plants are stationary and adjust phenotypic responses to survive in fluctuating environments [22, 26]. A wide spectrum of adaptive variation occurs

**2. Environmental changes impact phenotypic plasticity**

mechanisms in cultivated plants [2, 3, 5–11].

**3. The plasticity spectrum**

**40**

with a specific phenotypic response, and which is defined as phenotypic plasticity [14]. Three recognizable outcomes associated with a phenotypic response, as illustrated in **Figure 1**, are: (1) a neutral response, (2) an adaptive response, or (3) a maladaptive response [13, 22, 27]. Each panel illustrates the relationship between a phenotypic response and a change in environment. Red, green, or blue colored lines represent different genotypes or individuals [13, 22, 27].

A neutral response occurs when there is no observable change in plant fitness or plasticity after exposure to novel environmental stress (**Figure 1a**). Canalisation and developmental stability are components of neutral responses that create some confusion in understanding and mapping phenotypes [29]. Canalisation describes the occurrence of a constant phenotype in a given population that is not influenced by environmental or genetic regulation [29]. Developmental stability describes the degree to which organisms withstand environmental changes or genetic perturbations during development [29]. Canalisation measures gene rigidity or the resistance of genes to altered function during environmental changes [29, 30]. Canalisation is a useful measure of genetic robustness and is more frequently described than adaptive plasticity in plants [29, 30].

Adaptive responses occur in new environments and may or may not occur as a direct result of genetic variation [29]. Adaptive responses result in beneficial changes that maximize phenotypic fitness (**Figure 1b–d**) [27]. Not all phenotypic changes occur because of beneficial adaptive responses [27, 29, 30]. Individuals within a population may experience random passive phenotypic changes that are limited to specific phenotypic traits or that act more broadly impacting adaptive performance at all stages of plant development [29, 30]. Plasticity may be controlled by a single gene or many genes [31, 32]. The plasticity threshold of a plant is a function of individual, pleiotropic, and collective responses within a population. This mosaic of responses influences genotypic selection [33, 34].

### **Figure 1.**

*Recognition of the different reaction norms. The three major responses; neutral, adaptive, and maladaptive, which occur within the plasticity spectrum [13, 22, 27, 34, 35]. A neutral response (a). An adaptive response without genetic variation (b), or with genetic variation (c, d). A non-plastic or maladaptive response (e). All three phenotypic responses occurring simultaneously (f).*

Not all adaptive strategies are beneficial for plants and often result in decreased fitness or yield [35]. A maladaptive response describes a phenomenon which reflects the absence of plasticity (**Figure 1e**) [34]. Maladaptive responses are not easy to distinguish from neutral responses because the average response of the population may mask any decline in response by individuals within the population over a long period of time [35]. Maladaptive responses are often misinterpreted as adaptive responses and difficult to study genetically [34, 35].

All phenotypic responses, neutral, positive, and negative, may occur simultaneously within an individual or across a population (**Figure 1f**) [13]. Changes in plasticity may be measured by examining the relationship between a specific genotype (G) in a specific environment (E) [13]. A genotype-by-environment (GXE) study tracks genetic plasticity and is a powerful tool for targeted genotypic selection [13, 33, 34].
