Plasticity In Resource Allocation Research Articles

Plasticity in resource allocation of the invasive Phytolacca americana: Balancing growth, reproduction, and defense along urban–rural gradients

In response to varying environments along urban and rural gradients, invasive plants may strategically allocate resources to enhance their invasiveness. However, how invasive plants balance their resources for growth, reproduction, and defense as responses to biotic and abiotic factors across these gradients remain unclear. We conducted field surveys on the growth, reproduction, and herbivory of the invasive species Phytolacca americana across diverse urban and rural habitats. Leaf samples were collected to analyze the nutritional content, primary and secondary metabolites. We found that plant growth rates, specific leaf area, leaf nitrogen content, and concentrations of flavonoids and saponins were higher in urban habitats, while reproduction, herbivory, and carbon-to‑nitrogen ratios were lower than those in rural habitats. We also found a trade-off between growth rate and herbivory, as well as trade-offs among defense traits associated with herbivory (e.g., leaf mass per area, the inverse of leaf nitrogen content, and carbon‑nitrogen ratio) and the production of metabolites associated with abiotic stress tolerance (e.g., soluble sugars, flavonoids, and saponins). As earlier studies showed low levels of genetic diversity within and between populations, our findings suggest that the urban–rural gradient patterns of resource allocation are primarily phenotypic plasticity in response to herbivory in rural areas and abiotic factors in urban areas. Our study sheds light on the mechanisms by which urbanization affects plant invasions and offers insights for the implementation of their management strategies.

How does the timing of weapon loss influence reproductive traits and trade-offs in the insect Narnia femorata?

A longstanding goal of evolutionary biology is to understand among-individual variation in resource allocation decisions and the timing of these decisions. Recent studies have shown that investment in elaborate and costly weapons can result in trade-offs with investment in testes. In this study, we ask the following questions: At what point plasticity in resource allocation to these different structures ceases during development, if at all? Furthermore, can individuals tailor their reproductive behavior to accompany structural changes? We experimentally addressed these questions in the insect Narnia femorata, quantifying resource reallocation across development for the first time, using a phenotypic engineering approach. To investigate whether allocation plasticity diminishes throughout ontogeny, we induced weapon loss at a range of different developmental stages and examined subsequent testes mass and reproductive behavior. We found that relative testes mass increased as weapon investment decreased, implying a direct trade-off between testes and weapon investment. However, autotomy postadulthood ceased to induce larger testes mass. Intriguingly, losing a weapon while young was associated with extended adult mating duration, potentially enabling compensation for reduced fighting ability. Our results highlight the importance of examining the ontogeny of trade-offs between reproductive traits and the flexibility of the relationship between reproductive morphology and behavior.

Phenotypic plasticity in resource allocation to sexual trait of alligatorweed in wetland and terrestrial habitats

Environmental heterogeneity in resource availability affects invasive plant reproductive strategies and resource allocation to reproduction. Here, we conducted two field surveys to examine the effect of wetland and terrestrial habitats on inflorescence production and resource allocation to inflorescence of the amphibious invasive plant Alternanthera philoxeroides in its invasive range (China). We also specifically examined the effects of water availability, fertilizer application, and plant density (space) in a greenhouse experiment. In field surveys, inflorescence biomass, normal monoclinous flowers and ratio of inflorescences to shoots of plants from wetlands were about 2.4-, 0.8- and 1.3-fold higher than those from terrestrial habitats, respectively. In greenhouse experiment, plants with higher fertilizer application and lower competition conditions produced more inflorescences, and had a lower ratio of roots to shoots and a comparable ratio of inflorescences to shoot and root. Furthermore, water availability had a significant interactive effect when combined with fertilizer level or plant density on inflorescence production and resource allocation. Together, our results indicate that high resources, such as those found in wetland habitats, favor both vegetative growth and sexual trait in A. philoxeroides. However, in terrestrial habitats where resources are relatively poor, the invader can adapt to the environment by allocating more resources to vegetative growth for clonal reproduction and less resources for sexual trait. This phenotypic plasticity in resource allocation likely facilitates the plant to invade heterogeneous wetlands and terrestrial environments.

Context‐dependency of resource allocation trade‐offs highlights constraints to the evolution of floral longevity in a monocarpic herb

Floral longevity is a critical component of floral display, yet there is a conspicuous paucity of empirical research on its evolution within species. Evolutionary models of floral longevity are grounded in resource allocation theory and propose that selection acts on heritable variation to optimize longevity in light of competing floral construction and maintenance costs. Key assumptions remain untested within wild species. We measured maximum floral longevity alongside protandry, flower size, flower number and flowering rate across families of the monocarpic herb Sabatia angularis grown under high and low resources. We evaluated genetic variation, plasticity and correlations between display traits, including fundamental resource-allocation trade-offs and their interactions with resource availability. All display traits showed significant genetic variation. Resource availability influenced mean floral longevity and flower number, with genetic variation in these responses. Importantly, both floral longevity-flower number and flower number-size trade-offs were significant and stronger under low resources. This study reinforces the application of resource allocation theory to floral display trait evolution. Our work highlights the context-dependency of trade-offs and the potential importance of plasticity in resource allocation, with plants investing in the construction of new flowers at faster rates when resources are high rather than in the maintenance of longer-lived flowers.

Phenotypic plasticity of pre-adult egg maturation in a parasitoid: Effects of host-starvation and brood size.

Larvae of parasitoid wasps develop on a single arthropod host, and often face resource limitation that induces a tradeoff between egg maturation and somatic growth. Part of the variation in the growth-reproduction allocation was shown to be heritable, but how the larval developmental environment affects this allocation is not well-known. Detection of life history tradeoffs is often facilitated under stress conditions. We therefore exposed developing female larvae of the polyembryonic parasitoid Copidosoma koehleri (Hymenoptera: Encyrtidae) to laboratory manipulations aimed to restrict host resources (either host-starvation or high larval density). We compared the females’ body sizes and egg loads shortly after adult emergence (<24 h) to those of closely related control females, which developed at a lower larval density within non-starved hosts. Host-starvation reduced the females’ body sizes but not their initial egg loads. Females that experienced high larval density produced more eggs but were similar in body size to the low-density controls. Thus, the relative allocation to reproduction increased in response to both manipulations of host condition. Developmental duration and longevity were similar in all treatments. The negative correlation between body size and reproductive allocation, observed in the host-starvation treatment, is compatible with previous evidence from other parasitoids. In the high larval density treatment, however, reproductive allocation increased while body size was maintained, suggesting that the higher density increased rather than limited host resources per developing parasitoid female. The additional host resources that were diverted into egg production possibly resulted from increased feeding and body mass gain by hosts parasitized by large broods of wasps. Our results demonstrate phenotypic plasticity in resource allocation between growth and reproduction in a developing parasitoid. This plasticity may contribute to an adaptive balance between longevity and mobility vs. fecundity during the adult stage.

Seasonal reproductive tactics: annual timing and the capital-to-income breeder continuum.

Tactics of resource use for reproduction are an important feature of life-history strategies. A distinction is made between 'capital' breeders, which finance reproduction using stored energy, and 'income' breeders, which pay for reproduction using concurrent energy intake. In reality, vertebrates use a continuum of capital-to-income tactics, and, for many species, the allocation of capital towards reproduction is a plastic trait. Here, we review how trophic interactions and the timing of life-history events are influenced by tactics of resource use in birds and mammals. We first examine how plasticity in the allocation of capital towards reproduction is linked to phenological flexibility via interactions between endocrine/neuroendocrine control systems and the sensory circuits that detect changes in endogenous state, and environmental cues. We then describe the ecological drivers of reproductive timing in species that vary in the degree to which they finance reproduction using capital. Capital can be used either as a mechanism to facilitate temporal synchrony between energy supply and demand or as a means of lessening the need for synchrony. Within many species, an individual's ability to cope with environmental change may be more tightly linked to plasticity in resource allocation than to absolute position on the capital-to-income breeder continuum.This article is part of the themed issue 'Wild clocks: integrating chronobiology and ecology to understand timekeeping in free-living animals'.

Using hybrid automata modelling to study phenotypic plasticity and allocation strategies in the plant mycorrhizal mutualism

Plants are exemplified by high plasticity in resource allocation strategies which allows them to maximize their fitness under changing resource conditions. In many plant species, obtaining resources involves mutualistic interactions with arbuscular mycorrhizal fungi (AMF), where plants provide the AMF with sugars in exchange for soil nutrients like phosphorus (P). These nutrient exchange rates have high context dependency, influenced by both the cooperative level of the AMF species involved (a qualitative trait) and the ambient nutrient concentrations in the soil (a quantitative value). Because this context dependency arises from a mix of both quantitative and qualitative factors, standard ordinary differential equation (ODE) modeling methods often complicate the representation of resource allocation strategies. Here, we explore the utility of a hybrid automata modeling framework that can intuitively combine the qualitative AMF traits and quantitative nutrient concentrations. This allows for a better analysis and understanding of phenotypic plasticity in resource allocation in the plant–AMF, and other nutrient exchange mutualisms. We consider a focal strategy in which nutrients are allocated to growth at times of nutrient limitations, and to storage otherwise and ask how this changes plant allocation to growth vs. storage. We first model this system dynamically to show how the plant responds to different environmental conditions and interacts with AMF and show that our hybrid automata model can replicate experimental data from the plant–AMF system. From our work, novel perceptions into the well-studied plant–AMF symbiosis and testable hypotheses can be underlined: (1) leaf biomass does not increase proportionally with the level of AMF cooperation; (2) in the context of multiple AMF simultaneously colonizing a host–plant, a narrow variance of response is observed and explained by an auction-like mechanism of the AMF to acquire C from the plant.

Horn growth patterns in Alpine chamois

The analysis of horn growth may provide important information about the allocation of metabolic resources to secondary sexual traits. Depending on the selective advantages offered by horn size during intra- and inter-specific interactions, ungulates may show different investment in horn development, and growth variations within species may be influenced by several parameters, such as sex, age, or resource availability. We investigated the horn growth patterns in two hunted populations of Alpine chamois (Rupicapra r. rupicapra) in the Central Italian Alps. We tested the role of individual heterogeneity on the growth pattern and explored the variation in annulus length as a function of different factors (sex, age, hunting location, cohort). We then investigated the mechanisms underlying horn growth trajectories to test for the occurrence of compensatory or recovery growth and their potential differences between sexes and populations. Annulus length varied as a function of sex, age of individuals and, marginally, hunting location; no effect of cohort or individual heterogeneity was detected. Male and female chamois showed compensatory horn growth within the first 5½ years of life, though the partial convergence of horn trajectories in chamois suggests that this mechanisms would best be described as ‘recovery growth’. Compensation rates were greater in males than in females, while only compensatory growth rates up to 2½ years of age were different in the two populations. Besides confirming the sex- and age-dependent pattern of horn development, our study suggests that the mechanism of recovery growth supports the hypothesis of horn size as a weakly selected sexual trait in male and female chamois. Furthermore, the greater compensation rates in horn growth shown by male chamois possibly suggest selective effects of hunting on age at first reproduction, while different compensation rates between populations may suggest the occurrence of some plasticity in resource allocation to sexual traits in relation to different environments.

Sperm competition and the evolution of seminal fluid composition.

Male ejaculates include large amounts of seminal fluid proteins (Sfps) that influence male sperm competitive success. In spite of their diverse proximate functions, Sfps involved in sperm competition increase male fitness in one of three ways: (1) "avoidance" proteins help males avoid sperm competition, (2) "defense" proteins help males defend their sperm from displacement by the female's subsequent mate, and (3) "offense" proteins aid males in displacing sperm of preceding males. Here, we present a population genetic model of the evolution of allocation of finite resources by males to the three kinds of Sfps. We analyze the influence of relative efficiencies of different Sfps, of plasticity in resource allocation, and of differences in viability costs of Sfps. We find that in absence of plasticity or different viability costs, equal investment in defense and offense Sfps evolves, irrespective of their relative efficiency. In all cases, males evolve to invest more in avoidance when avoidance proteins are increasingly efficient, and when offense is more efficient than defense. Differences in viability costs result in lower investment in costly proteins, whereas plasticity has complex effects, influencing both the optimal seminal fluid composition and maintenance of variation in investment in these proteins across populations.

Quantifying multivariate plasticity: genetic variation in resource acquisition drives plasticity in resource allocation to components of life history

Acquisition and allocation of resources are central to life-history theory. However, empirical work typically focuses only on allocation despite the fact that relationships between fitness components may be governed by differences in the ability of individuals to acquire resources across environments. Here, we outline a statistical framework to partition the genetic basis of multivariate plasticity into independent axes of genetic variation, and quantify for the first time, the extent to which specific traits drive multitrait genotype-environment interactions. Our framework generalises to analyses of plasticity, growth and ageing. We apply this approach to a unique, large-scale, multivariate study of acquisition, allocation and plasticity in the life history of the cricket, Gryllus firmus. We demonstrate that resource acquisition and allocation are genetically correlated, and that plasticity in trade-offs between allocation to components of fitness is 90% dependent on genetic variance for total resource acquisition. These results suggest that genotype-environment effects for resource acquisition can maintain variation in life-history components that are typically observed in the wild.

Modeling the Evolution of Phenotypic Plasticity in Resource Allocation in Wing‐Dimorphic Insects

In nature, resource availability varies spatially and temporally both within and across generations, leading to variation in the amount of energy available to individuals. The optimal allocation strategy can change, depending on the amount of resources available to allocate to life-history functions. If so, selection should favor the evolution of allocation strategies that can respond to variation in environmental resource levels. We address this issue by using two quantitative genetic simulation models in a model system for studying trade-offs, wing-dimorphic insects. Wing dimorphic insects typically exhibit a trade-off in the allocation of resources between migratory ability and reproduction. In our models, we focus on allocation as a genetic trait and model the evolution of phenotypic plasticity in this trait in response to spatiotemporal variation in resource availability. We show that the evolved allocation strategy depends on the predictability of resource levels across time. Specifically, selection favors higher investment in flight under poor conditions in predictable environments and lower investment in unpredictable environments.

The relative generality of plant invasion mechanisms and predicting future invasive plants

This study presents an updated analysis of the relative generality of invasion mechanisms in invasive plants. We categorised eight invasion mechanisms into three classes, according to the ecological processes behind the invasions: physical environment mechanisms (phenotypic plasticity in environmental tolerance and evolutionary adaptation to physical environment), resource use mechanisms (resource competition, resource utilisation and allelopathy) and enemy release mechanisms (high growth/reproduction rate, evolutionarily increased competitive ability and phenotypic plasticity in resource allocation). An analysis of 133 invasive plant species in the literature showed the enemy release mechanisms are equally general as resource use mechanisms, while the physical environment mechanisms are less general. Among the eight specific invasion mechanisms, phenotypic plasticity (either in resource allocation or in environmental tolerance), allelopathy, evolutionarily increased competitive ability and high resource‐use efficiency are fairly common. Furthermore, chemical defence behaviour is very common in plant invaders. Species invading through enemy release were more likely to originate from Europe and those invading through resource competition/utilisation were often native to tropical and North America and Asia. Invaders with allelopathy were more likely to be from tropical and North America and those showing evolutionarily increased competitive ability were often native to temperate regions such as Europe and North America. Collectively, phenotypic plasticity, defence strategy and native status can be used not only to predict a plant’s invasiveness, but also for identifying the potential invasion mechanisms.

Sex allocation under simulated herbivory in the generalist perennial herb Paeonia broteroi (Paeoniaceae)

Theories of optimal resource allocation in flowering plants postulate that allocation to sexual functions are balanced. While many studies have found such evidence in hermaphroditic species among flowers, plants or populations, or at different phenological stages, it has not been supported by other studies. This has been explained by differences among genotypes in ability to acquire resources, resource partitioning among traits unrelated to reproduction or strong selection to maintain positive genetic correlation among traits. I studied how herbivory affected resource allocation to sexual functions in the perennial herb Paeonia broteroi (Paeoniaceae) by measuring a number of floral traits in control plants and in experimental plants under simulated herbivory. The species shows very little plasticity in resource allocation between sexual structures and functions, and appears to be highly sensitive to alterations in the balance of resource acquisition and allocation, with an immediate outcome in terms of seed production and a mid-term response in terms of sprouting and flowering. Plants' ability to collect resources for growth and reproduction before their senescence at the end of the reproductive season, are compromised. This may limit their reproductive potential, the maintenance and growth of their populations, and may influence their demographic state and the plants' ability to respond to selective pressures by external biotic agents.

Plasticity in Resource Allocation and Nitrogen-use Efficiency in Riparian Vegetation: Implications for Nitrogen Retention

In this work, we summarize our current understanding of the function of riparian zones and describe an investigation of changes in the production per unit nitrogen (N) taken up, or nitrogen-use efficiency (NUE) and resource allocation of a riparian shrub in response to changes in N availability. Empirical work included measuring leaf %N and root-to-shoot ratios (R:S) of individual riparian shrubs (Baccharis salicifolia, or seepwillow) growing at a range of N availabilities in the field and growing in fertilized and unfertilized plots in a field fertilization experiment. In both observational and experimental work, N availability was related positively to %N of plant tissues and negatively to R:S. We used a simulation model to investigate feedbacks between seepwillow responses to and effects on N availability. In the model, plasticity in resource allocation and NUE in response to changes in N led to lower productivity at low N supply and higher productivity and lower retention at high N supply than was observed in plants constrained to a constant %N and R:S. Furthermore, uptake became relatively more important as a retention mechanism when plants responded to high N supply. These feedbacks could have significant effects on N retention by riparian zones in watersheds receiving large fertilizer inputs of N or on ecosystems exposed to high rates of atmospheric N deposition.

Combining genetic variation and phenotypic plasticity in tradeoff modelling

Tradeoffs lead to antagonistic relationships between phenotypic traits and are thought to be determined both genetically and environmentally. We present here an allocation model that distinguishes between the genetic and environmental components of variation in resource allocation. In this model we introduced plasticity of resource allocation which was considered to be an adaptive response to environmental variations. The results show that resource allocation plasticity is a key parameter for the existence of environmental (i.e. inter environments and intra genotype) correlations and is therefore necessary to detect environment‐induced tradeoffs. We also investigated the impact of the resource allocation plasticity and other factors on genetic (i.e. inter genotypes) correlations. Our results show that resource allocation plasticity induces a masking effect of tradeoffs when studying genetic correlations and increases the masking effect of resource variation by making apparent correlations positive when negative correlations are expected. In addition, by simulating different sources of resource acquisition variation, we demonstrated that resource variation might have different effects on correlations according to the experimental design and the studied biological material. Further development of this model may be used to investigate the theoretical implications of tradeoffs in evolutionary biology and to improve design and interpretation of experimental studies.

Resource allocation in the submerged plant Vallisneria natans related to sediment type, rather than water‐column nutrients

Summary1. Phenotypic plasticity in resource allocation by Vallisneria natans was investigated in a greenhouse experiment, using three types of sediment [sandy loam, clay, and a 50 : 50 (by volume) mixture of the two sediments] and two levels of water‐column nutrient. The clay was collected from a highly eutrophic lake in Jiangsu Province, China, and the N and P concentrations applied in nutrient media were at the upper limits observed in most lakes of China.2. Growth and biomass allocation were significantly affected by sediment type, rather than water‐column nutrients. Plant growth in clay and the mixture were similar, and 2.4–3.4 times higher than that in sandy loam. Compared with the plants grown in clay or the mixed sediments, the plants grown in sandy loam allocated relatively more biomass to root (11–17% versus 7–8% of total biomass), and relatively less to leaf (76–82% versus 86–87% of total biomass). Plastic variations in root area were induced by sediment type alone (P &lt; 0.05), whereas the impacts of sediment type and water‐column nutrients on leaf area were insignificant (P &gt; 0.05).3. Plant N and P concentrations were significantly affected by both sediment type and water‐column nutrients. Increased nutrient availability in the water column enhanced plant N concentration by 3.5–20.2%, and plant P concentration by 19.1–25.8%.4. Biomass accumulation and plant nutrient concentration in plants grown in different sediment types and water‐column nutrients indicate that sediment type had more significant impacts on growth and N and P concentrations of V. natans than did water‐column nutrients. Changes in phenotype are a functional response to nutrient availability in sediment, rather than to water‐column nutrients.

Effects of nutrient availability on biomass allocation as well as constitutive and rapid induced herbivore resistance in poplar

Many studies have examined effects of nutrient availability on constitutive herbivore resistance of plants, but few have addressed effects on expression of rapid induced resistance (RIR). We quantified effects of two levels of nutrient availability on growth, biomass allocation, photosynthesis, and constitutive secondary metabolism of black poplar (Populus nigra). We also examined effects of nutrient availability on expression of constitutive resistance of poplar to gypsy moth (Lymantria dispar) and whitemarked tussock moth (Orgyia leucostigma), as well as RIR to both folivores in response to localized herbivory by gypsy moth.The high nutrient treatment had no effect on photosynthetic rate of poplar, but dramatically increased relative growth rate, total biomass, and total leaf area, while foliar phenolic concentrations and root:shoot ratio decreased. Plant growth was negatively correlated with foliar phenolic concentrations, which is consistent with predictions of the Growth/Differentiation Balance Hypothesis when increased nutrient availability increases growth without affecting photosynthesis. These responses of root:shoot ratio and constitutive secondary metabolism to nutrient availability are consistent with those proposed by models of adaptive phenotypic plasticity in resource allocation patterns.Nutrient availability affected constitutive resistance of poplar to first and fifth instar gypsy moth larvae, which grew much faster on high fertility plants. However, nutrient availability had no effect on constitutive resistance to whitemarked tussock moth. Localized herbivory elicited systemic RIR in poplar within 72 hours. However, the magnitude of RIR was dependent on nutrient availability, with differing effects on the two insect species. Expression of RIR to gypsy moth was most dramatic in the high fertility treatment. In contrast, RIR to whitemarked tussock moth was expressed only in the low fertility treatment. The idiosyncratic nature of effects of nutrient availability on constitutive and induced resistance challenges the value of using insect bioassays as surrogate measures of secondary metabolism for testing allocation models of plant defense, as well as the value of generalized plant defense models for predicting effects of environmental variation on resistance to specific herbivores. These results also suggest that the effects of nutrient availability on the expression of RIR may represent a largely over‐looked source of variation in plant/herbivore interactions.

Differentiation in populations of Hordeum spontaneum Koch along a gradient of environmental productivity and predictability: plasticity in response to water and nutrient stress

Plants from four populations of Hordeum spontaneum originating in distinct environments of Israel were compared for stress induced phenotypic plasticity. The environments ranged along a gradient of increasing rainfall amount and predictability from low (desert) to moderate (semisteppe batha) to high (Mediterranean grassland and mountain, the latter also experiencing frost stress). The plants were exposed to a set of four treatments: no stress (optimum water and nutrients), water, nutrient and both water and nutrient stress. Plants from the four populations (or ecotypes) exhibited different patterns of plasticity in response to the different stresses (water and nutrients) and in different trait categories (reproductive, fitness and resource allocation). The importance of plasticity in response to water stress appears to decrease, and to nutrient stress appears to increase along the increasing rainfall gradient. The mountain ecotype, growing in an area with high potential productivity (amount of rainfall) but experiencing periodic frosts, was the most plastic among ecotypes in resource allocation under both water and nutrient stress, but exhibited low plasticity in other trait categories. In contrast, the desert ecotype had low plasticity in resource allocation under water stress and the lowest plasticity among the four ecotypes in all trait categories in response to nutrient stress. The ecotype originating in Mediterranean grassland, a predictable and most favourable environment, was highly plastic in fitness and allocation traits in response to low nutrient levels which is likely to occur due to competition in productive environment. We discuss the observed differences in ecotype plasticity as part of their environmentally induced adaptive ‘strategies’. We found no support for the hypothesis that plants originating in environments with greater variation and unpredictability are more plastic. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society 2002, 75, 301–312.

Control of Phenotypic Plasticity Via Regulatory Genes

Control of Phenotypic Plasticity Via Regulatory Genes

Life history traits and resource allocation in the purple sea urchin Strongylocentrotus purpuratus (Stimpson)

Variation in recruitment and longevity of the purple sea urchin Strongylocentrotus purpuratus (Stimpson) along its latitudinal distribution suggests clinal differences in the life history traits of this species. Two complimentary approaches were employed to assess degree and nature of the intraspecific variation in life history traits. Growth, mortality and recruitment data were gathered in the field and in the laboratory sea urchins were held under the same conditions to determine the extent of plasticity in resource allocation. Both laboratory and field measurements indicate the observed demographic patterns are best attributed to phenotypic responses to varying environmental conditions rather than genetically determined intraspecific differences in life history traits.