Genetic differentiation in Plantago major: Growth and root respiration and their role in phenotypic adaptation

The root respiration and the growth of plants of four inbred lines of Plantago major L. were followed at two levels, of mineral nutrition. In addition the response to a transfer of plants from one condition to the other was studied. The activities of the cytochrome and of the alternative pathway wee determined and used to distinguish between genetic differences among the inbred lines and the plasticity within each inbred line. Root respiration and growth parameters differed significantly between the lines and were directly related to seed number per capsule (low respiratory activity and slow growth – 11 seeds per capsule; high respiratory activity and fast growth – 33 seeds per capsule).
Plasticity of respiration and growth parameters is expressed as differences in the total respiration, the activities of the cytochrome and of the alternative pathway, and in the shoot to root ratio, as a response to nutritional level or to changes of the strength of the nutrient solution. Differences in this plasticity in the four selected lines and in quickness of response to a change in mineral nutrition were directly related to the ecological strategy. These results are discussed in relation to the strategy of the genotypes for survival in the field. The high growth rate and the presence of plasticity in line 4 (ssp. Pleiosperma ) make this genotype act like an annual, following a ruderal strategy. The lower growth rate and the absence of plasticity in line 1 (ssp. major ) fit a more competitive strategy.     

Size and architectural traits as ontogenetic determinants of fitness in a phenotypically plastic annual weed (Amaranthus albus)

Abstract Plasticity of size and architectural traits, and their importance to reproductive fitness, were estimated in relation to nutrient availability in the annual Amaranthus albus . Seeds from seven field-collected genotypes were used to rear a first generation under uniform conditions. Seed families (inbred lines) from four first-generation plants per genotype were used to rear a second generation in a glasshouse for 10 weeks. Nine plants per family were regularly fertilized, while nine others were unfertilized. Size was estimated at 5, 8, and 10 weeks; architectural traits were recorded at 8 weeks (no. branches) and 10 weeks (no. branches and branch length). Fitness was assessed by the number of seeds per plant. Because traits were intercorrelated, size-scaled architectural traits were generated and allometric analyses performed. Genetic variation was analyzed for the second generation among inbred lines of the original genotypes, and among families within each genotype. For fertilized and unfertilized groups, early size (volume occupied at 5 weeks) and branch length per mass were significant determinants of fitness. The number of branches per size explained a smaller proportion of the variance in fitness. Genotype by treatment interaction was apparent for some traits, indicating genetic variation for plasticity, but plasticity of size did not change over ontogeny. Significant effects of genotype on size and architectural traits, and fitness, were detected mostly in the unfertilized group. Thus, selection is most likely to differentiate among genotypes in nutrient-poor environments. Lengthening of multiple branches increases seed output throughout the season, and genotypes with longer branches per unit mass have a selective advantage. Because early size is correlated with seed output, ontogenetic plasticity in response to improved soil resources allows opportunistic increases in fitness.     

Influence of plant genotype and environment on oviposition preference and offspring survival in a gallmaking herbivore

Summary Plant resistance to insect herbivores may derive from traits influencing herbivore preference, traits influencing the suitability of the plant as a host, or both. However, the plant traits influencing host-plant selection by ovipositing insect herbivores may not completely overlap those traits that affect larval survival, and distinct traits may exhibit different levels of genetic vs. environmental control. Therefore, resource supply to the host plant could affect oviposition preference and larval performance differently in different plant genotypes. To test this hypothesis, the effects of resistance level, plant genotype, and resource supply to the host plant on oviposition preference and larval performance of a gallmaking herbivore, and on various plant traits that could influence these, were examined. Replicates of four genotypes of Solidago altissima, grown under low, medium, or high levels of nutrient supply in full sun or with medium levels of nutrients in shade, were exposed to mass-released Eurosta solidaginis. The number of plants ovipunctured was significantly affected by plant genotype and the interaction between genotype and nutrient supply to the host plant: one susceptible and one resistant genotype were more preferred, and preference tended to increase with nutrient supply in the more-preferred genotypes. The growth rate of ovipunctured plants during the oviposition period was significantly greater than that of unpunctured plants. Bud diameter (which was strongly correlated with plant growth rate), leaf area, and leaf water content were significant determinants of the percentage of plants ovipunctured, explaining 74% of the variance. The number of surviving larvae was significantly affected by plant genotype, but no effect of nutrient or light supply to the host plant was detected. The ratio of bud diameter to bud length was positively related to the percentage of ovipunctured plants that formed galls, suggesting that the accurate placement of eggs near the apical meristem by ovipositing females may be easier in short, thick buds. No significant correlation was observed between oviposition preference and larval survival at the population level. These results suggest that the plant traits affecting oviposition preference may exhibit different magnitudes of phenotypic plasticity than those affecting larval survival, and that the degree of phenotypic plasticity in plant traits affecting oviposition preference may differ among genotypes within a species.     

Genetic differentiation in Plantago major: Ca2+- and Mg2+-stimulated ATPases from roots and their role in phenotypic adaptation

The Mg²⁺- and Ca²⁺-stimulated ATPase activities of the microsomal fractions of the roots of four inbred lines of Plantago major L. were followed at two levels of mineral nutrition. In addition the response of a transfer of plants from one condition to the other was studied. Kinetic properties of the ATPases (K_m and V_max) were calculated and used to differentiate between genetic differences among the inbred lines and the plasticity within each inbred line. The V_max values of the ATPase activity differed significantly between the lines and were directly related to seed number per capsule (low V_max→ 11 seeds per capsule, high V_max→ 33 seeds per capsule). In addition, the V_max values of the ATPase acitivty may be related to ecological strategy. Plasticity of enzyme activity is expressed in differences in the V_max values of the ATPase activity, as a response to nutritional level or changes of the strength of the nutrient solution. Differences in this plasticity in the four selected lines and in rapidity of response to a change in mineral nutrition were directly related to the ecological strategy. These results are discussed in relation to the strategy of the genotypes for survival in the field. The presence of plasticity in line 4 (ssp. pleiospema ) makes this genotype behave like an annual plant, following a ruderal strategy. The absence of plasticity in line 1 (ssp. major ) fits a more competitive strategy.     

Plasticity genes and plasticity costs: a new approach using an Arabidopsis recombinant inbred population

Earlier flowering is triggered by vernalization in some but not all Arabidopsis ecotypes, often reflecting allelic variation at the FRIGIDA (FRI) locus. Using a recombinant inbred (RI) population polymorphic at FRI, we examined fitness consequences of variation for plasticity. Flowering and fitness were scored for 68 RI genotypes following full and partial vernalization treatments. Within-environment and mixed-model anovas estimated variance components for a genotype effect and a G x E term, respectively. Selection analyses examined whether delayed bolting increases fitness; a plasticity costs analysis asked whether increased plasticity lowers fitness. We also explored whether trait QTL had environment-specific effects, colocated in the immediate vicinity of FRI, or overlapped with fitness QTL. Selection may favor fri alleles and constitutive early flowering, especially in conditions that only partially vernalize plants. Plasticity costs, detected only after partial vernalization and only marginally significant, were nonetheless consistent with FRI-FLC function. We discuss how information about QTL with environment-specific effects, fitness QTL, and knowledge about plasticity genes can improve interpretation of selection or plasticity cost analyses.     

Diverse genotypes of the amphibian‐killing fungus produce distinct phenotypes through plastic responses to temperature

Phenotypes are the target of selection and affect the ability of organisms to persist in variable environments. Phenotypes can be influenced directly by genes and/or by phenotypic plasticity. The amphibian‐killing fungus Batrachochytrium dendrobatidis (Bd) has a global distribution, unusually broad host range, and high genetic diversity. Phenotypic plasticity may be an important process that allows this pathogen to infect hundreds of species in diverse environments. We quantified phenotypic variation of nine Bd genotypes from two Bd lineages (Global Pandemic Lineage [GPL] and Brazil) and a hybrid (GPL‐Brazil) grown at three temperatures (12, 18 and 24°C). We measured five functional traits including two morphological traits (zoospore and zoosporangium sizes) and three life history traits (carrying capacity, time to fastest growth and exponential growth rate) in a phylogenetic framework. Temperature caused highly plastic responses within each genotype, with all Bd genotypes showing phenotypic plasticity in at least three traits. Among genotypes, Bd generally showed the same direction of plastic response to temperature: larger zoosporangia, higher carrying capacity, longer time to fastest growth and slower exponential growth at lower temperatures. The exception was zoospore size, which was highly variable. Our findings indicate that Bd genotypes have evolved novel phenotypes through plastic responses to temperature over very short timescales. High phenotypic variability likely extends to other traits and may facilitate the large host range and rapid spread of Bd.     

不同基因型玉米自交系锌营养敏感性差异研究

采用营养液培养,对5个不同玉米自交系5种供锌处理的营养特性进行研究。结果表明,不同玉米自交系对不同浓度辞反应的敏感性不同,最适宜的锌浓度为10^-7mol／L,最不适的辞浓度是10^-9moL／L;不同浓度的锌对玉米自交系生长的效应不同,对茎叶的生长影响较大,对根生长的影响相对较小;SN-11为锌敏感玉米自交系。178、邢K36、昌7—2为锌中度敏感基因型,鲁原92接近锌高效基因型。     

AN INTERPRETATION OF PHENOTYPIC PLASTICITY IN AGROPYRON REPENS (GRAMINAE)

Phenotypic plasticity and genotypic variation were studied in Agropyron repens L. (Beauv.) collected from populations in two grassland communities which differed in the length of time since the last major disturbance. Twenty genotypes were collected from each population. Each genotype was vegetatively propagated, and subjected to six different treatments in a greenhouse. Phenotypic plasticity and genotypic variability were measured as across- and within-treatment standardized variances respectively. Patterns of plasticity were measured by genotype correlations across treatments. The results were presented graphically by the regression method of Garbutt and Zangerl (1983). Analysis of variance revealed significant population, genotype and treatment effects. Significant positive correlations between magnitude and variability of performance were found for all characters. Phenotypic plasticity and magnitude of performance were generally greater in plants collected from the older established field. Evidence for greater specialization in the older population was suggested by negative correlations between performance in the most favorable and least favorable treatments and by greater dissimilarity of genotype response across treatments. A more variable phenotypic response across treatments (i.e., higher plasticity) for plants from the older population may therefore be a consequence of specialization and not an adaptive trait per se.     

Interclonal differences, plasticity and trade-offs of life history traits of Cyperus esculentus in relation to water availability

Cyperus esculentus is an exotic clonal (or pseudoannual) weed in Japan, and its range is steadily increasing. To investigate its interclonal variation and phenotypic plasticity in response to water availability, five clones of C. esculentus , collected from different sites in Japan, were grown singly in pots placed outdoors under dry and wet conditions. All the traits examined showed considerable variation among the five clones. However, two clones from Tochigi were similar to each other; thus, they might have originated from the same founder population. The clone from Ibaraki was quite different from the others. Therefore, it is suggested that the Japanese populations of C. esculentus might have resulted from multiple introductions of genotypes from geographically separated and, hence, genetically differentiated, source populations. All the clones also showed considerable plasticity in response to water availability. Clones with a larger ramet number had a greater plasticity, whereas tuber size was invariant across water treatments. Highly plastic traits had generally low interclonal variation in plasticity. All the clones had high productivity and produced more ramets and tubers under wet conditions than under dry conditions. Moreover, water availability could partially regulate the mode of its reproduction; wet conditions favored tuber production (vegetative propagation) while dry conditions favored sexual reproduction. A number of trade-offs occurred between the traits of clonal growth, storage and sexual reproduction, indicating that allocation among the competing functions/organs is mutually exclusive in plants. The results obtained here suggest that C. esculentus is more likely to invade wet habitats than dry habitats.     

Phenotypic plasticity with respect to salt stress response by Lotus glaber: the role of its AM fungal and rhizobial symbionts

Our hypothesis is that Lotus glaber (a glycophytic species, highly tolerant to saline-alkaline soils) displays a plastic root phenotypic response to soil salinity that may be influenced by mycorrhizal and rhizobial microorganisms. Uninoculated plants and plants colonised by Glomus intraradices or Mesorhizobium loti were exposed to either 150 or 0 mM NaCl. General plant growth and root architectural parameters (morphology and topology) were measured and phenotypic plasticity determined at the end of the salt treatment period. Two genotypes differing in their salt tolerance capacity were used in this study. G. intraradices and M. loti reduced the total biomass of non-salinised, sensitive plants, but they did not affect that of corresponding tolerant ones. Root morphology of sensitive plants was greatly affected by salinity, whereas mycorrhiza establishment counteracted salinity effects. Under both saline conditions, the external link length and the internal link length of mycorrhizal salt-sensitive plants were higher than those of uninoculated control and rhizobial treatments. The topological trend (TT) was strongly influenced by genotype x symbiosis interaction. Under non-saline conditions, nodulated root systems of the sensitive plant genotype had a more herringbone architecture than corresponding uninoculated ones. At 150 mM NaCl, nodulated root systems of tolerant plants were more dichotomous and those of the corresponding sensitive genotype more herringbone in architecture. Notwithstanding the absence of a link between TTs and variations in plant growth, it is possible to predict a dissimilar adaptation of plants with different TTs. Root colonisation by either symbiotic microorganisms reduced the level of root phenotypic plasticity in the sensitive plant genotype. We conclude that root plasticity could be part of the general mechanism of L. glaber salt tolerance only in the case of non-symbiotic plants.     

Growth Response of a Succulent Plant, Agave vilmoriniana, to Elevated CO(2)

Large (about 200 grams dry weight) and small (about 5 grams dry weight) specimens of the leaf succulent Agave vilmoriniana Berger were grown outdoors at Phoenix, Arizona. Potted plants were maintained in open-top chambers constructed with clear, plastic wall material. Four CO₂ concentrations of 350, 560, 675, and 885 microliters per liter were used during two growth periods and two water treatments. Small and large plants were grown for 6 months, while a few large plants were grown for 1 year. Wet-treatment plants received water twice weekly, whereas dry-treatment plants received slightly more water than they would under natural conditions. Plant growth rates in all treatments were significantly different between small and large specimens, but not between 6 month and 1 year large plants. Only the dry-treatment plants exhibited statistically different growth rates between the CO₂ treatments. This productivity response was equivalent to a 28% and 3-fold increase when mathematically interpolated between CO₂ concentrations of 300 and 600 microliters per liter for large and small plants, respectively.     

Experimental life-history evolution: selection on growth form and its plasticity in a clonal plant

The growth form along the continuum from compact phalanx plants to more loosely packed guerilla plants is an important life-history trait in clonal plants. Prerequisite for its evolution is heritable genetic variation. Starting with 102 genotypes of the stoloniferous herb Ranunculus reptans, we performed one selection experiment on spatial spread per rosette as measure of guerillaness (broad-sense heritability 0.198) and another on plasticity in this trait in response to competition (broad-sense heritability 0.067). After two generations, spatial spread was 36.9% higher in the high line than in the low line (realized heritability +/- SE 0.149 +/- 0.039). Moreover, compared with the low line genotypes of the high line had fewer rosettes, a lower proportion of flowering rosettes, a higher proportion of rooted rosettes, more branches per rosette, longer internodes and longer leaves. In the second experiment, we found no significant direct response to selection for high and low plasticity in spatial spread (realized heritability +/- SE -0.029 +/- 0.063), despite a significant correlated response in plasticity in the length of the first three stolon internodes. Our study indicates a high potential for further evolution of the clonal growth form in R. reptans, but not for its plasticity, and it demonstrates that the clonal growth form does not evolve independently of other clonal life-history characteristics.     

Effects of donor plant environment and light during incubation on anther cultures of some spring wheat (Triticum aestivum L.) cultivars

Four different growth environments (field, two phytotron greenhouses and one growth chamber) were compared, using two genotypes of spring wheat, one recalcitrant and one responsive. Field-grown plants gave inferior results. Large improvements could be made by improving the conditions, embryoid frequencies in the two genotypes reaching 77.1% and 183.9% per 100 anthers, respectively. High light intensity during the induction phase strongly suppressed induction in both genotypes, but stimulated regeneration of green plants in the recalcitrant genotype, which had the lowest regeneration ability. Weak, diffuse light did not inhibit induction while the positive effect on regeneration was maintained. Also, another recalcitrant genotype was grown in the field, together with two F₁-hybrids (recalcitrant x recalcitrant and recalcitrant x responsive). Evidence for a three-factor system was obtained.     

Interactions between green spruce aphid (Elatobium abietinum (Walker)) and Norway and Sitka spruce under high and low nutrient conditions

1 Green spruce aphid (Elatobium abietinum) is a serious pest of spruce (Picea spp.) in north‐west Europe, causing defoliation of one‐year‐old and older needles. 2 Relationships between population development of E. abietinum, needle loss and tree growth were compared for five pure genotypes of Sitka spruce and mixed‐genotype material of Sitka and Norway spruce, grown under high and low nutrient conditions. 3 Despite wide differences in flushing date between spruce genotypes, E. abietinum populations peaked on the same date on each genotype and on the mixed‐genotype material, irrespective of nutrient supply. 4 Larger aphid populations developed on trees grown under high nutrient conditions than under low nutrients. However, more needles were lost per aphid in the low nutrient treatment and overall defoliation rates in the two nutrient treatments were similar. 5 Total aphid numbers differed significantly between Sitka spruce genotypes within nutrient treatments, but not in relation to bud‐burst or needle terpene content. Reductions in height growth caused by infestation were greater (15–44%), and related to mean aphid densities and defoliation, in the low nutrient treatment, but were smaller (11–27%) and not related to aphid density and defoliation in the high nutrient treatment. 6 Development of E. abietinum populations was similar on Norway and Sitka spruce, but Norway spruce lost fewer needles. However, the effects of infestation on tree growth were more closely related to aphid density and were similar for Norway and Sitka spruce. 7 Infestation caused a decrease in total root dry weight of Norway and Sitka spruce in proportion to the reductions observed in above‐ground growth.     

Pathogen infection and selection on fertilization success in Cucumis sativus

We investigated whether resistant pollen genotypes can be selected for when the maternal plants are infected and whether infection can result to changes in the pistil nutrient level influencing reproductive outcome. Both resistance and susceptibility come with costs that may affect pre- and post-fertilization reproductive functions. We performed the study by crossing zucchini yellow mosaic virus resistant and susceptible pollen (from a hybrid donor) to infected and healthy maternal plants. We also analysed the pistil nutrient content in both treatments and found an increase of the susceptible and not resistant genotypes when maternal plants were infected. The level of nutrients K, P and S was higher in the pistils of the infected maternal plants than the healthy ones. Pistil nutrient level did not affect pollen tube growth rates, as indicated by seed siring patterns along the fruit. We propose that the effect on the siring ability of pollen carrying the susceptible and resistant alleles occurred at the post-fertilization stage, possibly as an indirect result of different growth rates of the two embryo genotypes under elevated nutrient conditions. We discuss our results with respect to possibilities of differential selection, costs and reproductive implications.     

Plastic responses in the metabolome and functional traits of maize plants to temperature variations

Environmentally inducible phenotypic plasticity is a major player in plant responses to climate change. However, metabolic responses and their role in determining the phenotypic plasticity of plants that are subjected to temperature variations remain poorly understood. The metabolomic profiles and metabolite levels in the leaves of three maize inbred lines grown in different temperature conditions were examined with a nuclear magnetic resonance metabolomic technique. The relationship of functional traits to metabolome profiles and the metabolic mechanism underlying temperature variations were then explored. A comparative analysis showed that during heat and cold stress, maize plants shared common plastic responses in biomass accumulation, carbon, nitrogen, sugars, some amino acids and compatible solutes. We also found that the plastic response of maize plants to heat stress was different from that under cold stress, mainly involving biomass allocation, shikimate and its aromatic amino acid derivatives, and other non‐polar metabolites. The plastic responsiveness of functional traits of maize lines to temperature variations was low, while the metabolic responsiveness in plasticity was high, indicating that functional and metabolic plasticity may play different roles in maize plant adaptation to temperature variations. A linear regression analysis revealed that the maize lines could adapt to growth temperature variations through the interrelation of plastic responses in the metabolomes and functional traits, such as biomass allocation and the status of carbon and nitrogen. We provide valuable insight into the plastic response strategy of maize plants to temperature variations that will permit the optimisation of crop cultivation in an increasingly variable environment.     

Mineral nutrient supply, cell wall adjustment and the control of leaf growth

The possibility that changes in the plasticity of expanding cell walls are involved in regulating early leaf growth responses to nutrient deficiencies in monocot plants was investigated. Intact maize seedlings (Zea mays L.) which were hydroponically grown with their roots in low-nutrient solution (1 mol m^?3 CaCl₂) showed early inhibition of first-leaf growth, as compared with seedlings on complete nutrient solution. This early inhibition of leaf growth was not associated with reduced cell production. However, segmental elongation along the cell expansion zone at the base of the leaf and the lengths of mature epidermal cells were reduced by the low-nutrient treatment. Solute (osmotic) potentials in the expanding leaf tissues were unchanged. In contrast, low-nutrient treatments significantly altered leaf plasticity, i.e. the irreversible extension caused by applying a small force in the direction of leaf growth. For example, in vivo plasticity decreased, along with leaf growth, after transfer of seedlings from complete nutrient solution to low-nutrient solution for 15 h. Conversely, in vivo plasticity increased, along with leaf growth, after transfer of plants previously grown on low-nutrient solution to complete nutrient solution for 15 h. The nutrient treatments also induced similar changes in the in vitro plasticity of the expanding leaf cell walls. There were no consistent changes in elasticity. Thus, reductions in the plasticity of expanding leaf cell walls appear to be involved in controlling the early inhibition of maize leaf growth by root imposition of nutrient stress.     

Adaptive plasticity in response to light and nutrient availability in the clonal plant Duchesnea indica

克隆植物蛇莓对光照强度和养分条件的适应性可塑性 表型可塑性可帮助植物缓冲环境压力并使其表型与当地环境相匹配,但目前仅少数性状的可塑性被广泛认为是适应性的。为充分理解可塑性的适应性意义,仍需进一步研究更多的植物功能性状及其环境因子。本研究将匍匐茎克隆植物蛇莓(Duchesnea indica)的21个基因型种植于不同的光照和养分条件下,并利用选择梯度分析检测了形态和生理可塑性对光照强度和养分有效性变化的适应性值。在遮荫条件下,蛇莓适合度(果实数、分株数和生物量)降低,节间缩短变细,成熟叶叶绿素含量降低,但叶柄长度、比叶面积、老叶叶绿素含量均增加。在低养分条件下,植株叶柄缩短,叶面积缩小变厚,叶绿素含量降低,但果实数量和根冠比增加。选择梯度分析表明,叶柄长度和老叶叶绿素含量对光照变化的可塑性是适应性的,老叶和成熟叶叶绿素含量对养分变化的可塑性也是适应性的。因此,不同性状的可塑性适应值取决于特定的生态背景。该研究的发现有助于理解克隆植物表型可塑性响应环境变化的适应性意义。     

Genetic architecture of plastic methyl jasmonate responses in Arabidopsis thaliana

The ability of a single genotype to generate different phenotypes in disparate environments is termed phenotypic plasticity, which reflects the interaction of genotype and environment on developmental processes. However, there is controversy over the definition of plasticity genes. The gene regulation model states that plasticity loci influence trait changes between environments without altering the means within a given environment. Alternatively, the allelic sensitivity model argues that plasticity evolves due to selection of phenotypic values expressed within particular environments; hence plasticity must be controlled by loci expressed within these environments. To identify genetic loci controlling phenotypic plasticity and address this controversy, we analyzed the plasticity of glucosinolate accumulation under methyl jasmonate (MeJa) treatment in Arabidopsis thaliana. We found genetic variation influencing multiple MeJa signal transduction pathways. Analysis of MeJa responses in the Landsberg erecta x Columbia recombinant inbred lines identified a number of quantitative trait loci (QTL) that regulate plastic MeJa responses. All significant plasticity QTL also impacted the mean trait value in at least one of the two "control" or "MeJa" environments, supporting the allelic sensitivity model. Additionally, we present an analysis of MeJa and salicylic acid cross-talk in glucosinolate regulation and describe the implications for glucosinolate physiology and functional understanding of Arabidopsis MeJa signal transduction.     

Effects of inbreeding on phenotypic plasticity in cultivated Phlox

Summary Inbreeding is known to increase developmental instability in outbreeding plants, and it has been argued that phenotypic plasticity in response to environmental variation might be similarly affected. To investigate whether phenotypic plasticity is altered by inbreeding, an outcrossed group and three successive generations of inbred cultivated Phlox drummondii were grown in six different treatments (Control, Low Water, Low Nutrient, Early and Late Leaf Removal, and Small Pots). Twelve plant characters were measured to determine the effects of the treatments and inbreeding. For those characters where inbreeding level by treatment interaction was indicated, the amounts and patterns of plasticity were examined to determine the source of the interaction. Despite substantial evidence for inbreeding depression of plant vigor and fecundity, there was no indication of an increase in the amount of phenotypic plasticity with progressive inbreeding. There was also no evidence that inbreeding systematically disrupts the pattern of plastic response to the environment.