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Plastic Trait (plastic + trait)
Selected AbstractsTHE PHENOTYPIC VARIANCE WITHIN PLASTIC TRAITS UNDER MIGRATION-MUTATION-SELECTION BALANCEEVOLUTION, Issue 6 2006Xu-Sheng Zhang Abstract How phenotypic variances of quantitative traits are influenced by the heterogeneity in environment is an important problem in evolutionary biology. In this study, both genetic and environmental variances in a plastic trait under migration-mutation-stabilizing selection are investigated. For this, a linear reaction norm is used to approximate the mapping from genotype to phenotype, and a population of clonal inheritance is assumed to live in a habitat consisting of many patches in which environmental conditions vary among patches and generations. The life cycle is assumed to be selection-reproduction-mutation-migration. Analysis shows that phenotypic plasticity is adaptive if correlations between the optimal phenotype and environment have become established in both space and/or time, and it is thus possible to maintain environmental variance (VE) in the plastic trait. Under the special situation of no mutation but maximum migration such that separate patches form an effective single-site habitat, the genotype that maximizes the geometric mean fitness will come to fixation and thus genetic variance (VG) cannot be maintained. With mutation and/or restricted migration, VG can be maintained and it increases with mutation rate but decreases with migration rate; whereas VE is little affected by them. Temporal variation in environmental quality increases VG while its spatial variance decreases VG. Variation in environmental conditions may decrease the environmental variance in the plastic trait. [source] Costly carotenoids: a trade-off between predation and infection risk?JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 4 2005I. T. VAN DER VEEN Abstract Carotenoid reserves in copepods seem costly in terms of predation risk because they make individuals conspicuous. However, carotenoids also seem to play an important role in immune defence as free radical scavengers. To test whether predation risk influences carotenoid levels and whether changes in carotenoid levels are related to changes in immune defence, I examined individual changes in large carotenoid and other lipid droplets upon exposure to predation risk and subsequent exposure to parasites in the copepod Macrocyclops albidus. Copepods reduced carotenoid reserves upon exposure to predators, through which they potentially avoided the costs of being conspicuous under predation risk. Thus, the size of carotenoid reserves is a plastic trait. Such a decrease in carotenoid reserves may also have a negative impact on the copepods' immune system as individuals that decreased their reserves suffered higher parasite prevalence upon exposure to the cestode Schistocephalus solidus. These results suggest that carotenoid reserves may be individually optimized to trade-off each individual's unique costs (predation risk) and benefits (immune defence) of having these reserves. [source] Using plant traits to compare sward structure and composition of grass species across environmental gradientsAPPLIED VEGETATION SCIENCE, Issue 1 2004M. Duru Abstract. Plant traits which may give an indication of a plant's strategy for nutrient acquisition and regeneration are known for numerous grassland species. This study aimed to establish whether there is any relationship between two plant traits: specific leaf area (SLA) and number of reproductive tillers, and sward structural characteristics which influence herbage intake by grazers (bulk density and digestibility, leaf:stem ratio). Comparison is made for nutrient-rich (Dactylis glomerata) and nutrient-poor (Festuca rubra) grass species. We hypothesized that these traits are responsive to environmental gradients and also act on the processes of the ecosystem. Both grasses were compared with two P-fertilizer rates in two localities (200 and 1300 m a.s.l.) which differed in their temperature:radiation ratios. For the vegetative phase SLA was well correlated with sward characteristics: D. glomerata, which has the higher SLA, has the lower bulk density and higher digestibility. The values of SLA and vegetation bulk density varied according to growing conditions (P-rate and temperature:radiation ratio), but the ranking of the species remained the same because the phenotypic plasticity that exists for plant traits was also observed for sward structure and composition. That suggested the possibility of grouping natural grassland species for their relevant characteristics for grazers according to SLA values. Over the reproductive phase, the proportion of stems was well correlated to the percentage of reproductive tillers. However, the percentage of reproductive tillers was a very plastic trait for both species, depending on the growing conditions, and resulting in a density-dependent effect, particularly for F. rubra. The species studied were too plastic and too similar in their regenerative strategy so that there is no unique relationship between percentage of reproductive tillers and stem proportion, regardless of the species and the growing conditions. The number of reproductive tillers is not a suitable plant trait which could be used to rank species for leaf and stem proportions in the sward. [source] Quantifying the dynamics of sugar concentration in berries of Vitis vinifera cv. Shiraz: a novel approach based on allometric analysisAUSTRALIAN JOURNAL OF GRAPE AND WINE RESEARCH, Issue 2 2007VICTOR O. SADRAS Abstract Concentrations of key compounds (e.g. sugar) in berries are the net result of relative changes in the amount of compound per berry and berry size. The complex nature of concentrations is widely recognised, but the widespread use of chronological scales for comparisons implies that ontogenetic drift or size-dependent effects are often overlooked. This paper presents an allometric analysis of sugar concentration in berries of cv. Shiraz as a way to formally account for ontogenetic drift. Our starting point is the double-sigmoid growth pattern of a grape berry where we distinguish Phase 1, from flowering to veraison; Phase 2, from veraison to peak berry fresh mass, and Phase 3, after peak fresh mass. Phase 3 explicitly accounts for the late season shrinkage typical of Shiraz berries. We advance an allometric model of sugar per berry with berry fresh mass, rather than time, as descriptor. The condition for an increase in sugar concentration in Phase 2 is that the relative rate of sugar accumulation per berry (RSB) exceeds the relative rate of berry net accumulation of fresh mass (RFM). This is equivalent to an allometric coefficient, calculated as the slope of the regression between amount of sugar per berry and berry mass in a log-log scale, being greater than 1. For Phase 3, the condition for increase of sugar concentration is that a large reduction in berry mass offsets any putative change of sugar per berry, yielding an allometric coefficient < 1. Such an allometric model was tested against measured data from sixteen contrasting crops resulting from the combination of eight water regimes and two seasons. Berry mass peaked between 96 and 105 days after anthesis, and these dates were used to separate Phases 2 and 3. In Phase 2, the relative rate of increase in sugar per berry varied from 0.01 to 0.02 d -1 in comparison to the relative rate of increase in berry fresh mass that varied from 0.0038 to 0.0066 d -1. Sugar per berry thus increased 2.4,3.3 times faster than berry mass, with allometric coefficients between 1.98 and 2.91 accounting for 78% of the variation in the relative rate of change of sugar concentration. In Phase 3, the relative rate of change in sugar per berry was not different from zero (P 0.05) in most cases, whereas the rate of change in berry size ranged from ,0.0013 to ,0.0035 d -1 and was significant (P < 0.05) in 14 out 16 cases. The small changes in sugar per berry and the net loss of berry material yielded allometric coefficients between 0.17 and 1.11, which accounted for 72% of the variation in the relative rate of change in sugar concentration. We conclude that a model, which pivots around peak berry mass, with allometric coefficients above 1 in Phase 2 and below 1 in Phase 3, is suitable to quantitatively account for ontogenetic drift in the dynamics of sugar concentration in berries of Shiraz. This allometric approach demonstrated that sugar per berry during the stage of berry shrinkage is a plastic trait under significant environmental influence. For the same genotype, environmental conditions could determine either, a putative backflow of water accounting for net loss of berry fresh mass (RFM < 0) that could also carry some sugar from berries back to the parent vine (RSB < 0) or a small gain of sugar (RSB 0) closely coupled with a net loss of berry fresh mass (P= 0.003). [source] REPLICATED EVOLUTION OF INTEGRATED PLASTIC RESPONSES DURING EARLY ADAPTIVE DIVERGENCEEVOLUTION, Issue 4 2006Kevin J. Parsons Abstract Colonization of a novel environment is expected to result in adaptive divergence from the ancestral population when selection favors a new phenotypic optimum. Local adaptation in the new environment occurs through the accumulation and integration of character states that positively affect fitness. The role played by plastic traits in adaptation to a novel environment has generally been ignored, except for variable environments. We propose that if conditions in a relatively stable but novel environment induce phenotypically plastic responses in many traits, and if genetic variation exists in the form of those responses, then selection may initially favor the accumulation and integration of functionally useful plastic responses. Early divergence between ancestral and colonist forms will then occur with respect to their plastic responses across the gradient bounded by ancestral and novel environmental conditions. To test this, we compared the magnitude, integration, and pattern of plastic character responses in external body form induced by shallow versus open water conditions between two sunfish ecomorphs that coexist in four postglacial lakes. The novel sunfish ecomorph is present in the deeper open water habitat, whereas the ancestral ecomorph inhabits the shallow waters along the lake margin. Plastic responses by open water ecomorphs were more correlated than those of their local shallow water ecomorph in two of the populations, whereas equal levels of correlated plastic character responses occurred between ecomorphs in the other two populations. Small but persistent differences occurred between ecomorph pairs in the pattern of their character responses, suggesting a recent divergence. Open water ecomorphs shared some similarities in the covariance among plastic responses to rearing environment. Replication in the form of correlated plastic responses among populations of open water ecomorphs suggests that plastic character states may evolve under selection. Variation between ecomorphs and among lake populations in the covariance of plastic responses suggests the presence of genetic variation in plastic character responses. In three populations, open water ecomorphs also exhibited larger plastic responses to the environmental gradient than the local shallow water ecomorph. This could account for the greater integration of plastic responses in open water ecomorphs in two of the populations. This suggests that the plastic responses of local sunfish ecomorphs can diverge through changes in the magnitude and coordination of plastic responses. Although these results require further investigation, they suggest that early adaptive evolution in a novel environment can include changes to plastic character states. The genetic assimilation of coordinated plastic responses could result in the further, and possibly rapid, divergence of such populations and could also account for the evolution of genes of major effect that contribute to suites of phenotypic differences between divergent populations. [source] The heritability of inducible defenses in tadpolesJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 4 2005R. A. RELYEA Abstract The evolution of plastic traits requires phenotypic trade-offs and heritable traits, yet the latter requirement has received little attention, especially for predator-induced traits. Using a half-sib design, I examined the narrow-sense heritability of predator-induced behaviour, morphology, and life history in larval wood frogs (Rana sylvatica). Many of the traits had significant additive genetic variation in predator (caged Anax longipes) and no-predator environments. Whereas most traits had moderate to high heritability across environments, tail depth exhibited high heritability with predators but low heritability without predators. In addition, several traits had significant heritability for plasticity, suggesting a potential for selection to act on plasticity per se. Genetic correlations confirmed known phenotypic relationships across environments and identified novel relationships within each environment. This appears to be the first investigation of narrow-sense heritabilities for predator-induced traits and confirms that inducible traits previously shown to be under selection also have a genetic basis and should be capable of exhibiting evolutionary responses. [source] Interclonal differences, plasticity and trade-offs of life history traits of Cyperus esculentus in relation to water availabilityPLANT SPECIES BIOLOGY, Issue 3 2001BO LI Abstract 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. [source] | ||||||||||