Plasticity In Life-history Traits Research Articles

REPRODUCTIVE ENERGY ALLOCATION AND LONG-TERM ENERGY STORES IN A VIVIPAROUS LIZARD (EULAMPRUS TYMPANUM)

When animals reproduce, does energy for the brood come from stored reserves (from food eaten months or years before), or from food eaten during the current reproductive season? Variation in the duration of energy storage prior to reproduction is an important, but little-studied, axis of life history variation. We experimentally manipulated the availability of resources to females of a long-lived viviparous lizard (Eulamprus tympanum, Scincidae) in the first year of a two-year study to assess the relative importance of current food intake vs. stored reserves as sources of energy for breeding. Females given greater access to high temperatures (and hence, to resources) in the laboratory amassed larger caudal energy stores than did females with lesser opportunities. Energy intake during gestation slightly influenced offspring size, but the magnitude of energy stores prior to ovulation had a more dramatic effect: females with larger caudal energy stores produced much larger litters in the following year. Growth rates of females were unaffected by basking treatments or by reproduction in either year, but females that reproduced in the second year showed a large concomitant decrease in caudal energy stores compared to females that did not reproduce, indicating a large energetic cost of reproduction. Hence, reproductive output within this species can be influenced by resource availability over 12 months prior to reproduction, and simple comparisons of reproductive output with current resource availability may fail to detect the ways in which phenotypically plastic life history traits are influenced by environmental features. In addition to an appropriate temporal framework, models of resource allocation should also incorporate the possible roles of physiological and morphological constraints (e.g., maternal inability, in some species, to modify postovulation reproductive expenditure) and trade-offs with other life history currencies (e.g., decrements in maternal survival due to high relative clutch masses). The time lag between resource acquisition and expenditure may have significant consequences for a population’s demographic response to shifts in resource availability or predation pressure (via tail autotomy). Finally, this study illustrates the way in which thermal aspects of the environment can influence life history phenotypes in ectothermic vertebrates with long-term energy stores.

Plasticity in Life-History Traits

We describe the impact of recent life-history plasticity theory on insect studies, particularly on the interface between genetics and plasticity. We focus on the three-dimensional relationship between three key life-history traits: adult size (or mass), development time and growth rate, and the connections to life cycle regulation, host plant choice, and sexual selection in seasonal environments. The review covers fitness consequences of variation in size, development time and growth rate, and effects of sex, photoperiod, temperature, diet, and perceived mortality risk on these traits. We give special attention to evidence for adaptive plasticity in growth rates because of the important effects of such plasticity on the expected relationships between development time and adult size and, hence, on the use of life-history, fitness, and optimality approaches in ecology, as well as in genetics.

Phenotypic plasticity in age and size at maturity and its effects on the integrated phenotypic expressions of life history traits of Cardamine flexuosa (Cruciferae)

AbstractWe analyzed variation in phenotypic plasticity of life history traits between two Cardamine flexuosa populations based on differences in plasticity of age and size at maturity. C. flexuosa (Cruciferae) is a facultative, vernalization‐sensitive, long‐day annual, and its phenology and the phenotypic expressions of many life history traits are largely controlled by photoperiod and vernalization in natural populations. We used plants from two populations which differed in their responses to chilling and photoperiod treatments. The timing of developmental processes was changed by controlling temperature and photoperiod regimes in growth chambers. Plasticity in size at maturity was analyzed as changes in a growth trajectory using two parameters, age at maturity (Δt) and growth rate (k). Both traits showed plasticity, but differences between the populations were found mostly for Δt. Distinctive differences in size at maturity of individuals in the two populations were mainly due to different amounts of plasticity in Δt. Variations in plasticity of nine other life history traits and their associations to age and size at maturity were also analyzed. Variation for eight of the traits can be described, at least in part, as a function of age and size at maturity for both populations, and most of the variation in the total number of seeds was explained by age and size at maturity. Only age at maturity had any effect on changes in resource allocation. The nine life history traits were integrated through associated character expressions with age and size at maturity. Changes in the association between a trait and age and/or size at maturity were rather conservative compared to changes in the plasticity of a trait between the two populations. Associations with age and size at maturity are mostly explicable in terms of inherent relationships in the developmental processes, and they may limit the ecological range expansion and the adaptive evolution of plasticity in C. flexuosa. The negative correlation between reproductive allocation and age at maturity can be a cost of delaying maturation in C. flexuosa.

GENETIC VARIATION FOR PHENOTYPIC PLASTICITY IN THE LARVAL LIFE HISTORY OF SPADEFOOT TOADS (SCAPHIOPUS COUCHII).

Phenotypic plasticity in life-history traits is common. The relationship between phenotype and environment, or reaction norm, associated with life-history plasticity can evolve by natural selection if there is genetic variation within a population for the reaction norm and if the traits involved affect fitness. As with other traits, selection on plasticity in a particular trait or in response to a particular environmental factor may be constrained by trade-offs with other traits that affect fitness. In this paper, I experimentally evaluated broad-sense genetic variation in the reaction norms of age and size at metamorphosis in response to two environmental factors, food level and temperature. Differences among full-sib families in one or both traits were evident in all treatments. However, variation among families in their responses to each treatment (genotype-environment interaction) resulted in variation among treatments in estimated heritabilities and genetic correlations. Age at metamorphosis was equally sensitive to temperature in all families, but size at metamorphosis was more sensitive to temperature in some families than in others. Size at metamorphosis was equally sensitive to food level in all families, but age at metamorphosis was sensitive to food in some families but not in others. At high temperature or low food, the genetic correlation between age and size at metamorphosis was positive, generating a potential trade-off between metamorphosing early to attain higher larval survival and metamorphosing later to achieve larger size. This trade-off extends across treatments: families with the largest average size at metamorphosis achieved larger size with the longest average and greatest plasticity in age at metamorphosis. Other families achieved shorter average larval periods by exhibiting greater plasticity in size at metamorphosis but had the smallest average size at metamorphosis. This trade-off may reflect an underlying functional constraint on the ability to respond optimally to all environments, resulting in persistent genetic variation in reaction norms.

Phenotypic plasticity of life-history traits in clonal and sexual fish (Poeciliopsis) at high and low densities.

Models of resource allocation strategies predict an array of life-history responses of individuals living in resource-stressed versus non-stressed environments. I tested a number of these predictions using three fish strains (a sexual and two clonal strains) in high and low density treatments. To examine the plasticity of life-history traits in females raised in these two environments, I measured survival, growth, egg production, egg size, and proportion mature at 10 weeks of age. Survival was not affected by density treatment. However, both growth and overall egg production were lower in females from the high density treatments, and reproductive maturity was significantly delayed at the high density for all strains. Egg production per unit size was not affected by density in any strain, signifying that differences in the numbers of eggs produced was merely a reflection of the differences in size of fish in the two density treatments. Egg size was also unaffected by density in all strains. These results are related to models of resource allocation in stressful environments. There was a consistent pattern of increased reproductive investment in the sexual strain relative to the two clonal strains. The sexual strain matured earlier, produced more eggs per unit body weight, and had larger eggs than either clone at both densities. These results are interpreted by considering the predicted adaptive responses of these three strains to the long-term environmental differences in their natural habitats.

Phenotypic plasticity for life history traits in Drosophila melanogaster. II. Epigenetic mechanisms and the scaling of variances

Abstract We manipulated developmental time and dry weight at eclosion in 15 genotypes of Drosophila melanogaster by growing the larvae in 9 environments defined by 3 yeast concentrations at 3 temperatures. We observed how the genetic and various environmental components of phenotypic variation scaled with the mean values of the traits.Temperature, yeast, within‐environmental factors and genotype influenced the genotypic and environmental standard deviations of the two traits in patterns that point to very different modes of physiological and developmental action of these factors. Since different factors affected the environmental and genetic components of the phenotypic variation either in parallel or inversely, we conclude that environmental heterogeneity may have small or large effects on evolutionary rates depending on which factors cause the heterogeneity. The analysis also suggests that the scaling of variances with the mean is not as trivial as is often assumed when coefficients of variation are computed to “standardize” variation.

Phenotypic plasticity for life history traits in Drosophila melanogaster. I. Effect on phenotypic and environmental correlations

AbstractAll 36 possible crosses among 6 homozygous lines of Drosophila melanogaster were tested for their phenotypic response in developmental time and dry weight at eclosion to variation in temperature and yeast concentration. This method was chosen because it allows one to produce the same heterozygous offspring repeatedly for testing under more conditions than could be handled at once. We estimated the effects of yeast concentration and temperature and their interaction on both the phenotypic and the environmental components of variation and covariation of the two traits. Development was slower at low temperatures and yeast concentrations, and dry weight and viability were lower at higher temperatures and lower yeast levels. Interactions of the two factors with the crosses and with each other indicated that there were genetic differences in plasticity and that the sensitivity of a trait to one factor depended on the level of the other. The covariation of the two traits was generally weak within an environment. Across environments, its sign depended on the factor that changed between the environments: positive for temperature, negative for yeast concentration. These findings can be explained in terms of an established growth model for Drosophila larvae. We conclude that for plastic traits with moderate or low heritability, the relationship between the phenotypic and genetic covariance matrices may be a complex function of the environmental factors that affect the traits. Some implications for the prediction of the evolution in fluctuating environments are outlined.

Modern Ecology: Basic and Applied Aspects.

Preface. Editorial advisors. List of contributors. I. MORPHOLOGY, STAND STRUCTURE, AND COMPETITION. 1. Morphology in modern ecological research (W. Eber). 2. Vegetation structure, phytomass and phenology of the dry thorn scrub of Curacao, West Indies (M.J.A. Werger, C. de Bok and B. Oranje). 3. Structure and phytomass production of a pioneer community (M. Jochimsen and D. Janzen). 4. Survival and growth beneath and near parents: The case of Myrcianthes fragrans (Myrtaceae) (D.F. Whigham and E. Cabrera Cano). 5. Colonizing success in plants: Genetic variation and phenotypic plasticity in life history traits in Capsella bursa-pastoris (H. Hurka and B. Neuffer). 6. Niches of longevity and stress (F. Klotzli). II. MASS AND WATER BALANCES AT STAND LEVEL 7. Plasticity of the photosynthetic production of Galium aparine L. (W.L. Kutsch and L. Kappen). 8. Diversity of photosynthetic responses in the mesic and arid Mediterranean-type climate regions of southern Africa (M.C. Rutherford). 9. The combination of measurements and mathematical modelling for assessing canopy structure effects (U. Tappeiner and A. Cernusca). 10. The water balance of deciduous forests: methods and models (B. Saugier and J.-Y. Pontailler). 11. Combination effects of water and salt stress on growth, hydration and pigment composition in wheat ( Triticum aestivum L. ): A mathematical modelling approach (K.H. Kreeb and T. Chen). 12. Ecosystem research on grassland in the Austrian Alps and in the Central Caucasus (A. Cernusca). III. MINERALS AND VEGETATION-SOIL INTERACTIONS 13. Multi-element analysis in plant material (B. Markert). 14. Significance of nutrient relations and symbiosis for the competitive interaction between grasses and legumes in tropical savannas (E. Medina and B. Bilbao). 15. Correlations between the microbial activity, and water, air, temperature and nutrient status of different soils under different land use (H.-P. Blume, L. Beyer and F. Friedrich). IV. DISTURBANCES AND MANAGEMENT OF SEMI-NATURAL AND AGRICULTURAL SYSTEMS 16. Fire, dry heat and germination of savanna grasses in Botswana (W.H.O. Ernst). 17. Does intermediate disturbance increase species richness within deciduous forest understory? (R.J. Reader, K.C. Taylor and D.W. Larson). 18. Response of a Bromus erectus grassland Mesobromion to abandonment and different cutting regimes (H. Dierschke and M. Engels). 19. Phytosociology of vineyards - results, problems, tasks (O. Wilmanns and A. Bogenrieder). 20. The dissipation of energy through soil invertebrates in wheat field and meadow (L. Ryszkowski). V. EUTROPHICATION AND POLLUTION IN TERRESTRIAL SYSTEMS 21. Lead tolerance of annuals at roadsides (U. Hellmuth and W. Schmidt). 22. Environmental mutagenesis: mutational load in natural populations of Eisenia fetida ? (W. Nau and W. Kohler). 23. The sublethal enchytraeid test system: guidelines and some results (W. Westheide and D. Bethke-Beilfuss). 24.

Seasonal plasticity in life history traits: growth and development in Polygonia c-album (Lepidoptera: Nymphalidae)

The potentially multivoltine comma butterfly, Polygonia c-album L., hibernates in the adult stage. The adult seasonal morph is demonstrated to be a good indicator of whether an individual has entered reproductive diapause or is developing directly to sexual maturation. This fact, and the assumption that a short development time is not equally important to all categories of individuals, was used to test predictions on variation in life-history traits among categories (morphs and sexes) and environments (temperature and photoperiod) at the level of individuals and to some extent families and populations (the univoltine Stockholm population and the partially bivoltine Oxford population). Individuals developing to adults in a short time were expected to be smaller and lighter as a result of a basic trade-off between the two traits. Development times varied in accordance with predictions, but in most cases this was due to plastic growth and development in both the larval and pupal stages rather than through variation in size or weight, i.e. size was a highly canalized trait. This suggests a relationship between plasticity and canalization and a strong potential for plasticity to shield life-history traits from selection. Individuals regulated development times also within developmental pathways, in response to photoperiods indicating the progression of the season. These and other results suggest that development times are not normally minimized in temperate butterflies unless this is enforced by direct development and protandry. There is thus scope for a high degree of adaptive plasticity in growth- and developmental rates which may devalue the basic trade-offs assumed by life-history theory and account for inconsistencies with its predictions.

Phenotypic plasticity in life-history traits of femaleThalassoma bifasciatum (Pisces: Labridae): 2. Correlation of fecundity and growth rate in comparative studies

The cost of reproduction is a central concept in theories of life-history evolution. One way to empirically examine the tradeoff between current reproduction and future reproductive prospects is to use natural intraspecific variation in life-history traits. However, this approach is complicated by the sensitivity of life-history traits to variation in the level of resources. We report here an attempt to measure the cost of increasing reproductive activity in populations of female bluehead wrasse,Thalassoma bifasciatum, a coral-reef fish. All of the significant correlations of fecundity and growth rate were positive, in contradiction to the tradeoff predicted by the cost concept. In one of two regions studied, the populations with relatively high mean growth rate had a relatively large mean fecundity. The trait means were also positively associated over time: in months of rapid growth, female reproductive activity was high. Even after removing the effects of habitat and time period in a comparison of individual traits, no growth cost to reproduction appears. Variation in the abundance of resources over space and time is likely to interfere with the measurement of the cost of reproduction in many natural systems.

Phenotypic Plasticity in Life-History Traits of Female Thalassoma bifasciatum (Pisces: Labridae). 1. Manipulations of Social Structure in Tests for Adaptive Shifts of Life-History Allocations

Phenotypic Plasticity in Life-History Traits of Female Thalassoma bifasciatum (Pisces: Labridae). 1. Manipulations of Social Structure in Tests for Adaptive Shifts of Life-History Allocations

Plasticity in life-history traits of the bark beetle Ips calligraphus as influenced by phloem thickness.

Reproduction and development of Ips calligraphus (Germar) (Coleoptera: Scolytidae) occur primarily in the phloem (inner bark) tissue of its pine hosts. In slash pine (Pinus elliottii Engelm. var. elliottii), phloem thickness can vary widely from tree to tree. We compared adult residence time and fecundity and progeny development time, body size, and sex ratio of this beetle when reared in slash pine bolts and bark slabs with phloem thicker or thinner than average adult body width. Most studies were conducted at 20°, 25°, and 30° C. Residence time of parent males and females decreased with increasing temperature but it was not affected by phloem thickness. Residence time of parent males was about 2 days shorter than that of parent females at each temperature. Reproductive fitness was greater in thick phloem at all temperatures as measured by faster larval development, earlier emergence of progeny (F 1 ) adults, and emergence of more progeny adults per parent female. Progeny survival was similar between phloem those from thick phloem, and their sex ratio was female biased (1:2 vs 1:1, male:female). When allowed to inhabit thick phloem, the progeny (F 2) of adults from thin phloem were just as large and of similar sex ratio (1:1) as were progeny of F 1 adults from thick phloem. The high degree of plasticity in the life-history traits of this beetle may enable it to successfully colonize pines that vary widely in phloem thickness.

Life-History Variation in a Stream Population of Musculium partumeium (Bivalvia:Pisidiidae)

This study reports on the life-history traits of a stream population of the clam Musculium partumeium. The population displays two generations per year: a spring-born generation (SG) which reproduces twice (fall and following spring) and a fall-born generation (FG) which reproduces once in the spring. Traits for FG and SG generations are, respectively: maximum shell length, 5.1 and 6.1 mm; annual reproductive output (number of young born per average adult), 16 and 38; larval growth rate, 0.15 and 0.08 mm/wk; larval mortality, 67 and 48%; intrinsic rate of increase (r) 0.011 and 0.019/day. Compared with values for other populations of M. partumeium, our results were generally intermediate between those displayed by permanent pond populations (with 2 generations/year) and those of ephemeral pond populations (1 generation/year). This species appears to display a wide range of phenotypic plasticity in life-history traits.

The Evolution of Phenotypic Plasticity in Life-History Traits: Predictions of Reaction Norms for Age and Size at Maturity

The Evolution of Phenotypic Plasticity in Life-History Traits: Predictions of Reaction Norms for Age and Size at Maturity

Phenotypic Plasticity in Life-History Traits: Demographic Effects and Evolutionary Consequences

Although much life-history theory assumes otherwise, most life-history traits exhibit phenotypic plasticity in response to environmental factors during development. Plasticity has long been recognized as a potentially important factor in evolution, is known to be under genetic control, and may or may not be adaptive. The notion of adaptive plasticity contrasts with the idea that developmental homeostasis is a major evolutionary goal. The conflict was resolved in principle by Ashby's cybernetic analysis of homeostasis, which showed how plasticity in “response variables” might act to screen “essential variables” from the impact of environmental disturbance. To apply this analysis to life-history plasticity, it must be incorporated into a demographic model. An approach is presented here using life cycle graphs and matrix projection models. Plasticity in response to temporal variation leads to time-varying matrix models: plasticity in response to spatial variation leads to models structured by criteria other than age. The adaptive value of such plasticity can be assessed by calculating its effects on a suitable measure of fitness: long-term growth rate for time-invariant models, expected growth rate discounted by variance for time-varying models. Three examples are analyzed here: plasticity in the rate of development from one instar to the next in a stage-classified model, plasticity in multiplicative yield components, and plasticity in dormancy as a response to environmental cues. Development rate plasticity is adaptive if reproductive value increases from the instar in question to the next, maladaptive otherwise. Plasticity in yield components reduces fitness variance, and hence is adaptive, if the responses of successive developmental steps ( e.g. , flowers/stem, seeds/flower) are negatively correlated. Plasticity in dormancy is adaptive if it responds to the same factor(s) influencing mortality, but with opposite sign. A number of important problems, including trade-offs between genetic and phenotypic adaptation and the distinction between continuous and discontinous plasticity remain to be solved.