Variation In Growth Trajectories Research Articles

Osteohistology of a Triassic dinosaur population reveals highly variable growth trajectories typified early dinosaur ontogeny

Intraspecific variation in growth trajectories provides a fundamental source of variation upon which natural selection acts. Recent work hints that early dinosaurs possessed elevated levels of such variation compared to other archosaurs, but comprehensive data uniting body size, bone histology, and morphological variation from a stratigraphically constrained early dinosaur population are needed to test this hypothesis. The Triassic theropod Coelophysis bauri, known from a bonebed preserving a single population of coeval individuals, provides an exceptional system to assess whether highly variable growth patterns were present near the origin of Dinosauria. Twenty-four histologically sampled individuals were less than a year to at least four years old and confirm the right-skewed age distribution of the Coelophysis assemblage. Poor correlations among size, age, and morphological maturity strongly support the presence of unique, highly variable growth trajectories in early dinosaurs relative to coeval archosaurs and their living kin.

High Phenotypic Plasticity in a Prominent Plant Invader along Altitudinal and Temperature Gradients.

Studies on plant growth and trait variation along environmental gradients can provide important information for identifying drivers of plant invasions and for deriving management strategies. We used seeds of the annual plant invader Ambrosia artemisiifolia L. (common ragweed) collected from an agricultural site in Northern Italy (226 m. a.s.l; Mean Annual Air Temperature: 12.9 °C; precipitations: 930 mm) to determine variation in growth trajectories and plant traits when grown along a 1000-m altitudinal gradient in Northern Italy, and under different temperature conditions in the growth chamber (from 14/18 °C to 26/30 °C, night/day), using a non-liner modeling approach. Under field conditions, traits related to plant height (maximum height, stem height, number of internodes) followed a three-parameter logistic curve. In contrast, leaf traits (lateral spread, number of leaves, leaf length and width) followed non-monotonic double-Richards curves that captured the decline patterns evident in the data. Plants grew faster, reaching a higher maximum plant height, and produced more biomass when grown at intermediate elevations. Under laboratory conditions, plants exhibited the same general growth trajectory of field conditions. However, leaf width did not show the recession after the maximum value shown by plants grown in the field, although the growth trajectories of some individuals, particularly those grown at 18 °C, showed a decline at late times. In addition, the plants grown at lower temperatures exhibited the highest value of biomass and preserved reproductive performances (e.g., amount of male inflorescence, pollen weight). From our findings, common ragweed exhibits a high phenotypic plasticity of vegetative and reproductive traits in response to different altitudes and temperature conditions. Under climate warming, this plasticity may facilitate the shift of the species towards higher elevation, but also the in situ resistance and (pre)adaptation of populations currently abundant at low elevations in the invasive European range. Such results may be also relevant for projecting the species management such as the impact by possible biocontrol agents.

Perinatal determinants of growth trajectories in children born preterm.

BackgroundA growing amount of evidence indicates in utero and early life growth has profound, long-term consequences for an individual’s health throughout the life course; however, there is limited data in preterm infants, a vulnerable population at risk for growth abnormalities.ObjectiveTo address the gap in knowledge concerning early growth and its determinants in preterm infants.MethodsA retrospective cohort study was performed using a population of preterm (< 37 weeks gestation) infants obtained from an electronic medical record database. Weight z-scores were acquired from discharge until roughly two years corrected age. Linear mixed effects modeling, with random slopes and intercepts, was employed to estimate growth trajectories.ResultsThirteen variables, including maternal race, hypertension during pregnancy, preeclampsia, first trimester body mass index, multiple status, gestational age, birth weight, birth length, head circumference, year of birth, length of birth hospitalization stay, total parenteral nutrition, and dextrose treatment, were significantly associated with growth rates of preterm infants in univariate analyses. A small percentage (1.32% - 2.07%) of the variation in the growth of preterm infants can be explained in a joint model of these perinatal factors. In extremely preterm infants, additional variation in growth trajectories can be explained by conditions whose risk differs by degree of prematurity. Specifically, infants with periventricular leukomalacia or retinopathy of prematurity experienced decelerated rates of growth compared to infants without such conditions.ConclusionsFactors found to influence growth over time in children born at term also affect growth of preterm infants. The strength of association and the magnitude of the effect varied by gestational age, revealing that significant heterogeneity in growth and its determinants exists within the preterm population.

Genomic and life-history discontinuity reveals a precinctive lineage for a deep-water grouper with gene flow from tropical to temperate waters on the west coast of Australia

We address a critical knowledge gap for the Eightbar Grouper, Hyporthodus octofasciatus, one of the largest groupers targeted in mostly tropical, deep-water fisheries, using genetic analyses of mitochondrial DNA (mtDNA; N = 248) and age and growth information (N = 727) from specimens collected from the eastern Indian Ocean to the western central Pacific Ocean. We additionally used a genotype-by-sequencing approach on a subset of these samples (N = 94) to determine the extent of egg and larval dispersal between tropical and temperate regions along the west coast of Australia (WA). Discontinuity in mtDNA and nuclear genomes, and marked variation in growth trajectories and longevity revealed a distinct, non-interbreeding cryptic lineage in WA. The WA lineage appears to be geographically isolated from the oceanic Indo-West Pacific (IP) lineage and precinctive to a single continuous coastline from tropical to temperate waters (covering > 2200 km and ∼20° of latitude). The Hyporthodus phylogeny reveals a possible allopatric speciation scenario with sister lineages endemic to the east (i.e. H. ergastularius) and west (i.e. WA lineage of H. octofasciatus) coasts of Australia, each diverging from a broader IP distributed ancestor (i.e. IP lineage of H. octofasciatus) in the early Pleistocene Epoch. Sustainable management of these species therefore needs to consider their evolutionary distinction, in addition to aspects of their life-history strategies and limited geographic distribution that infers high vulnerability to fishing at relatively low levels of exploitation.

Subtle individual variation in indeterminate growth leads to major variation in survival and lifetime reproductive output in a long‐lived reptile

Abstract The consequences of individual variation in life‐history traits have been well studied due to their importance in evolutionary ecology. However, a trait that has received little empirical attention is the rate of indeterminate growth. In long‐lived ectotherms, subtle variation in growth after maturity could have major effects over the animals’ lifetimes. These effects are difficult to measure due to the challenges involved in reliably estimating individual variation in the face of environmental stochasticity, and the need to account for trade‐offs among growth, reproduction and survival. However, modelling advances have made such analysis possible if long‐term high‐quality datasets are available. We used an integrated state‐space modelling framework to reveal relationships between indeterminate growth, reproduction and survival in a population of North American snapping turtles (Chelydra serpentina) using a 41‐year dataset for 298 adult females. A hierarchical version of the von Bertalanffy model fitted to data on carapace lengths showed substantial individual variation in growth trajectories, and hierarchical models fitted to clutch‐mass data and recapture histories showed that reproductive output and survival probability increased with size. Integration of these models revealed no detectable trade‐offs—i.e., individual growth parameters were not correlated with size‐specific survival or reproduction rates, and individual variation in reproductive output did not affect the size‐specific survival rate. Consequently, individual variation in growth parameters was estimated to result in &gt;2‐fold variation in post‐maturity life expectancy and &gt;4‐fold variation in expected lifetime reproductive output. These results illustrate that indeterminate growth can have major fitness consequences in long‐lived species. We suggest that the individual variation in growth rates reflects variation in environments experienced during development or later life. An understanding of this variation may be essential for predicting the population dynamics of long‐lived species under threat and identifying the most important environments to protect. A plain language summary is available for this article.

Characterizing early child growth patterns of height-for-age in an urban slum cohort of Bangladesh with functional principal component analysis

BackgroundEarly childhood is a critical stage of physical and cognitive growth that forms the foundation of future wellbeing. Stunted growth is presented in one of every 4 children worldwide and contributes to developmental impairment and under-five mortality. Better understanding of early growth patterns should allow for early detection and intervention in malnutrition. We aimed to characterize early child growth patterns and quantify the change of growth curves from the World Health Organization (WHO) Child Growth Standards.MethodsIn a cohort of 626 Bangladesh children, longitudinal height-for-age z-scores (HAZ) were modelled over the first 24 months of life using functional principal component analysis (FPCA). Deviation of individual growth from the WHO standards was quantified based on the leading functional principal components (FPCs), and growth faltering was detected as it occurred. The risk factors associated with growth faltering were identified in a linear regression.ResultsNinety-eight percent of temporal variation in growth trajectories over the first 24 months of life was captured by two leading FPCs (FPC1 for overall growth and FPC2 for change in growth trajectory). A derived index, adj-FPC2, quantified the change in growth trajectory (i.e., growth faltering) relative to the WHO standards. In addition to HAZ at birth, significant risk factors associated with growth faltering in boys included duration of breastfeeding, family size and income and in girls maternal weight and water source.ConclusionsThe underlying growth patterns of HAZ in the first 2 years of life were delineated with FPCA, and the deviations from the WHO standards were quantified from the two leading FPCs. The adj-FPC2 score provided a meaningful measure of growth faltering in the first 2 years of life, which enabled us to identify the risk factors associated with poor growth that would have otherwise been missed. Understanding faltering patterns and associated risk factors are important in the development of effective intervention strategies to improve childhood growth globally.Trial registrationClinicalTrials.gov Identifier: NCT02734264, registered 22 March, 2016.

Evolution of adult size depends on genetic variance in growth trajectories: a comment on analyses of evolutionary dynamics using integral projection models

Summary Integral projection models (IPMs) are an extension of stage‐structured population models to continuous classes or traits, such as body size. Recent studies have used age‐structured IPMs to investigate the relative contributions of evolutionary versus demographic responses of quantitative traits to environmental change. However, I argue here that evolutionary responses are likely to be underestimated by this approach, because it does not fully capture how phenotypic differences between individuals and genotypes accumulate along life, and are transmitted across generations. Trait transitions upon survival and reproduction are treated in IPMs by two classes of functions. First, an ‘inheritance’ function relates the trait of a newborn to that of its adult parent, on the time‐scale of a reproductive event. Secondly, growth functions relate the traits of surviving individuals between successive ages. This differs from the quantitative genetic approach, where parent–offspring resemblance is generally quantified for age‐specific trait values, and on the time‐scale of a generation. More importantly, it is unclear to what extent age‐structured IPMs account for the fact that phenotypic and genetic variances of adult size are largely caused by differential growth among individuals and genotypes in multicellular organisms. I use simple simulations of growth trajectories to ask what the transition functions from IPMs can tell us about the contribution of genetic evolution to phenotypic change. These simulations illustrate that a flat inheritance function is perfectly compatible with substantial response to selection in adults. They further show that the growth functions from IPMs may obscure genetic differences in body size that accumulate along life owing to genetic variation in growth trajectories. IPMs are a powerful tool for investigating age‐dependent components of phenotypic selection, and the demographic consequences of plastic responses that act through environmental effects on growth. But using age‐structured IPMs to project evolutionary dynamics requires combining them with measurements of age‐specific additive genetic variances and cross‐age additive genetic covariances, to accurately describe the accumulation of phenotypic differences across ages, and their transmission across generations.

Determining individual variation in growth and its implication for life-history and population processes using the empirical Bayes method.

The differences in demographic and life-history processes between organisms living in the same population have important consequences for ecological and evolutionary dynamics. Modern statistical and computational methods allow the investigation of individual and shared (among homogeneous groups) determinants of the observed variation in growth. We use an Empirical Bayes approach to estimate individual and shared variation in somatic growth using a von Bertalanffy growth model with random effects. To illustrate the power and generality of the method, we consider two populations of marble trout Salmo marmoratus living in Slovenian streams, where individually tagged fish have been sampled for more than 15 years. We use year-of-birth cohort, population density during the first year of life, and individual random effects as potential predictors of the von Bertalanffy growth function's parameters k (rate of growth) and (asymptotic size). Our results showed that size ranks were largely maintained throughout marble trout lifetime in both populations. According to the Akaike Information Criterion (AIC), the best models showed different growth patterns for year-of-birth cohorts as well as the existence of substantial individual variation in growth trajectories after accounting for the cohort effect. For both populations, models including density during the first year of life showed that growth tended to decrease with increasing population density early in life. Model validation showed that predictions of individual growth trajectories using the random-effects model were more accurate than predictions based on mean size-at-age of fish.

Differences in growth trajectories between white British and Pakistani infants in the UK: analysis of the Born in Bradford birth cohort study

BackgroundGrowth during infancy is recognised as being important to future health and wellbeing. Infants born to south Asian mothers are lighter than those born to white mothers; however, information about growth during infancy of south Asians in the UK is largely unknown. We use multilevel linear spline models to describe differences in growth of UK-born white British and Pakistani origin infants from birth to 2 years. MethodsMultilevel linear spline models with knot points at 4 months and 9 months were fitted separately to weight and length data from birth to 2 years from 1434 singleton births (642 white British and 792 Pakistani) from the Born in Bradford prospective birth cohort, born between Aug 24, 2008, and Sept 4, 2009. These models allow for individual variation in growth trajectories and for the change in scale and variance in the measurements over time for all available data from all eligible children under a missing-at-random assumption. We used measurement data from two sources: clinic visits and measurements routinely obtained by health visitors. Four coefficients describe mean birthweight and length and the mean growth in the cohort for the three time periods: birth to 4 months, 4–9 months, and 9–24 months. Sex and ethnic differences in growth trajectories were estimated by fitting interaction terms in the random effects models. Models were further adjusted for maternal smoking, gestational age, and maternal height. FindingsLinear spline multilevel models for weight and length with knot points at 4 months and 9 months fitted the data well; the differences between actual and predicted measurements were small in each period, and individual level residuals were normally distributed. Pakistani boys were on average 0·21 kg lighter (95% CI −0·29 to −0·12) than white British boys, and Pakistani girls were 0·18 kg lighter (–0·26 to −0·10) and 0·5 cm shorter (–0·91 to −0·03) than white British girls at birth. Pakistani boys and girls gained length faster than their white British counterparts between 0 and 4 months (0·3 cm per month [0·1 to 0·5] for boys and 0·4 cm per month [0·2 to 0·6] for girls) and gained more weight per month between 9 and 24 months (0·01 kg per month [0·003 to 0·03] for boys and 0·03 kg per month [0·02 to 0·04] for girls). At age 2 years both ethnic groups had similar weight, but Pakistani boys and girls were longer. Adjustment for maternal smoking, gestational age, and maternal height did not substantially change these differences. InterpretationDifferences exist between the growth trajectories of Pakistani boys and girls and white British boys and girls. Pakistani boys and girls are lighter and shorter at birth than their white British counterparts, but gain weight and length more quickly in infancy. By age 2 years both ethnic groups have similar weight, but Pakistani boys and girls have become taller on average than their white British counterparts. The faster growth in Pakistani children could be beneficial for their early infant or childhood health. However, if the greater rate of weight gain is driven by greater fat gain in this population it could have adverse long-term consequences for their cardiometabolic health and contribute to the increased risk of diabetes and cardiovascular disease in south Asian adults. FundingNational Institute for Health Research (Programme Grants for Applied Research, RP-PG-0407-10044).

Allometric Scaling of Metabolism, Growth, and Activity in Whole Colonies of the Seed‐Harvester AntPogonomyrmex californicus

The negative allometric scaling of metabolic rate with body size is among the most striking patterns in biology. We investigated whether this pattern extends to physically independent eusocial systems by measuring the metabolic rates of whole functioning colonies of the seed-harvester ant Pogonomyrmex californicus. These intraspecific scaling data were compared to the predictions of an additive model developed to estimate collective metabolic rates. Contrary to the prediction of the additive model, colony metabolic rate allometry resembled the pattern commonly observed interspecifically for individual organisms, scaling with colony mass(0.75). Among the same-aged colonies, net growth rate varied by up to sevenfold, with larger colonies exhibiting higher net growth efficiency than smaller colonies. Isolated worker groups exhibited isometric metabolic rate scaling, suggesting that the social environment of the colony is critical to regulating individual patterns of work output. Within the social environment, individual worker locomotor velocities exhibited power-law distributions that scaled with colony size so that larger colonies exhibited a greater disparity between active and inactive ants than did smaller colonies. These results demonstrate that behavioral organization within colonies may have a major influence on colony-level metabolism and in generating intraspecific variation in growth trajectories.

Functional mapping of growth and development

Understanding how an organism develops into a fully functioning adult from a mass of undifferentiated cells may reveal different strategies that allow the organism to survive under limiting conditions. Here, we review an analytical model for characterizing quantitative trait loci (QTLs) that underlie variation in growth trajectories and developmental timing. This model, called functional mapping, incorporates fundamental principles behind biological processes or networks that are bridged with mathematical functions into a statistical mapping framework. Functional mapping estimates parameters that determine the shape and function of a particular biological process, thus providing a flexible platform to test biologically meaningful hypotheses regarding the complex relationships between gene action and development.

Growth Trajectories of Preterm Infants: Birth to 12 Years

Introduction Birth weight often is used to predict how preterm infants will grow, but scant attention has been paid to the effect of neonatal morbidities on growth trajectories. We investigated birth weight and neonatal morbidity in preterm infants’ growth to age 12 years. Method A five-group, prospective, longitudinal study was conducted with 194 infants: 46 full term; 29 healthy preterm without morbidity; 56 preterm with medical illness (MPT); 34 preterm with neurologic illness; and 29 preterm small for gestational age (SGA). Height, weight, and body mass index were measured at six ages. Results The full-term group had greater height than the preterm groups to age 8 years, when healthy preterm and MPT groups caught up. Only the SGA group had smaller height at age 12 years. The MPT, preterm with neurologic illness, and SGA groups had lower weight through age 12 years. Body mass index was appropriate for preterm groups by age 4 years. Across time, neonatal morbidity had a significant effect on height and weight trajectories. Birth weight was significant for weight trajectories only. Discussion With variation in growth trajectories, details of neonatal morbidity in health history interviews will inform child health assessments.

Growth trajectories and size-dependent reproduction in the highly invasive grass Microstegium vimineum

To better understand the ecological and evolutionary processes that underlie the ability of invasive plants to colonize and spread in a region, basic data on quantitative genetic variation in growth and reproduction of plants from contrasting microsites are desirable. The annual grass Microstegium vimineum is an invasive colonizer of the herbaceous layer in forests of the eastern United States. This greenhouse study utilized seeds collected from maternal plants in a shady forest or sunny edge microsite in central New Jersey, USA, to examine variation in growth trajectories and size-dependent reproduction. Questions addressed were (1) do growth trajectories vary significantly among families and between microsites? and (2) does reproductive mass scale with vegetative size? The trajectory for shoot dry mass over time was significantly related to microsite, due apparently to greater growth over the final 8 weeks of plants from the interior compared to those from the edge. It is suggested that a growth increase late in the season enables plants to maximize reproduction when light conditions improve following canopy leaf senescence. Number of tillers exhibited significant variation among families within microsites, but growth trajectories did not. Positive phenotypic and genetic correlations were detected between reproductive and vegetative mass per tiller; thus selection may favor large tillers to increase seed output, a critical life history trait for an invasive weed.

Ontogeny of sexual dimorphism and phenotypic integration in heritable morphs

In this study we investigated the developmental basis of adult phenotypes in a non-model organism, a polymorphic damselfly (Ischnura elegans) with three female colour morphs. This polymorphic species presents an ideal opportunity to study intraspecific variation in growth trajectories, morphological variation in size and shape during the course of ontogeny, and to relate these juvenile differences to the phenotypic differences of the discrete adult phenotypes; the two sexes and the three female morphs. We raised larvae of different families in individual enclosures in the laboratory, and traced morphological changes during the course of ontogeny. We used principal components analysis to examine the effects of Sex, Maternal morph, and Own morph on body size and body shape. We also investigated the larval fitness consequences of variation in size and shape by relating these factors to emergence success. Females grew faster than males and were larger as adults, and there was sexual dimorphism in body shape in both larval and adult stages. There were also significant effects of both maternal morph and own morph on growth rate and body shape in the larval stage. There were significant differences in body shape, but not body size, between the adult female morphs, indicating phenotypic integration between colour, melanin patterning, and body shape. Individuals that emerged successfully grew faster and had different body shape in the larval stage, indicating internal (non-ecological) selection on larval morphology. Overall, morphological differences between individuals at the larval stage carried over to the adult stage. Thus, selection in the larval stage can potentially result in correlated responses in adult phenotypes and vice versa.

Divergent juvenile growth and development mediated by food limitation and foraging in the water strider Aquarius remigis (Heteroptera: Gerridae)

AbstractThe factors leading to variation in growth, development and body size are of central importance for the study of life histories. I investigated the effect of food limitation on patterns of growth and development in the water strider Aquarius remigis (Heteroptera: Gerridae). Groups of 10 juveniles were allowed to develop under field conditions at three different food levels. Food limitation prolonged juvenile development, reduced growth rates and led to smaller adult body size and weight, the most common life‐history response in ectotherms; it also increased the variance among individuals in these traits, demonstrating variance accumulation suggesting divergent growth. Evidence that this resulted from competition among individuals for limited food was equivocal. On the one hand, direct observation of foraging nymphs showed that larger instar individuals were more likely to obtain monopolizable prey items than expected by chance, independent of food level. On the other hand, there was only a trend for the variance in moulting dates to increase when striders were raised in groups as opposed to singly at various temperatures in a controlled laboratory experiment. When food limitation prolongs juvenile development, variance accumulation with age can result from food limitation per se, as well as from random or heritable variation in growth trajectories. Foraging competition may amplify this effect, but not necessarily so. Therefore, it must not be assumed that divergent growth is necessarily caused by food competition.

A mechanistic model for genetic machinery of ontogenetic growth.

Two different genetic mechanisms can be proposed to explain variation in growth trajectories. The allelic sensitivity hypothesis states that growth trajectory is controlled by the time-dependent expression of alleles at the deterministic quantitative trait loci (dQTL) formed during embryogenesis. The gene regulation hypothesis states that the differentiation in growth process is due to the opportunistic quantitative trait loci (oQTL) through their mediation with new developmental signals. These two hypotheses of genetic control have been elucidated in the literature. Here, we propose a new statistical model for discerning these two mechanisms in the context of growth trajectories by integrating growth laws within a QTL-mapping framework. This model is developed within the maximum-likelihood context, implemented with a grid approach for estimating the genomic positions of the deterministic and opportunistic QTL and the simplex algorithm for estimating the growth curve parameters of the genotypes at these QTL and the parameters modeling the residual (co)variance matrix. Our model allows for extensive hypothesis tests for the genetic control of growth processes and developmental events by these two types of QTL. The application of this new model to an F(2) progeny in mice leads to the detection of deterministic and opportunistic QTL on chromosome 1 for mouse body mass growth. The estimates of QTL positions and effects from our model are broadly in agreement with those by traditional interval-mapping approaches. The implications of this model for biological and biomedical research are discussed.

Phenotypic variation in growth trajectories in the Arctic charr Salvelinus alpinus.

Animals with determinate growth have shown little variation in individual growth patterns, but similar analyses for animals with indeterminate growth have been lacking. We analysed the amount of phenotypic variation in growth patterns across ages among individuals of a hatchery-based population of Arctic charr, Salvelinus alpinus, Salmonidae, using the infinite-dimensional model and including the effects of group size structure. There was little phenotypic variation in growth trajectories: individuals that were small (in relation to the mean) early in life were among the smallest 2.5 years later. If the genetic variation reflects phenotypic variation, not much evolutionary change can be expected. Our results show that there are ecological conditions that determine the strong covariation of size across ages, most likely size-related dominance behaviour, which can mask the true variation of growth patterns. Thus, social interactions can have strong evolutionary effects on traits not directly involved in the behavioural interactions.

Evolutionary significance of genotypic variation in developmental reaction norms for a perennial grass under competitive stress

The developmental reaction norm (DRN) represents the set of ontogenetic trajectories that can be produced by a genotype exposed to different environmental conditions. Genetic variation in the DRN for growth traits and in the patterns of biomass allocation is critical to phenotypic evolution in heterogeneous environments. The DRN and patterns of biomass allocation were investigated in 11 clones of the caespitose, corm-forming, perennial grass Phleum pratense in relation to competitive stress imparted by Lolium perenne in a 16 week glasshouse experiment. A separate experiment assessed the ability of basal buds flanking a corm to sprout and the relationship of corm mass to sprout mass for the same clones. Corm fresh mass varied among clones and was significantly correlated with the dry mass of the tillers that sprouted from basal buds. In the competition experiment, clones in competitive environments varied significantly from those in non-competetive environments in terms of their DRNs for number of tillers and shoot dry mass. Thus, selection of DRNs would favour different genotypes in the two environments and at different times. Significant negative genetic correlations were detected for tiller number and mean tiller mass in the noncompetitive, but not the competitive, environment. Biomass allocation to stem bases was significantly greater for clones under competitive stress. Allocation to storage tissues such as corms may be adaptive if it enhances persistence in the competitive field environments typically occupied by caespitose grasses. Root and shoot allocation showed a significant clone by competition interaction. For P. pratense, genotypic variation in growth trajectories plays an important role in determining variation in individual performance, a condition necessary for the continued evolution of the DRN.

Individual variation in growth trajectories: phenotypic and genetic correlations in ontogeny of the house finch (Carpodacus mexicanus)

Abstract We studied patterns of growth in a recently established natural population of the house finch (Carpodacus mexicanus) to examine whether phenotypic and genetic covariation among age-specific trait values is likely to constrain morphological change favoured by selection acting on adults. We found variable patterns of allometric relationships during ontogeny, and documented relatively weak covariations among ages or among traits in individual growth trajectories. Frequent compensatory growth largely cancelled out the initial differences among nestlings, potentially enabling house finches to raise offspring under diverse and unpredictable environmental conditions. Moderate levels of additive genetic variance in morphological traits throughout ontogeny, and relatively low and fluctuating phenotypic and genetic covariation among ages imply strong potential for evolutionary change in morphological traits under selection. This conclusion is consistent with the profound population-level divergence in morphological patterns that accompanied very successful colonization of most of North America by the house finch over the last 50 years.

HETEROCHRONY WITHIN SPECIES: CRANIOFACIAL GROWTH IN GIANT, STANDARD, AND DWARF RABBITS.

Change in developmental timing is one source of heritable variation upon which selection can act. However, the amount of variation possible in ontogenetic trajectories is often unknown. We used three different-sized conspecific breeds of domestic rabbits to investigate the extent of variation in growth trajectories of craniofacial morphology. The growth and adult morphology of several structures (one soft tissue and 15 skeletal) were quantified and analyzed. We took two views of radiographs at close time intervals throughout ontogeny, from one week of age through adult size. Measurements from the radiographs were analyzed using a Gompertz growth model. Between-breed differences in model parameters were tested using one-way ANOVA. Few significant differences existed between the white and giant rabbits, but several differences were found between the white and dwarf breeds. Similarly, comparisons of adult morphology showed that white and giant rabbits are the same shape, while dwarf rabbits have shorter and broader snouts than white rabbits. The variation in size among breeds appeared to be due to differences in the length of time spent growing at rates near the maximum growth rate. While no one parameter of this model quantifies this pattern, differences in duration of maximum growth rate can be seen in the first derivative of the growth trajectory. Small changes in the model's parameters that measure rate and timing of growth have large morphological consequences, indicating that heterochronic changes are important sources of variation.