Variation In Individual Growth Rates Research Articles

The relationships between growth rate and mitochondrial metabolism varies over time

Mitochondrial metabolism varies significantly between individuals of the same species and can influence animal performance, such as growth. However, growth rate is usually determined before the mitochondrial assay. The hypothesis that natural variation in mitochondrial metabolic traits is linked to differences in both previous and upcoming growth remains untested. Using biopsies to collect tissue in a non-lethal manner, we tested this hypothesis in a fish model (Dicentrarchus labrax) by monitoring individual growth rate, measuring mitochondrial metabolic traits in the red muscle, and monitoring the growth of the same individuals after the mitochondrial assay. Individual variation in growth rate was consistent before and after the mitochondrial assay; however, the mitochondrial traits that explained growth variation differed between the growth rates determined before and after the mitochondrial assay. While past growth was correlated with the activity of the cytochrome c oxidase, a measure of mitochondrial density, future growth was linked to mitochondrial proton leak respiration. This is the first report of temporal shift in the relationship between growth rate and mitochondrial metabolic traits, suggesting an among-individual variation in temporal changes in mitochondrial traits. Our results emphasize the need to evaluate whether mitochondrial metabolic traits of individuals can change over time.

Individual growth of the Flathead Knob‐scaled Lizard, Xenosaurus platyceps, from tropical and temperate populations

AbstractGrowth rates of ectotherms are frequently affected by environmental conditions, such as temperature, precipitation, and prey availability. However, local adaptation to environmental conditions could influence geographic variation in growth rates. We studied growth rates of the Flathead Knob‐scaled Lizard, Xenosaurus platyceps, from a tropical population and a temperate population in Tamaulipas, Mexico. We used a field study and a common garden experiment to examine the extent and potential causes of variation in individual growth rates between these two populations from contrasting environments. Field‐determined growth rates in the tropical population were greater than those in the temperate population. In a laboratory common garden experiment that manipulated food availability and temperature for neonates from each population, neonates from the tropical population grew faster than those from the temperate population. Neonates kept at higher temperatures grew faster than those kept at lower temperature. In addition, growth rates of neonates from temperate and tropical populations did not differ at low temperature, but neonates from the tropical population grew faster at the higher temperature than did the neonates from the temperate population. Food treatment did not affect individual growth rates in these lizards, although there was a trend for neonates grown with higher food availability to grow faster. Our results suggest that not only does the warm environment of the tropical population contribute to the observed differences in field growth rates, but there is a genetic difference in the ability of the tropical population to take advantage of the warmer temperatures to increase growth ratesAbstract in Spanish is available with online material.

Mutualism as a Plant Functional Trait: Linking Variation in the Mycorrhizal Symbiosis to Climatic Tolerance, Geographic Range, and Population Dynamics

Plant functional traits, commonly defined as anatomical, physiological, and morphological characters that influence individual fitness and population growth, and thus ecological distribution, have been studied for more than a century. Plant interactions with microbial mutualists could also be functional traits because they influence how plants respond to environmental variation, but tests of this hypothesis are rare. I explored whether variation in the plant mutualism with arbuscular mycorrhizal (AM) fungi is associated with climatic tolerances, geographic range size, and fitness components (survival, reproduction, individual growth) that influence population growth. Analyses were done with categorical and quantitative metrics of mutualism variation to determine whether outcomes were consistent. Plants that are always colonized by AM fungi (AM state) occurred in warmer climates than either plants that are never colonized by AM fungi (NM state) or plants that vary in whether they are colonized (AMNM state), whereas AMNM plants had larger geographic ranges than either AM or NM plants. The effect of variation in individual growth rate on population growth rate was significantly higher in AMNM and NM plants than in AM plants, whereas the effect that variation in survival and reproduction had on population growth rate did not differ among mycorrhizal states. Quantitative variation in the mutualism, expressed as mycorrhizal growth response (MGR; biomass ratio of AM fungal–inoculated plants to noninoculated controls) rarely predicted climate tolerances and geographic range size. These findings suggest that mycorrhizal state is a functional trait based on traditional definitions but that MGR may not necessarily reflect functionally meaningful variation in the mutualism, at least not beyond the context of the conditions in which it was measured. Nonetheless, these findings provide the first evidence linking variation in mycorrhizal mutualism to the fitness components that influence population growth, implying that variation in plant interactions with mycorrhizal fungi has consequences for plant population dynamics.

Size and variation in individual growth rates among food web modules

AbstractThe complexity of food webs can be reduced to fundamental modules of trophic interactions that repeat to form reticulate webs. Omnivory, defined as feeding on more than one trophic level, is a module that is found in food webs more often than predicted by chance, likely because it confers stability. Yet, little is known about how omnivore and other food web modules affect individuals in the food web. Here, we constructed four different experimental food web modules using a blue mussel predator, zooplankton consumer, and phytoplankton resource. By manipulating the predator's access to the consumer and providing resource subsidies, we produced exploitative competition, food chain and omnivory food web modules, and a consumer‐resource interaction. We used RNA:DNA ratios to measure the growth rate of the consumer in each food web. In 24‐h experiments, growth rates of the consumer in the omnivory food web were significantly higher and more variable than in the other modules. Our results suggest that higher growth rates and variation at the individual scale may weaken the strength of predator–consumer interactions and help explain the ubiquity of omnivory in real food webs.

Predicting changes in mandibular length and total anterior facial height using IGF-1, cervical stage, skeletal classification, and gender.

BackgroundThe purpose of this study was to predict the annual growth rate of the mandible and total anterior facial height using IGF-1 levels together with cervical stage, skeletal classification, and gender.MethodsTwenty-five orthodontic patients (12 females and 13 males) had their cervical stages, blood-spot IGF-1 levels, and cephalometric parameters measured at 1-year intervals. The number of years each patient was followed up varied between 1 and 5 years resulting in 43 12-month intervals collected from 77 observations. Descriptive, bivariate, and regression analyses were used to analyze this data.ResultsThe linear regression model for predicting the annual mandibular growth rate was significant at p < 0.01 with an R-square value of 0.52. We found that the average IGF-1 level for the interval, the change in IGF-1 level, and the presence of a skeletal class III pattern were statistically significant predictors of mandibular growth. The regression model for predicting the annual change in anterior facial height was significant at p < 0.01 with an R-square value of 0.42. We found that the change in IGF-1 level was the only statistically significant predictor of this outcome.ConclusionsThe proposed method which combines IGF-1 levels with information that is readily available to clinicians can be used to predict the timing and intensity of the growth spurt. These factors together explain more of the observed individual variation in growth rate than any of the factors used in isolation.

Relative magnitude of cohort, age, and year effects on size at age of exploited marine fishes

Variation in individual growth rates contributes to changes over time in compensatory population growth and surplus production for marine fishes. However, there is little evidence regarding the prevalence and magnitude of time-varying growth for exploited marine fishes in general, whether it is best approximated using changes in length-at-age or weight-at-length parameters, or how it can be represented parsimoniously. We therefore use a database of average weight in each year and age for 91 marine fish stocks from 25 species, and fit models with random variation in length and weight parameters by year, age, or cohort (birth-year). Results show that year effects are more parsimonious than age or cohort effects and that variation in length and weight parameters provide roughly similar fit to average weight-at-age data, although length parameters show a greater magnitude of variability than weight parameters. Finally, the saturated model can explain nearly 2/3 of total variability, while a single time-varying factor can explain nearly 1/2 of variability in weight-at-age data. We conclude that time-varying growth can often be estimated parsimoniously using a single time-varying factor, either internally or prior to including ‘empirical’ weight at age in population dynamics models.

Vertical stratification reduces competition for light in dense tropical forests

Differential growth response to light level is widely accepted as a potential mechanism for maintaining tree species richness in tropical forests. The position of tree species in the hierarchy of the canopy is considered an important indicator of species light capture and growth strategy. Paradoxically, the relative importance of species identity and competition for light in determining individual tree growth is poorly documented at the adult stage. In this study, we used a hierarchical Bayesian model to quantify the overall importance of species identity, light and belowground competition as determinants of tree growth in French Guiana tropical forest. Light competitive status is assessed by a crown exposure score and below ground competition is estimated from local crowding. We examined species sensitivity to both types of competition in relation to adult stature.Our results are based on annual diameter increments of more than 13,510 stems from 282 species monitored over 10years. Mean annual growth rate was 0.11cmy−1 with species identity explaining 35% of the individual variation in growth rate. Crown exposure and local crowding explained 3.5% and 2.4% of the variation in growth rate, respectively. Predicted changes in growth rate as crown exposure (resp. local crowding) index changed from lower to upper interquartile level was 0.03cmy−1 (resp. 0.02cmy−1). Species sensitivity to crown exposure and to local crowding were positively correlated (i) with predicted growth rate at high-light standardized conditions and (ii) with adult stature.This vertical niche partitioning is invoked to explain the limited contribution made by level of light competition for predicting individual tropical tree growth as the community-level response is dominated by the abundance of small-statured species with low sensitivity to light level.Light appears to drive the stem growth rate of tropical trees through species differentiation more than through individual tree growth limitation. This vertical stratification complements the previously reported regeneration niche and together these provide evidence for light niche partitioning in the three-dimensional space of tropical forests.

Interactions between body mass and water temperature cause energetic bottlenecks in juvenile steelhead

AbstractAcross taxa, it is generally accepted that there are fitness advantages to rapid growth early in life. For stream‐dwelling salmonids, however, high temperatures and associated energetic costs during the summer growing season might offset or even prevent the competitive advantage of large body size. Our overall objective was to understand the relative importance of factors that can cause variation in growth rates in an age‐0 cohort of wild steelhead (Oncorhynchus mykiss) in Idaho, USA, where temperatures approach, and temporarily exceed, their tolerance level. For individually tagged fish inhabiting the same stream reach, we found that growth rates were negatively related to fish mass (slopes of the two best approximating models were both −0.024). Comparing growth rates from 16 different stream reaches throughout the watershed, we found that temperature‐induced metabolic cost was the single best approximating model (AIC wi = 1.0) of the variation in individual growth rates. The bioenergetic model showed that mass‐specific metabolic costs decreased with mass, but the absolute energetic demands increased over the same size range. Because temperature had a multiplicative effect on metabolic cost, our results suggest that the effect of food limitation increased with fish size. We conclude that high water temperatures pose energetic bottlenecks and can be a potentially strong mechanism limiting growth in juvenile salmonids in summer, particularly as streams in the region experience warming trends.

Influence of social factors on the nocturnal activity pattern of the noble crayfish,Astacus astacus(Crustacea, Decapoda) in recirculating aquaculture systems

The social environment plays a major role in the control of growth in many crustaceans, but little is known on the mechanisms involved. Two- and three-year-old noble crayfish, Astacus astacus are strictly nocturnally active. In the present article, we studied social effects on the pattern of nocturnal activity, represented by the time which the animals spent outside shelters. For this purpose, the activity of groups of uniformly large (‘dominant’) and uniformly small (‘subordinate’) individuals were recorded at different densities both separately and in mixed set-ups. In crowded laboratory cultures, the presence of larger (dominant) conspecifics was found to reduce the time which smaller (subordinate) individuals spent outside shelters in search of food and feeding by about one-third. It is suggested that this asymmetric inhibitory effect is an element of the functional chain which ultimately results in an extremely wide variation in individual growth rates of communally reared A. astacus. The relevance of the findings to crayfish aquaculture is discussed.

Response to Phosphorus Limitation Varies among Lake Populations of the Freshwater Snail Potamopyrgus antipodarum

Local adaptation – typically recognized as higher values of fitness-related traits for native vs. non-native individuals when measured in the native environment - is common in natural populations because of pervasive spatial variation in the intensity and type of natural selection. Although local adaptation has been primarily studied in the context of biotic interactions, widespread variation in abiotic characteristics of environments suggests that local adaptation in response to abiotic factors should also be common. Potamopyrgus antipodarum, a freshwater New Zealand snail that is an important model system for invasion biology and the maintenance of sexual reproduction, exhibits local adaptation to parasites and rate of water flow. As an initial step to determining whether P. antipodarum are also locally adapted to phosphorus availability, we examined whether populations differ in their responses to phosphorus limitation. We found that field-collected juvenile P. antipodarum grew at a lower rate and reached an important size threshold more slowly when fed a relatively low vs. a relatively high- phosphorus diet. We also detected significant across-population variation in individual growth rate. A marginally significant population-by-dietary phosphorus interaction along with a two-fold difference across populations in the extent of suppression of growth by low phosphorus suggests that populations of P. antipodarum may differ in their response to phosphorus limitation. Local adaptation may explain this variation, with the implication that snails from lakes with relatively low phosphorus availability should be less severely affected by phosphorus limitation than snails from lakes with higher phosphorus availability.

The effects of intermittent exposure to low-pH and low-oxygen conditions on survival and growth of juvenile red abalone

Abstract. Exposure of nearshore animals to hypoxic, low-pH waters upwelled from below the continental shelf and advected near the coast may be stressful to marine organisms and lead to impaired physiological performance. We mimicked upwelling conditions in the laboratory and tested the effect of fluctuating exposure to water with low-pH and/or low-oxygen levels on the mortality and growth of juvenile red abalone (Haliotis rufescens, shell length 5–10 mm). Mortality rates of juvenile abalone exposed to low-pH (7.5, total scale) and low-O2 (40% saturation, mg L−1) conditions for periods of 3 to 6 h every 3–5 days over 2 weeks did not differ from those exposed to control conditions (O2: 100% saturation, 12 mg L−1; pH 8.0). However, when exposure was extended to 24 h, twice over a 15-day period, juveniles experienced 5–20% higher mortality in the low-oxygen treatments compared to control conditions. Growth rates were reduced significantly when juveniles were exposed to low-oxygen and low-pH treatments. Furthermore, individual variation of growth rate increased when juveniles were exposed simultaneously to low-pH and low-O2 conditions. These results indicate that prolonged exposure to low-oxygen levels is detrimental for the survival of red abalone, whereas pH is a crucial factor for their growth. However, the high individual variation in growth rate under low levels of both pH and oxygen suggests that cryptic phenotypic plasticity may promote resistance to prolonged upwelling conditions by a portion of the population.

Growth variability of brook charr (Salvelinus fontinalis) in coastal maine

AbstractBrook charr inhabit a wide variety of habitats and exhibit considerable growth variation within and among populations. We used biannual mark–recapture electrofishing surveys and PIT tags at two streams in coastal Maine to examine spatial and temporal variability in brook charr growth. We documented considerable stream‐to‐stream and year‐to‐year variation in the growth of coastal brook charr. Based on 2892 recaptures between 2006 and 2010, we developed a suite of linear mixed models to examine variation in individual growth rates at Stanley Brook as a function of environmental variables. We distilled physical habitat data from surveys in 2010 into principle components for entry into the growth model. Growth was related primarily to an interaction between season and body length, mean water temperature, and instream location. Growth rates were highest in the summer, and smaller individuals grew more rapidly than larger conspecifics in the same stream. Individuals using habitats closer to the head of tide grew faster than those in upstream locations. Physical habitat variation was not an important control of individual growth variation within Stanley Brook. We suggest local variability in growth rates should be considered when developing management strategies for coastal populations.

Maintenance of phenotypic variation: repeatability, heritability and size-dependent processes in a wild brook trout population.

Phenotypic variation in body size can result from within-cohort variation in birth dates, among-individual growth variation and size-selective processes. We explore the relative effects of these processes on the maintenance of wide observed body size variation in stream-dwelling brook trout (Salvelinus fontinalis). Based on the analyses of multiple recaptures of individual fish, it appears that size distributions are largely determined by the maintenance of early size variation. We found no evidence for size-dependent compensatory growth (which would reduce size variation) and found no indication that size-dependent survival substantially influenced body size distributions. Depensatory growth (faster growth by larger individuals) reinforced early size variation, but was relatively strong only during the first sampling interval (age-0, fall). Maternal decisions on the timing and location of spawning could have a major influence on early, and as our results suggest, later (>age-0) size distributions. If this is the case, our estimates of heritability of body size (body length = 0.25) will be dominated by processes that generate and maintain early size differences. As a result, evolutionary responses to environmental change that are mediated by body size may be largely expressed via changes in the timing and location of reproduction.

Physiological mechanisms underlying a trade-off between growth rate and tolerance of feed deprivation in the European sea bass (Dicentrarchus labrax)

The specific growth rate (SGR) of a cohort of 2000 tagged juvenile European sea bass was measured in a common tank, during two sequential cycles comprising three-weeks feed deprivation followed by three-weeks ad libitum re-feeding. After correction for initial size at age as fork length, there was a direct correlation between negative SGR (rate of mass loss) during feed deprivation and positive SGR (rate of compensatory growth) during re-feeding (Spearman rank correlation R=0.388, P=0.000002). Following a period of rearing under standard culture conditions, individuals representing 'high growth' phenotypes (GP) and 'high tolerance of feed deprivation' phenotypes (DP) were selected from either end of the SGR spectrum. Static and swimming respirometry could not demonstrate lower routine or standard metabolic rate in DP to account for greater tolerance of feed deprivation. Increased rates of compensatory growth in GP were not linked to greater maximum metabolic rate, aerobic metabolic scope or maximum cardiac performance than DP. When fed a standard ration, however, GP completed the specific dynamic action (SDA) response significantly faster than DP. Therefore, higher growth rate in GP was linked to greater capacity to process food. There was no difference in SDA coefficient, an indicator of energetic efficiency. The results indicate that individual variation in growth rate in sea bass reflects, in part, a trade-off against tolerance of food deprivation. The two phenotypes represented the opposing ends of a spectrum. The GP aims to exploit available resources and grow as rapidly as possible but at a cost of physiological and/or behavioural attributes, which lead to increased energy dissipation when food is not available. An opposing strategy, exemplified by DP, is less 'boom and bust', with a lower physiological capacity to exploit resources but which is less costly to sustain during periods of food deprivation.

Ecology and Life History of Coaster Brook Trout and Potential Bottlenecks in Their Rehabilitation

AbstractLake Superior once supported abundant lake‐dwelling brook trout Salvelinus fontinalis called coasters; however, only scattered remnant populations remained by the early 20th century. Owing to their early decline, there is little information about their ecology and life history, yet such information is vital for the ecologically based rehabilitation and management of coasters. This study reviews the ecology of coaster brook trout from a life history perspective and presents quantitative data on the biology and status of the few populations that have been studied. Within the Lake Superior basin, some brook trout are stream residents while others are lacustrine or adfluvial. Although the variation in migratory behavior may be related to individual energetics, the role of evolution and the proximate factors triggering specific life histories remain uncertain. Comparisons of recent biological data from populations in the Lake Superior basin show that the northern populations have longer lengths at age and length frequency distributions skewed toward longer individuals. The degrees to which this difference is driven by variation in individual growth rates and size‐selective mortality are unknown. All known populations around the Lake Superior basin appear to have a small number of individuals and are thus of conservation concern. We believe that biotic interactions such as competition with introduced salmonines (in particular coho salmon Oncorhynchus kisutch) have a strong negative influence on the individual and population performance of coasters. Coupled with high past and recent mortality from fisheries, these factors may create bottlenecks limiting the growth and rehabilitation of the remnant populations. Lake Superior coaster brook trout are persisting, albeit uncertainly, under conditions different from those in which they once thrived. Management focused on native ecosystem rehabilitation may foster the return of these fish as abundant members of Great Lakes food webs, and recent basinwide restrictions on length and catch limits are a positive step toward enhancing their rehabilitation and evolution.

Growth variation and fin damage in Atlantic cod ( Gadus morhua L.) fed at graded levels of feed restriction

Atlantic cod (initial weight 55, 250 and 450 g) were deprived of feed for 1 month or fed one of two diets differing in crude protein and lipid levels at rations corresponding to about 25, 50, 75 or 130% of group satiation for two months. The fish were individually weighed at the start, mid and end of the experiment and growth variation and fin damage were registered. The fin damage patterns differed between size groups; 55 g cod had most wounds on the dorsal fins whereas the pectoral fins were the most damaged in the 250 g fish. The incidence of damage in these groups was high and increased significantly when feeding was restricted. In the 450 g cod there was little fin damage and the incidence did not seem to depend on diet treatment. In the 55 and 250 g cod groups, fast growing fish had lower incidence of fin damage than fish that grew slowly, suggesting that the fish that received most aggression were prevented from feeding. However, a similar trend was registered in non-fed fish, showing that the recipients of aggression also suffered other disadvantages. The variation in individual growth rates increased when feeding was restricted and the distribution was differently skewed depending on feeding level. The data provide evidence that competition is an important factor limiting growth of individual cod held in groups in culture.

Geographic Variation in Somatic Growth of Redside Shiner

AbstractThe geographic variation in growth rate and resulting body size is poorly known for most fish species. In this paper, we used data derived from otoliths to describe patterns of growth in redside shiners Richardsonius balteatus from seven native populations across the southern portion of its range, and we compare growth with latitude, elevation, and growing season to determine which of these environmental factors best predicts the growth patterns among these populations. To determine whether observed differences in growth resulted from environmental or genetic variation, we conducted a common‐environment experiment on fish from three of the seven populations that showed contrasting patterns between latitude and length of growing season. Redside shiners exhibited about a 60% difference in size at age among populations in their natural environments. Growing season length was the best predictor of body size among these populations (Akaike weight = 0.78). In a common environment, temperature‐specific growth rates differed among populations, indicating that some of the observed differences in size at age among populations are genetically based. Although populations of redside shiners with shorter growing seasons exhibited higher field growth rates than expected, the pattern of variation in individual growth rates among populations in a common environment was not consistent with either a countergradient variation model or a local adaptation model of growth.

Growth‐rate variation in brown trout in small neighbouring streams: evidence for density‐dependence?

The within‐ and among‐population variation in individual growth rate of brown trout Salmo trutta L. was studied in five small neighbouring streams (seven isolated populations) within a distance of 70 km in east Norway. Observed growth rate was only weakly correlated with predicted maximum growth rate based on laboratory models, and there was a significant interaction with site. A generalized linear model showed that growth rate was positively correlated with temperature, but also that growth rate decreased as the summer season progressed. This might indicate either a seasonal decline in food availability or appetite, or a change in energy allocation strategy. Growth rate decreased with increasing fish age, probably as an effect of sexual maturation of older fish, and differential allocation of protein and lipid among different size‐groups of brown trout. After adjusting for variation in temperature, season, and fish mass, there was still significant among‐site variation in growth rate. A significant part of this variation was due to variation in brown trout density and the presence or absence of Alpine bullhead Cottus poecilopus. Growth rate decreased with increasing brown trout density, and was lower in the presence than in the absence of Alpine bullhead after correcting for variation in brown trout density. This last result may indicate the presence of interspecific competition.

The relationship between food density and short term assimilation rates in Potamopyrgus antipodarum and Deleatidium sp.

Much of the variation in individual growth rates can be attributed to differences in individual feeding rates. Therefore, in order to build predictive models of individual, or population growth, the factors influencing an individual's feeding rate must be described. An important determinant of the feeding rate is the relationship between the local abundance of food and the individual's ingestion rate – otherwise known as the functional response. We determined functional responses for two species of invertebrate grazers: the snail Potamopyrgus antipodarum and the mayfly Deleatidium sp., by measuring their assimilation rate with increasing densities of radiolabelled periphyton. The assimilation rates were consistent with the Holling Type II or Michelis Menten functional response curve. The parameters of the functional response yielded estimates of the search area and handling time for the stream invertebrates. Our functional response data indicate that the half-saturation food density for P. antipodarum and Deleatidium sp. were ∼980 mg and 3200 mg AFDM m−2, respectively, suggesting that Deleatidium growth may be subject to food limitation more often than is P. antipodarum – despite the lower assimilation efficiency of the latter species.

Learning different regularities: the acquisition of noun plurals by German-speaking children

The acquisition of German noun plurals was examined on the basis of two-hour spontaneous speech samples from 6 children between 1;4 and 3;8 recorded every 5-6 weeks, and from 15 children recorded every 20 weeks. Adult speech was also sampled. Onset of use of plural forms was early, with variation in individual growth rates of type frequencies. Children used the different German plural markings from early on. Growth rates of type frequencies per different plural class corresponded to adult frequencies, with -n and -e plurals displaying fastest growth. At age 2;10 relative type frequencies per plural class differed from adult use, but not at age 3;8. Errors were produced from the beginning, with high error rates. Major error types, - n, - s, partial marking, and no marking did not differ in frequencies. Error patterns reflected the regularities of the German plural marking system.