Statistical analysis of structural compensatory growth: how can we reduce the rate of false detection?

Short-term starvation at different feeding regimes on appetite responses, feeding utilization and physiological indices, of red hybrid tilapia (Oreochromis mossambicus × Oreochromis niloticus) fingerlings reared in brackish water

A 42 day factorial trial (3x2) was designed to evaluate the effect of short-term starvation with different feeding frequencies on performance, feed utilization, physiological status and appetite responses of red hybrid tilapia fingerlings. Eighteen plastic tanks with a capacity of (55 L) were used to accomplish this work. Fingerlings with an average initial weight of 23 g ± 0.2 (SE) were randomly stocked at a rate of 8 fingerlings/aquarium. Six groups were designated as the following: II/ED: fish was fed twice every day; IV/ED: fish fed four times every day; II/EOD: fish fed twice every other day (alternate-day feeding or one day of feeding followed by another of fasting); IV/EOD: was fed four times every other day; II/EO3D: fish fed twice every other three days (three day of feeding followed by another of fasting) and IV/EO3D: fish fed four times every other three days. Fish were fed on commercial diets 30 % protein (4 % of biomass). Results showed insignificant differences between fish fed every other day and those fed every day in some growth indicators. In the same trend, the interaction between feed deprivation and feeding frequency cleared that fingerlings of IV/EOD did not significantly differ with those fed every day in growth indices. Moreover this treatment was the best in feed conversion efficiency and several physiological indicators.

Changes in weight gain, digestive and metabolic enzyme activities in Labeo rohita fingerlings in response to multiple stress exposure and dietary nutraceutical

A feeding trial was conducted for 4 months to study the effect of a nutraceutical conglomerate at different levels (0, 0.1, and 0.5%) on stress-exposed (high stocking density, H and feed restriction, R) Labeo rohita fingerlings. Six isonitrogenous diets with a crude protein of 35% were prepared for the different treatments, viz. THR0, THR1, THR5, TNS0, TNS1 and TNS5. Stress significantly reduced the weight gain and feeding of 0.1% nutraceutical improved it in both stress-exposed and non-exposed groups from 3 months onwards. Two-and three-month stress-exposed groups exhibited lower (p < 0.05) protease activity, while amylase activity was significantly higher in 2-month stress-exposed groups. Higher lipase activity was found in stress-exposed groups irrespective of the duration of stress. Higher serum glutathione peroxidase (GPx), aspartate aminotransferase (AST), alanine aminotransferase (ALT), and hepatic and muscle lactate dehydrogenase (LDH) activities were observed in the THR0 groups; however, THR1 showed a lower activity of these enzymes. Increased malate dehydrogenase (MDH) and glucose-6-phosphate dehydrogenase (G6PDH) activity was recorded in the 1st and 2nd months stress-exposed groups. However, THR1 group exhibited a reduced MDH and G6PDH activity compared to THR0 group in 1st and 2nd months. Hence, it can be concluded that the duration of multiple stress exposure adversely affected the digestive and metabolic enzymes activities and feeding of 0.1% nutraceutical conglomerates could restore the activities of digestive and metabolic enzymes in rohu fingerlings.

Associations between metabolic traits and growth rate in brown trout (Salmo trutta) depend on thermal regime

Metabolism defines the energetic cost of life, yet we still know relatively little about why intraspecific variation in metabolic rate arises and persists. Spatio-temporal variation in selection potentially maintains differences, but relationships between metabolic traits (standard metabolic rate (SMR), maximum metabolic rate (MMR), and aerobic scope) and fitness across contexts are unresolved. We show that associations between SMR, MMR, and growth rate (a key fitness-related trait) vary depending on the thermal regime (a potential selective agent) in offspring of wild-sampled brown trout from two populations reared for approximately 15 months in either a cool or warm (+1.8°C) regime. SMR was positively related to growth in the cool, but negatively related in the warm regime. The opposite patterns were found for MMR and growth associations (positive in warm, negative in the cool regime). Mean SMR, but not MMR, was lower in warm regimes within both populations (i.e. basal metabolic costs were reduced at higher temperatures), consistent with an adaptive acclimation response that optimizes growth. Metabolic phenotypes thus exhibited a thermally sensitive metabolic 'floor' and a less flexible metabolic 'ceiling'. Our findings suggest a role for growth-related fluctuating selection in shaping patterns of metabolic variation that is likely important in adapting to climate change.

Growth, body condition and contest performance after early-life food restriction in a long-lived tropical fish

Adverse conditions during early life can cause lasting body size deficits with effects on social and sexual competition, while an accelerated growth response can allow animals to catch up in body size but can be physiologically costly as well. How animals balance growth deficits and growth compensation is predicted to depend on the effects of each on lifetime fitness. We investigated the effects of experimental early-life food restriction on growth, body condition, and adult contest competition in a cichlid fish (Tropheus sp.). Their longevity and aseasonal breeding suggest that, with view on lifetime reproductive success, temporarily growth-restricted Tropheus should rather invest extra time in reaching competitive body size than risk the potential costs of accelerated growth. However, size-selective predation pressure by gape size-limited piscivores may have favored the evolution of an accelerated growth response to early-life delays. Experimentally food-restricted fish temporarily reduced their growth rate compared to a control group, but maintained their body condition factor at the control level throughout the 80-week study period. There was no evidence for an accelerated growth response following the treatment, as the food-restricted fish never exceeded the size-specific growth rates that were measured in the control group. Food-restricted fish caught up with the body size of the control group several months after the end of the treatment period and were as likely as control fish to win size-matched contests over territories. Regardless of feeding regime, there were sex-specific differences in growth rates and in the trajectories of condition factors over time. Females grew more slowly than males but maintained their condition factors at a high level throughout the study period, whereas the males' condition factors declined over time. These differences may reflect sex-specific contributions of condition and body size to adult fitness that are associated with female mouthbrooding and male competition for breeding territories.

Morphological and physiological consequences of a dietary restriction during early life in bats

Early life adverse conditions can have major consequences on an individual’s life history traits. Oxidative stress has been hypothesized to be one main mechanism underlying the negative consequences of early life adverse conditions. To test this hypothesis, we restricted the food availability of Seba’s short-tailed bat (Carollia perspicillata) mothers of unweaned pups for 10 days, followed by ad libitum provisioning. We also had a control, unrestricted group. We explored the morphological consequences of dietary restriction during early life by measuring growth rate. We also measured four markers of blood oxidative balance during growth. We assessed the level of cortisol, and its inactive form cortisone, in the hair of the pups at the end of growth. Finally, we monitored survival during the first year. Food restriction triggered a slowdown in growth followed by catch-up growth when ad libitum feeding was restored which did not lead to full compensation in size or mass compared to control individuals. We found that higher growth rate was associated with elevated oxidative damage, suggesting an oxidative cost to growth. However, we found no clear evidence for physiological costs specific to the catch-up growth. Survival after a year was not impacted by the treatment, the oxidative balance or the level of glucocorticoids at the end of growth. In conclusion, our results show that individuals were able to efficiently mitigate the short-term consequences of adverse early life conditions. However, consequences might arise in the long-term, and could impact reproductive success or lifespan.

Early life starvation has stronger intra-generational than transgenerational effects on key life-history traits and consumption measures in a sawfly

Resource availability during development shapes not only adult phenotype but also the phenotype of subsequent offspring. When resources are absent and periods of starvation occur in early life, such developmental stress often influences key life-history traits in a way that benefits individuals and their offspring when facing further bouts of starvation. Here we investigated the impacts of different starvation regimes during larval development on life-history traits and measures of consumption in the turnip sawfly, Athalia rosae (Hymenoptera: Tenthredinidae). We then assessed whether offspring of starved and non-starved parents differed in their own life-history if reared in conditions that either matched that of their parents or were a mismatch. Early life starvation effects were more pronounced within than across generations in A. rosae, with negative impacts on adult body mass and increases in developmental time, but no effects on adult longevity in either generation. We found some evidence of higher growth rates in larvae having experienced starvation, although this did not ameliorate the overall negative effect of larval starvation on adult size. However, further work is necessary to disentangle the effects of larval size and instar from those of starvation treatment. Finally, we found weak evidence for transgenerational effects on larval growth, with intra-generational larval starvation experience being more decisive for life-history traits. Our study demonstrates that intra-generational effects of starvation are stronger than transgenerational effects on life-history traits and consumption measures in A. rosae.

Carry-over effects of early thermal conditions on somatic and germline oxidative damages are mediated by compensatory growth in sticklebacks

Most studies of climate change impacts focus on the effects of summer temperatures, which can immediately impact fitness of breeders, but winter temperatures are expected to have a greater impact on development and growth of animals with long-lasting consequences. Exposure to warmer temperatures can increase cellular oxidative damage in ectotherms. Yet, it is unknown whether thermal stress during early life has prolonged effects on oxidative status during adulthood. In an experiment using F1 fish originated from a wild three-spined stickleback population at the southern edge of its European distribution, we examined whether experimental thermal conditions experienced in winter had carry-over effects on oxidative status and telomere length, a marker of accumulated stress, in the soma and germline during adulthood. For this, oxidative DNA damage, enzymatic antioxidant activities and telomere length were measured three months after the termination of the temperature manipulation. In addition, we tested whether such delayed effects, if any, were due to individuals' compensatory growth after experiencing unfavourable growth conditions in winter. Warm acclimation during winter induced increased levels of oxidative DNA damage in muscle and sperm and increased enzymatic antioxidant defences in muscle during the breeding season. Telomere length of adult fish was not influenced by thermal conditions experienced during early life. Winter temperature manipulation influenced fish to alter the temporal pattern of growth trajectories across the juvenile and adult stages. Fish reared in warm winter conditions grew at a slower rate than the controls during the period of temperature manipulation then accelerated body mass gain to catch up during the breeding season. Faster somatic growth during the breeding season incurred a higher cost in terms of oxidative damage in the warm-treated individuals. For the first time, we experimentally show the long-lasting detrimental effects of thermal stress on and the positive link between catch-up growth and oxidative DNA damage in the soma and germline. Winter temperature increases due to climate change can reduce fertility and survival of fish by inducing catch-up growth. The detrimental effects of winter climate change may accumulate across generations through the pre-mutagenic DNA damage in the germline.

Digestive and locomotor capacity show opposing responses to changing food availability in an ambush predatory fish

Metabolic rates vary widely within species, but little is known about how variation in the ‘floor’ [i.e. standard metabolic rate (SMR) in ectotherms] and ‘ceiling’ [maximum metabolic rate (MMR)] for an individual's aerobic scope (AS) are linked with digestive and locomotor function. Any links among metabolic traits and aspects of physiological performance may also be modulated by fluctuations in food availability. This study followed changes in SMR, MMR, and digestive and locomotor capacity in southern catfish (Silurus meridionalis) throughout 15 days of food deprivation and 15 days of refeeding. Individuals downregulated SMR during food deprivation and showed only a 10% body mass decrease during this time. Whereas critical swim speed (U_crit) was robust to food deprivation, digestive function decreased after fasting with a reduced peak oxygen uptake during specific dynamic action (SDA) and prolonged SDA duration. During refeeding, individuals displayed rapid growth and digestive function recovered to pre-fasting levels. However, refed fish showed a lower U_crit than would be expected for their increased body length and in comparison to measures at the start of the study. Reduced swimming ability may be a consequence of compensatory growth: growth rate was negatively correlated with changes in U_crit during refeeding. Southern catfish downregulate digestive function to reduce energy expenditure during food deprivation, but regain digestive capacity during refeeding, potentially at the cost of decreased swimming performance. The plasticity of maintenance requirements suggests that SMR is a key fitness trait for in this ambush predator. Shifts in trait correlations with food availability suggest that the potential for correlated selection may depend on context.

Summary: Southern catfish downregulate digestive function and metabolic rate during food deprivation, but regain digestive capacity during refeeding, potentially at the cost of decreased swimming performance.

Alternative competition-induced digestive strategies yield equal growth, but constrain compensatory growth in red-eyed treefrog larvae

Compensatory growth is well documented across taxa and provides a fitness advantage to animals who would otherwise reach a smaller reproductive size. We investigated the role of competition-induced gut plasticity in facilitating a compensatory response in red-eyed treefrog larvae. We reared larvae at low, medium, and high densities with different per capita resources, environments known to produce individuals with long and short guts. We then transferred larvae to competitively equal environments to determine if longer guts provided an advantage when resources became available. We predicted that larvae from higher densities with longer guts would exhibit hyperphagia and compensatory growth. We measured growth over 1-week, as well as the time to and size at metamorphosis. To assess mechanisms underlying the growth response, we measured diet transit time and intake. Growth, development, and metamorph snout-vent length did not differ between larvae with long and short guts. Instead, different gut lengths were associated with dramatically different feeding strategies. Medium- and high-density larvae fed at rates far below what their guts could accommodate. However, the combination of low intake and longer guts extended diet transit times, presumably increasing digestibility. This unexpected strategy achieved the same results as that of low-density larvae, which ate twice as much food, but passed it more quickly through a shorter gut. The lack of a compensatory response may be attributed to the costs of accelerated growth and weak seasonal time constraints in the tropics. This suggests that although compensatory growth is widespread among animals, expression of the response may vary with environmental context. J. Exp. Zool. 323A: 778-788, 2015. © 2015 Wiley Periodicals, Inc.

Telomere dynamics in wild brown trout: effects of compensatory growth and early growth investment

After a period of food deprivation, animals often respond with a period of faster than normal growth. Such responses have been suggested to result in decreased chromosomal maintenance, which in turn may affect the future fitness of an individual. Here, we present a field experiment in which a food deprivation period of 24 days was enforced on fish from a natural population of juvenile brown trout (Salmo trutta) at the start of the high-growth season in spring. The growth of the food-deprived fish and a non-deprived control group was then monitored in the wild during 1 year. Fin tissue samples were taken at the start of the experiment and 1 year after food deprivation to monitor the telomere dynamics, using reduced telomere length as an indicator of maintenance cost. The food-deprived fish showed partial compensatory growth in both mass and length relative to the control group. However, we found no treatment effects on telomere dynamics, suggesting that growth-compensating brown trout juveniles are able to maintain their telomeres during their second year in the stream. However, body size at the start of the experiment, reflecting growth rate during their first year of life, was negatively correlated with change in telomere length over the following year. This result raises the possibility that rapid growth early in life induces delayed costs in cellular maintenance.

Population divergence in compensatory growth responses and their costs in sticklebacks

Compensatory growth (CG) may be an adaptive mechanism that helps to restore an organisms’ growth trajectory and adult size from deviations caused by early life resource limitation. Yet, few studies have investigated the genetic basis of CG potential and existence of genetically based population differentiation in CG potential. We studied population differentiation, genetic basis, and costs of CG potential in nine-spined sticklebacks (Pungitius pungitius) differing in their normal growth patterns. As selection favors large body size in pond and small body size in marine populations, we expected CG to occur in the pond but not in the marine population. By manipulating feeding conditions (viz. high, low and recovery feeding treatments), we found clear evidence for CG in the pond but not in the marine population, as well as evidence for catch-up growth (i.e., size compensation without growth acceleration) in both populations. In the marine population, overcompensation occurred individuals from the recovery treatment grew eventually larger than those from the high feeding treatment. In both populations, the recovery feeding treatment reduced maturation probability. The recovery feeding treatment also reduced survival probability in the marine but not in the pond population. Analysis of interpopulation hybrids further suggested that both genetic and maternal effects contributed to the population differences in CG. Hence, apart from demonstrating intrinsic costs for recovery growth, both genetic and maternal effects were identified to be important modulators of CG responses. The results provide an evidence for adaptive differentiation in recovery growth potential.

Effects of variation in nutrition on male morph development in the bulb mite Rhizoglyphus robini

In male dimorphic species, growth influences morph expression and thereby the reproductive success of males. However, how variation in nutritional conditions affects male morph development and whether males can compensate for lost growth is poorly known. Here, we performed an experiment where males of the bulb mite (Rhizoglyphus robini)-which are fighters, able to kill other mites, or benign scramblers-were offered high quality food during the larval stage, but food of high or low quality during the protonymph and tritonymph (=final) stage. When food quality was low during the latter two stages, males matured smaller, later and were more likely to be a scrambler than when food quality was high. We found no evidence for compensatory growth: when males had low quality food only during the protonymph stage, they matured at the same age, but grew at a slower rate and matured at a smaller size than males that had high quality food throughout ontogeny. Furthermore, males that experienced this transient period of low food quality were less likely to mature as a fighter. Interestingly, scrambler increase in body size during the protonymph and tritonymph stages was always lower than that of fighters. Given the strong link between adult size and fitness, combined with the different development times and life histories of the male morphs, the lack of ability to compensate for a transient period of food deprivation during ontogeny is likely to have consequences for the dynamics of bulb mite populations.

Growth trajectory influences temperature preference in fish through an effect on metabolic rate

Most animals experience temperature variations as they move through the environment. For ectotherms, in particular, temperature has a strong influence on habitat choice. While well studied at the species level, less is known about factors affecting the preferred temperature of individuals; especially lacking is information on how physiological traits are linked to thermal preference and whether such relationships are affected by factors such feeding history and growth trajectory.

This study examined these issues in the common minnow Phoxinus phoxinus, to determine the extent to which feeding history, standard metabolic rate (SMR) and aerobic scope (AS), interact to affect temperature preference.

Individuals were either: 1) food deprived (FD) for 21 days, then fed ad libitum for the next 74 days; or 2) fed ad libitum throughout the entire period. All animals were then allowed to select preferred temperatures using a shuttle-box, and then measured for SMR and AS at 10 °C, estimated by rates of oxygen uptake. Activity within the shuttle-box under a constant temperature regime was also measured.

In both FD and control fish, SMR was negatively correlated with preferred temperature. The SMR of the FD fish was increased compared with the controls, probably due to the effects of compensatory growth, and so these growth-compensated fish preferred temperatures that were on average 2·85 °C cooler than controls fed a maintenance ration throughout the study. Fish experiencing compensatory growth also displayed a large reduction in activity. In growth-compensated fish and controls, activity measured at 10 °C was positively correlated with preferred temperature.

Individual fish prefer temperatures that vary predictably with SMR and activity level, which are both plastic in response to feeding history and growth trajectories. Cooler temperatures probably allow individuals to reduce maintenance costs and divert more energy towards growth. A reduction in SMR at cooler temperatures, coupled with a decrease in spontaneous activity, could also allow individuals to increase surplus AS for coping with environmental stressors. In warming climates, however, aquatic ectotherms could experience frequent fluctuations in food supply with long-lasting effects on metabolic rate due to compensatory growth, while simultaneously having limited access to preferred cooler habitats.

Molecular characterization and expression patterns of myogenin in compensatory growth of Megalobrama amblycephala

Myogenin (myog) is a muscle-specific basic helix-loop-helix (bHLH) transcription factor that plays an essential role in regulating skeletal muscle development and growth. To investigate molecular characterization of myog and the effect of starvation/refeeding on the gene expression, we isolated the myog cDNA sequence and analyzed the expression patterns using quantitative real-time polymerase chain reaction in Megalobrama amblycephala. Sequence analysis indicated that M. amblycephala myog shared an analogous structure with the highly conserved His/Cys-rich, bHLH and C-terminal helix III domains with other vertebrates. Sequence alignment and phylogenetic tree showed that M. amblycephala myog had the highest identity with the homologues of Ctenopharyngodon idella and Cyprinus carpio. Spatio-temporal expression patterns revealed that myog mRNA levels at the segmentation period and 12 h post-hatching (hph) were significantly higher than at other development stages (P<0.05). Furthermore, the highest myog expression level was predominantly observed in white muscle compared with the other types of muscle. Fish body weight continuously decreased during 21-day starvation and then significantly increased after 7days of refeeding and reached the similar level to the control at 21days of refeeding, indicating that the pattern of complete compensatory growth possibly occurred in M. amblycephala; meanwhile, the relative somatic growth rate after refeeding was also dramatically higher than the control group. In addition, the myog expression decreased during 21days of starvation and then exhibited a strong rebound effect after 7days of refeeding and subsequently declined gradually to the control level by 21days of refeeding.

Fast growers sprint slower: effects of food deprivation and re-feeding on sprint swimming performance in individual juvenile European sea bass

While many ectothermic species can withstand prolonged fasting without mortality, food-deprivation may have sublethal effects of ecological importance, including reductions in locomotor ability. Little is known about how such changes in performance in individual animals are related either to mass loss during food-deprivation or growth rate during re-feeding. This study followed changes in the maximum sprint swimming performance of individual European sea bass Dicentrarchus labrax throughout 45 days of food-deprivation and 30 days of re-feeding. Maximum sprint speed did not show a significant decline until 45 days of food deprivation. Among individuals, the reduction in sprinting speed at this time was not related to mass loss. After 30 days of re-feeding, mean sprinting speed had recovered to match that of control fish. Among individuals, however, maximum sprinting speed was negatively correlated with growth rate after the resumption of feeding. This suggests that the rapid compensatory growth that occurs during re-feeding after a prolonged fast carries a physiological cost in terms of reduced sprinting capacity, the extent of which shows continuous variation among individuals in relation to growth rate. The long-term repeatability of maximum sprint speed was low when fish were fasted or fed a maintenance ration, but was high among control fish fed to satiation. Fish that had been previously food deprived continued to show low repeatability in sprinting ability even after the initiation of ad libitum feeding, probably stemming from variation in compensatory growth among individuals and its associated negative effects on sprinting ability. Together these results suggest that food limitation can disrupt hierarchies of maximum sprint performance within populations. In the wild, the cumulative effects on locomotor capacity of fasting and re-feeding could lead to variable survival among individuals with different growth trajectories following a period of feed deprivation.

And the last shall be first: heterochrony and compensatory marine growth in sea trout (Salmo trutta)

Early juvenile growth is a good indicator of growth later in life in many species because larger than average juveniles tend to have a competitive advantage. However, for migratory species the relationship between juvenile and adult growth remains obscure. We used scale analysis to reconstruct growth trajectories of migratory sea trout (Salmo trutta) from six neighbouring populations, and compared the size individuals attained in freshwater (before migration) with their subsequent growth at sea (after migration). We also calculated the coefficient of variation (CV) to examine how much body size varied across populations and life stages. Specifically, we tested the hypothesis that the CV on body size would differ between freshwater and marine environment, perhaps reflecting different trade-offs during ontogeny. Neighbouring sea trout populations differed significantly in time spent at sea and in age-adjusted size of returning adults, but not on size of seaward migration, which was surprisingly uniform and may be indicative of strong selection pressures. The CV on body size decreased significantly over time and was highest during the first 8 months of life (when juvenile mortality is highest) and lowest during the marine phase. Size attained in freshwater was negatively related to growth during the first marine growing season, suggesting the existence of compensatory growth, whereby individuals that grow poorly in freshwater are able to catch up later at sea. Analysis of 61 datasets indicates that negative or no associations between pre- and post-migratory growth are common amongst migratory salmonids. We suggest that despite a widespread selective advantage of large body size in freshwater, freshwater growth is a poor predictor of final body size amongst migratory fish because selection may favour growth heterochrony during transitions to a novel environment, and marine compensatory growth may negate any initial size advantage acquired in freshwater.

Growth pattern responses to photoperiod across latitudes in a northern damselfly

Background

Latitudinal clines in temperature and seasonality impose strong seasonal constraints on ectotherms. Studies of population differentiation in phenotypic plasticity of life history traits along latitudinal gradients are important for understanding how organisms have adapted to seasonal environments and predict how they respond to climate changes. Such studies have been scarce for species with a northern distribution.

Methodology/Principle Finding

Larvae of the northern damselfly Coenagrion johanssoni originating from semivoltine central, partivoltine northern, and partivoltine northernmost Swedish populations were reared in the laboratory. To investigate whether larvae use photoperiodic cues to induce compensatory growth along this latitudinal gradient, larvae were reared under two different photoperiods corresponding to a northern and southern latitude. In addition, field adult size was assessed to test the strength of possible compensatory growth mechanisms under natural conditions and hatchling size was measured to test for maternal effects. We hypothesized that populations originating from lower latitudes would be more time constrained than high-latitude populations because they have a shorter life cycle. The results showed that low-latitude populations had higher growth rates in summer/fall. In general northern photoperiods induced higher growth rates, but this plastic response to photoperiod was strongest in the southernmost populations and negligible in the northernmost population. During spring, central populations grew faster under the southern rather than the northern photoperiod. On the other hand, northern and northernmost populations did not differ between each other and grew faster in the northern rather than in the southern photoperiod. Field sampled adults did not differ in size across the studied regions.

Conclusion/Significance

We found a significant differentiation in growth rate across latitudes and latitudinal difference in growth rate response to photoperiod. Importantly, growth responses measured at a single larval developmental stage in one season may not always generalize to other developmental stages or seasons.

Catch-up and targeted growth following variable duration protein restriction: effects on bone and body mass

Protein malnutrition leads to growth retardation that can be reversed through catch-up growth, once normative nutrition is restored. Because growth is a dynamic process, catch-up capacity is likely influenced by the maturity of the animal and/or the duration of the insult, in addition to the type of insult experienced. We compared length of malnutrition, sexual dimorphism, body mass, and skeletal growth. Eighty Rattus norvegicus were divided into 10 treatment groups (five diets; male and female) and followed for more than 1 year. At weaning, animals were placed on either a control or low-protein isocaloric diet. Three experimental groups were switched to the control diet at 40, 60, or 90 days. Beginning with 21 days of age, animals were weighed daily and radiographed throughout the study. To determine the presence of catch-up growth, growth rates (GRs) were calculated (linear regression) for 20-day time spans before and after diet changes and compared among treatment groups. Targeted growth was measured as final size or as the coefficient of variation with age. These results show that 1) protein-restricted animals experience catch-up growth with dietary rehabilitation; 2) for females, catch-up GRs are proportional to GRs in control animals at the same age as the timing of dietary rehabilitation but not for males; and 3) targeted growth was observed in some, but not all, aspects of anatomy. The length of the tibia and humerus was indistinguishable from controls, regardless of length of malnutrition or gender, whereas the ulna and male body mass exceeded control sizes. Although most measures decreased in variation with ontogeny, the tibia failed to do so. These results support a complex biological regulation of catch-up and targeted growth. The implications for selection are that flexible and responsive developmental trajectories may have an advantage over those programed into a single size.

Juvenile compensatory growth has negative consequences for reproduction in Trinidadian guppies (Poecilia reticulata)

Compensatory or 'catch-up' growth may be an adaptive mechanism that buffers the growth trajectory of young organisms from deviations caused by reduced food availability. Theory generally assumes that rapid juvenile compensatory growth impacts reproduction only through its positive effects on age and size at maturation, but potential reproductive costs to juvenile compensatory growth remain virtually unexplored. We used a food manipulation experiment to examine the reproductive consequences of compensatory growth in Trinidadian guppies (Poecilia reticulata). Compensatory growth did not affect adult growth rates, litter production rates or investment in offspring size. However, compensatory growth had negative effects on litter size, independent of the effects of female body length, resulting in a 20% decline in offspring production. We discuss potential mechanisms behind this observed cost to reproduction.