Compensatory Growth Response Research Articles

Ration restriction, compensatory growth and pituitary growth hormone gene expression in Labeo rohita

An experiment to investigate the compensatory growth (CG) response of Labeo rohita was conducted in two phases: a first phase (6 weeks) in which triplicate groups of fish were subjected to feed restriction (5, 25, 50 and 75 % of satiation) or satiation feeding (control) and a second phase (6 weeks) of satiation feeding for all treatment groups. CG in body weight occurred in groups which were under moderate feed restriction (50–75 % of satiation) under phase 1, but more severe feed restrictions resulted in lower weight gain. Improved feed conversion ratio (FCR) (1.6 ± 0.05 and 1.9 ± 0.03) relative to control (2.1 ± 0.06) was observed in the fish that displayed CG following moderate feed restriction (50–75 % of satiation). At the end of the experiment, body moisture, lipid and protein content were not significantly different between moderately restricted fish and the control. After the first phase, there was no significant difference in the expression of pituitary growth hormone (GH) gene between groups, but at the end of the experiment, significantly lower GH expression was observed in the fish subjected to a restriction of 25 and 50 % of satiation during phase 1. Exploiting the ability of fishes to undergo CG in terms of weight gain and improved FCR without major changes in body composition can be considered as an effective management practice.

Overcompensation of circulating and local insulin-like growth factor-1 during catch-up growth in hybrid striped bass ( Morone chrysops × Morone saxatilis ) following temperature and feeding manipulations

Abstract Teleosts and other aquatic ectotherms have the ability to withstand prolonged periods of low water temperatures (cold-acclimation) and fasting, and can often respond with phases of accelerated (compensatory) growth when favorable conditions are restored. We assessed whether complete feed restriction prior to (24 °C, days 0–23) and/or during (14 °C, days 24–114) a simulated period of cold-acclimation could elicit episodes of compensatory growth (CG) and catch-up growth upon warm-up to 24 °C and satiation feeding (days 115–148). Control hybrid striped bass (HSB: Morone chrysops × Morone saxatilis ) were fed to satiation throughout the entire experiment under these temperature fluctuations. Compensatory growth and ultimately catch-up growth were achieved in groups of HSB that were deprived of feed during either the initial period at 24 °C (days 0–23), during the cold-acclimation period (14 °C, days 24–114), or during both of these periods (days 0–114). Further, it appears that HSB are better able to compensate for weight loss when skeletal length is not significantly compromised during the treatment period, which occurred in HSB feed restricted during cold-acclimation only. The most dramatic CG responses were defined by specific growth rates (SGRs) up to 4.2 times that of controls and were accompanied by hyperphagia and improvements in temporal and overall feed conversion. Levels of plasma insulin-like growth factor (IGF)-1 and muscle IGF-1 mRNA were significantly correlated to growth rate for all groups throughout the experiment (R 2 = 0.40, 0.23, respectively), with an overcompensation of both observed in HSB with the most elevated SGRs during the CG response. Interestingly, opposing trends were observed between muscle mRNA expression of growth hormone receptor (GHR)-1 and -2, with fasting at 24 °C and 14 °C resulting in depressed levels of GHR-1 and elevated levels of GHR-2 relative to controls. Levels of muscle myostatin (MSTN)-1 mRNA were significantly depressed in HSB fasted at 24 °C and/or 14 °C while MSTN-2 mRNA was lower following initial feed restriction at 24 °C. Likewise, levels of unprocessed pro-MSTN (precursor) and mature MSTN protein were both depressed in fasted fish at 24 °C. This study demonstrates that a previous period of feed restriction and cold-acclimation followed by realimentation at more favorable water temperatures produces a strong CG response and catch-up growth in fish. These studies also suggest that an overcompensation of circulating and local IGF-1 along with changes in MSTN mRNA and protein expression may contribute to accelerated growth rates characteristic of CG. Furthermore, our studies indicate that overall feed conversion can improve by as much as 30% with CG induced through temperature and feeding manipulations with no adverse effects on growth of HSB. This raises the possibility that CG protocols can improve production efficiency of HSB and other temperate teleosts in pond or tank culture.

Compensatory growth response and carcass quality after a period of lysine restriction in lean meat type barrows

Because research indicates that responses on dietary restrictions may depend on the gender of pigs, we examined the interaction between the lysine level in different feeding periods and the performance and carcass quality of barrows in a 2 × 2 factorial trial. In total 192 barrows were divided over 32 pens of six animals, and each pen was assigned to one of four dietary treatments: (1) high lysine levels in the growing (25–42 kg body weight [BW]), early finishing (42–73 kg BW) and in the late finishing period (73–110 kg BW) (Group HH); (2) high lysine levels in the growing and early finishing period, and low lysine level in the late finishing period (Group HL); (3) low lysine levels in the growing and early finishing period, and high lysine level in the late finishing period (Group LH); and (4) low lysine levels in all periods (Group LL). To obtain the high lysine diets, L-lysine, as well as L-threonine, DL-methionine and L-tryptophan, were added to the low-lysine diets. The low-lysine diets contained 20% (in growing) or 30% (in finishing) lysine less than the high-lysine diets. Feeding Diet LH increased the daily gain and decreased the feed-to-gain ratio in the subsequent late finishing phase (p < 0.05). Between start and slaughter, Group LL showed lower daily gain and a higher feed-to-gain ratio than the three other groups (p < 0.05). Carcass yield and lean meat percentage depended on sufficient amino acid (AA) provision in the late finishing feed (p < 0.05). Lowering the AA concentrations in the diet decreased the amount of lysine needed per kg gain and per kg lean gain (p < 0.05). An interaction between AA levels in the different phases and lean gain was observed, with Group LL showing lower lean gain than the other three groups (p < 0.05). This study shows that strategic provision of a sufficient amount of AAs either in the growing and early finishing period or in the late finishing period largely counteracts the negative effects of AA restriction in other feeding phases. Barrows can show compensatory growth after a period of AA restriction. The results of the present study show that a sufficient level of lysine in the late finishing feed rather than in the growing and early finishing feed is important for obtaining good carcass quality.

Compensatory growth strategies are affected by the strength of environmental time constraints in anuran larvae

Organisms normally grow at a sub-maximal rate. After experiencing a period of arrested growth, individuals often show compensatory growth responses by modifying their life-history, behaviour and physiology. However, the strength of compensatory responses may vary across broad geographic scales as populations differ in their exposition to varying time constraints. We examined differences in compensatory growth strategies in common frog (Rana temporaria) populations from southern and northern Sweden. Tadpoles from four populations were reared in the laboratory and exposed to low temperature to evaluate the patterns and mechanisms of compensatory growth responses. We determined tadpoles' growth rate, food intake and growth efficiency during the compensation period. In the absence of arrested growth conditions, tadpoles from all the populations showed similar (size-corrected) growth rates, food intake and growth efficiency. After being exposed to low temperature for 1 week, only larvae from the northern populations increased growth rates by increasing both food intake and growth efficiency. These geographic differences in compensatory growth mechanisms suggest that the strategies for recovering after a period of growth deprivation may depend on the strength of time constraints faced by the populations. Due to the costs of fast growth, only populations exposed to the strong time constraints are prone to develop fast recovering strategies in order to metamorphose before conditions deteriorate. Understanding how organisms balance the cost and benefits of growth strategies may help in forecasting the impact of fluctuating environmental conditions on life-history strategies of populations likely to be exposed to increasing environmental variation in the future.

Adaptive β-cell proliferation increases early in high-fat feeding in mice, concurrent with metabolic changes, with induction of islet cyclin D2 expression.

Type 2 diabetes (T2D) is caused by relative insulin deficiency, due in part to reduced β-cell mass (11, 62). Therapies aimed at expanding β-cell mass may be useful to treat T2D (14). Although feeding rodents a high-fat diet (HFD) for an extended period (3-6 mo) increases β-cell mass by inducing β-cell proliferation (16, 20, 53, 54), evidence suggests that adult human β-cells may not meaningfully proliferate in response to obesity. The timing and identity of the earliest initiators of the rodent compensatory growth response, possible therapeutic targets to drive proliferation in refractory human β-cells, are not known. To develop a model to identify early drivers of β-cell proliferation, we studied mice during the first week of HFD exposure, determining the onset of proliferation in the context of diet-related physiological changes. Within the first week of HFD, mice consumed more kilocalories, gained weight and fat mass, and developed hyperglycemia, hyperinsulinemia, and glucose intolerance due to impaired insulin secretion. The β-cell proliferative response also began within the first week of HFD feeding. Intriguingly, β-cell proliferation increased before insulin resistance was detected. Cyclin D2 protein expression was increased in islets by day 7, suggesting it may be an early effector driving compensatory β-cell proliferation in mice. This study defines the time frame and physiology to identify novel upstream regulatory signals driving mouse β-cell mass expansion, in order to explore their efficacy, or reasons for inefficacy, in initiating human β-cell proliferation.

Compensatory growth response of sailfin molly, Poecilia latipinna (Lesueur, 1821) to starvation and refeeding

Compensatory growth response and body composition of male sailfin molly, Poecilia latipinna subjected to short-term starvation and subsequent feeding were studied for 54 days. Four feeding schedules were used in this study: C, Control (were fed to apparent satiation throughout the experiment); T1, Treatment 1 (3 days Starvation and 6 days refeeding); T2, Treatment 2 (6 days Starvation and 12 days refeeding); T3, Treatment 3 (9 days Starvation and 18 days refeeding). At the end of the experiment, the starved fish gained a body weight comparable to that of the control fish. There were no differences in condition factor, specific growth rate and weight gain between the starved and control fish at the end of the experiment. Daily feed intake was significantly higher in T3 than that in the control. Short-term starvation did not influence protein, lipid and ash contents. Moisture content of T2 and T3 fish were significantly higher than those of T1 and control fish. The results indicated that complete compensation occurred in the starved fish and that this species can tolerate to short term starvation without any significant effects on growth and feeding performance.

Density-Dependent Compensatory Growth in Brown Trout (Salmo trutta) in Nature

Density-dependence is a major ecological mechanism that is known to limit individual growth. To examine if compensatory growth (unusually rapid growth following a period of imposed slow growth) in nature is density-dependent, one-year-old brown trout (Salmo trutta L.) were first starved in the laboratory, and then released back into their natural stream, either at natural or at experimentally increased population density. The experimental trout were captured three times over a one-year period. We found no differences in growth, within the first month after release (May-June), between the starved fish and the control group (i.e. no evidence of compensation). During the summer however (July-September), the starved fish grew more than the control group (i.e. compensation), and the starved fish released into the stream at a higher density, grew less than those released at a natural density, both in terms of weight and length (i.e. density-dependent compensation). Over the winter (October-April), there were no effects of either starvation or density on weight and length growth. After the winter, starved fish released at either density had caught up with control fish in body size, but recapture rates (proxy for survival) did not indicate any costs of compensation. Our results suggest that compensatory growth in nature can be density-dependent. Thus, this is the first study to demonstrate the presence of ecological restrictions on the compensatory growth response in free-ranging animals.

Compensatory growth following various time lengths of restricted feeding in rainbow trout (O ncorhynchus mykiss ) under summer conditions

This study was conducted to determine the effects of various time lengths of restricted feeding at 0.5% of body weight on compensatory growth (CG) in rainbow trout under summer conditions. Seven treatments with triplicate tanks consisted of control (C) fed to satiation over 98 days and the remainder being one (R1) to six (R6) weeks of restriction and then refeeding for the remaining 8 weeks of the experiment. At the end of the experiment R1 and R2 were able to catch up with C. Repeated measures anova suggested a convergence in body mass but not in body length (structure), whereas there was an association between mass and structural CG responses. Hyperphagia and transiently better food utilisation were main mechanisms of the observed CG. Organosomatic indices of the restricted groups were significantly reduced at the end of the restriction periods, but were restored to the control fish levels by the end of the refeeding period. There was a linear increase in body moisture and a decrease in lipid and lipid/lean body mass ratio with the severity of the restriction periods, but these trends vanished by the end of refeeding. The findings of the present experiment suggest that restricted feeding and the following realimentation to elicit CG as a management tool can be used in rainbow trout, but for no more than 2 weeks under summer conditions.

Endocrine regulation of compensatory growth in fish.

Compensatory growth (CG) is a period of accelerated growth that occurs following the alleviation of growth-stunting conditions during which an organism can make up for lost growth opportunity and potentially catch up in size with non-stunted cohorts. Fish show a particularly robust capacity for the response and have been the focus of numerous studies that demonstrate their ability to compensate for periods of fasting once food is made available again. CG is characterized by an elevated growth rate resulting from enhanced feed intake, mitogen production, and feed conversion efficiency. Because little is known about the underlying mechanisms that drive the response, this review describes the sequential endocrine adaptations that lead to CG; namely during the precedent catabolic phase (fasting) that taps endogenous energy reserves, and the following hyperanabolic phase (refeeding) when accelerated growth occurs. In order to elicit a CG response, endogenous energy reserves must first be moderately depleted, which alters endocrine profiles that enhance appetite and growth potential. During this catabolic phase, elevated ghrelin and growth hormone (GH) production increase appetite and protein-sparing lipolysis, while insulin-like growth factors (IGFs) are suppressed, primarily due to hepatic GH resistance. During refeeding, temporal hyperphagia provides an influx of energy and metabolic substrates that are then allocated to somatic growth by resumed IGF signaling. Under the right conditions, refeeding results in hyperanabolism and a steepened growth trajectory relative to constantly fed controls. The response wanes as energy reserves are re-accumulated and homeostasis is restored. We ascribe possible roles for select appetite and growth-regulatory hormones in the context of the prerequisite of these catabolic and hyperanabolic phases of the CG response in teleosts, with emphasis on GH, IGFs, cortisol, somatostatin, neuropeptide Y, ghrelin, and leptin.

Plant systemic induced responses mediate interactions between root parasitic nematodes and aboveground herbivorous insects.

Insects and nematodes are the most diverse and abundant groups of multicellular animals feeding on plants on either side of the soil–air interface. Several herbivore-induced responses are systemic, and hence can influence the preference and performance of organisms in other plant organs. Recent studies show that plants mediate interactions between belowground plant parasitic nematodes (PPNs) and aboveground herbivorous insects. Based on the knowledge of plant responses to pathogens, we review the emerging insights on plant systemic responses against root-feeding nematodes and shoot-feeding insects. We discuss the potential mechanisms of plant-mediated indirect interactions between both groups of organisms and point to gaps in our knowledge. Root-feeding nematodes can positively or negatively affect shoot herbivorous insects, and vice versa. The outcomes of the interactions between these spatially separated herbivore communities appear to be influenced by the feeding strategy of the nematodes and the insects, as well as by host plant susceptibility to both herbivores. The potential mechanisms for these interactions include systemic induced plant defense, interference with the translocation and dynamics of locally induced secondary metabolites, and reallocation of plant nutritional reserves. During evolution, PPNs as well as herbivorous insects have acquired effectors that modify plant defense responses and resource allocation patterns to their advantage. However, it is also known that plants under herbivore attack change the allocation of their resources, e.g., for compensatory growth responses, which may affect the performance of other organisms feeding on the plant. Studying the chemical and molecular basis of these interactions will reveal the molecular mechanisms that are involved. Moreover, it will lead to a better understanding of the ecological relevance of aboveground–belowground interactions, as well as support the development of sustainable pest management technologies.

Effect of Feeding–Fasting Cycles on Oxygen Consumption and Bioenergetics of Female Yellow Perch

AbstractWe measured growth and oxygen consumption of age‐1 yellow perch Perca flavescens subjected to ad libitum (control) or variable feeding cycles of 2 (i.e., 2 d of feed, 2 d of deprivation), 6, or 12 d for a 72‐d period. Individual, female yellow perch (initial weight = 51.9 ± 0.9 g [mean ± SE]) were stocked in 110‐L aquaria to provide six replicates per treatment and fed measured rations of live fathead minnow Pimephales promelas. Consumption, absolute growth rate, growth efficiency, and oxygen consumption were similar among feeding regimens. However, growth trajectories for fish on the 2‐d cycle were significantly lower than other feed–fast cycles. Hyperphagia occurred in all treatments. Bioenergetics model simulations indicated that consumption was significantly underestimated (t = 5.4, df = 4, P = 0.006), while growth was overestimated (t = −5.5, df = 4, P = 0.005) for fish on the 12‐d cycle. However, model errors detected between observed and predicted values were low, ranging from −10.1% to +7.8%. We found that juvenile yellow perch exhibited compensatory growth (CG), but none of the feed–fast treatments resulted in growth overcompensation. Likewise, we found no evidence that respiration rates varied with CG, implying that yellow perch bioenergetics models could be used to predict the effects of feeding history and CG response on food consumption and fish growth.

Effect of different feeding regimes on growth in juvenile Atlantic cod, Gadus morhua L.

Different feeding regimes (fasting/re-feeding and reduced feeding) were tested in a 131day trial with 1400 juvenile (mean±SE, 132g±1) Atlantic cod (Gadus morhua) in order to see if a compensatory growth response could be elicited, and if hyperplastic growth was stimulated during the compensatory growth phase. The Atlantic cod was fed in compliance with the following five feeding (F) fasting (S) schedules: the control group (Cont) was fed 100% according to a commercial growth table every day, the second group was fed 50% for two weeks and 100% for four weeks (S50), the third group was fed 100% every secondday and 0% the following day (ALT), the fourth group was fasted one week and fed 100% two weeks (S1W), and the last group was starved two weeks and fed 100% four weeks (S2W). At the termination of the experiment, the body mass of the fish in the control, ALT and S50 groups were significantly higher than the fish in S1W and S2W groups. The shorter fasting treatment groups (ALT and S50) consumed significantly less feed (42.9 and 37.5% less feed, respectively) compared to control whereas final weight did not differ between these three groups. Growth rate was highest in the S50 group (0.78%day−1), and lowest in the longer fasting period groups (S1W, 0.59%day−1 and S2W, 0.57%day−1). White muscle fibre diameter, white muscle fibre density and the percentage of small fibres below 25μm was measured in the control and S2W group and did not differ at any sample point during the experiment. There were minor differences between the groups in percentage distribution of fibre diameter classes. The results demonstrate that feeding costs can be drastically reduced without compromising biomass growth by using feeding on alternate days or by periodically fasting and re-feeding juvenile cod.

Quantitative analysis of compensatory and catch‐up growth in diverse taxa

1. 'Compensatory growth' and 'catch-up growth' are often used interchangeably to describe the faster than optimal growth that occurs following a period of dietary restriction in the development of many animals. Concerns about the statistical analysis of these studies have drawn attention to the risk of false detection in reports of compensatory and catch-up growth. 2. This study aims to quantify the degree to which these compensatory responses occur across the animal kingdom. In addition, this study distinguishes the two terms, 'compensatory growth' and 'catch-up growth', to clarify the fitness consequences of rapid growth. Compensatory growth refers to a faster than usual growth rate, while catch-up growth implies attainment of control size. 3. Eight meta-analyses and meta-regression analyses were conducted on data extracted from 88 papers, including 11 taxonomic classes. The results confirmed that both growth tactics (i.e. compensatory and catch-up growth) occur across a wide range of taxa and result in decreased direct fitness components. 4. Importantly, the meta-analytic methods used made it possible to identify the specific experimental techniques that most successfully promoted rapid growth after restriction and key differences in the responses of the four major groups (mammals, birds, fish and arthropods) to dietary restriction. Endotherms are more likely to show a compensatory growth response because of their determinate growth; in contrast, the indeterminate and saltatory growth tactics of fish and arthropods reduce the pressure to rapidly achieve a large size. 5. Among the first meta-analyses to be conducted in this field, this study provides valuable support for the premises of compensatory and catch-up growth and also discusses weaknesses in experimental design, and possible solutions, in compensatory growth research. For example, we recommend conducting the experiment within the most linear phase of an animal's growth to avoid analytical complications arising from size-dependent growth, and our results indicate that dietary dilution more closely resembles quantitative restriction than clutch size and intermittent feeding restriction methods when normal quantitative restriction is not possible.

Compensatory growth responses of seedlings of Pharbitis purpurea (Convulvulaceae) to tissue removal at different seeding depths of seeds

AbstractTissue damage to seedlings can limit their later growth, and the further effects may be greater with increasing seedling age. Seedlings, however, can minimize the effect of damage through compensatory growth. Seedlings of Pharbitis purpurea grow in frequently disturbed habitats and generally tolerate damage to leaf tissues. We evaluated the compensatory responses of the cotyledon to different levels of defoliation and their effect on seedling growth and development. We also examined the relationship between seeding depth and compensatory growth. We tested seven defoliation treatments with one or both cotyledons and/or the apical meristem of seedlings removed from seeds buried at a seeding depth of either 2 or 5 cm. We then measured 12 growth traits of the seedlings to assess development and growth compensation. The area, thickness, biomass, and longevity of the remaining cotyledon were also measured to quantify increased growth as result of treatment effects at both seeding depths. The results showed that defoliation reduced seedling height, belowground length, and total biomass significantly in subsequent growth in all treatments. However, defoliation treatments had direct positive impacts on growth at 2 cm depth compared with 5 cm depth. In contrast, the compensation of cotyledon area (Carea), biomass (Cmass), and thickness (Cthickness) was greater at 5 cm depth than at 2 cm depth. The results thus indicate that P. purpurea seedlings adopted a compensatory growth strategy to resist leaf loss and minimize any adverse effects using the remaining cotyledon. Increasing seeding depth can aggravate the compensatory growth of remain cotyledon after partial defoliation.

Compensatory growth response of European sea bass (Dicentrarchus labraxL.) under cycled starvation and restricted feeding rate

The compensatory growth response of the European sea bass (Dicentrarchus labrax) that faced cycling starvation and restricted ration was assessed. Juveniles (10.5 g) were stocked into 15 tanks at a density of 25 fish per tank. Five different feeding regimes were tested on triplicate groups of fish: CSatiation: control fed for 60 days without deprivation, CRestricted: 25% restricted feeding, S-R: 1 day starvation then 4 days CRestricted feeding, R-F: 1 day CRestricted feeding then 4 days CSatiation feeding, and, finally, S-F: 1 day starvation then 4 days CSatiation feeding. The specific growth rate of fish in the CSatiation (2.5 ± 0.06% day−1), S-F (2.5 ± 0.11% day−1) and R-F (2.4 ± 0.18% day−1) were significantly higher than that of CRestricted (2.2 ± 0.05% day−1) or S-R (2.0 ± 0.01% day−1). Fish in S-F group were able to achieve catching up with the CSatiation. There was no significant difference in feed conversion rates but R-F and S-F consumed approximately 34% more feed than CSatiation following the first re-feeding day. Although, the highest lipid content was observed in CSatiation (14.4%), S-R (33.3% dry matter) had the highest water content compared with the CSatiation and CRestricted (37.8% and 36.9% dry matter respectively). In conclusion, it may be concluded that sea bass has rapid response to cycling starvation/re-feeding and that a 25% restricted feeding ratio is insufficient to invoke a compensatory growth response in sea bass.

The effects of nutrient availability on tolerance to herbivory in a brown seaweed

Summary1. Plants can resist herbivory through mechanisms of resistance (traits that reduce the amount of tissue lost to herbivores) and tolerance (traits that reduce the negative effects of herbivory on plant fitness). The expression of such traits requires the allocation of plant resources, and consequently, trade‐offs between tolerance and resistance can occur in plants. For marine algae, little is currently known about the expression of tolerance, the relationship between tolerance and resistance, and the impact of resource availability on these traits.2. We manipulated herbivory (simulated or real) and nutrient availability in a series of laboratory and field experiments to test for tolerance to different types of damage under varying resource conditions in the brown alga Sargassum cf. podacanthoides. In addition to growth and photosynthetic responses of the alga, we measured the concentration of phlorotannins (secondary metabolites associated with resistance in many brown algae) to test for possible phenotypic trade‐offs between traits of tolerance and resistance. Furthermore, we assessed whether the limiting resource model (LRM) could predict algal tolerance under different resource conditions.3. Sargassum cf. podacanthoides expressed traits of tolerance (increased growth rates and reallocation of resources) that were specific to both the type and severity of herbivory encountered. Consistent with the predictions of the LRM, nitrogen enrichment did not alter the compensatory growth responses of the alga. Correlations between growth and phlorotannin content were variable, dependent on the measure of growth analysed, and only weakly influenced by nutrient availability. Nutrient enrichment, however, consistently changed within‐alga patterns of tissue composition and photosynthetic activity.4. Synthesis. Herbivory in the marine environment is often severe, and, similar to higher plants, tolerance to herbivory may be an important mechanism that maintains the productivity of marine algae. We demonstrate the potential applicability of the terrestrially derived LRM to predict algal tolerance under eutrophic conditions. Nutrient‐induced changes to within‐alga patterns of tissue composition should also be considered when evaluating the effects of nutrient enrichment on marine communities. Furthermore, as in higher plants, the relationships between traits of tolerance and resistance are variable in algae, and trade‐offs cannot be assumed.

Lack of compensatory growth response in gilthead seabream ( Sparus aurata) juveniles following starvation and subsequent refeeding

This study assessed the effect of short (one or two weeks) feed deprivation periods on compensatory growth response of gilthead seabream juveniles. A 10 weeks growth trial was performed and three different feeding protocols were tested: control group (C) fed to apparent satiation twice a day, 6 days a week, during the whole experimental period; one week or two weeks unfed groups (groups U1 and U2, respectively) and re-fed for the rest 8 weeks of the trial as the control group. Each feeding protocol was tested in triplicate groups of fish with an initial body weight of 58 g. Starvation for one or two weeks induced significant losses of body weight that, comparatively to the control group, totaled 18.5 and 30.5% for U1 and U2 group, respectively. An intense mobilization of liver lipid and glycogen was observed after 1 or 2 weeks of starvation while perivisceral lipids, eviscerated-body lipids and energy contents were only decreased in fish unfed for 2 weeks. During the subsequent re-feeding period no recovery of body weight lost was noticed in the previously unfed groups, and feed intake and feed efficiency were identical in all groups. No differences between slopes of growth trajectory between the control and unfed groups were noticed, indicating no convergence of growth of unfed groups towards that of control group. A total recovery of the whole-body composition, organ indices, liver and viscera composition was observed at the end of the trial. Overall, gilthead seabream juveniles were not able to compensate growth after the feed starvation imposed. Therefore, it can be concluded, that under the experimental conditions applied short – one or two weeks – feed restriction periods are not advisable as management strategy to be used in gilthead seabream production.

Effect of protein restriction with subsequent re-alimentation on compensatory growth of juvenile soft-shelled turtles (Pelodiscus sinensis)

The effects of protein restriction with subsequent re-alimentation on compensatory growth (CG) of juvenile soft-shelled turtles (Pelodiscus sinensis) were investigated. The turtles were fed five diets containing different crude protein content (T1: 29.24%, T2: 31.42%, T3: 34.19%, T4: 37.16%, C: 43.31%), while the energy content remained constant for 4 weeks (restriction period) and then re-fed a diet (43.31% crude protein) for 7 weeks (re-alimentation period). During the restriction period, feed conversion ratio (FCR) significantly increased in all protein-restricted groups (T1–T4) compared with the control group (C). At the end of the restriction period, body mass in groups T1 and T2 was significantly lower than that in the control group. During the re-alimentation phase, weekly body mass gain in group T1 was greater than that of the control from week 5 to week 10. FCR significantly decreased in group T1 compared with the control. No significant differences in final body mass between C and T1 groups were found at the end of the re-alimentation period. These results indicated that soft-shelled turtles receiving a diet in which protein was reduced from 43.31 to 29.24% (approximate 33% reduction) for 4 weeks achieved a 6 week complete CG response.

The NAB-Brk Signal Bifurcates at JNK to Independently Induce Apoptosis and Compensatory Proliferation

Apoptosis operates to eliminate damaged or potentially dangerous cells. This loss is often compensated by extra proliferation of neighboring cells. Studies in Drosophila imaginal discs suggest that the signal for the additional growth emanates from the dying cells. In particular, it was suggested that the initiator caspase Dronc mediates compensatory proliferation (CP) through Dp53 in wing discs. However, the exact mechanism that governs this CP remained poorly understood. We have previously shown that elimination of misspecified cells due to reduced Dpp signaling is achieved by the interaction of the co-repressor NAB with the transcriptional repressor Brk, which in turn induces Jun N-terminal kinase-dependent apoptosis. Here, we performed a systematic in vivo loss- and gain-of-function analysis to study NAB-induced death and CP. Our findings indicate that the NAB primary signal activates JNK, which in turn transmits two independent signals. One triggers apoptosis through the pro-apoptotic proteins Reaper and Hid, which in turn promote activation of caspases by the apoptosome components Ark and Dronc. The other signal induces CP in a manner that is independent of the death signal, Dronc, or Dp53. Once induced, the apoptotic pathway further activates a CP response. Our data suggest that JNK is the candidate factor that differentiates between apoptosis that involves CP and apoptosis that does not.

Partial pneumonectomy of telomerase null mice carrying shortened telomeres initiates cell growth arrest resulting in a limited compensatory growth response.

Telomerase mutations and significantly shortened chromosomal telomeres have recently been implicated in human lung pathologies. Natural telomere shortening is an inevitable consequence of aging, which is also a risk factor for development of lung disease. However, the impact of shortened telomeres and telomerase dysfunction on the ability of lung cells to respond to significant challenge is still largely unknown. We have previously shown that lungs of late generation, telomerase null B6.Cg-Terc(tm1Rdp) mice feature alveolar simplification and chronic stress signaling at baseline, a phenocopy of aged lung. To determine the role telomerase plays when the lung is challenged, B6.Cg-Terc(tm1Rdp) mice carrying shortened telomeres and wild-type controls were subjected to partial pneumonectomy. We found that telomerase activity was strongly induced in alveolar epithelial type 2 cells (AEC2) of the remaining lung immediately following surgery. Eighty-six percent of wild-type animals survived the procedure and exhibited a burst of early compensatory growth marked by upregulation of proliferation, stress response, and DNA repair pathways in AEC2. In B6.Cg-Terc(tm1Rdp) mice carrying shortened telomeres, response to pneumonectomy was characterized by decreased survival, diminished compensatory lung growth, attenuated distal lung progenitor cell response, persistent DNA damage, and cell growth arrest. Overall, survival correlated strongly with telomere length. We conclude that functional telomerase and properly maintained telomeres play key roles in both long-term survival and the early phase of compensatory lung growth following partial pneumonectomy.