Ali, M., Nicieza, A., Wootton, R. J. (2003). Compensatory growth in fishes: a response to growth depression. ? Fish and Fisheries, 4, (2), 147-190. Sponsorship: Royal Society of London ? Chinese Academy of Sciences Exchange awardCompensatory growth (CG) is a phase of accelerated growth when favourable conditions are restored after a period of growth depression. CG reduces variance in size by causing growth trajectories to converge and is important to fisheries management, aquaculture and life history analysis because it can offset the effects of growth arrests. Compensatory growth has been demonstrated in both individually housed and grouped fish, typically after growth depression has been induced by complete or partial food deprivation. Partial, full and over-compensation have all been evoked in fish, although over-compensation has only been demonstrated when cycles of deprivation and satiation feeding have been imposed. Individually housed fish have shown that CG is partly a response to hyperphagia when rates of food consumption are significantly higher than those in fish that have not experienced growth depression. The severity of the growth depression increases the duration of the hyperphagic phase rather than maximum daily feeding rate. In many studies, growth efficiencies were higher during CG. Changes in metabolic rate and swimming activity have not been demonstrated yet to play a role. Periods of food deprivation induce changes in the storage reserves, particularly lipids, of fish. Apart from the strong evidence for the restoration of somatic growth trajectories, CG is a response to restore lipid levels. Although several neuro-peptides, including neuropeptide-Y, are probably involved in the control of appetite, their role and the role of hormones, such as growth hormone (GH) and insulin-like growth factor (IGF), in the hyperphagia associated with CG are still unclear. The advantages of CG probably relate to size dependencies of mortality, fecundity and diet that are characteristic of teleosts. These size dependencies favour a recovery from the effects of growth depression if environmental factors allow. High growth rates may also impose costs, including adverse effects on future development, growth, reproduction and swimming performance. Hyperphagia may lead to riskier behaviour in the presence of predators. CG's evolutionary consequences are largely unexplored. An understanding of why animals grow at rates below their physiological capacity, an evaluation of the costs of rapid growth and the identification of the constraints on growth trajectories represent major challenges for life-history theory.Peer reviewe

The canonical model of sex-chromosome evolution predicts that, as recombination is suppressed along sex chromosomes, gametologs will progressively differentiate, eventually becoming heteromorphic. However, there are numerous examples of homomorphic sex chromosomes across the tree of life. This homomorphy has been suggested to result from frequent sex-chromosome turnovers, yet we know little about which forces drive them. Here, we describe an extremely fast rate of turnover among 28 species of Ranidae. Transitions are not random, but converge on several chromosomes, potentially due to genes they harbour. Transitions also preserve the ancestral pattern of male heterogamety, in line with the ‘hot-potato’ model of sex-chromosome transitions, suggesting a key role for mutation-load accumulation in non-recombining genomic regions. The importance of mutation-load selection in frogs might result from the extreme heterochiasmy they exhibit, making frog sex chromosomes differentiate immediately from emergence and across their entire length.

This study examines behavioral and physiological responses of juvenile Atlantic salmon (Salmo salar) adopting alternative life history patterns following a period of reduced growth. We manipulated the growth rates of premigratory and nonmigratory salmon by either reducing food availability or maintaining water at low temperature (4-6ЊC). A third group of fish was kept at ambient temperatures (12-14ЊC) and fed ad libitum to provide a control. Fish in both experimental groups exhibited compensatory growth after the manipulation period, even though the manipulations had slowed growth rather than caused mass loss. The timing and duration of compensatory growth were affected by the nature of the constraint and the developmental pathway adopted. Compensatory responses were more persistent and stronger among premigratory fish than among nonmigratory. Fish kept at low temperature did not accelerate growth immediately after transfer to ambient temperatures, but they subsequently grew faster than controls for up to 215 d after the end of the manipulation period. This mitigated the effects of the period of low temperatures, although by the end of the experiment they were still smaller than the controls. Fish on reduced rations showed no such time lag, and they grew significantly faster than controls immediately upon regaining access to full rations. These fish attained the same body size as controls by the end of the experiment (day 215). The manipulations caused fish to reduce their growth in mass more than their rate of skeletal growth, but all fish achieved ''normal'' mass for their length (as compared to controls) within a week of transfer to full feeding or ambient temperature. The main mechanism underlying compensatory growth rates was apparently the increase of intake rates, although this was insufficient to explain the strong compensation shown by temperature-manipulated fish in the presence of larger (and thus competitively superior) individuals. Instead these fish enhanced their growth rate by apparently increasing the duration of the daily feeding period, and avoiding aggressive interactions. We interpret the observed compensation for periods of slowed growth as indicating that growth rate is normally submaximal and can be increased if the animal has fallen below its expected trajectory; thus premigratory fish may have shown a greater compensation because survival rates during migration are strongly size-dependent.

Aim The climate variability hypothesis (CVH) states that a positive relationship may exist between the breadth of thermal tolerance range and the level of climatic variability experienced by taxa with increasing latitude, especially in terrestrial ectotherms. Under CVH, we expected to find a correspondence between both thermal tolerance limits (CTmax and CTmin), ambient extreme temperature and the range sizes of species. We examined the validity of these predictions in a lowland tropical and a temperate tadpole assemblage.Location Lowland Neotropics (Bahia, Brazil) and Palaearctic (Iberian Peninsula and North Africa).Method We employed phylogenetic eigenvector regression (PVR) and Pagel's lambda to analyse phylogenetic signals in CTmax and CTmin. We used phylogenetic regression analyses (PGLS) to test the relationships between thermal limits, range size and temperature predictors (measured at the macroscale and microhabitat levels) and phy-ANOVA to compare both the physiological traits and thermal regimen in both tropical and temperate assemblages.Results We documented moderate-to-strong phylogenetic signal in both heat and cold tolerance. Temperate-zone tadpoles had broader thermal tolerances than tropical ones. Thermal tolerance range was correlated with range sizes and was explained by seasonal thermal range predictors at the global scale. Both macro-and microclimate temperature variables provided the best predictive multivariate models of thermal limits at the global scale. Microclimatic predictors, however, were the main determinants of CTmax and CTmin variation at the local level of tropical and temperate communities respectively.Main conclusions Thermal tolerance range increases with latitude in tadpoles due to the higher increase in cold tolerance in temperate tadpoles. At the global scale, both macro-and microenvironment thermal information were reliable predictors of critical thermal limits and thermal tolerance range, as CVH predicts. However, thermal limits were best predicted by temperatures of the micro-habitat at the regional level, thus suggesting that physiological thermal boundaries may be governed by thermal selection.

Summary 1.Anurans exhibit high levels of growth-mediated phenotypic plasticity in age and size at metamorphosis. Although temperature and food quality exert a strong influence on larval growth, little is known about the interacting effects of these factors on age and size at metamorphosis. 2. Plasticity in growth rates, maximum larval mass, mass loss, larval period and size at metamorphosis was examined in Iberian Painted Frogs ( Discoglossus galganoi Capula, Nascetti, Lanza, Bullini & Crespo 1985) under different combinations of temperature and diet quality. 3. Temperature and diet had strong effects on the maximum size reached by tadpoles throughout the premetamorphic stages. Larval body mass varied inversely with temperature. The effect of diet depended on temperature; larvae fed on a 'carnivorous' diet (rich in protein and lipids) achieved a larger size than larvae offered an 'herbivorous' diet (rich in carbohydrates) at 17 ° C but not at 12 or 22 ° C. 4. Larval period was insensitive to diet composition, and varied only with temperature. Primarily the interacting effects of food quality and temperature affected size at metamorphosis. Size at metamorphosis varied inversely with temperature under the plant-and the animal-based diets. However, the carnivorous diet resulted in bigger metamorphs at 17 and 22 ° C, but did not influence final mass at 12 ° C. Maximum size over the larval period explained most of the variation in mass loss after the premetamorphic growing phase.

Juvenile brown trout Salmo trutta from natural populations reacted to the presence of piscivorous brown trout by increasing the use of refuges. In contrast, second-generation hatchery fish and the offspring of wild fish raised under hatchery conditions were insensitive to predation risk. The diel pattern of activity also differed between wild and hatchery brown trout. Second-generation hatchery fish were predominantly active during daytime regardless of risk levels. Wild fish, however, showed a shift towards nocturnal activity in the presence of predators. These findings emphasize the potential role of domestication in weakening behavioural defences. They support the idea that the behavioural divergence between wild and domesticated individuals can arise from a process of direct or indirect selection on reduced responsiveness to predation risk, or as a lack of previous experience with predators.

In salmonids, there seems to be a positive correlation between standard metabolic rate and growth rate under artificial rearing conditions. Several recent studies have suggested that phenotypic correlations between physiological or behavioural traits and developmental or life history responses might be common when assayed in low-complexity habitats but rare in those with a high degree of spatiotemporal complexity. This study provides the first test of the connection between metabolic and growth rates of juvenile brown trout (Salmo trutta) in natural streams. In two out of four streams, there was no relationship between metabolic rates and subsequent growth, whereas in the two others, growth and metabolic rates were negatively correlated. Furthermore, survival rates were either unaffected or negatively correlated with metabolic rates. These results reveal complex relationships between metabolic rate, growth, and environmental variability and suggest that (i) in the wild, negative selection on high metabolic rates may result from both juvenile mortality and reduced growth rates, (ii) the conclusions derived from laboratory experiments are not directly applicable to natural populations, and (iii) the correlations between metabolic rate and growth can prove useful after selection of the appropriate spatial and temporal scales.

In organisms with complex life cycles, environmentally induced plasticity across sequential stages can have important consequences on morphology and life history traits such as developmental and growth rates. However, previous research in amphibians and other ectothermic vertebrates suggests that some morphological traits are generally insensitive to environmental inductions. We conducted a literature survey to examine the allometric responses in relative hind leg length and head shape of post-metamorphic anuran amphibians to induced environmental (temperature, resource level, predation and desiccation risk) variation operating during the larval phase in 44 studies using 19 species. To estimate and compare plastic responses across studies, we employed both an index of plasticity and effect sizes from a meta-analysis. We found contrasting trait responses to different environmental cues. Higher temperatures increased development more than growth rate and induced smaller heads but not overall shifts in hind leg length. In contrast, an increment in resource availability increased growth more than development, with a parallel increase in hind leg length but no change in head shape. Increases in predation risk decreased both development and growth rates and slightly reduced relative hind leg length, but there was no change in head shape. Pond desiccation induced quick development and low growth rates, with no changes in morphology. Across environments, both hind leg and head shape plasticity were positively correlated with growth rate plasticity. However, plasticity of developmental rate was only correlated with head shape plasticity. Overall, these results suggest that environmental trends predicted by global warming projections, such as increasing pond temperature and accelerating pond desiccation, will significantly influence hind leg and head morphology in metamorphic frogs, which may affect performance and, ultimately, fitness.