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.