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Reactions to stress vary between individuals, and physiological and behavioral responses tend to be associated in distinct suites of correlated traits, often termed stress coping styles. A connection between physiology, behavior, and cognition was recently demonstrated in strains of rainbow trout (Oncorhynchus mykiss) selected for consistently high or low cortisol responses to stress. Compared to high-responsive (HR) fish the low-responsive (LR) strain display better retention of a conditioned response, and tend to show proactive behavior such as enhanced aggression, social dominance, and rapid resumption of feed intake in new environments. Marked differences between HR and LR trout in brain monoamine neurochemistry have also been reported. In line with these studies, experiments with the lizard Anolis carolinensis reveal connections between monoaminergic activity in limbic structures, proactive behavior in novel environments, and the establishment of social status via agonistic behavior.Together these observations suggest that within-species diversity of behavioral and cognitive correlates of stress responsiveness is maintained by natural selection over a wide range of animal groups. This diversity may underlie several seemingly different phenomena such as stress coping style, behavioral syndromes, and animal personalities.

Marine life is controlled by multiple physical and chemical drivers and by diverse ecological processes. Many of these oceanic properties are being altered by climate change and other anthropogenic pressures. Hence, identifying the influences of multifaceted ocean change, from local to global scales, is a complex task. To guide policy-making and make projections of the future of the marine biosphere, it is essential to understand biological responses at physiological, evolutionary and ecological levels. Here, we contrast and compare different approaches to multiple driver experiments that aim to elucidate biological responses to a complex matrix of ocean

SUMMARYWe show that crucian carp (Carassius carassius) living in normoxic(aerated) water have gills that lack protruding lamellae, the primary site of O2 uptake in fish. Such an unusual trait leads to a very small respiratory surface area. Histological examination showed that the lamellae(secondary lamellae) of these fish were embedded in a cell mass (denoted embedded lamellae). When the fish were kept in hypoxic water, a large reduction in this cell mass occurred, making the lamellae protrude and increasing the respiratory surface area by ∼7.5-fold. This morphological change was found to be reversible and was caused by increased apoptosis combined with reduced cell proliferation. Carp with protruding lamellae had a higher capacity for oxygen uptake at low oxygen levels than fish with embedded lamellae, but water and ion fluxes appeared to be increased, which indicates increased osmoregulatory costs. This is, to our knowledge, the first demonstration of an adaptive and reversible gross morphological change in the respiratory organ of an adult vertebrate in response to changes in the availability of oxygen.

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