Biochemical adaptation: unity in principles, diversity in solutions.

The collection of papers in this special issue of The Journal of Experimental Biology (JEB) focuses largely on a theme that characterizes much of the research in the broad field of biochemical adaptation: unity in diversity. The ‘unity’ in question refers to the capacities of taxonomically diverse organisms evolved in vastly different environments to sustain a common set of biochemical structures and carry out a common set of biochemical processes, based on common principles. The ‘diversity’ refers to the challenges that arise in sustaining this unity of structure and function under a vast range of physical and chemical conditions, creating solutions specific to a particular environment. These challenges arise in large part from a common source; the large molecular systems that are found in all cells (proteins, nucleic acids and large assemblages such as membranes) are notoriously sensitive to the physical and chemical conditions they face. Thus, to achieve a unityof function– tobe capableofworkingacross the ranges of temperature, osmolality, acidity, water availability, hydrostatic pressure and oxygen content – a vast array of biochemical adaptations is required. No single species can survive, at least in a metabolically active state, across the full range of any of these environmental variables. Rather, pervasive modification of all of these biochemical systems is required – either through evolutionary change or by means of phenotypic modification during an organism’s lifetime (acclimation and acclimatization). Changes in the content of an organism’s genetic ‘tool kit’, the appropriate orchestration of the activities of these genes and the post-translational regulation of proteins underlie much of the capacity of organisms to thrive across a remarkable set of environmental conditions. These phenomena, in large measure, are what excite and motivate investigators of the processes of biochemical adaptation. The evolution of studies of biochemical adaptation has been driven by several forces. Certainly, August Krogh’s proselytizing of “choosing the right [‘most convenient’ in his terminology] organism for the question at hand” has served as a powerful stimulus for diversifying the types of organisms that biologists study. Conceptual advances, such as the recognition of the roles of small organic molecules and water in providing a ‘fit’ milieu for macromolecules, the key importance of symbioses and the regulatory role of different types of RNA, have led to major changes in our thinking. Technical advances – both for laboratory experimentation and for obtaining organisms from diverse environments – have also been a major contributor to the advancement of the study of biochemical adaptation. ‘Omics’ methodologies have helped us appreciate the scope of the responses in transcription and translation that accompany acclimation and acclimatization. Eco-mechanical studies have helped to define the physical and chemical conditions experienced on both fine and large temporal and spatial scales, thereby elucidating more fully the