ADAPTIVE PLASTICITY AND PLASTICITY AS AN ADAPTATION - A SELECTIVE REVIEW OF PLASTICITY IN ANIMAL MORPHOLOGY AND LIFE-HISTORY

During the last decade there has been a rapidly growing interest in th e study of phenotypic plasticity in animals. Confused terminology in t his field of research may be one reason why the focus of many studies is not as clear as it could be. The field of plasticity highlights the general problem of demonstrating adaptation. We discuss the terminolo gy and methodology of plasticity studies, with particular reference to the question of which patterns should be considered evidence for plas ticity as an adaptation to the environment, and how to find such evide nce. We suggest a terminology where plasticity can be ''adaptive'' (i. e. beneficial, and maintained by selection) with respect to a function without strictly being an adaptation for it (evolutionary origin link ed to this function), and vice versa. Modifications of the original re action norm, seen today as differences in plasticity between populatio ns and species, can be adaptations for a function even when the plasti city itself is not (it may follow from constraints or from selection f or another function). We selectively review cases reported as evidence of adaptive plasticity in animal morphology and life history, choosin g examples from a wide range of taxa to illustrate our criteria for wh at should be called ''adaptive'' and ''adaptation'' when applied to pl asticity.