Proc. R. Soc. B (2005) 272, 877–886
Published online 7 May 2005
Stress-induced variation in evolution: from behavioural plasticity to genetic assimilation
Alexander V. Badyaev

Extreme environments are closely associated with phenotypic evolution, yet the mechanisms behind this relationship are poorly understood. Several themes and approaches in recent studies significantly further our understanding of the importance that stress-induced variation plays in evolution. First, stressful environments modify (and often reduce) the integration of neuroendocrinological, morphological and behavioural regulatory systems. Second, such reduced integration and subsequent accommodation of stress-induced variation by developmental systems enables organismal 'memory' of a stressful event as well as phenotypic and genetic assimilation of the response to a stressor. Third, in complex functional systems, a stress-induced increase in phenotypic and genetic variance is often directional, channelled by existing ontogenetic pathways. This accounts for similarity among individuals in stress-induced changes and thus significantly facilitates the rate of adaptive evolution. Fourth, accumulation of phenotypically neutral genetic variation might be a common property of locally adapted and complex organismal systems, and extreme environments facilitate the phenotypic expression of this variance. Finally, stress-induced effects and stress-resistance strategies often persist for several generations through maternal, ecological and cultural inheritance. These transgenerational effects, along with both the complexity of developmental systems and stressor recurrence, might facilitate genetic assimilation of stress-induced effects. Accumulation of phenotypically neutral genetic variance by developmental systems and phenotypic accommodation of stress-induced effects, together with the inheritance of stress-induced modifications, ensure the evolutionary persistence of stress–response strategies and provide a link between individual adaptability and evolutionary adaptation.

CybeRose note: Behavior, in plants, is the ability to change form and function in order to accomodate environmental changes. The existence of an "organismal memory" may sometimes lead to odd and novel changes if the present environmental stress provokes "memory" of two or more ancient adaptations — none of which are precisely appropriate in the new context. However, in this jumble of attempted responses, one or more may prove at least partially useful. These may then become the beginnings of new adaptatios, should the stress become a new way of life. Or, to the plant breeder, these fumblings may lead to useful new traits.