Stress-induced variation in evolution: from behavioural plasticity to genetic assimilation

Abstract

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.

Phenotypic diversity, population structure and stress protein-based capacitoring in populations of Xeropicta derbentina, a heat-tolerant land snail species

“…Moderate stress is essential for healthy growth and development of organisms (Müller 2003) and, under stressful conditions, organisms tend to increase their phenotypic variation (Waddington 1942;Jablonka et al 1995;Badyaev 2005). In contrast to the traditional point of view, that only gene-based differences in organisms determine their fitness, there is now increasing evidence that organisms are able to adaptively modify their developmental program according to the environment (Dusheck 2002;Sultan 2007;Bolker 2012).…”

Morphological plasticity reduces the effect of poor developmental conditions on fledging age in mourning doves

“…Plasticity during development is important in both ecological and evolutionary processes (West-Eberhard 1989;Schew & Ricklefs 1998;West-Eberhard 2003;Badyaev 2005;Gil et al 2008). Developmental plasticity can have adaptive fitness consequences realized at different stages of an individual's life history, including long-term benefits for the adult phenotype (West-Eberhard 2003), immediate benefits during development (Altwegg 2002;Gil et al 2008) and mediating effects on transitions between life-history stages (Newman 1992;Badyaev et al 2006;Gotthard 2008).…”

Genomics of Adaptation to Multiple Concurrent Stresses: Insights from Comparative Transcriptomics of a Cichlid Fish from One of Earth’s Most Extreme Environments, the Hypersaline Soda Lake Magadi in Kenya, East Africa

“…Since such a scenario does not necessarily mean that freshwater inducible genes are not expressed, a combination of genes derived from both effects may lead to increased numbers of DEGs. This phenomenon is best understood in the context of genetic assimilation, in which genes and consequently traits that are unconditionally adaptive become genetically fixed (canalized) such that they may continue to be expressed long after the stressor has been removed (Stearns 1994;Badyaev 2005;Lande 2009). Several studies suggest that constitutive up-regulation (transcriptome uploading) of stress-responsive genes may actually represent a major phenomenon in animals evolved under chronic environmental stress (Latta et al 2012;Purohit et al 2014).…”

“…Whether both act in an independent or complementary manner is still a widely debated topic (Merila 2012;Merila and Hendry 2014). Some studies suggest that populations may initially respond to stressful conditions through behavioral and phenotypic plasticity followed closely by genetic assimilation (canalization), which fixes beneficial traits that have been environmentally induced in the population (Badyaev 2005;Lande 2009). In A. grahami, several behavioral and physiological adaptations to its challenging habitat have been described.…”