Environments and evolution: interactions between stress, resource inadequacy and energetic efficiency

Abstract

Evolutionary change is interpreted in terms of the near-universal ecological scenario of stressful environments. Consequently, there is a premium on the energetically efficient exploitation of resources in a resource-inadequate world. Under this environmental model, fitness can be approximated to energetic efficiency especially towards the limits of survival. Furthermore, fitness at one stage of the life-cycle should correlate with fitness at other stages, especially for development time, survival and longevity; 'good genotypes' under stress should therefore be at a premium. Conservation in the wild depends primarily on adaptation to abiotically changing habitats since towards the limits of survival, genomic variation is rarely restrictive. The balance between energetic costs under variable environments and energy from resources provides a model for interpreting evolutionary stasis, punctuational and gradual change, and specialist diversification. Ultimately, a species should be in an equilibrium between the physiology of an organism and its adaptation to the environment. The primary key to understanding evolutionary change should therefore be ecological, highlighting energy availability in a stressed world; this approach is predictive for various patterns of evolutionary change in the living and fossil biota.

Inbreeding by Environmental Interactions Affect Gene Expression in Drosophila melanogaster

“…We also found that the majority of genes being differentially expressed were upregulated in inbred lines compared with noninbred lines under temperature stress (supplemental Figure 2 and Table 2 at http://www.genetics.org/ supplemental/). This supports the hypothesis that the energy requirements are higher in homozygous individuals exposed to heat stress and is indirect support for the hypothesis that better performance of heterozygous individuals partly derives from their reduced energy expenditure for maintenance metabolism (Koehn and Bayne 1989;Myrand et al 2002;Parsons 2004Parsons , 2005. In further support of this interpretation are results showing that the inbred lines investigated here are less heat resistant and have lower productivity (estimated as eggs laid per unit time) compared to the noninbred lines .…”

“…This is a clear indication that inbreeding affects the network of chemical reactions that are essential in forming ATP, NADPH, and building blocks for biosyntheses. Myrand et al (2002) and Parsons (2004Parsons ( , 2005 have shown and discussed that higher resistance to environmental stress in heterozygous individuals can be explained by their lower basic metabolic needs, leaving more energy available for resisting stressful conditions. In this study we found that a higher number of functional groups and single genes were differentially expressed in inbred lines compared with outbred lines after exposure to 36°.…”

Antagonistic pleiotropy and the stress theory of aging

“…In any case, the heritability of stressresistance traits can be very high at extremes implying strong selection, while that of competitive ability approaches zero. The long-term evolutionary significance of competition should therefore be low, and perhaps best viewed as second-order effects with the potential to modify the energy costs of abiotic stresses (Parsons 1996(Parsons , 2005.…”

“…Fitness maxima should occur in the benign region of the continuum where abiotic stresses are relatively mild, corresponding to the most likely habitats of organisms (Parsons 2005). For temperature, fitness maxima should occur in regions of some temperature perturbations reflecting those of wild habitats, because a constant temperature or wide fluctuations should be disadvantageous.…”

“…Under the stressful scenario pertaining in free-living populations, high energetic and metabolic efficiency should therefore be associated with high (electrophoretic) heterozygosity, high stress resistance, survival, vitality, vigor and resilience, high homeostasis and metabolic stability, low fluctuating asymmetry, rapid development, high mating success, and improved survivorship which normally translates into a long lifespan. The expectation of positive associations among these fitness traits contrasts with more conflicting results obtained under more benign conditions where tradeoffs can more readily develop, which is a complication now to be considered (Parsons 2005(Parsons , 2007a.…”