7 - Evolution and Stress Responses to Changes in Environment

Abstract

Major diversifications in metazoans, during the last 600 million years, including the Cambrian explosion, coincide with major shifts in the climatic and geological conditions that significantly affected their conditions of living. This chapter presents the stress responses of metazoans as responses to changes in their environment, reflecting on their evolution and adaptation techniques. It presents a historical account of the study of evolution of the animal kingdom. The paleontological evidence, at a geological scale, strongly suggests that a causal relationship between the drastic changes in the environment and diversification of animal taxa exists. Environmental stress is a strong cue for adaptative developmental plasticity. In response to stressful stimuli, vertebrates sometimes activate mechanisms of morphological adaptation that allow them to adapt to particular unpredictable changes in environment. Depending on the environmental conditions and species, the animal response to stress condition always consists of adaptive changes in behavior, physiology, morphology, and life history. Also, environmental stress, heat shock, and also chemical stress, osmotic stress, and neuronal/metabolic stress sometimes induce expression of a group of heat shock factors (HSFs), such as Hsp70 and Hsp90, which are HSFs believed to represent a buffering system necessary for normal development by acting as chaperones contributing to normal folding of other proteins. In response to various stressors, animals can modify the synaptic morphology and, consequently, the properties of respective neural circuits. This may also lead to changes in stress set points. Such changes are described in the study using various examples.