Functional plasticity of the developing cardiovascular system: examples from different vertebrates.

Technical advances that have made it possible to perform physiological measurements on very small organisms, including those in embryonic and larval stages, have resulted in the formation of the discipline of developmental physiology. The transparency and size of developing organisms in some areas permit insights into physiological processes that cannot be obtained with opaque, adult organisms. On the other hand, it is widely accepted that without eggs, there are no chickens, so physiological adaptations during early life are just as important to species survival as those manifested by adults. Physiological adaptations of early developmental stages, however, are not always the same as patterns known in adults; they often follow their own rules. The adaptability of early developmental stages demonstrates that development is not stereotyped and a phenotype is not just the result of genetic information and the expression of a certain series of genes. Environmental factors influence phenotype production, and this in turn results in flexibility and plasticity in physiological processes. This article comprises exemplary studies presented at the Fourth International Conference in Africa for Comparative Physiology and Biochemistry (Maasai Mara, Kenya, 2008). It includes a brief introduction into technical advances, discusses the developing cardiovascular system of various vertebrates, and demonstrates the flexibility and plasticity of early developmental stages. Fluid forces, oxygen availability, ionic homeostasis, and the chemical environment (including, e.g., hormone concentrations or cholesterol levels) all contribute to the shaping and performance of the cardiovascular system.