10 – the biology of metamorphosis

SYNOPSIS. Biochemical adaptation to environmental parameters such as temperature appears to involve two distinct types of changes in the organism's chemistry. On the one hand, the quantities of certain molecular species present in the cells may change. Alternatively, the actual types of molecules present may vary. Rainbow trout ( Salmo gairdneri ) acclimated to warm and cold temperatures exhibit a striking example of this latter type of adaptation. For all enzymes we have examined in this species, distinct “warm” and “cold” isozymes are present. The isozymes found in warmacclimated (18°C) trout function well only at temperatures above 10–12°C. The isozymes present in cold-acclimated (4°C) trout function optimally at 2-5°C, temperatures this species normally encounters in winter. These data, plus information on comparable changes in membrane lipids, lead us to propose that adult poikilotherms may undergo a considerable degree of “biochemical restructuring” on a seasonal basis. The factors which control this “restructuring,” and the rates at which the process occurs at high and low temperatures, are topics for future investigation.

Biochemical Adaptation to the Environment

The American Cockroach

Adaptations of the spadefoot toad Scaphiopus couchi, to desert environments

The article discusses advances in osmoregulation and excretion with emphasis on how multicellular animals in different osmotic environments regulate their milieu interieur. Mechanisms of energy transformations in animal osmoregulation are dealt with in biophysical terms with respect to water and ion exchange across biological membranes and coupling of ion and water fluxes across epithelia. The discussion of functions is based on a comparative approach analyzing mechanisms that have evolved in different taxonomic groups at biochemical, cellular and tissue levels and their integration in maintaining whole body water and ion homeostasis. The focus is on recent studies of adaptations and newly discovered mechanisms of acclimatization during transitions of animals between different osmotic environments. Special attention is paid to hypotheses about the diversity of cellular organization of osmoregulatory and excretory organs such as glomerular kidneys, antennal glands, Malpighian tubules and insect gut, gills, integument and intestine, with accounts on experimental approaches and methods applied in the studies. It is demonstrated how knowledge in these areas of comparative physiology has expanded considerably during the last two decades, bridging seminal classical works with studies based on new approaches at all levels of anatomical and functional organization. A number of as yet partially unanswered questions are emphasized, some of which are about how water and solute exchange mechanisms at lower levels are integrated for regulating whole body extracellular water volume and ion homeostasis of animals in their natural habitats. © 2014 American Physiological Society.

Mavis M. Cragg

Papers

The adaptation of amphibian waste nitrogen excretion to dehydration.

A comparative study of nitrogen excretion in some Amphibia and reptiles.