Biomarkers of Defense, Tolerance, and Ecological Consequences - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 45

3
Biomarkers of Defense, Tolerance,
and Ecolo gical Consequences
Claude Amiard-Triquet, Carole Cossu-Leguille, and Catherine Mouneyrac
CONTENTS
3.1 Introduction .......................................................................................................................... 45
3.2 Tolerance to Chemical Stress in Chronically Exposed Populations ............................. 46
3.3 Biomarkers of Defense ........................................................................................................ 51
3.3.1 Mechanisms of Defense against Metals ............................................................... 51
3.3.2 Antioxidative Defenses ........................................................................................... 52
3.3.3 Phases I and II Enzymes ......................................................................................... 55
3.3.4 Stress Proteins .......................................................................................................... 56
3.3.5 Multixenobiotic Resistance ..................................................................................... 57
3.4 Ecological Consequences of Tolerance .............................................................................. 58
3.4.1 Conservation of Biodiversity .................................................................................. 58
3.4.2 Cost of Tolerance ...................................................................................................... 60
3.4.3 Contamination of Food Webs ................................................................................ 62
3.5 Conclusions ........................................................................................................................... 64
References ....................................................................................................................................... 65
3.1 Introduction
Tolerance may be defined as the ability of organisms to cope with stress, either natural
(such as temperature changes, salinity variations, oxygen level fluctuations, and plant
toxins) or anthropogenic, resulting from chemical input of many different classes of
contaminants into the environment. Tolerance resulting from physiological acclimation
acquired during the course of the life of an organism exposed to sublethal concentrations
of contaminants is not inheritable. However, tolerance leading to a genetic adaptation in
response to selection pressure in populations exposed to toxicants may be transmitted
to the progeny. Resistance is frequently used in the scientific literature as a synonym for
tolerance. Several authors have tried to clarify these terms, for example, Lotts and Stewart
(1995) and Morgan et al. (2007), but the definitions they proposed were strongly different,
and none of them is currently generally adopted. Nevertheless, the use of the term resis-
tance is usually preferred by authors interested in the genetic basis of an organism's ability
to survive in a contaminated environment.
Responses to chemical stress may be assessed using the methodology of biomarkers and
specifically in the case of tolerance, the so-called biomarkers of defense (De Lafontaine
et al. 2000). These biomarkers were developed on the basis of research on a variety of
45