Variation in immune defence as a question of evolutionary ecology

Abstract

The evolutionary-ecology approach to studying immune defences has generated a number of hypotheses that help to explain the observed variance in responses. Here, selected topics are reviewed in an attempt to identify the common problems, connections and generalities of the approach. In particular, the cost of immune defence, response specificity, sexual selection, neighbourhood effects and questions of optimal defence portfolios are discussed. While these questions still warrant further investigation, future challenges are the development of synthetic concepts for vertebrate and invertebrate systems and also of the theory that predicts immune responses based on a priori principles of evolutionary ecology.

Simple and noninvasive method for assessment of digestive efficiency: Validation of fecal steatocrit in greenfinch coccidiosis model

“…For instance, intestinal and other infections often result in decline in body mass, but without measuring digestive capacity, it would be impossible to distinguish whether the effect of infection on body mass was caused by depletion of bodily reserves, reduced food intake, or malabsorption. Such studies would thus importantly contribute to understanding the mechanisms of how exactly parasites and pathogens impinge on fitness, a goal often not attained in immunoecological research (e.g., Schmid‐Hempel, 2003). …”

The unavoidable costs and unexpected benefits of parasitism: Population and metapopulation models of parasite-mediated competition

“…We limit our analysis to trade-offs between reproduction and immunity that are due to the evolutionary cost of maintaining a high immunity level, rather than the cost of mounting an immune response after infection (Schmid-Hempel, 2003). Such maintenance costs are apparent in the cellular defense response in insects.…”

“…Recent models have shown that the evolutionary dynamics of host-parasite models may differ depending on whether hosts try to fight off parasites through lower transmission rates, higher recovery rates, or higher tolerance (Boots and Bowers, 1999;van Boven and Weissing, 2004). Models have also explored the cost of maintaining the baseline level of immunity, versus the cost that is incurred when genes are up-regulated in response to a parasite (Kraaijeveld et al, 2002;Lochmiller and Deerenberg, 2000;Schmid-Hempel, 2003). The costs of up-regulating defense machinery are only incurred by the infected individuals, whereas the standing costs for maintaining the immune system are incurred by both susceptible and infected individuals.…”

“…Costs of immunity can be separated into two distinct classes-the standing defense cost of maintaining an immune system, and the acute cost of up-regulating the immune system once an individual is infected (Kraaijeveld et al, 2002;Lochmiller and Deerenberg, 2000;Schmid-Hempel, 2003). While many experimental studies have focused on the acute cost of up-regulating the immune system (reviewed in (Kraaijeveld et al, 2002)), artificial selection experiments have demonstrated that costs of standing immunity can lead to decreases in growth, competitive ability, and reproduction (Boots and Begon, 1993;Kraaijeveld and Godfray, 1997b;Yan et al, 1997).…”

Cold‐seeking behaviour mitigates reproductive losses from fungal infection in Drosophila

“…If the response to infection represents an adaptive shift in life‐history strategy, we would expect that infected animals would benefit appreciably more from inhabiting the preferred temperature than control animals; we would expect that the temperature preference would provide benefits one life‐history trait at a cost to other traits; and we would expect that the response ultimately results in increased offspring production for infected animals. This is especially of interest to ecological immunologists as all host defence traits are expected to be costly and trade‐off with other host life‐history traits (Sheldon & Verhulst 1996; Schmid‐Hempel 2003). …”