Hormesis on life-history traits: is there such thing as a free lunch?

Abstract

The term "hormesis" is used to describe dose-response relationships where the response is reversed between low and high doses of a stressor (generally, stimulation at low doses and inhibition at high ones). A mechanistic explanation is needed to interpret the relevance of such responses, but there does not appear to be a single universal mechanism underlying hormesis. When the endpoint is a life-history trait such as growth or reproduction, a stimulation of the response comes with costs in terms of resources. Organisms have to obey the conservation laws for mass and energy; there is no such thing as a free lunch. Based on the principles of Dynamic Energy Budget theory, we introduce three categories of explanations for hormesis that obey the conservation laws: acquisition (i.e., increasing the input of energy into the individual), allocation (i.e., rearranging the energy flows over various traits) and medication (e.g., the stressor is an essential element or acts as a cure for a disease or infection). In this discussion paper, we illustrate these explanations with cases where they might apply, and elaborate on the potential consequences for field populations.

Hormesis depends upon the life-stage and duration of exposure: Examples for a pesticide and a nanomaterial

“…This question is important because it can determine how hormetic effects may relate to effects at the population level. Jager et al (2013) highlight the important point that organisms have to obey the conservation laws for mass and energy, with the suggestion there may well be "no such thing as a free lunch". These authors present three explanations for observed hormesis, namely increased acquisition (i.e.…”

“…As emphasised by Jager et al (2013) organisms have to obey the conservation laws for mass and energy and hence trade-off between traits can be expected to be the norm, with implications for the relationship between hormesis effects and fitness.…”

“…The increase in reproduction has been linked to a reduction in growth as well as other more complex traits (Weltje et al, 2005). Recognising this, Jager et al (2013) used the principles of Dynamic Energy Budget theory to identify three categories of explanations for hormesis that obey mass and energy conservation laws. These were related to…”

“…may a series of parallel trials carried out using cohorts at different life stages may be able to provide some indication of the variation in response patterns resulting from exposure in relation to the age and life stage of the exposed organism (Spurgeon et al, 2003). Inclusion of such data in life-table analyses have the potential to integrate these effects to provide a valuable overview of the potential fitness consequences of low concentration exposure (Forbes et al, 2011) and the role of possible mechanisms (Jager et al, 2013). …”

Hormesis

“…However, generalizations, according to which ''hormetic-like biphasic dose responses may represent a general biological dose-response pattern or strategy'' 11 are not sufficiently supported by scientific evidence. 15,16 Moreover, hormesis merely further defines one response; but most toxicoses have many responses. 10 Some noxious agents can have a cumulative effect or act synergistically with other harmful factors, for example, on the cells with a limited or no potential for cellular regeneration such as cardiomyocytes or neurons.…”