Meeting Abstract

S2.3  Monday, Jan. 4  The heat dissipation limitation theory and the evolution of life histories SPEAKMAN, John; University of Aberdeen j.speakman@abdn.ac.uk

The traditional view of energy in life history evolution is that energy is a limited environmental resource. Animals are therefore forced to allocate this limited resource selectively between processes that ensure survival, and those that enable reproduction. The evolutionary solution to this problem is presumed to depend on the extrinsic risks of mortality. Low extrinsic risks of mortality favour strategies of longevity assurance, and reduced reproduction, while high extrinsic mortality risks promote increased investment in reproduction at the expense of longevity assurance. A key factor driving the variation in extrinsic mortality is body size. This evolutionary framework is suggested to lead to the familiar relationships between fecundity and body size and longevity and body size. The heat dissipation limit (HDL) theory provides a different conceptual perspective on the evolution of life histories in relation to body size. I suggest that rather than being limited, energy supplies in the environment are often unlimited, and that animals instead are constrained in their ability to expend energy by their maximal capacity to dissipate heat generated as a by product of their metabolism. This novel theoretical framework leads to a new interpretation of the evolution of life histories. In particular, the convergence of the theoretical maximal heat dissipation capacity with the basal metabolic rate constrains the ability of animals to invest in reproduction as they get larger. I suggest that this is the primary reason why fecundity declines as animal size increases. Because large animals are constrained by their heat dissipation capacity to have low reproductive rates, only those large animals living in habitats with low extrinsic mortality could evolve longevity assurance mechanisms to survive long enough to have viable populations: leading to the familiar patterns of life history trade-offs and their links to extrinsic mortality rates.