The Metabolic Cost of Information- a Fundamental Factor in Visual Ecology

To better understand the adaptations of form to function that constitute much of contemporary visual ecology, we examine the costs and the benefits associated with the first stages of vision. Taking the blowfly as a model, the major metabolic costs are the metabolic energy used to support the mass of the eye during locomotion and the metabolic energy used to generate electrical signals. These account for 10% of total metabolic rate at rest, and 3% in flight. This significant contribution to total metabolic rate helps to explain the numerous adaptations that maximize the efficiency with which the components of sensory systems capture and encode information. To further understand these adaptations, metabolic costs are related to sensory benefit by modelling basic optical and biophysical constraints, and by making measurements. The appropriate measure of benefit is the quantity of information coded, in bits. The cost is the consumption of ATP. Cost-benefit relationships follow the law of diminishing returns and this increases the pressure to reduce sense organs to the essential minimum. Ultimately the costs and the uses made of information by individuals should be related to fitness.