Meeting Abstract
Simple roles for photoreception are likely to have preceded more demanding ones such as vision. The driving force behind this evolution is the improvement and elaboration of animal behaviours using photoreceptor input. Because the basic role for all senses is to support behaviour, I argue here that this ‘behavioural drive’ is more relevant than the popular concept of “sensory drive”. Photoreception serves many different types of behaviour, from simple shadow responses to visual communication. Based on minimum performance requirements for different types of tasks, photoreceptors have been argued to have evolved from non-directional receptors, via directional receptors, to low resolution vision, and finally to high resolution vision. Through this sequence, the performance requirements on the photoreceptors have gradually changed from broad to narrow angle reception and from slow to fast response. Also the requirements of high absolute sensitivity and good signal/noise ratio are likely to have increased as photoreceptors have taken on the control of ever more advanced and demanding behaviours. We can assume that the first animal behaviours required only very simple and low-performance sensory input. Selection for more efficient behaviours would drive evolution towards better sensory performance, and this in turn would allow for evolution of new and more demanding behaviours as soon as the sensory performance reaches the minimum requirements of the new behaviour. Here I use photoreception as examples to show that new behaviours would only evolve if their sensory performance requirements to some degree overlap with the corresponding requirements of already existing behaviours. I argue that this need for sensory ‘performance continuity’ in the behavioural drive has been one of the most important factors guiding animal evolution.
