Fig. 5. Resting and maximum energy consumption of photoreceptors scales with their performance. Comparison of four homologous fly R1–6 photoreceptors from (smallest to largest): Drosophila melanogaster, D. virilis, Calliphora vicina and Sarcophaga carnaria. The largest photoreceptors are capable of transmitting more information but expend more energy at rest (squares; solid line) and whilst signalling (circles; broken line) than the smaller photoreceptors. This shows that neural performance is related to energy consumption at rest and whilst signalling. Adapted from Niven et al. (Niven et al., 2007).