Figure 4. The Relationship between the Signalling Cost and the Fixed (Dark) Cost for R1–6 Photoreceptors from the Four Species S. carnaria, C. vicina, D.virilis, and D. melanogaster .

(A) The rate of hydrolysis of ATP molecules during signalling at each effective photon rate.

(B) The maximum signalling cost versus the fixed cost for each of the four R1–6 photoreceptor types. The maximum is the signalling cost measured at the brightest light levels.

(C) The ratio of total cost to fixed cost of each photoreceptor type at each effective photon rate.