Plachetzki, D.; Fong, C.; Oakley T. 2010. "The evolution of phototransduction from an ancestral cyclic nucleotide gated pathway". Proceedings of the Royal Society / Biological sciences277 (1690): 1963–1969. doi:10.1098/rspb.2009.1797. PMID 20219739.
Shichida Y.; Matsuyama T. 2009. "Evolution of opsins and phototransduction". Philosophical transactions of the Royal Society of London. Series B, Biological sciences. 364 (1531): 2881–2895. doi:10.1098/rstb.2009.0051. PMID 19720651