Epistatic Adaptive Evolution of Human Color Vision
Shozo Yokoyama, Jinyi Xing, Yang Liu, Davide Faggionato, Ahmet Altun, William T. Starmer
Published: December 18, 2014DOI: 10.1371/journal.pgen.1004884
Abstract
Establishing genotype-phenotype relationship is the key to understand the molecular mechanism of phenotypic adaptation. This initial step may be untangled by analyzing appropriate ancestral molecules, but it is a daunting task to recapitulate the evolution of non-additive (epistatic) interactions of amino acids and function of a protein separately. To adapt to the ultraviolet (UV)-free retinal environment, the short wavelength-sensitive (SWS1) visual pigment in human (human S1) switched from detecting UV to absorbing blue light during the last 90 million years. Mutagenesis experiments of the UV-sensitive pigment in the Boreoeutherian ancestor show that the blue-sensitivity was achieved by seven mutations. The experimental and quantum chemical analyses show that 4,008 of all 5,040 possible evolutionary trajectories are terminated prematurely by containing a dehydrated nonfunctional pigment. Phylogenetic analysis further suggests that human ancestors achieved the blue-sensitivity gradually and almost exclusively by epistasis. When the final stage of spectral tuning of human S1 was underway 45–30 million years ago, the middle and long wavelength-sensitive (MWS/LWS) pigments appeared and so-called trichromatic color vision was established by interprotein epistasis. The adaptive evolution of human S1 differs dramatically from orthologous pigments with a major mutational effect used in achieving blue-sensitivity in a fish and several mammalian species and in regaining UV vision in birds. These observations imply that the mechanisms of epistatic interactions must be understood by studying various orthologues in different species that have adapted to various ecological and physiological environments.
Author Summary
Mapping the genotype-phenotype relationship is necessary to understand how variable phenotypes have evolved in nature. The blue-sensitive visual pigment in human (human S1) evolved from the UV-sensitive pigment in the Boreoeutherian (or Boreotherian) ancestor (AncBoreotheria S1) by seven mutations. Mutagenesis experiments reveal that 4,008 (~80%) of all 5,040 possible evolutionary trajectories connecting from AncBoreotheria S1 to human S1 are terminated prematurely. Quantum chemical analyses suggest that the premature termination of trajectories was caused by containing a dehydrated nonfunctional pigment. Phylogenetic analysis further suggests that the blue-sensitivity was achieved only gradually and almost exclusively by the seven non-additively interacting amino acids. During the period between 45 and 30 My ago, human S1 was in the final stage of developing its blue-sensitivity. This was the time when two red-sensitive pigments appeared by gene duplication and one of them became green-sensitive. Trichromatic color vision in the human lineage was fully developed by 30 My ago by interprotein epistasis among the three visual pigments. Manipulation of the genetically engineered ancestral molecule is the key to recapitulate the evolution of phenotypic adaptation and that of epistatic interaction separately.
Quote:So you and Frank are peddling the "invisible unicorn" bullshit eh?This will all be understood in time.
Good luck, but prdon if I say that your thinking is just shy of any understanding.
