Adaptive Gene Loss in Vertebrates: Photosensitivity as a Model Case

Wayne L Davies, University of Oxford, Oxford, Oxfordshire, UK

Published online: January 2011

DOI: 10.1002/9780470015902.a0022890

Current evolutionary thinking aims to amalgamate the conjectures first set out in Darwin's The Origin of Species with modern genetics to form a unified theory of phylogenetic change that explains the mechanisms mediating the diversity of life. With the advent of molecular biology, it has been shown that the mechanics of evolution fundamentally exert their effect at the molecular level and any genetic modification ultimately becomes fixed in the host genome if the resultant phenotype allows an organism to become better adapted to its ecology. The vertebrate colour visual sensory system, and the photopigment genes that form the first step in light detection, represents an ideal model to illustrate the influence of evolution at a molecular level, which through gene loss, duplication and genome rearrangement may allow an organism to adapt to an ever changing (and spectrally unique) environment.

Key Concepts:

  • Modern evolutionary thought seeks to amalgamate a multitude of scientific disciplines to produce a unified theory of phylogenesis.
  • Evolution fundamentally exerts its influence at the molecular level of genomes, genes, RNAs and proteins.
  • Evolutionary mechanic is a continuous process and specific genetic changes become selectively fixed if the resultant phenotype allows an organism to be better suited to a particular environment.
  • Adaptive evolution is the result of an ongoing interaction between an organism's physiology, its drive to survive and reproduce and its immediate ecology.
  • The mechanisms that mediate molecular adaptation have permitted the multiplicity of ecological niches to be colonised by a myriad of diverse life forms.
  • Sophisticated sensory systems ultimately form the interface that mediates the complex interactions between organisms and varied environments.
  • The vertebrate visual system is a model case for determining the mechanics of adaptive evolution.
  • In addition to gene duplication, genome rearrangement and genetic drift, gene loss is a major player in shaping the genetic substrate on which molecular adaptation may act.

Keywords: vertebrate; gene; opsin; adaptation; ecology; evolution

Figure 1. Schematic (a) side view and (b) aerial view of an opsin, showing the presence of seven transmembrane domains (yellow) typical of the GPCR superfamily. Opsin residues involved in spectral tuning (coloured) and the retinal chromophore (orange) are shown.
Figure 2. A phylogenetic tree of vertebrate opsin evolution, showing the presence of five main opsin classes in the pouched lamprey and those lost from the genome of the sea lamprey.
Figure 3. A vertebrate lineage cladogram showing how the repertoire of opsins adapts through gene loss and duplication as a function of differential ecology. The presence of five opsins, which first evolved in the basal lampreys, is conserved at each major node (yellow star), except for the mammals where gene loss occurred early and throughout the mammalian lineage.
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Related Sub-Topics:

Sensory Systems | Adaptive Evolution | Molecular Evolution | Evolution: Theories and Ideas | Evolutionary Processes | Protein Evolution
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Article Title: Adaptive Gene Loss in Vertebrates: Photosensitivity as a Model Case
 
How to Cite close
Davies, Wayne L(Jan 2011) Adaptive Gene Loss in Vertebrates: Photosensitivity as a Model Case. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0022890]