Opsin genes (pictured in blue) are present in the cnidarian Hydra, the first evidence of sight in animals.
Credit: David Plachetzki/UCSB
By peering deep into evolutionary history, scientists have discovered the origins of photosensitivity in animals: vision genes called opsins that first appeared in the aquatic animal species Hydra magnipapillata. The hydras have no eyes or light-receptive organs, but they have the genetic pathways to be able to sense light.
The research provides a glimpse into the evolutionary history of life on Earth. The information gathered by the study, as well as the techniques used to obtain it, can help astrobiologists understand the mechanisms behind evolution. Unlocking the keys to evolution is important in determining how life could adapt to inhabit environments on other planets, and in predicting how life on Earth will continue to thrive alongside our ever-changing biosphere.or even beyond our planet in the environment of space.
The hydras have no eyes or light-receptive organs, but they have the genetic pathways to be able to sense light.
The findings are published in this week's issue of the scientific journal PLoS ONE.
The biologists--David Plachetzki and Todd Oakley of the University of California at Santa Barbara--are the first to look at light receptive genes in cnidarians (corals, jellyfish and sea anemones), of which hydras are members.
Hydras are found in most freshwater ponds, lakes and streams in temperate and tropical regions, and are predatory animals that feed on small aquatic invertebrates.
All known life on Earth has a similar DNA-based chemistry, and by studying how this chemistry works scientists have unlocked many secrets about the evolution of life on Earth. If life as we know it exists elsewhere in the Universe, these findings may help us understand how life could survive on distant worlds.and where to search for it.
The scientists speculate that hydras use light sensitivity in order to find prey. The hydras have opsin proteins all over their bodies, but the proteins are concentrated in the mouth area.
"Because we don't find opsins in earlier branching animals like sponges, we can put a date on the evolution of light sensitivity in animals," said Plachetzki. "We now have a time frame for the evolution of animal light sensitivity. We know its precursors existed roughly 600 million years ago."
"These results are significant to advancing our understanding of the early evolution of sight in animals, and show how simple genetic changes can produce visual pigments that begin the pathway to the evolution of sight," said Jerry Cook, program director in NSF's division of environmental biology, which funded the research.
Oakley said that there are only a handful of cases where scientists have documented the very specific mutational events that have given rise to new features during evolution.
"We show very clearly that these changes in a particular duplicated gene, opsin, allowed the new genes to interact with different proteins in new ways," he said. "Today, these different interactions underlie the genetic machinery of vision."
Scientist Bernie Degnan of the University of Queensland in Brisbane, Australia, provided bioinformatics tools to complete the study. The Hydra magnipapillata genome project is conducted by the Institute for Genomic Research, part of the J. Craig Venter Institute.
Related Web Sites
30 Rings on the Tree of Life
Our Earliest Animal Ancestors
Tracking Back Animal Evolution
We are One
The Structure of Origins
Finding Our Roots