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University of California, Davis
March 5, 2012

New research from the University of California shows how the ability
to detect light could have evolved before anything like an eye.

As published today (March 5) in the journal BMC Biology, the research
is based on the stinging mechanism in the tiny, brainless and eyeless
freshwater polyp Hydra magnipapillata. Part of a group of animals
called cnidarians that includes sea anemones, corals and jellyfish, a
hydra is essentially a mouth surrounded by tentacles armed with
stinging cells, or cnidocytes.

The researchers — David Plachetzki, now a postdoctoral researcher at
UC Davis, working with undergraduate Caitlin Fong and Professor Todd
Oakley in the Department of Ecology, Evolution and Marine Biology at
UC Santa Barbara — discovered a simple nervous system linking the
stinging cells and nerve cells that detect light using a process
similar to the human eye’s.

The nerve cells express a set of genes including opsin, a
light-sensitive pigment; cyclic nucleotide gated ion channels; and
arrestin. These components are basically the same as those in the
light-detecting pathway in animals with eyes, including people.

The hydra fire their stingers less in bright than in dim light, the
researchers found. When they blocked one of the pathway’s components,
the hydra acted as if they were in dim light and fired their stingers
more.

Most of the hydra’s cnidarian relatives lack eyes. But all cnidarians
have cnidocyte stinging cells.

“This capacity for stinging cell regulation by light-sensitive
neurons could have predated the evolution of eyes in cnidarians,”
Plachetzki said. Future work will be aimed at how these findings
relate to the evolution of eyes in other groups of animals.

The National Science Foundation funded the work.

Media contact(s):
* David Plachetzki, Center for Population Biology,
plachetzki@ucdavis.edu
* Andy Fell, UC Davis News Service, (530) 752-4533, ahfell@ucdavis.edu

Special thanks to Craig Quirolo