CORVALLIS, Ore. - In work to trace the "biological clocks" of animals to their genetic and molecular roots, researchers at Oregon State University have found that eyes may not have a monopoly on receiving or reacting to light.
Studies done with fruit flies suggest that other bodily tissues, including renal and reproductive organs, can respond directly to light and continue their "daily rhythms" with no input from the insect's eyes or brain.
It appears that biological response to time periods and light-dark cycles - what is more often known as circadian rhythm or a biological clock - can have a profound and direct impact on fertility in some species.
And as more information becomes available about circadian rhythms, which operate in animals ranging from insects to mice and humans, the biological impact of this clock seems to be increasingly complex and important.
"Chronobiologists are now learning more about how, in humans, our biological clocks can affect everything from sleep to body temperature, our nervous system, moods, sensitivity to medications, work productivity and many other things," said Jadwiga Giebultowicz, an OSU assistant professor of entomology.
But the biology is sufficiently complex, Giebultowicz said, that researchers such as herself are just beginning to tap the genetic basis for this behavior in tiny insects, and are still far from understanding its operations in humans.
Researchers may find, Giebultowicz said, that species have more than one biological clock, operating in more than one type of bodily tissue, and with biological impacts which may be far more extensive than had been presumed.
Insects, indeed, seem to have biological clocks that are very important to their reproduction and survival. In one study Giebultowicz has confirmed that constant exposure to light can "switch off" the biological clock in gypsy moths and - among other impacts - cause them to become infertile.
That research also showed that the moth's testes and other reproductive tissue had a direct response to light-dark cycles which operates quite independently of the insect's eyes or brains.
In fruit fly brains, efforts of many scientists have established that two genes called "period" and "timeless" are involved in a biological clock that control rhythmic behavior. These genes appear to interact with each other and have a feedback loop that helps regulate the process.
In an OSU project with fruit flies - which have tough little bodies that can survive four days or more without a head - researchers have found expression of these genes not only where one might expect, in their eyes and brain, but also operating in renal tissue long after the insect's head had been removed.
Other studies will continue.
"We'd like to find out, for instance, what the overall health impacts are on flies if you disrupt their biological clocks," Giebultowicz said. "We already know it will impact their fertility, and it may do much more than that."
The OSU research program is also trying to identify different molecules, other than just those in the eye, that may be photoreceptive and play a role in how light can affect the biological processes of a species. And another area of interest is to see if some of these genes that control the biological clock in one species will be conserved and carried over to other species.
"It's possible that there are some central players which will turn out to be common to a range of organisms, possibly including humans," Giebultowicz said.
"If anything is clear, it's that biological rhythms are extremely complex," Giebultowicz said. "Right now my colleagues working with clocks of mammals are trying to moderate all this hype about melatonin, and people who think it will solve all their problems. There just isn't enough research to understand how something like that works."