Academics discover variation in circadian clock protein in fruit flies

The circadian clock is a molecular network that generates daily rhythms, and is present in both plants and animals. A University of Leicester research team led by Dr Eran Tauber has studied genetic variation in circadian clock genes in wild populations of the fruit fly, Drosophila melanogaster -- and has discovered that their genes have developed different genetic variations that are functionally important.

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The paper, entitled 'Molecular evolution of a pervasive natural amino-acid substitution in Drosophila cryptochrome', has been published in PLOS ONE, a peer-reviewed international online publication.

The research focuses on examining a protein called Cryptochrome (CRY), a blue light photoreceptor which synchronises the circadian clock of the fruit fly with the environmental light-dark cycle. CRY is involved in circadian clock functioning in both plants and animals, including humans.

Adaptive variations have resulted in two versions of the CRY protein existing in fruit flies, both with a different amino acid present -- these amino acids affect the circadian clock of the fruit fly.

Dr Tauber said: "The fruit-fly has been a major model organism in the study of the circadian clock, and our collection of strains from various wild populations allow us to identify changes in the genes that serve as molecular adaptations of populations to their local environments.

"We have analysed the sequence of this genes in flies from different European populations and identified many variations. One of these variations involves a single DNA base change resulting in two versions of the protein, each with a different amino acid."

Bioinformatic analysis of the protein structure was carried out by Dr Ralf Schmid from the University of Leicester's Department of Biochemistry, and suggests that this single mutation has a profound effect on the protein structure of the fruit fly.

Dr Mirko Pegoraro, a researcher from the University of Leicester, said: "The fact that the two versions of the protein are present in similar proportions in all the fruit fly populations that we sampled suggests that this variation is functionally important in the species and is actively maintained by natural selection.

"We have tested the behaviour of the flies that express the different CRY proteins and found some interesting and significant differences in their activity pattern during the day, and adult emergence from their pupae the fact that a single amino acid change can result in a different behaviour is an extraordinary discovery."

The study generated large fly populations with different frequencies of the two CRY variants. The team monitored the dynamics of the variants for nearly a year -- about 20 fly generations.

The frequency of the genetic variants became similar in a controlled research environment, simulating the frequencies observed in the wild. Using this kind of experimental evolution allowed the team to demonstrate that this variation is actively maintained by the species, although the exact mechanism is yet to be identified.

The research was carried for nearly six years and was funded by grants from the Natural Environment Research Council (NERC) and the Biotechnology and Biological Sciences Research Council (BBSRC), to Dr Eran Tauber and Prof. Bambos Kyriacou at the Department of Genetics.

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Bats use water ripples to hunt frogs

As the male túngara frog serenades female frogs from a pond, he creates watery ripples that make him easier to target by rivals and predators such as bats, according to researchers from The University of Texas at Austin, the Smithsonian Tropical Research Institute (STRI), Leiden University and Salisbury University. A túngara frog will stop calling if it sees a bat overhead, but ripples continue moving for several seconds after the call ceases. In the study, published this week in the journal Science, researchers found evidence that bats use echolocation -- a natural form of sonar -- to detect these ripples and home in on a frog. The discovery sheds light on an ongoing evolutionary arms race between frogs and bats.

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The male túngara frog (Physalaemus pustulosus), native to Central and South America, spends his nights calling from shallow ponds, attempting to attract the attention of a mate. Yet his call, which is based on a pattern of "whines" and "chucks," inadvertently creates a multisensory display that can be exploited by both friend and foe.

As the amorous amphibian calls out, his vocal sac continually inflates and deflates, like a pulsing balloon. This pulsating sac creates a visual cue, but also creates a third signal -- ripples in the surface of the pond.

"A general theme of this research is that the way we communicate with any kind of a signal is by creating a disturbance in the environment," said Mike Ryan, co-author on the study and professor in the Department of Integrative Biology at UT Austin. "When we vocalize, we're causing changes in the air pressure around us and that's what our ears hear. When we use visual signals, light bounces off whatever pigments we're using and is transmitted to the receiver. Anything we do disturbs the environment, whether it's intended as a communication signal or not."

The researchers found that frog-eating bats (Trachops cirrhosus) were much more likely to attack a target that had both frog calls and ripples radiating from it than one with frog calls and no ripples. This suggests that they can detect these ripples, most likely with echolocation. However, bats appear to lose this advantage if the area around the frog is cluttered with leaf litter, which may stop the ripples from propagating.

"The interesting thing is that these frogs have evolved a strategy to escape predation," said lead author Wouter Halfwerk, a postdoctoral researcher at UT Austin who is also affiliated with STRI and Leiden University. "When a frog detects the shadow of a bat overhead, his first defense is to stop calling immediately. Unfortunately for the frog, the water ripples created by his call do not also stop immediately. The ripples continue to emanate out for several seconds, creating a watery bull's-eye on the frog. Bats use the ripples, thereby beating the anti-predator strategy."

On the other hand, the ripples seem to enhance the response of rival male frogs to the initial caller.

The researchers found that when a call was accompanied by ripples, other male frogs were more likely to respond than if the call was broadcast by itself. In addition, when they did respond, they did so with more gusto.

If a call accompanied by water ripples was outside a male's zone of defense, a circle about 15 cm across, rival males would call more than twice as fast as they would if they just heard the initial call by itself. If the call, again with ripples, was inside their territory rival frogs tended to call less, often stopping altogether and deflating their vocal sacs, presumably getting ready to rumble or run.

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