Cricket, the tiny insect, is not just good at making spooky noises at night; it has now helped researchers understand more about the body’s sleep–wake cycle or the circadian rhythm.
The team from Okayama University in Japan and Indian Institute of Science Education and Research (IISER) Thiruvananthapuram, looked at how changes in atmospheric temperature can affect the behaviour and molecular mechanism of the clock genes.
They locked up a few adult crickets in a totally dark environment and exposed the insects to 30 degree C for 12 hours and 25 degree C for the remaining 12 hours. They found that the activity of the insects increased when the temperature dropped. In fact, the activity started one hour before the transition period. “The insects being nocturnal perceived the drop in temperature as evening setting and started its activity,” explains Nisha N Kannan from IISER Thiruvananthapuram and first author of the paper published in Zoological Science.
Till now, drosophila or fruit fly has been considered as a model organism and have been used in many studies. So why cricket? According to Dr. Nisha, the circadian machinery of crickets shows both drosophila and mammal-like traits. “Studying crickets would help us understand the diversification of insect clocks and how it has evolved across the kingdom,” she says.
The team also studied the clock genes — period, timeless, cryptochrome2 and cycle — to see if the temperature changes altered them.
The team looked at the optical lobe of the cricket to decode whether the change in activity is mediated through the expression levels of the clock genes. “In drosophila, the body clock control is in the brain scattered across 150 neurons and in humans, we have the suprachiasmatic nucleus region in the brain composed of thousands of neurons that control our circadian rhythm. Similarly, in crickets, it has been found that the optical lobe (located in the anterior segment of the brain), which receives the visual information from the retina, houses the clock controls,” adds Dr. Nisha.
Changes were seen in the period and timeless mRNA expression indicating these are the initial clock gene components that respond to changes in the external environmental temperature.
The case of mammals
Will this hold true for humans? In mammals, in addition to the master clock present in the brain, peripheral circadian clocks too operate, which means that the cells and tissues throughout our body have their own individual clocks.
Dr. Nisha explains that this peripheral circadian clock can be affected by temperature changes but our master clock in the brain is resistant to temperature changes.
Our brain has evolved to even override the peripheral circadian clock, so, fortunately, temperature changes (unless very extreme) cannot affect our body clock.