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Seasonal Changes: Short Winter Days Trigger Aggression In Female Hamsters

Nov 18, 2015 06:50 PM EST
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As the weather starts to get colder, female hamsters may start acting out. That is, according to a recent Indiana University (IU) study, short winter days trigger an aggressive hormonal response in some animals. This could help researchers better understand appropriate aggression in humans.

For their study, researchers observed the behaviors of Siberian hamsters (Phodopus sungorus), which have a similar adrenal system to humans. Knowing the animals are very territorial, researchers sparked aggressive actions by placing individuals in situations where one would be perceived as an intruder on the other's property. This is when researchers found the hormonal mechanism linked to increased aggression in females differs from that found in males, according to a new release.

"This study reveals a ripe area for research," Nikki Rendon, lead author and a Ph.D. student in biology, said in the release. "The results show for the first time that melatonin acts directly on the adrenal glands in females to trigger a 'seasonal aggression switch' from hormones in the gonads to hormones in the adrenal glands -- a major contrast to how this mechanism works in males."

Melatonin is a hormone that helps control sleep and wake cycles, meaning that levels of this hormone increase during the night and lower during the day. While previous studies have found a link between shorter days and aggression in animals, the recent study is the first to reveal that melatonin acts directly on the adrenal glands in females to trigger the release of dehydroepiandrosterone, or DHEA, which is a sex steroid known to control aggression.

"This study, which builds upon our previous work investigating the connection between short days and aggression in males, shows noteworthy hormonal mechanisms in females and provides important new insights into the role of sex in these mechanisms," Gregory Demas, a professor of biology at IU, added.

Researchers directly observed behavioral differences by exposing 130 hamsters to long days for a week, after which time they exposed 45 of the hamsters to shorter days instead, for about ten weeks. While females exposed to shorter days exhibited increased levels of both melatonin and DHEA and became more aggressive, those exposed to consistently long days were not affected. This suggests that sex hormones play an important role in controlling aggression. 

Their study was recently published in the journal Proceedings of the Royal Society B.  

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