Short Days Cause Female Hamster Aggression

(CN) - Shorter days trigger aggression hormones in female hamsters, according to an Indiana University study that researchers say could help better understand human aggression.

Siberian hamsters were used in the study because their adrenal system is similar to those of humans, the university said.

Researchers exposed 130 hamsters to long days for a week before exposing 45 of the hamsters to shorter days for 10 weeks.

The female hamsters that had experienced shorter days were more likely to get into fights, and they also showed physical changes in their adrenal glands, according to an Indiana University Bloomington press release.

Nikki Rendon, the study's author, said the hormonal response is different in males.

"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," Rendon said in a statement.

Rendon is a lab member of biology professor Gregory Demas, who also worked on the project. His previous research showed that hamsters' wintertime aggression comes from adrenal hormones rather than from the testes and ovaries.

"The study, which builds on 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," Demas said.

Rendon said that female humans and animals are often underrepresented in scientific studies. She said the hamster aggression study "reveals a ripe area for research."

"By conducting this research on females, we are increasing our understanding of hormones and social behavior in a field currently dominated by discussions on testosterone regulating aggression in males," Rendon said.

The work could help advance research on the treatment of inappropriate aggression in humans, according to Indiana University Bloomington.

The university, the National Institutes of Health and the National Science Foundation supported the study.

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