A new study from researchers at Azabu University in Japan suggests that house cats’ gut microbiomes and hormones like cortisol, oxytocin and testosterone may explain why some felines get along well with each other and others are more aloof.
“Cats are solitary and territorial, but they have evolved to acquire the abilities and skills to live in groups,” Hikari Koyasu, lead author from Azabu University, tells Inverse’s Tara Yarlagadda.
Researchers split 15 shelter cats into groups, placing five random cats in three 13-by-25-foot rooms for two weeks. Over this time period, they used video cameras to observe the cats' behavior, and they collected urine and feces to measure hormones and microbial species present.
They found that cats with higher cortisol and testosterone concentrations exhibited fewer social behaviors like grooming, sharing food or sniffing, while those with lower amounts of cortisol and testosterone were more social. Additionally, cats with similar microbiomes had more frequent contact with each other, and cats with higher testosterone levels were more likely to try to escape, per the study. The results were published in the journal PLOS ONE.
Unexpectedly, oxytocin—often called the “love hormone”—was lower in cats exhibiting more social behaviors.
“We were surprised at the results,” Koyasu tells NBC News’ Sarah Sloat. “Even though a positive correlation between oxytocin and affiliative behavior has been reported in animals living in groups, results in [these] cats were the opposite. Cats with high oxytocin had less affiliative behavior with other cats.”
These findings show that hormones may act differently across species, Maren Huck, a cat expert at the University of Derby who wasn’t involved in the study, tells NBC News. Carlo Siracusa, a professor of clinical animal behavior and welfare at the University of Pennsylvania, tells the publication that cats may show affection differently than other animals.
“Cats use proximity, but not necessarily physical contact, to show how much they like another individual—the closer, the friendlier,” he says to NBC News. “It would have been interesting to know if cats [in the study] with a higher level of oxytocin spent more time in proximity of other cats, but not necessarily physically interacting with other cats.”
Because the cats were of different or unknown ages and backgrounds, “we do not consider our results to be applicable to all cat groups,” Koyasu tells Inverse. Future research should look into how factors like spending time together as juveniles and changes in environmental conditions affect social behaviors. And though the study showed correlations between hormones and behaviors, causality is unknown. The authors conclude in the study that research conducted over a longer period of time may be required to provide “more comprehensive information.”