New research provides evidence that the physical damage of catnip (Nepeta cataria) and silver vine (Actinidia polygama) leaves by feline licking and chewing enhances the release of iridoids — compounds repellent to arthropods such as mosquitoes — and, in combination with enhanced self-anointing to transfer iridoids to the fur, acts to provide stronger chemical pest defense.
A cat (Felis catus) licks and chews silver vine (Actinidia polygama) leaves. Image credit: Masao Miyazaki & Reiko Uenoyama.
Plants produce compounds to defend themselves against herbivorous insects, some of which ingest and store the plant compounds in their body tissues, providing them with defense against predators or parasites.
Humans and other mammals exploit these compounds without needing to eat plants to gain chemical defense by using plant-emitted insect repellents in the local environment or a behavioral mechanism such as self-anointing their bodies with the plants.
Domestic cats (Felis catus) show an unusual but characteristic response toward catnip and silver vine leaves that comprises licking and chewing the plants, face and head rubbing against the plants, and rolling over on the plants.
Although this has often been interpreted by pet owners as a playful behavior among cats that appeared to be intoxicated by these specific plant species, scientists recently demonstrated that the rubbing and rolling behavior can protect cats from mosquito bites.
This characteristic feline behavioral response is induced by olfactory stimulation by iridoids that are emitted from the leaves of these plants and thought to play a role in plant chemical defense.
Although catnip produces the iridoid nepetalactone, silver vine produces a more complex mixture of nepetalactol, dihydronepetalactone, isodihydronepetalactone, iridomyrmecin, and isoiridomyrmecin.
Some of these compounds are known to be repellent to a broad range of insects, including mosquitoes and stable flies.
“Even in the famous musical Cats there are scenes where you see a cat intoxicate another cat using catnip powder,” said study’s lead author Professor Masao Miyazaki, an animal behavior researcher at Iwate University.
“We found that physical damage of silvervine by cats promoted the immediate emission of total iridoids, which was 10-fold higher than from intact leaves.”
“Not only were more iridoids released, but their composition changed in ways that seemed to encourage the cats.”
“Nepetalactol accounts for over 90% of total iridoids in intact leaves, but this drops to about 45% in damaged leaves as other iridoids greatly increase,” he said.
“The altered iridoid mixture corresponding to damaged leaves promoted a much more prolonged response in cats.”
To test if the felines were reacting to these compounds specifically, the cats were given dishes with pure nepetalactone and nepetalactol.
“Cats show the same response to iridoid cocktails and natural plants except for chewing,” Professor Miyazaki said.
“They lick the chemicals on the plastic dish and rub against and roll over on the dish.”
“When iridoid cocktails were applied on the bottom of dishes that were then covered by a punctured plastic cover, cats still exhibited licking and chewing even though they couldn’t contact the chemicals directly.”
“This means that licking and chewing is an instinctive behavior elicited by olfactory stimulation of iridoids.”
The team now plans to find which gene is responsible for cats’ reaction to catnip and silver vine.
“Our future studies promise to answer the key remaining questions of why this response is limited to felids, and why some cats don’t respond to these plants,” Professor Miyazaki said.
The results appear in the journal iScience.
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Reiko Uenoyama et al. Domestic cat damage to plant leaves containing iridoids enhances chemical repellency to pests. iScience, published online June 14, 2022; doi: 10.1016/j.isci.2022.104455
Source link: https://www.sci.news/biology/cats-plant-damaging-behavior-10905.html
