The dog handshake is initially rewarded with food
Scientists in Austria say they have found a basic form of jealousy in dogs.
The Vienna-based researchers showed that dogs will stop doing a simple task when not rewarded if another dog, which continues to be rewarded, is present.
Writing in the journal PNAS, the scientists say this shows a sensitivity in dogs that was only previously found in primates.
The researchers now plan to extend their experiments to look at co-operative behaviour in wolves.
The experiment consisted of taking pairs of dogs and getting them to present a paw for a reward. On giving this "handshake" the dogs received a piece of food.
One of the dogs was then asked to shake hands, but received no food. The other dog continued to get the food when it was asked to perform the task.
The dog without the reward quickly stopped doing the task, and showed signs of annoyance or stress when its partner was rewarded.
To make sure that the experiment was really showing the interaction between the dogs rather than just the frustration of not being rewarded, a similar experiment was conducted where the dogs performed the task without the partner. Here they continued to present the paw for much longer.
The dog sees its partner rewarded
Dr Frederike Range from the department of neurobiology and cognition research at the University of Vienna, says this shows that it was the presence of the rewarded partner which was the greater influence on their behaviour.
"The only difference is one gets food and the other doesn't, they are responding to being unequally rewarded." she said.
The researchers say this kind of behaviour, where one animal gets frustrated with what is happening with another, has only been observed in primates before.
Studies with various types of monkeys and chimpanzees show they react not only to seeing their partners receiving rewards when they are not, but also to the type of reward.
The dog study also looked at whether the type of reward made a difference. Dogs were given either bread or sausage, but seemed to react equally to either. Dr Range says this may be because they have been trained.
"It's through the fact they have to work for the reward, this confers it with a higher value," she said.
The researchers say this behaviour, reacting to others receiving rewards, may represent an earlier stage in the evolution of co-operative behaviours seen in human and primates.
"I think it's a precursor, simpler than in humans, it's a selfish behaviour, they don't react to seeing others treated unfairly. With humans they react, say it's unfair, we can't see anything like that in the dogs," said Dr Range.
The researchers say the type of behaviour exhibited in the experiment is probably due to the dog's close association with humans. Dr Range says other animals need to be studied to really show how animals naturally exhibit jealousies or cooperate.
The dog soon refuses to raise a paw
"I'm sure that it's not something that evolved with the dogs, we will have to test it in wolves and other cooperating species," she said.
Dr Range is currently rearing wolf cubs in order to perform similar experiments. She says the wolves will be able to do the paw test, but that it is really the wrong experiment. She regards this as something unnatural, that dogs are taught by their owners.
"They can give the paw, but it's not the right test. We must take the human out of the equation, then we can compare directly wolves with dogs."