Do dogs exhibit jealous behaviors when their owner attends to their companion dog?

Jealousy appears to have clear adaptive functions across species: it emerges when an important social relationship with a valued social partner is threatened by third-party that is perceived as a rival. Dyads of dogs living together and their owners were tested adapting a procedure devised to study jealousy in young human siblings. Owners at first ignored both dogs while reading a magazine (Control episode), and then petted and praised one of the dogs while ignoring the other, and vice versa (Experimental episodes). We found several differences in the dogs' behavior between the Experimental episodes and the Control episode, even though only monitoring (gazing at the owner) was exhibited for a significantly greater amount of time in the Experimental episodes. Remarkable individual behavioral differences emerged, suggesting that the dogs' reactions could be influenced by the relationships that they establish with their owner and the companion dog. Overall, current results do not clearly support our prediction that the ignored dogs would exhibit more behaviors aimed at regaining the owner's attention when their owner directed attention and care to a companion dog, compared to the control situation. The great intra- and inter-dyad behavioral variability and the choice to test cohabiting dogs could have prevented the emergence of a clear jealous reaction. These findings do not exclude that dogs may exhibit a primordial form of jealousy in a realistic situation, but an additional research is needed to fully gauge which situations, if any, could trigger jealousy in dogs and to rule out alternative explanations.