A dog's dish - half empty or half full?

We know that humans vary in their underlying temperament (negative versus positive mood), with ~50% of the variation due to genetic factors.  It turns out that dogs also show variation, with more negative underlying moods predicting the degree of their distress upon separation (Being left a home alone, with the most common separation-related behaviors being vocalising, destruction and toileting). Mendl et al. test for underlying optimism/pessimism involved placing bowls in two rooms. One bowl contained food, while another was empty. After training the dogs to understand that bowls can sometimes be empty, and sometimes full, they began to place bowls in ambiguous locations. Dogs that quickly raced to the locations were more optimistic, and in search of food. Those that did not were deemed pessimistic. The more separation anxiety a dog expressed while in isolation, the more likely the dog was to have a pessimistic reaction.