Learning of an oddity rule by pigeons in a four-choice touch-screen procedure

Relational learning in honeybees (Apis mellifera): Oddity and nonoddity discrimination

Honeybee learning is surprisingly similar to vertebrate learning and one implication is that the basic associative learning principles are also similar. This research extends the work to more complex cognitive phenomena. Forager bees were trained individually to visit a laboratory window for sucrose. On each training trial for all experiments, bees found three stimuli, two identical and one different. In Experiments 1 and 2, stimuli were three-dimensional two-color patterns, and in Experiments 3 and 4, stimuli were two-color patterns displayed on a computer monitor. Training was trial-unique, that is, a different triad of stimuli was presented on each trial. In Experiments 1 and 3, choice of odd was rewarded and choice of nonodd was punished. In Experiments 2 and 4, choice of nonodd was rewarded and choice of odd was punished. On every trial, the initial choice was recorded and correction permitted. Honeybees learned to choose the odd stimulus in Experiments 1 and 3 and the nonodd stimuli in Experiments 2 and 4. The results provide compelling evidence of oddity and nonoddity learning, often interpreted as relational learning in vertebrates. Whether the mechanism of such learning in honeybees is similar to that of vertebrate species remains to be determined.

Abstract-concept learning of difference in pigeons

Many species have demonstrated the capacity to learn abstract concepts. Recent studies have shown that the quantity of stimuli used during training plays a critical role in how subjects learn abstract concepts. As the number of stimuli available in the training set increases, so too does performance on novel combinations. The role of set size has been explored with learning the concept of matching and same/different but not with learning the concept of difference. In the present study, pigeons were trained in a non-matching-to-sample task with an initial training set of three stimuli followed by transfer tests to novel stimuli. The training set was progressively doubled eight times with learning and transfer following each expansion. Transfer performance increased from chance level (50 %) at the smallest set size to a level equivalent to asymptotic training performance at the two largest training set sizes (384, 768). This progressive novel-stimulus transfer function of a non-matching (difference) rule is discussed in comparison with results from a similar experiment where pigeons were trained on a matching rule.

Insect herbivores should follow plants escaping their relatives

Neighboring plants within a local community may be separated by many millions of years of evolutionary history, potentially reducing enemy pressure by insect herbivores. However, it is not known how the evolutionary isolation of a plant affects the fitness of an insect herbivore living on such a plant, especially the herbivore’s enemy pressure. Here, we suggest that evolutionary isolation of host plants may operate similarly as spatial isolation and reduce the enemy pressure per insect herbivore. We investigated the effect of the phylogenetic isolation of host trees on the pressure exerted by specialist and generalist enemies (parasitoids and birds) on ectophagous Lepidoptera and galling Hymenoptera. We found that the phylogenetic isolation of host trees decreases pressure by specialist enemies on these insect herbivores. In Lepidoptera, decreasing enemy pressure resulted from the density dependence of enemy attack, a mechanism often observed in herbivores. In contrast, in galling Hymenoptera, enemy pressure declined with the phylogenetic isolation of host trees per se, as well as with the parallel decline in leaf damage by non-galling insects. Our results suggest that plants that leave their phylogenetic ancestral neighborhood can trigger, partly through simple density-dependency, an enemy release and fitness increase of the few insect herbivores that succeed in tracking these plants.