How to explore a new environment: exploratory tactics of the black rat (Rattus rattus).

The black rat (Rattus rattus) is a unique model for studying exploratory tactics due to its enormous colonizing potential. Considerable behavioral variability and consistent interindividual differences might help populations inhabit new environments and persist there even under intense pressure. Additionally, the affinity of the black rat for climbing might be another advantage, widening their potential niche. In this study, we describe the exploratory tactics of the black rats when introduced to a novel environment. In the first experiment, we tested 12 rats and calculated repeatability of their behaviors across 12 sessions of an enriched open-field test. We concluded that climbing is a highly repeatable behavior that serves as an important source of interindividual variability. In the second experiment, we tested 24 black rats in a unique L-shaped arena. Each rat was tested twice. We found that the majority of rats distributed their activity evenly, exploring each part of the apparatus for a similar amount of time, thus maximizing their chances of finding resources. Nevertheless, these "even" explorers still greatly differed in their level of activity, orderliness and affinity for climbing, generating large variability. In contrast, the minority of rats concentrated their activity only on a section of the new environment and were therefore characterized as selective explorers. Overall, we concluded that a combination of such exploratory tactics as well as a bias for even explorers enables black rats to quickly colonize new environments and persist there even under unfavorable conditions.

Emotions triggered by live arthropods shed light on spider phobia.

Spiders are mostly harmless, yet they often trigger high levels of both fear and disgust, and arachnophobia (the phobia of spiders) ranks among the most common specific animal phobias. To investigate this apparent paradox, we turned to the only close relatives of spiders that pose a real danger to humans: scorpions. We adopted a unique methodology in order to assess authentic emotions elicited by arthropods. Over 300 respondents were asked to rate live specimens of 62 arthropod species (including spiders, scorpions, cockroaches, and other insects) based on perceived fear, disgust, and beauty. We found that species' scores on all three scales depended on the higher taxon as well as on body size. Spiders, scorpions, and other arachnids scored the highest in fear and disgust, while beetles and crabs scored the highest in beauty. Moreover, all chelicerates were perceived as one cohesive group, distinct from other arthropods, such as insects or crabs. Based on these results, we hypothesize that the fear of spiders might be triggered by a generalized fear of chelicerates, with scorpions being the original stimulus that signals danger.