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 affnity 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 frst experiment,we tested 12 rats and calculated repeatability of their behaviors across 12 sessions of an enriched open-feld 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 fnding resources.Nevertheless,these“even”explorers still greatly differed in their level of activity,orderliness and affnity 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.

Does reproductive mode affect sexually-selected coloration?Evaluating UV-blue spots in parthenogenetic and bisexual lizards of the genus Darevskia

Sexual selection often leads to evolution of conspicuous signals,raising the chances of attracting not only potential mates,but also predators.In lacertid lizards,ultraviolet(UV)-blue spots on flanks and shoulders represent such a trait.Some level of correlation between male and female ornamen-tation is also known to exist.Therefore,the phenotype of females may change in the absence of sexual selection.We tested this hypothesis on a complex of parthenogenetic and bisexual lizards of the genus Darevskia.We evaluated area,counts,and chromatic properties(UV opponency,sat-uration)of UV-blue spots and compared the values between the clones and their bisexual progeni-tor species.We found a fair heterogeneity between the parthenogenetic species,but no general tendency toward higher crypsis or conspicuousness.Values of the parthenogens were not signifi-cantly different from the values of sexual females.A possible explanation is that the changes in se-lective forces associated with parthenogenetic reproduction are too small to affect the resulting pattern of selective pressures on the studied traits,or that the phenotypes of the parthenogens re-sult from the unique combination of parental genomes and are conserved by clonal reproduction.

Morphological characteristics of blood cells in monitor lizards:is erythrocyte size linked to actual body size?

Blood cell morphology and count are not uniform across species.Recently,between-species comparisons revealed that the size of red blood cells is associated with body size in some lizard taxa,and this finding was interpreted in the context of the metabolic theory.In the present study,we examined the numbers and the size of blood cells in 2 species of monitor lizards,the mangrove-dwelling monitor(Varanus indicus)and the savannah monitor(V.exanthematicus),and we compared these traits in individuals of different body size.The results revealed that during the course of ontogeny,the size of red blood cells increases with body mass.Because the mass-specific metabolic rate decreases with body size and the cell volume-to-surface ratio decreases with the cell size,changes in the erythrocyte size might be the result of oxygen transport adjustment.