Separation at weaning from the family is stressful for naturally group-living, but not solitary-living, male African striped mice Rhabdomys

摘要

Early separation from a family is stressful for young mammals, but might be more stressful for group-living than solitary species. Using juvenile males of three African striped mice Rhabdomys taxa that are either group (R. pumilio) or solitary (R. dilectus dilectus and R. d. chakae) living, we predicted greater separation anxiety in R. pumilio than R. dilectus because group-living could reduce anxiety in R. pumilio. Three brothers from each of 10 litters per taxon were randomly assigned soon after natural weaning (25 days) to one of three treatments for 10 days: (1) remained with the family (philopatric); (2) separated from the family by a wire mesh barrier (separated); and (3) isolated from the family (isolated). Males were individually tested in a four-arm maze to assess their anxiety responses and sampled for corticosterone concentrations 20 mins and 10 days later. Compared to R. dilectus males, R. pumilio males showed a greater treatment response to separation: philopatric males used the light arms of the maze less and had higher corticosterone concentrations compared to isolated males, which spent the most time in the light arms and had the lowest corticosterone concentrations overall; separated males showed an intermediate behavioural response, but had similar corticosterone concentrations to philopatric males. Thus, separation from a family group is more stressful in group-living Rhabdomys and this stress response dissipates with time. Philopatry and group-living may be more important for young R. pumilio, whereas dispersal at weaning is an important life history event for solitary R. dilectus.