Interactions among siblings fall on a continuum with competition and cooperation at opposite ends of the spectrum. Prior work on the burying beetle Nicrophorus vespilloides suggests that parental care shifts the balance between competition and cooperation by masking a density-dependent shift from cooperation to competition. However, these results should be interpreted with caution because they were based on correlational evidence for an association between larval density at dispersal and mean larval mass at dispersal. Here...