Helping syndrome is partially confirmed in the eusocial naked mole-rat.

In highly organized animal societies, behavioural heterogeneity of the members can be crucial for group success. In contrast to eusocial insects, in which task specialization is common, a clear division of labour is often absent in cooperatively breeding species. In these species, contributions to different tasks are sometimes positively correlated across individuals; this phenomenon is called helping syndrome. Previously, eusocial naked mole-rats, Heterocephalus glaber , were thought to display a helping syndrome consisting of burrowing, food carrying and nest building. However, previous studies combined different burrowing tasks in which the locomotive patterns varied widely, possibly missing substantial variation in the behavioural types of individuals. Therefore, it is necessary to reexamine the relations between task contributions among naked mole-rats in more detail. This study analysed six types of activities including four tasks in captive naked mole-rats, and partially confirmed the presence of a helping syndrome in nonbreeding individuals. Frequencies of different activities were significantly positively correlated across individuals in some combinations, but were not significantly correlated in other combinations. Also, individual behavioural types did not simply depend on activity time. Although age- or size-based polyethisms were found in different trends across task types, the results of the correlations between tasks remained mostly unchanged after controlling for the effects of age or body mass. This suggests large interindividual variation that could not be sufficiently explained by age- or size-based polyethisms. The partial support of a helping syndrome suggested that the task allocation system among these eusocial mammals may be more complex than previously assumed. • Contributions to different tasks are often positively correlated in helpers. • The correlations were partially positive in the naked mole-rat. • Age- or size-based polyethisms were found in different trends across task types. • Relationships between tasks did not change even accounting for age or body mass. [ABSTRACT FROM AUTHOR]