The number of experiments for each pattern of composition.

<p>Three colonies (I, II, III) are separately shown.</p

A Distinct Role of the Queen in Coordinated Workload and Soil Distribution in Eusocial Naked Mole-Rats

<div><p>We investigated how group members achieve collective decision-making, by considering individual intrinsic behavioural rules and behavioural mechanisms for maintaining social integration. Using a simulated burrow environment, we investigated the behavioural rules of coordinated workload for soil distribution in a eusocial mammal, the naked mole-rat (<em>Heterocephalus glaber</em>). We tested two predictions regarding a distinct role of the queen, a socially dominant individual in the caste system: the presence of a queen would increase the workload of other caste individuals, and the cues by a queen would affect the soil distribution. In experiment 1, we placed four individuals of various castes from the same colony into an experimental burrow. Workers exhibited the highest frequency of workload compared to other castes. The presence of a queen activated the workload by other individuals. Individuals showed a consistent workload in a particular direction so as to bias the soil distribution. These results suggest that individuals have a consensus on soil distribution and that the queen plays a distinct role. In experiment 2, we placed the odour of a queen in one of four cells and observed its effect on other individuals’ workload and soil distribution. Relative to other cells, individuals frequently dug in the queen cell so the amount of soil in the queen cell decreased. These results suggest that queen odour is an important cue in coordinated workload and soil distribution in this species.</p> </div

Relationships between workload and the type of workload (consensus building or opposite).

<p>Results given are by each caste category (black circles: queen; grey circles: reproductive males; white circles: workers) in experiments 1 and 2. (a, b) In experiment 1, the proportion of consensus building (a: removing soils from the emptied cell vs. its opposite; b: carrying soils into a filled cell vs. its opposite) of the total frequency of sweeping behaviour is shown (number of individuals: queen, n = 3; reproductive males, n = 5; and workers, n = 23). In experiment 2, the proportion of consensus building (removing soils from a queen cell vs. its opposite; number of individuals: reproductive males, n = 5; and workers, n = 16). (c) The frequency of digging in each cell. In experiment 1, the number on the x-axis indicates the order of cells according to the number of soils after the experiments (1 indicates a cell with the least number of soils, and 4 denotes a cell with the largest number of soils). In experiment 2, ‘queen’ and ‘other’ indicate a cell with the queen odour and other cells, respectively. Asterisk indicates a significant difference (p<0.05). Individual mean ±1 S.E. is shown.</p

The effect of presence of a queen on workload (sweeping, n = 4902; digging, n = 5970) by other caste individuals in experiment 1.

<p>RM: reproductive males. W: workers. The identity of colony (n = 3) and individual (n = 28) were determined at random. (See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0044584#pone-0044584-t001" target="_blank">Table 1</a> for the number of trials in each colony.).</p

Illustrated explanation of our definition of “consensus” and “opposite” sweeping.

<p>(a) emptying <i>vs</i>. filling an emptied cell; (b) emptying <i>vs.</i> filling a filled cell.</p

The total frequency of (a) sweeping and (b) digging behaviours during a 90 minute experiment.

<p>Results shown are for each caste in different experimental settings (Q: a queen, n = 3; RM: reproductive males, <i>n</i> = 5; and W: workers, <i>n</i> = 23). Asterisk indicates a significant difference. Individual mean ±1 S.E. is shown.</p

Experimental setup.

<p>Four cells were connected by tunnels in a circle. In total, 300 ‘soil’ particles of different colours were placed in each cell at the beginning of the experiment.</p

The total frequency of (<i>a</i>) sweeping and (<i>b</i>) digging behaviours during a 90 minute experiment.

<p>Results shown are for each caste (RM: reproductive males and W: workers) in different experimental settings. Q(–): experiment 1 without a queen (RM: <i>n = </i>5; W: <i>n</i> = 21); Q(+): experiment 1 with a queen (RM: <i>n</i> = 5; W: <i>n</i> = 23); exp 2: experiment 2 (RM: <i>n</i> = 5; W: <i>n</i> = 16). Asterisk indicates a significant difference. Individual mean ±1 S.E. is shown.</p