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

The number of experiments for each pattern of composition.

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

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 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

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 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

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

Chromosomal Aberrations in Large Japanese Field Mice (<i>Apodemus speciosus</i>) Captured near Fukushima Dai-ichi Nuclear Power Plant

Since the Fukushima Dai-ichi Nuclear Power Plant accident, radiation effects on nonhuman biota in the contaminated areas have been a major concern. Here, we analyzed the frequencies of chromosomal aberrations (translocations and dicentrics) in the splenic lymphocytes of large Japanese field mice (<i>Apodemus speciosus</i>) inhabiting Fukushima Prefecture. <i>A. speciosus</i> chromosomes 1, 2, and 5 were flow-sorted in order to develop <i>A. speciosus</i> chromosome-specific painting probes, and FISH (fluorescence in situ hybridization) was performed using these painting probes to detect the translocations and dicentrics. The average frequency of the translocations and dicentrics per cell in the heavily contaminated area was significantly higher than the frequencies in the case of the noncontaminated control area and the slightly and moderately contaminated areas, and this aberration frequency in individual mice tended to roughly increase with the estimated dose rates and accumulated doses. In all four sampling areas, the proportion of aberrations occurring in chromosome 2 was approximately >3 times higher than that in chromosomes 1 and 5, which suggests that <i>A. speciosus</i> chromosome 2 harbors a fragile site that is highly sensitive to chromosome breaks induced by cellular stress such as DNA replication. The elevated frequency of chromosomal aberrations in <i>A. speciosus</i> potentially resulting from the presence of a fragile site in chromosome 2 might make it challenging to observe the mild effect of chronic low-dose-rate irradiation on the induction of chromosomal aberrations in <i>A. speciosus</i> inhabiting the contaminated areas of Fukushima