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Worker policing without genetic conflicts in a clonal ant - PubMed

  • ️Wed Jan 01 2003

Worker policing without genetic conflicts in a clonal ant

A Hartmann et al. Proc Natl Acad Sci U S A. 2003.

Abstract

In group-living animals, mutual policing to suppress reproduction is an important mechanism in the resolution of conflict between selfish group members and the group as a whole. In societies of bees, ants, and wasps, policing against the production of males by other workers is expected when egg laying by workers decreases the average inclusive fitness of individual group members. This may result (i) from the relatedness of workers being lower to worker than to queen-derived males or (ii) from a lowered overall colony efficiency. Whereas good evidence exists for policing behavior caused by genetic conflicts, policing caused by efficiency factors has not been demonstrated. We investigated the regulation of reproduction in the ant Platythyrea punctata, a species in which colonies are clones because workers are capable of producing female offspring by thelytokous parthenogenesis. Reproductive conflicts resulting from differences in genetic relatedness are therefore not expected, but uncontrolled reproduction by all workers could lead to the destruction of sociality. Here we show that worker policing by aggressive attacks against additionally reproducing workers keeps the number of reproducing workers low. Furthermore, through experimental manipulation of the number of brood items per colony, we show that worker policing can enhance group efficiency.

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Figures

Fig. 1.
Fig. 1.

Number of attacks directed toward ORs (▪), NRs (formula image), and nonreproductives (formula image; only colonies D–F; mean ± SD) observed after the reunion of two separated colony fragments of P. punctata (observation time: colony A, 210 min; colony B, 230 min; colonies C–F, 420 min; colony D, 240 min). In colonies A–D NRs received more attacks than ORs and nonreproductive workers, suggesting worker policing.

Fig. 2.
Fig. 2.

Number of attacks received by ORs and NRs from nonreproductive workers from colony parts 1 (formula image) and 2 (▪) (Wilcoxon matched-pair test; ***, P < 0.001; **, P < 0.01; n.s., not significant; observation time: colony A, 210 min; colony B, 230 min; colonies C and E, 420 min; colony D, 240 min).

Fig. 3.
Fig. 3.

Mean ratio of the number of workers to the number of larvae (A) and the number of total brood items (cocoons, larvae, and eggs) in test (•) and control colonies (○) (± SD) (B). There was no difference between test and control colonies in the worker to larvae ratio later than 24 days and in the worker to brood ratio later than 15 days after the manipulation (Student's t test, all P > 0.05) of observation.

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