Competition over workers: fertility signalling in wingless queens of <Emphasis Type="Italic">Hypoponera opacior</Emphasis> |
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Authors: | S Foitzik J Fröba M H Rüger V Witte |
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Institution: | 1.Zoological Institute, Evolutionary Biology,Johannes Gutenberg University Mainz,Mainz,Germany;2.Department Biology II, Behavioural Ecology,Ludwig-Maximilians-Universit?t München,Planegg-Martinsried,Germany |
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Abstract: | The ant Hypoponera opacior exhibits alternative reproductive morphs associated with distinct sexual behaviours. Wingless, worker-like gynes mate in
fall in their mother nest. Subsequently, these polygynous nests divide and wingless queens disperse on foot accompanied by
workers, which help during nest foundation. Local resource competition amongst wingless queens was indicated by male-biased
sex ratios. Queens compete over access to workers, and this competition manifests in dominance interactions. We colour-marked
queens and workers to study this behaviour. Marked queens were treated aggressively and frequently killed by nestmates, whilst
similarly labelled workers were readopted. We hypothesise that mated wingless queens—although they resemble workers in external
morphology—differ chemically and that fertile queens with divergent odours are not tolerated. Thereby, sterile H.
opacior workers avoid the risk to raise offsprings of unrelated queens. However, when nests split, workers should base their decision
which queen to follow not only on relatedness, but also on queen fertility. Cuticular hydrocarbon profiles of queens could
serve as an honest signal for workers. Indeed, gas chromatography showed that hydrocarbon composition differs between workers
and mated queens and is linked to ovary development in queens. Workers and unmated queens exhibit complex profiles of short-chained
hydrocarbons, whilst fertile queens carry few, long-chained alkenes and branched alkanes. Furthermore, ovary length was correlated
to the relative amounts of characteristic hydrocarbons of queens. The chemical profile was also associated with eye size—an
unalterable trait in adult insects—suggesting that larval nutrition and consequently body size affects adult ovary development. |
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