Abstract
The ant Hypoponera opacior exhibits alternative reproductive morphs of males and females associated with distinct sexual behaviours. Our long-term study reports strong seasonality in sexual production with a mating season in early and one in late summer. Winged (alate) reproductives emerge in June, swarm during the monsoon season and establish new colonies independently. In contrast, wingless worker-like (ergatoid) reproductives that appear in late August mate within their natal or adjacent nests and either do not disperse or establish new nests close by. These divergent dispersal patterns allowed us to analyse the impact of local factors on investment strategies by comparing sex allocation between and within the two reproductive events. The optimal sex ratio for ergatoid reproductives should be influenced both by competition for matings between brothers (local mate competition) and rivalry among young locally dispersing queens for workers, nest sites or food (local resource competition). The greater importance of local resource competition was demonstrated both by a male-biased sex ratio for wingless sexuals and a stronger increase in the number of males with total sexual production than for the number of queens. Microsatellite analysis revealed that inter-nest variation in relatedness asymmetry cannot explain split sex ratios in the August generation. Instead, nests with related ergatoid males raised a male-biased sex ratio contrary to the expectations under local mate competition. In conclusion, male bias in wingless H. opacior indicates that local mate competition is less strong than local resource competition among ergatoid queens over the help of workers during nest foundation.
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Acknowledgements
We are grateful to the SWRS for accommodation and support. We thank the “Western Regional Climate Centre” for providing weather data online (www.wrcc.org). We are thankful to the Munich ant group for helpful comments on the manuscript. Funding came from the DFG (German Science Foundation; Fo 289/5-1, 3) and two grants (SWRS Student Support Fund) from the American Museum of Natural History (New York) in 2004 and 2005.
We declare that the experiments comply with the current laws of the country in which they were performed. The authors declare that they have no conflict of interest.
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Foitzik, S., Kureck, I.M., Rüger, M.H. et al. Alternative reproductive tactics and the impact of local competition on sex ratios in the ant Hypoponera opacior . Behav Ecol Sociobiol 64, 1641–1654 (2010). https://doi.org/10.1007/s00265-010-0977-1
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DOI: https://doi.org/10.1007/s00265-010-0977-1