ORIGINAL PAPER Alternative reproductive tactics and the impact of local competition on sex ratios in the ant Hypoponera opacior Susanne Foitzik & Ilka Maria Kureck & Markus Hannes Rüger & Dirk Metzler Received: 21 March 2010 / Revised: 27 April 2010 / Accepted: 29 April 2010 / Published online: 19 May 2010 # Springer-Verlag 2010 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. Keywords Alternative reproductive strategies . Sex allocation . Local mate competition . Local resource competition . Relatedness asymmetry . Relatedness . Social insects Introduction In many animal and plant taxa, alternative reproductive strategies within a single sex were shown to allow flexible reactions to environmental and social conditions (Gross 1996; Lovett-Doust and Lovett-Doust 1990). The ability to vary morphological, behavioural, physiological and life history traits can enable an individual or—in the case of social insects—a colony to maximise its reproductive success under a wide range of conditions. The majority of alternative reproductive strategies and tactics that have been described are conditional strategies with alternative tactics of the male sex (Gross 1996). Males are under stronger intrasexual selection because of severe competition for access to females and higher variation in mating success (Gadgil 1972; Trivers 1972). In contrast to the general greater diversity in male reproductive strategies, alternative reproductive phenotypes are more common among social Hymenopteran females. The ancestral states in ants are winged males and females that conduct mating flights. Males in those large swarms undergo scramble competition Communicated by L. Sundström Electronic supplementary material The online version of this article (doi:10.1007/s00265-010-0977-1) contains supplementary material, which is available to authorized users. S. Foitzik (*) : I. M. Kureck : M. H. Rüger : D. Metzler Department Biology II, Behavioural Ecology, Ludwig-Maximilians-Universität München, Grosshadernerstr. 2, 82152 Planegg-Martinsried, Germany e-mail: foitzik@biologie.uni-muenchen.de Behav Ecol Sociobiol (2010) 64:1641–1654 DOI 10.1007/s00265-010-0977-1