Male mating tactics and lethal combat in the nonpollinating fig wasp Sycoscapter australis

Abstract

Fatal fights are rare in the majority of animal species but are a common component of mate competition between wingless males of some species of fig-associated wasps. We investigated fatal fighting in Sycoscapter australis, a nonpollinating fig wasp found in the syconia (inflorescences) of the Moreton Bay fig, Ficus macrophylla. Overall, about 25% of males sustained fatal injuries during the mate competition period. Measurement and analysis of 349 males revealed a sevenfold difference in mandible size between the largest and smallest individuals, as well as evidence for dimorphism in the mandibles, which showed positive allometry in relation to other body parts. Small and large males did not differ significantly in their injury levels. Mandibles are the main weapons used in fights and injury levels were highest in syconia where males on average had larger mandibles. Injury levels also increased with the estimated operational sex ratio in a syconium, although this variable explained little of the variation. In contrast to the usual assumptions about wingless male fig wasps, a significant number (17%) of males emerged from their natal syconia. Females emerged at a fairly constant rate over many hours, consistent with contest competition between males for access to matings. In contrast, the more numerous females of the pollinating wasp speciesPleistodontes froggatti showed a strong peak in emergence, consistent with scramble competition between males for access to mates.