Optimization of host species raiding preference relative to temperature and host defensive capability by the kidnapper ant Temnothorax americanus

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Novotny, Nolan
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Kidnapper ants raid host-species colonies, abscond with brood, and raise host workers that work for the kidnapper colony. Temnothorax americanus uses Temnothorax ambiguus, Temnothorax curvispinosus and Temnothorax longispinosus as hosts. In southern Ontario, T. curvispinosus colonies are absent, while free living T. ambiguus colonies occur in warm microhabitats and T. longispinosus colonies occupy cooler microhabitats, presumably achieving optimal performance in species typical microhabitat. In choice tests T. americanus preferentially selects pupae of the host species whose temperature optimum is opposite to the temperature conditions of the T. americanus colony, possibly reflecting a preference to retrieve the least well defended host species relative to temperature. I tested whether that temperature dependent pupal retrieval preference extends to raiding preference for whole colonies and whether the defensive capability of T. ambiguus and T. longispinosus against T. americanus raids depends on temperature. I acclimatized T. americanus colonies and their hosts to 25°C or 15°C in controlled environment chambers and offered simultaneous choices of standardized nests of the two host species to assess any effect of temperature on host species raiding preference. I also allowed T. americanus to raid each host species within either temperature and recorded the numbers of host species casualties, kidnapper casualties, salvaged brood and captured brood, and the length of raids to assess any effects of temperature and species on defensive capability. I also tested for associations between kidnapper colony composition and raiding success. There was no effect of temperature or host species on raiding preference or host defensive capability, suggesting that host species are raided without preference and are equally well defended regardless of temperature. Recent prior raiding experience did increase kidnapper ant success in raids and larger T. americanus colonies captured more brood. Defensive capability does not appear to drive the documented temperature-dependent pupal retrieval preference. It is possible that temperature instead influences the volatility of the cuticular-hydrocarbon profiles of the pupae of the host species differentially, thus affecting the attractiveness of the pupae to kidnapper colony members, though future work is needed to determine exactly what drives this temperature dependent pupal retrieval preference.
Behavioural ecology, Social parasitism, Optimization, Ants, Temnothorax americanus, Slave-making ant, Kidnapper ant