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Abstract

Male Madagascar hissing cockroaches, Gromphadorhina portentosa Schaum (Dictyoptera: Blaberidae) have a well-defined dominance hierarchy that has been assumed to explain the outcome of most competitive interactions. We studied whether males of this species would alter their level of aggression towards unfamiliar rivals as a function of changing resource availability and value – two factors that are key to aggression levels in non-hierarchical species. We quantified male aggression as three variables (aggressive state – behaviours measured by their duration; aggressive act – behaviours measured by their frequency of occurrence; aggressive latency – the latency to first aggressive behaviour, either state or act) and tested for any context-specific variation within each by manipulating both territorial status (males were either residents or intruders) and access to mates (female present or absent). Both the presence of a female and territorial status affected male aggression towards rivals as measured by duration of aggressive state. Highest levels of aggression were displayed by residents when a female was present. These results show that inter-male aggression in G. portentosa is tuned to the immediate expected payoff from fighting, and not exclusively aimed at establishing dominance relationships (which can affect future payoffs).