Eavesdropping selects for conspicuous signals.

Animal communication signals generally evolve to become increasingly conspicuous for intended receivers [1]. However, such conspicuous signals are also more susceptible to eavesdropping, i.e. exploitation by unintended receivers [2]. It is typically thought that eavesdroppers harm signalers and select against conspicuous signals [3]. But, if signal conspicuousness deters eavesdroppers by indicating a cost, all receivers benefit. This may occur when eavesdroppers exploit food recruitment signals but need to fight for food access [4]. Using eusocial insects, stingless bees, we show that conspicuous signals can indicate competitive costs and enable signalers to escape eavesdropper-imposed costs. The dominant eavesdropper, Triogona hyalinata, avoided higher levels of Trigona spinipes pheromone that indicate a food source difficult to win, and showed attraction to lower pheromone levels that indicate a relatively undefended resource. Our decision-analysis model reveals that eavesdropping individuals that can assess takeover costs can benefit their colony by recruiting to weakly defended resources and avoiding costly takeover attempts. © 2014 Elsevier Ltd