[Show abstract][Hide abstract] ABSTRACT: Animal communication signals generally evolve to become increasingly conspicuous for intended receivers . However, such conspicuous signals are also more susceptible to eavesdropping: exploitation by unintended receivers . It is typically thought that eavesdroppers harm signalers and select against conspicuous signals . 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 . 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, Trigona hyalinata, avoided higher levels of T. 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 who assess takeover costs can benefit their colony by recruiting to weakly defended resources and avoiding costly takeover attempts.
Current Biology 07/2014; 24(1):R598-599. · 9.49 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Foragers can improve search efficiency, and ultimately fitness, by using social information: cues and signals produced by other animals that indicate food location or quality. Social information use has been well studied in predator-prey systems, but its functioning within a trophic level remains poorly understood. Eavesdropping, use of signals by unintended recipients, is of particular interest because eavesdroppers may exert selective pressure on signaling systems. We provide the most complete study to date of eavesdropping between two competing social insect species by determining the glandular source and composition of a recruitment pheromone, and by examining reciprocal heterospecific responses to this signal. We tested eavesdropping between Trigona hyalinata and Trigona spinipes, two stingless bee species that compete for floral resources, exhibit a clear dominance hierarchy and recruit nestmates to high-quality food sources via pheromone trails. Gas chromatography-mass spectrometry of T. hyalinata recruitment pheromone revealed six carboxylic esters, the most common of which is octyl octanoate, the major component of T. spinipes recruitment pheromone. We demonstrate heterospecific detection of recruitment pheromones, which can influence heterospecific and conspecific scout orientation. Unexpectedly, the dominant T. hyalinata avoided T. spinipes pheromone in preference tests, while the subordinate T. spinipes showed neither attraction to nor avoidance of T. hyalinata pheromone. We suggest that stingless bees may seek to avoid conflict through their eavesdropping behavior, incorporating expected costs associated with a choice into the decision-making process. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00265-010-1080-3) contains supplementary material, which is available to authorized users.
Behavioral Ecology and Sociobiology 04/2011; 65(4):763-774. · 2.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Competition for floral resources is a key force shaping pollinator communities, particularly among social bees. The ability of social bees to recruit nestmates for group foraging is hypothesized to be a major factor in their ability to dominate rich resources such as mass-flowering trees. We tested the role of group foraging in attaining dominance by stingless bees, eusocial tropical pollinators that exhibit high diversity in foraging strategies. We provide the first experimental evidence that meliponine group foraging strategies, large colony sizes and aggressive behavior form a suite of traits that enable colonies to improve dominance of rich resources. Using a diverse assemblage of Brazilian stingless bee species and an array of artificial "flowers" that provided a sucrose reward, we compared species' dominance and visitation under unrestricted foraging conditions and with experimental removal of group-foraging species. Dominance does not vary with individual body size, but rather with foraging group size. Species that recruit larger numbers of nestmates (Scaptotrigona aff. depilis, Trigona hyalinata, Trigona spinipes) dominated both numerically (high local abundance) and behaviorally (controlling feeders). Removal of group-foraging species increased feeding opportunities for solitary foragers (Frieseomelitta varia, Melipona quadrifasciata and Nannotrigona testaceicornis). Trigona hyalinata always dominated under unrestricted conditions. When this species was removed, T. spinipes or S. aff. depilis controlled feeders and limited visitation by solitary-foraging species. Because bee foraging patterns determine plant pollination success, understanding the forces that shape these patterns is crucial to ensuring pollination of both crops and natural areas in the face of current pollinator declines. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00040-009-0055-8) contains supplementary material, which is available to authorized users.