Olfactory eavesdropping between two competing stin

Authors: Elinor M Lichtenberg Michael Hrncir Izabel C Turatti James C Nieh

Publish Date: 2010/11/18

Volume: 65, Issue: 4, Pages: 763-774

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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 highquality 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 decisionmaking processAnimals at multiple trophic levels actively search for patchily distributed food such as mobile prey flowering or fruiting trees or carrion Such consumers can improve search efficiency and ultimately fitness by using information provided by the food itself or other organisms in the vicinity Giraldeau 1997 Dornhaus and Chittka 2004 Use of social information sensu Danchin et al 2004 by foragers appears to be widespread Information can come from signals features or behaviors that have evolved to alter the behavior of the receiver in a specific way or cues which did not evolve because of such effects Maynard Smith and Harper 2003 When signals provide such information unintended receivers that use it are exhibiting “interceptive eavesdropping” Because signals evolve through selection for information flow they are vulnerable to selective pressures exerted by eavesdroppers Peake 2005 Evolutionary and ecological effects of eavesdropping may be particularly strong and diverse in the context of foraging because resultant increases in food discovery efficiency cascade through food webs Kean et al 2003 Many examples show predators and prey benefiting from social information to locate prey and avoid predators respectively eg sources in Stowe et al 1995 Peake 2005 Seppänen et al 2007 Valone 2007 However social information can also improve search efficiency within a trophic level In this latter context heterospecific eavesdropping on signals and “spying” using social information provided by cues Wisenden and Stacey 2005 can affect community structure Such strategies can 1 increase the frequency of interaction among competitors Seppänen et al 2007 or 2 drive the formation and maintenance of foraging groups Goodale et al 2010 that provide benefits eg protection that overcome costs of food sharing Stevens and Gilby 2004Despite the ecological implications of eavesdropping little is known about how dominant and subordinate species competing for food use social information To date only a handful of studies have investigated interceptive eavesdropping on food location or quality signals by heterospecifics Exploitation of heterospecific food location cues has also received some attention primarily with social insects Experiments suggest that subordinate species can avoid competitors eg Pimm et al 1985 Fletcher 2008 Evans et al 2009 Slaa and Hughes 2009 or depleted resources eg Nakashima et al 2002 Yokoi et al 2007 by using heterospecific visitation signals and cues This latter phenomenon may be quite sophisticated bumble bees can learn to be attracted or repelled by social information depending on their past experience with the food source use it to determine when flowers replenish their nectar and increase rejection of visited flowers when the visitor was an aggressive species Avoidance of depleted resources through detection of chemical or visual cues likely saves bees time Goulson 2009 thereby increasing foraging efficiency Dominant species on the other hand are sometimes attracted to food cues and signals of heterospecific competitors reviewed in Slaa and Hughes 2009 Goodale et al 2010 This diversity of responses suggests the rules governing eavesdropping and spying within a trophic level are more complex than in predator–prey situations and require more sophisticated decision making Coolen et al 2003 To understand these rules and the effects of social information on communities and signaling systems we must further investigate withintrophiclevel eavesdropping and spying across a range of species

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