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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2010.06.018 Byline: Sandra Steiger (a)(b), Josef K. Muller (b) Abstract: Burying beetles exhibit elaborate biparental care, in which a male and a female bury a carcass upon which they rear their brood and defend it against conspecific competitors. If an intruder succeeds in taking over the carcass, it kills the entire brood and rears its own young on the remaining resource. However, the resident male and female are able to discriminate between an intruder and their breeding partner, and assist their mate in driving off intruders of either sex. Efficient brood guarding requires effective recognition and discrimination mechanisms. Theory predicts that the setting of the optimal acceptance threshold should be affected by the rates of interaction with desirable and undesirable individuals, and shift towards a less permissive threshold when the probability of encountering intruders increases. Here we provide a critical test of acceptance-threshold theory by investigating discrimination rules during reproduction in the burying beetle Nicrophorus vespilloides. The beetles typically discriminate between their breeding partners and conspecific intruders based on a class-specific discrimination rule: they generally accept beetles that are also caring for larvae (whether their own partner or not), but are aggressive towards all nonbreeding beetles. However, we demonstrate that this recognition system is flexible at the level of individual experience and changes with context. After the introduction of an intruder, rejection rate increased, which was manifested as a shift from class-specific to individual-specific discrimination: males suddenly began discriminating between their own breeding partner and novel breeding females, and were more aggressive towards the latter. We show that the plasticity in the recognition system is not caused by template updating, but instead by a flexible acceptance threshold. Our experiments suggest that breeding males learn the individual features of their own breeding partner, but set their acceptance threshold depending on the risk of encountering an intruder. Author Affiliation: (a) Behavior, Ecology, Evolution & Systematics Section, School of Biological Sciences, Illinois State University, U.S.A. (b) Faculty of Biology, Department of Evolutionary Biology and Ecology, University of Freiburg, Germany Article History: Received 25 March 2010; Revised 20 April 2010; Accepted 19 May 2010 Article Note: (miscellaneous) MS. number: A10-00208

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2009.09.019 Byline: Wolf Haberer (a), Sandra Steiger (a)(b), Josef K. Muller (a) Abstract: In recent years, studies have shown that animals can communicate their physiological state or condition by means of chemical signals. However, as the chemicals involved in the condition-dependent signals have rarely been identified, evolutionary mechanisms that ensure their reliability are not well understood. We identified a volatile chemical signal that may serve as a reliable indicator of hormonal state in burying beetles, and is involved in their partner recognition system. Burying beetles reproducing on carcasses are able to distinguish between their breeding partners and infanticidal conspecifics. This discrimination depends on breeding status, which is positively linked to juvenile hormone III (JH III) titre. Breeding Nicrophorus vespilloides beetles, in contrast to nonbreeding ones, emitted considerable amounts of (E)-methylgeranate. The amount of emitted (E)-methylgeranate was positively correlated with juvenile hormone titres known from other burying beetle studies. Moreover, our behavioural experiments showed that dummies treated with methylgeranate induced tolerant behaviour, whereas control dummies were treated aggressively. The fact that (E)-methylgeranate and JH III share a conspicuous structural similarity and the same biosynthetic pathway may explain how the reliability of the signal for JH titre is ensured. We discuss the implications of our results in the light of theoretical work on the evolution of chemical communication, particularly on the origin of chemical signals. Author Affiliation: (a) Faculty of Biology, Department of Evolutionary Biology and Ecology, University of Freiburg, Germany (b) Behavior, Ecology, Evolution and Systematics Section, School of Biological Sciences, Illinois State University, USA Article History: Received 25 June 2009; Revised 4 August 2009; Accepted 9 September 2009 Article Note: (miscellaneous) MS. number: 09-00428