The Impact of Environmental Factors on the Efficacy of Chemical Communication in the Burying Beetle (Coleoptera: Silphidae).

There is growing evidence that a wide range of insect sex pheromones are condition dependent and play a fundamental role in mate choice. However, the effectiveness of pheromonal communication might not only depend on internal factors of the sender, but also on attributes of the microhabitat, in which the signaler chooses to emit its chemical signal. For example, the degree of anthropogenic land use might affect how successful the signal is transmitted, as land use has been shown to affect animal communities and the complexity of biotic interactions. To test the hypothesis that parameters of the microenvironment determine males' ability to attract females via their sex pheromone, we used the burying beetle Nicrophorus vespilloides Herbst (Coleoptera: Silphidae) as our model system. We exposed 144 males across differently managed forest stands and analyzed the impact of 29 environmental parameters. Our data revealed that human land use intensity had no effect on a male's attractiveness. However, the harvested tree biomass positively affected the proportion of competitors attracted. Furthermore, we found that soil characteristics were important factors determining the amount and body size of females a male was able to attract. Consequently, we present evidence that the environmental context of a signaling male influences the effectiveness of chemical signaling either because it affects the transmission process or the prevailing abundance of potential signal receivers. Thus, our results demonstrate that males need to make careful decisions about the location where they emit their pheromone, as this choice of microhabitat has an impact on their fitness.

Variation in sex pheromone emission does not reflect immunocompetence but affects attractiveness of male burying beetles-a combination of laboratory and field experiments.

Life history theory predicts a trade-off between male sexual trait expression and immunocompetence. Using burying beetles, Nicrophorus vespilloides, as a model, we investigated the relationship between male immune function, sex pheromone emission, and attractiveness under field conditions. In the first experiment, we tested whether there is a positive correlation between immune capacity, sex pheromone characteristics (quantity, relative composition, and time invested in pheromone emission), and male attractiveness. As a measurement of immune capacity, we used an individual's encapsulation ability against a novel antigen. In the second experiment, we specifically examined whether a trade-off between chemical trait expression and immune function existed. To this end, we challenged the immune system and measured the subsequent investment in sex pheromone emission and the attractiveness of the male under field conditions. We found that a male's immunocompetence was neither related to the emission of the male's sex pheromone nor to its attractiveness in the field. Furthermore, none of the immune-challenge treatments affected the subsequent investment in pheromone emission or number of females attracted. However, we showed that the same males that emitted a high quantity of their sex pheromone in the laboratory were able to attract more females in the field. Our data suggest that the chemical signal is not a reliable predictor of a male's immunocompetence but rather is a general important fitness-related trait, with a higher emission of the sex pheromone measured in the laboratory directly affecting the attractiveness of a male under field conditions.

Staying with the young enhances the fathers' attractiveness in burying beetles.

Studying the relationship between parental and mating effort helps us to understand the evolution of parental care and, consequently, has been the subject of many theoretical and empirical investigations. Using burying beetles as a model, we found no correlation between the intensity of a sexual signal (sex pheromone quantity) and the amount of care provided by males. However, males that were given the opportunity to breed and care for young went on to produce a higher amount of their sexual signal and attracted three times more females in the field than control males that were not given the opportunity to breed. The likely explanation for our finding is that specific aspects of care in burying beetles, that is the defense and preservation of a nutrient rich breeding resource, a small vertebrate cadaver, is not only beneficial for the offspring but also for the adults themselves. Obtaining a good carrion meal possibly enables males to store resources that they can subsequently allocate toward sexual signaling. Collectively, our results highlight that conditions can exist where male participation in brood care has a positive effect on its sexual attractiveness. This in turn might have facilitated the evolution of male assistance in parental care.

Beyond species recognition: somatic state affects long-distance sex pheromone communication.

Long-range sex pheromones have been subjected to substantial research with a particular focus on their biosynthesis, peripheral perception, central processing and the resulting orientation behaviour of perceivers. Fundamental to the research on sex attractants was the assumption that they primarily coordinate species recognition. However, especially when they are produced by the less limiting sex (usually males), the evolution of heightened condition dependence might be expected and long-range sex pheromones might, therefore, also inform about a signaller's quality. Here we provide, to our knowledge, the first comprehensive study of the role of a male's long-range pheromone in mate choice that combines chemical analyses, video observations and field experiments with a multifactorial manipulation of males' condition. We show that the emission of the long-distance sex pheromone of the burying beetle, Nicrophorus vespilloides is highly condition-dependent and reliably reflects nutritional state, age, body size and parasite load--key components of an individual's somatic state. Both, the quantity and ratio of the pheromone components were affected but the time invested in pheromone emission was largely unaffected by a male's condition. Moreover, the variation in pheromone emission caused by the variation in condition had a strong effect on the attractiveness of males in the field, with males in better nutritional condition, of older age, larger body size and bearing less parasites being more attractive. That a single pheromone is influenced by so many aspects of the somatic state and causes such variation in a male's attractiveness under field conditions was hitherto unknown and highlights the need to integrate indicator models of sexual selection into pheromone research.