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

Abstract

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.

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

“…All levels of biodiversity, ranging from organisms to ecosystems, are expected to be affected by several environmental components influenced by climate change ( Parmesan 2006 , Bellard et al 2012 ). In a previous study, we found that daytime temperature affected the amount of beetles that a male was able to attract: the higher the daytime temperature was, the lower was the amount of attracted beetles ( Chemnitz et al 2017a ). In our current study, daytime temperature did not affect the amount of beetles attracted.…”

“…In general, our experimental design ensured that a female’s mate choice was only based on a male’s long-range sex pheromone and was not affected by visual cues or contact pheromones ( Chemnitz et al 2015 , 2017a ,b). Although experimental males were all reared under the same laboratory conditions, they might still have differed in their body condition and quality, which could affect pheromone emission ( Chemnitz et al 2015 , 2017a ). As the aim of our study was to determine whether environmental parameters influenced a male’s attractiveness, irrespective of any intrinsic effects, we controlled for the latter by exposing overall six different males per plot.…”

“…The male sex pheromone of N. vespilloides consists of two substances, ethyl 4-methyl heptanoate (EMH) and ( E )-geranylacetone (GA) ( Haberer et al 2008 , 2017 ; Chemnitz et al 2015 , 2017a ). Our recent study has shown that the same males that emitted a higher quantity of their sex pheromone in the laboratory are able to attract more females under field conditions ( Chemnitz et al 2017a ).…”

“…The male sex pheromone of N. vespilloides consists of two substances, ethyl 4-methyl heptanoate (EMH) and ( E )-geranylacetone (GA) ( Haberer et al 2008 , 2017 ; Chemnitz et al 2015 , 2017a ). Our recent study has shown that the same males that emitted a higher quantity of their sex pheromone in the laboratory are able to attract more females under field conditions ( Chemnitz et al 2017a ). Moreover, the sex pheromone provides information about various aspects of an individual’s condition and has been found to be dependent on internal factors such as the actual nutritional state, age, body size, and parasite load ( Chemnitz et al 2015 , 2017b , 2018 ).…”

Immunological female role tested on artificial plugs in three scorpion species

“…A small hole was made in the parafilm to access the genital operculum of the individual, and the artificial plug was gently inserted up to the end of the atrium by lifting the operculum with straight tweezers (Fig 1B, D, F). The surface of the artificial plug was slightly roughened with sandpaper to reach a rough surface and enhance the adhesion of hemocytes to the artificial genital plugs [95-96]. This procedure does not cause any damage to the female genitalia.…”