Variability in Sexual Pheromones Questions their Role in Bumblebee Pre-Mating Recognition System

Abstract

Sex-specific chemical secretions have been widely used as diagnostic characters in chemotaxonomy. The taxonomically confused group of bumblebees has reaped the benefit of this approach through the analyses of cephalic labial gland secretions (CLGS). Most of currently available CLGS descriptions concern species from the West-Palearctic region but few from the New World. Here, the CLGS of four East-Palearctic species Bombus deuteronymus, B. filchnerae, B. humilis, and B. exil (subgenus Thoracobombus) are analysed. Our results show high levels of variability in the major compounds in B. exil. In contrast, we describe a low differentiation in CLGS compounds between B. filchnerae and its phylogenetically closely related taxon B. muscorum. Moreover, the chemical profiles of B. filchnerae and B. muscorum are characterized by low concentrations of the C16 component, which is found in higher concentrations in the other Thoracobombus species. This raises the possibility that courtship behavior as well as environmental constraints could affect the role of the bumblebee males' CLGS.

Thoracobombus from Mexico: a description of the male species-specific cephalic labial gland secretions

“…As mentioned in Brasero et al 2017 about B. muscorum and B. filchnerae , the CLGS composition of B. pensylvanicus also includes very low concentrations of compounds below 18 carbons. This observation therefore strengthens our hypothesis, suggesting that the long pre-mating recognition distance could be mediated by cues other than the CLGS such nest site choice (i.e., the habitat) or nest scent (Brasero et al 2017).…”

“…However, even if this population is very similar to the population of Chiapas, major differentiations are found in abundant and minor compounds (Figure 2, Supplementary file 2). Such cases have already been described by comparing different species such as B. filchnerae and B. muscorum (Brasero et al 2017), as well as within the Cullumanobombus subgenus .…”

“…However, many aspects related to the ecology of these secretions are still unknown. Preliminary studies made (Brasero et al 2017;Brasero 2018) have shown that males prenuptial behavior influenced the composition of these secretions. Indeed, in males performing patrolling behavior, the average molecular mass of abundant compounds at the beginning of chromatograms is significantly smaller than that of other males performing nest waiting or perching behaviors.…”

“…These secretions are involved in bumblebee pre-mating recognition by attracting conspecific virgin females (Ayasse and Jarau 2014) but additional analyses are needed to determine which compounds are directly involved in sexual recognition. Moreover, they provide efficient diagnostic characters for species delimitation (Bergström et al 1981;Brasero et al 2015Brasero et al , 2017Lecocq et al 2015;Rasmont et al 2005;Svensson and Bergström 1979;Terzo et al 2003). Within bumblebees, cephalic labial gland secretions of 88 species are currently known (Brasero 2018).…”

Adding attractive semio-chemical trait refines the taxonomy of Alpinobombus (Hymenoptera: Apidae)

“…For these taxa, we observed quantitative differences involving very minor compounds (median < 0.20%) close to our threshold of 0.1% which have probably not a major role in pre-mating recognition (Appendix S2). Brasero et al (2017) and Terzo et al (2005) showed intraspecific variability in the CLGS of different bumblebee species. Several compounds could be abundant or absent according to the specimen analyzed.…”