Fertility signals in the bumblebee Bombus terrestris (Hymenoptera: Apidae)

Abstract

In eusocial Hymenoptera, queen control over workers is probably inseparable from the mechanism of queen recognition. In primitively eusocial bumblebees (Bombus), worker reproduction is controlled not only by the presence or absence of a dominant queen but also by other dominant workers. Furthermore, it was shown that the queen dominance is maintained by pheromonal cues. We investigated whether there is a similar odor signal released by egg-laying queens and workers that may have a function as a fertility signal. We collected cuticular surface extracts from nest-searching and breeding Bombus terrestris queens and workers that were characterized by their ovarian stages. In chemical analyses, we identified 61 compounds consisting of aldehydes, alkanes, alkenes, and fatty acid esters. Nest-searching queens and all groups of breeding females differed significantly in their odor bouquets. Furthermore, workers before the competition point (time point of colony development where workers start to develop ovaries and lay eggs) differed largely from queens and all other groups of workers. Breeding queens showed a unique bouquet of chemical compounds and certain queen-specific compounds, and the differences toward workers decrease with an increasing development of the workers' ovaries, hinting the presence of a reliable fertility signal. Among the worker groups, the smallest differences were found after the competition point. Egg-laying females contained higher total amounts of chemical compounds and of relative proportions of wax-type esters and aldehydes than nest-searching queens and workers before the competition point. Therefore, these compounds may have a function as a fertility signal present in queens and workers.

Disentangling the effect of insemination and ovary development on the cuticular hydrocarbon profile in the bumblebee Bombus terrestris (Hymenoptera: Apidae)

“…Therefore, even if we consider an effect of age on the CHC profiles in B. terrestris queens, the effect of breeding status and insemination seems to be more pronounced. Differences in the cuticular profiles between workers and nest-searching queens in B. terrestris have been already shown in a previous study by Sramkova et al (2008). In their study, however, hydrocarbons and polar compounds have not been analyzed separately.…”

“…Substances not occurring in at least 50 % of all individuals of one group were removed from the dataset. Furthermore, we discarded compounds shorter than C19 as potential contaminants from the analysis in congruence with a former study (Sramkova et al 2008).…”

“…This result is supported by the fact that several alkadienes contribute most to the separation of virgin nonbreeding queens and virgin breeding queens. So far, studies in bumblebees have found a large amount of different substance classes such as alkanes, alkenes, aldehydes, methyl-branched alkanes, and wax-type esters to allow separation between groups (Ayasse et al 1995;Sramkova et al 2008). Furthermore, in different eusocial insects different substances seem to be driving separation between groups (e.g., Sledge et al 2001;Smith et al 2015).…”

“…Foraging workers, virgin, and nonbreeding queens have undeveloped ovaries, whereas breeding queens and dominant egglaying workers have fully developed ovaries (Ayasse et al 1995;Bloch et al 2000;Geva et al 2005). Cuticular profiles of the different castes within one colony revealed an honest signaling of dominance and fertility: the more the ovaries of a worker are developed, the more their cuticular profile resembles the cuticular profile of the queen (Sramkova et al 2008). Sramkova et al (2008) were also able to show large differences in the cuticular profile depending on the breeding status of the queen, where nonbreeding queens differed from breeding queens in variety and amount of substances found on the cuticle.…”

“…Strong effects of fertility on the CHC profile and thus distinct queen specific CHC profiles have already been found in social wasps (e.g., Sledge et al 2001Sledge et al , 2004, ants (e.g., Monnin et al 1998;Peeters et al 1999;Liebig et al 2000;Heinze et al 2002;Dietemann et al 2003Dietemann et al , 2005Smith et al 2008Smith et al , 2009, and bumblebees (Ayasse et al 1995;Sramkova et al 2008). However, in the majority of those studies, potential effects of insemination and ovarian development on CHC profiles were not investigated separately.…”