Cryptic castes, social context and colony defence in a social bee, Tetragonula carbonaria

Abstract

Division of labour in social insect colonies is facilitated in two ways: through temporal sharing of tasks or by morphologically specialised castes. In casteless species, colony defence is maintained by morphologically indistinct workers, who lack the obvious defensive specialisation of polymorphic species. Discrimination of intruders is carried out via antenna, which also detects defensive social cues such as alarm pheromones. Despite their functional importance however, antennal morphology is rarely considered in studies of nestmate recognition. We investigated antennal morphology and the necessity of social cues in mediating defensive behaviour across differentially tasked workers of a casteless social bee, Tetragonula carbonaria. Our results suggest that the current understanding of division of labour in casteless worker species remains poorly understood, with differences in antennal morphology and aggression creating morphologically and behaviourally distinct ‘cryptic castes’. Further, we found that defensive behaviour was only elicited near nest odours, highlighting the importance of mediating aggression among workers.

Sight in a Clique, Scent in Society: Plasticity in the Use of Nestmate Recognition Cues Along Colony Development in the Social Wasp Polistes dominula

“…This implies that age (foundresses are several months old, while workers are only days/weeks old) or caste-related differences (foundresses are reproductive individuals while workers are not) could have played a role. While we believe that age is unlikely to have an influence, as Polistes wasps are able to perform NMR within a few hours after emergence (thus well before the time at which they were tested) (reviewed in Signorotti et al, 2015), we cannot discard the hypothesis of differences between castes in the NMR system as it has been shown in a social bee (Wittwer and Elgar, 2018). Previous studies offered mixed evidence for the related species Polistes fuscatus: one study documented differences in recognition between queens and workers (with queens having a more restrictive acceptance threshold than workers against unrelated conspecific intruders; Fishwild and Gamboa, 1992), while a more recent experiment found no evidence of such a queen-worker variation in recognition (with workers showing similar ability in familiar recognition compared to queens; Injaian and Tibbetts, 2014).…”

Task-Specific Recognition Signals Are Located on the Legs in a Social Insect

“…However, body size seems unlikely to be used as a cue for task discrimination because the effect size is very small (displayers head width 1.994 ± 0.012 mm, foragers 1.955 ± 0.010 mm, nest maintainers 1.939 ± 0.011 mm). While task discrimination can be linked with body size (for example, physical castes) it is also associated with chemical signals (Kaib et al, 2000) and sensory structures associated with chemical communication (Wittwer and Elgar, 2018).…”

Morphological assessment of the sensilla of the antennal flagellum in different castes of the stingless bee Tetragonisca fiebrigi

“…In the bees Apis mellifera (Frasnelli et al , ), Melipona quadrifasciata (Ravaiano et al , ), and Melipona scutellaris (Nascimento, Salomão & Martins, ), there are 6, 13, and 7 different types of sensilla, respectively. Within the same species, differences in terms of types and distribution of sensilla also may be related to caste and sex or different tasks individuals perform in the colony (Sheridan, Iversen & Itagaki, ; Mysore, Shyamala & Rodrigues, ; Ravaiano et al , ; Wittwer & Elgar, ). For instance, males of A. mellifera have a higher number of placodea sensilla than workers, allowing them to locate the queen (Esslen & Kaissling, ; Stort & Moraes‐Alves, ).…”