Interspecific variation of antennal lobe composition among four hornet species

Abstract

Olfaction is a crucial sensory modality underlying foraging, social and mating behaviors in many insects. Since the olfactory system is at the interface between the animal and its environment, it receives strong evolutionary pressures that promote neuronal adaptations and phenotypic variations across species. Hornets are large eusocial predatory wasps with a highly developed olfactory system, critical for foraging and intra-specific communication. In their natural range, hornet species display contrasting ecologies and olfactory-based behaviors, which might match to adaptive shifts in their olfactory system. The first olfactory processing center of the insect brain, the antennal lobe, is made of morphological and functional units called glomeruli. Using fluorescent staining, confocal microscopy and 3D reconstructions, we compared antennal lobe structure, glomerular numbers and volumes in four hornet species (Vespa crabro, Vespa velutina, Vespa mandarinia and Vespa orientalis) with marked differences in nesting site preferences and predatory behaviors. Despite a conserved organization of their antennal lobe compartments, glomeruli numbers varied strongly between species, including in a subsystem thought to process intraspecific cuticular signals. Moreover, specific adaptations involving enlarged glomeruli appeared in two species, V. crabro and V. mandarinia, but not in the others. We discuss the possible function of these adaptations based on species-specific behavioral differences.

Evolution of the neuronal substrate for kin recognition in social Hymenoptera

“…For the sake of consistency, we therefore refer to this group of glomeruli as T B in the remainder of this review, irrespective of the species being discussed. In both lineages, this cluster is located dorsally (according to neuroaxis; Strausfeld, 2002), close to the antennal nerve entrance (caudal), and is composed of a relatively high number of small and similar‐size glomeruli (Nakanishi et al ., 2010; Kelber et al ., 2010; Zube et al ., 2008; Couto et al ., 2017, 2021). This cluster also contrasts with other areas of the AL, as immunohistochemical studies revealed an identical lack of serotoninergic innervation in the T B cluster of carpenter ants and hornets (Fig.…”

“…Consequently, nest‐mate recognition would become simpler in eusocial species, as individuals mostly interact with surrounding relatives. In our opinion, this hypothesis can be rejected in the case of the BaS subsystem, because the system is well developed in obligate eusocial species such as ants and hornets (Nakanishi et al ., 2010; McKenzie et al ., 2016; Couto et al ., 2021).…”