Monday, 29 May 2017

The high cost of communication among social bees




May 26, 2017 by Christopher Packham report
 
(Phys.org)—Eusocial insects are predominantly dependent on chemosensory communication to coordinate social organization and define group membership. As the social complexity of a species increases, individual members require a greater diversity of signals. The communications of highly social insects such as wasps are well documented, but relatively little is known about the evolutionary transition between solitary and social living.
An international collaborative of researchers recently conducted a study of halictid bees in order to determine how the metabolic cost of chemosensory organs changes during such transitions. They theorized that changes in social structure would be reflected in changes to the expensive antennae sensory systems of insects. 

The researchers imaged the antennae of adult females from 36 species that ranged across a spectrum from completely solitary to highly social, and analyzed sensilla density using digital statistical software. The tests confirmed their theory: As sociality is gained and lost in halictid bees, convergent changes occur in both sensilla structures and the chemical signals of the groups. Social insects invest more in these systems than solitary bees, and as group complexity increases, communications develop higher diversity. "Taken together," the authors write, "these results suggest that there is a strong link between the evolution of social behavior and investment in communication." 

The researchers note that sensilla density did not increase as sociality was gained; ancestrally solitary halictids had sensilla densities similar to eusocial species. The researchers compare this seeming paradox to the evolution of cave-dwelling animal species that lose the sense of vision, but whose visual organs and brain structures, while functionally redundant, never become completely vestigial.

However, secondarily solitary halictids—those bees that switched rapidly from social to solitary—exhibited marked decreases in sensilla density as communications declined. "Importantly, the reduction we observed in this group is not a complete vestigilization. Instead, it represents a decreased investment in antennal sensilla, perhaps in the absence of complex communication associated with group living," the authors write.

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