title: Repeated evolution of soldier sub-castes suggests parasitism drives social complexity in stingless bees.
abstract: The differentiation of workers into morphological castes represents an important evolutionary innovation that is thought to improve division of labor in insect societies. Given the potential benefits of task-related worker differentiation, it is puzzling that physical worker castes, such as soldiers, are extremely rare in social bees and absent in wasps. Following the recent discovery of soldiers in a stingless bee, we studied the occurrence of worker differentiation in 28 stingless bee species from Brazil and found that several species have specialized soldiers for colony defence. Our results reveal that worker differentiation evolved repeatedly during the last ~ 25 million years and coincided with the emergence of parasitic robber bees, a major threat to many stingless bee species. Furthermore, our data suggest that these robbers are a driving force behind the evolution of worker differentiation as targets of robber bees are four times more likely to have nest guards of increased size than non-targets. These findings reveal unexpected diversity in the social organization of stingless bees.Although common in ants and termites, worker differentiation into physical castes is rare in social bees and unknown in wasps. Here, Grüter and colleagues find a guard caste in ten species of stingless bees and show that the evolution of the guard caste is associated with parasitization by robber bees.
authors.affiliation: Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, CEP 14040-901, Ribeirão Preto, São Paulo, Brazil. cgrueter@uni-mainz.de.|Institute of Zoology, Johannes Gutenberg University Mainz, Johannes von Müller Weg 6, 55099, Mainz, Germany. cgrueter@uni-mainz.de.
authors.forename: Christoph
authors.initials: C
authors.lastname: Grüter
authors.affiliation: Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, CEP 14040-901, Ribeirão Preto, São Paulo, Brazil.|Institute of Zoology, Johannes Gutenberg University Mainz, Johannes von Müller Weg 6, 55099, Mainz, Germany.
authors.forename: Francisca H I D
authors.initials: FH
authors.lastname: Segers
authors.affiliation: Embrapa Amazônia Oriental, Belém, CEP: 66095-903, Pará, Brazil.
authors.forename: Cristiano
authors.initials: C
authors.lastname: Menezes
authors.affiliation: Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, CEP 14040-901, Ribeirão Preto, São Paulo, Brazil.
authors.forename: Ayrton
authors.initials: A
authors.lastname: Vollet-Neto
authors.affiliation: Departamento de Genética, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, CEP: 14049-900, Ribeirão Preto, São Paulo, Brazil.
authors.forename: Tiago
authors.initials: T
authors.lastname: Falcón
authors.affiliation: Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, CEP 14040-901, Ribeirão Preto, São Paulo, Brazil.
authors.forename: Lucas
authors.initials: L
authors.lastname: von Zuben
authors.affiliation: Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, CEP 14040-901, Ribeirão Preto, São Paulo, Brazil.
authors.forename: Márcia M G
authors.initials: MM
authors.lastname: Bitondi
authors.affiliation: Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, CEP 14040-901, Ribeirão Preto, São Paulo, Brazil.
authors.forename: Fabio S
authors.initials: FS
authors.lastname: Nascimento
authors.affiliation: Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, CEP 14040-901, Ribeirão Preto, São Paulo, Brazil.
authors.forename: Eduardo A B
authors.identifier: 0000-0001-6017-6364
authors.initials: EA
authors.lastname: Almeida
mesh_terms: D000818:Animals; D005260:Female; D008297:Male; D000374:Aggression / Q000502:physiology; D001516:Bees / Q000033:anatomy & histology / Q000145:classification / Q000502:physiology; D001522:Behavior, Animal / Q000502:physiology; D005075:Biological Evolution; D049628:Body Size; D001938:Brazil; D010802:Phylogeny