Unrelated males in societies of a facultatively social bee

Abstract

Societies of social Hymenoptera usually consist of groups of closely related females in which the dominant female(s) is specialized for reproduction and subordinate females care for immature offspring. Studying simple societies allows the identification of factors responsible for early stages of evolution of sociality. Here, we examined facultative social nesting in the species Ceratina chalybea using nest dissection, observation of nests, and evaluation of relatedness using microsatellite loci. Social nests were composed of an old female and on average 3.38 young adults and 2.05 newly provisioned brood cells. Social nests had a smaller number of brood cells, and empty cells made up a smaller proportion of the nest in comparison with solitary nests. Moreover, social nesting was strongly associated with nest reuse. Almost all of the young adults present were males, and about half of them were unrelated to the old female. The old female was the only member of the society who performed regular foraging. Feeding of mature offspring by the mother is typical for Ceratina bees. We suppose that social nests emerge when the mother begins provisioning new brood cells in the same nest where young adults are still present. As young adults do not perform physically demanding or risky activities, they incur little or no cost, but they can benefit from the food they obtain from the old female. Our results suggest that relatedness may be unimportant for eusociality maintenance when costs of helping behaviour are small.

Keywords:

• Eusociality
• relatedness
• male helper
• nesting biology
• bee
• Ceratina chalybea

Acknowledgements

We are grateful to all of the people who helped us with field experiments: Vojtěch Brož, Kateřina Čermáková, Marcela Dokulilová, Tereza Fraňková, Antonín Hlaváček, Lukáš Janošík, Jiří Janoušek, Barbora Kašparová, Karel Kodejš, Celie Korittová, Eva Matoušková, Zuzana Matějková, Blanka Mikátová, Jitka Mrozková, Karel Plavec, Daniela Reiterová, Tadeáš Ryšan, Jitka Waldhauserová, Šimon Zeman. We are also grateful to Podyjí National Park for permitting our research and for their friendliness. We also thank the Catholic priest Marian Husek for accommodation during our field research in the rectory in Havraníky village.

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability statement

Datasets generated during this study are available as supplementary material of this article.

Additional information

Funding

The Grant Agency of Charles University in Prague (Grant GAUK 764119/2019) and the Specific University Research project Integrative Animal Biology (Grant SVV 260434/2020) supported this research.