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R Soc Open Sci. 2018 Feb 7;5(2):171332. doi: 10.1098/rsos.171332. eCollection 2018 Feb.

External immunity in ant societies: sociality and colony size do not predict investment in antimicrobials.

Author information

1
The Biomimicry Center, Arizona State University, Tempe, AZ 85287, USA.
2
Research & Collections, North Carolina Museum of Natural Sciences, Raleigh, NC 27601, USA.
3
Department of Biological Sciences, North Carolina State University, Raleigh, NC 27695, USA.
4
Biological Sciences, Campbell University, Buies Creek, NC 27506, USA.
5
Department of Entomology, Center for Pollinator Research, Pennsylvania State University, University Park, PA 16802, USA.
6
Department of Applied Ecology, North Carolina State University, Raleigh, NC 27695, USA.
7
Center for Macroecology, Evolution and Climate, University of Copenhagen, Copenhagen, 2100Denmark.

Abstract

Social insects live in dense groups with a high probability of disease transmission and have therefore faced strong pressures to develop defences against pathogens. For this reason, social insects have been hypothesized to invest in antimicrobial secretions as a mechanism of external immunity to prevent the spread of disease. However, empirical studies linking the evolution of sociality with increased investment in antimicrobials have been relatively few. Here we quantify the strength of antimicrobial secretions among 20 ant species that cover a broad spectrum of ant diversity and colony sizes. We extracted external compounds from ant workers to test whether they inhibited the growth of the bacterium Staphylococcus epidermidis. Because all ant species are highly social, we predicted that all species would exhibit some antimicrobial activity and that species that form the largest colonies would exhibit the strongest antimicrobial response. Our comparative approach revealed that strong surface antimicrobials are common to particular ant clades, but 40% of species exhibited no antimicrobial activity at all. We also found no correlation between antimicrobial activity and colony size. Rather than relying on antimicrobial secretions as external immunity to control pathogen spread, many ant species have probably developed alternative strategies to defend against disease pressure.

KEYWORDS:

antibiotics; antimicrobial secretions; ants; entomopathogens; social immunity; social insects

Conflict of interest statement

We have no financial or non-financial competing interests to declare.

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