Reduced entomopathogen abundance in Myrmica ant nests-testing a possible immunological benefit of myrmecophily using Galleria mellonella as a model.

Sämi Schär,Nicolai V Meyling,David R Nash,Louise L M Larsen

doi:10.1098/rsos.150474

Abstract

Social insects such as ants have evolved collective rather than individual immune defence strategies against diseases and parasites at the level of their societies (colonies), known as social immunity. Ants frequently host other arthropods, so-called myrmecophiles, in their nests. Here, we tested the hypothesis that myrmecophily may partly arise from selection for exploiting the ants’ social immunity. We used larvae of the wax moth Galleria mellonella as ‘model myrmecophiles’ (baits) to test this hypothesis. We found significantly reduced abundance of entomopathogens in ant nests compared with the surrounding environment. Specific entomopathogen groups (Isaria fumosorosea and nematodes) were also found to be significantly less abundant inside than outside ant nests, whereas one entomopathogen (Beauveria brongniartii) was significantly more abundant inside nests. We therefore hypothesize that immunological benefits of entering ant nests may provide us a new explanation of why natural selection acts in favour of such a life-history strategy.

Highlights

Group life has many advantages compared with a solitary lifestyle, and some of the ecologically most dominant organisms2015 The Authors
To examine the basis of this hypothesis, we studied the abundance of entomopathogens in nests of Myrmica rubra (Linnaeus) and Myrmica ruginodis (Nylander), both host ants of various myrmecophiles [10], using larvae of the wax moth Galleria mellonella (Linnaeus) as ‘model myrmecophiles’
The number of G. mellonella larvae per sample found dead with a pathogen was lower in soil from ant nests compared with soil from control points (GLMM, nests versus controls: z = −4.15, p < 0.0001)

Summary

Introduction

Group life has many advantages compared with a solitary lifestyle, and some of the ecologically most dominant organisms. Live in groups [1]. Social life often comes at the cost of increased risk of infectious disease, 2 as the frequent interactions between social organisms and the high densities in which they normally occur facilitate transmission of pathogens and parasites [2,3,4]. Some group-living animals have evolved collective immune defence against diseases, known as social immunity [5]. Social insects have developed behavioural and chemical countermeasures against diseases in order to avoid infection and transmission [5]. A widespread behavioural strategy against diseases is hygienic behaviour such as allogrooming [6] and removal of dead corpses from the nest [7]

Methods

Results

Conclusion