Abstract
BackgroundThe Argentine ant, Linepithema humile, is a widespread invasive ant species that has successfully established in nearly all continents across the globe. Argentine ants are characterised by a social structure known as unicoloniality, where territorial boundaries between nests are absent and intraspecific aggression is rare. This is particularly pronounced in introduced populations and results in the formation of large and spatially expansive supercolonies. Although it is amongst the most well studied of invasive ants, very little work has been done on this ant in South Africa. In this first study, we investigate the population structure of Argentine ants in South Africa. We use behavioural (aggression tests) and chemical (CHC) approaches to investigate the population structure of Argentine ants within the Western Cape, identify the number of supercolonies and infer number of introductions.ResultsBoth the aggression assays and chemical data revealed that the Western Cape Argentine ant population can be divided into two behaviourally and chemically distinct supercolonies. Intraspecific aggression was evident between the two supercolonies of Argentine ants with ants able to discriminate among conspecific non-nestmates. This discrimination is linked to the divergence in cuticular hydrocarbon profiles of ants originating from the two supercolonies.ConclusionsThe presence of these two distinct supercolonies is suggestive of at least two independent introductions of this ant within the Western Cape. Moreover, the pattern of colonisation observed in this study, with the two colonies interspersed, is in agreement with global patterns of Argentine ant invasions. Our findings are of interest because recent studies show that Argentine ants from South Africa are different from those identified in other introduced ranges and therefore provide an opportunity to further understand factors that determine the distributional and spread patterns of Argentine ant supercolonies.
Highlights
The Argentine ant, Linepithema humile, is a widespread invasive ant species that has successfully established in most continents across the globe
Similar to other invasive ants, Argentine ants are characterised by a social structure known as unicoloniality, where territorial boundaries are absent and intraspecific aggression between physically separate nests is rare [25,26,27,28,29]
Pairwise aggression tests, adapted from earlier studies [20,25,30] were used to assess the pattern of intraspecific aggression among Argentine ants within the Western Cape
Summary
The Argentine ant, Linepithema humile, is a widespread invasive ant species that has successfully established in most continents across the globe. Argentine ants are characterised by a social structure known as unicoloniality, where territorial boundaries between nests are absent and intraspecific aggression is rare. This is pronounced in introduced populations and results in the formation of large and spatially expansive supercolonies. The Argentine ant, Linepitheman humile, originates from South America and has successfully established on six continents and several oceanic islands Their colony structure is the best studied of invasive ant species [20,21,22,23,24]. It is well established that aggression between ants from different colonies is determined by genetic similarity and similarity in cuticular hydrocarbon profiles (CHC) [23,29], which represent recognition signals in ants and other insects [30,38,39,40]
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