Large scale unicoloniality: the population and colony structure of the invasive Argentine ant (Linepithema humile) in New Zealand

Abstract

The Argentine ant is native to South America and has spread widely across the globe. In this study, we use genetic analyses and behavioural assays to examine the colony structure of Argentine ants in New Zealand. Diet modification studies were also carried out in order to help identify what factors influence these behavioural assays. There was no aggression observed between any pairings tested across the North Island of New Zealand, though we found that diet manipulations in the laboratory could lead to low levels of aggression between previously amiable Argentine ant nests. The New Zealand population of Argentine ants was characterized by low levels of genetic variation in six microsatellite loci from their nuclear genome. Additionally, the population also lacked significant genetic structuring with no patterns of regional differentiation or isolation by distance. An analysis of molecular variation (AMOVA) found that the majority of genetic variation was present at a nest level (93% of total genetic variance), with little genetic differentiation observed within or between regions (3 -4% of total genetic variance). No correlation between aggression and genetic relatedness was observed. This evidence suggests that Argentine ants in New Zealand effectively form a unicolonial population, which is likely the result of colonization from a single source population. As far as we know, this is the first country to have an entirely unicolonial population of Argentine ants.

The worldwide expansion of the Argentine ant

“…The success of the Argentine ant as an invading species is mainly explained by its social organization (Human & Gordon, 1996;Holway, 1998;Holway & Suarez, 2004) that is characterized by individuals mixing freely within large supercolonies, which may expand over thousands of km (Tsutsui et al, 2000;Giraud et al, 2002;Corin et al, 2007a;Suhr et al, 2009). Two explanations have been proposed for the occurrence of such large supercolonies in the introduced range.…”

“…One supercolony from the native range seems to have been particularly successful (see also Brandt et al, 2009;Sunamura et al, 2009a), being the source of extant supercolonies spanning about 6000 km in Europe ('main supercolony', Giraud et al, 2002), 1000 km in California ('large supercolony', Tsutsui et al, 2003), 2800 km in Australia (Suhr et al, 2009) and 900 km in New Zealand (Corin et al, 2007a), and two growing supercolonies in Hawaii and Japan (this study; 'Hiroshima Bay group' or 'main', Hirata et al, 2008;Sunamura et al, 2009a,b). The size and lifespan (> 100 years) of these introduced supercolonies contrast with those of native supercolonies that typically have a size of a few hundred metres Vogel et al, 2009) and a longevity of only a few years (Vogel et al, 2009).…”

The widespread collapse of an invasive species: Argentine ants ( Linepithema humile ) in New Zealand

“…Introduced populations form high-density, widespread, highly aggressive, unicolonial populations and can deleteriously influence native communities [6]. First observed in New Zealand in Auckland during 1990, the species has since spread widely around the country assisted by human-mediated dispersal [7]. The dates and locations of newly observed infestations have been recorded for many populations [5], which typically range in size from a few to several hundred hectares.…”

Nest connectivity and colony structure in unicolonial Argentine ants

“…The sizes of supercolonies, with boundaries measured by aggression tests, vary widely. In the introduced range, supercolonies span thousands of square kilometers in California, Europe, New Zealand and Australia (Tsutsui et al, 2000;Giraud et al, 2002;Corin et al, 2007;Bjçrkman et al, 2008) and extend across disjunct areas, islands and continents (Wetterer and Wetterer, 2006); other supercolonies in Southeastern USA and Japan are less than 2500 square meters (Buczkowski et al, 2004;Sunamura et al, 2007) similar in size to those in the native range of Argentina (Heller, 2004;Pedersen et al, 2006). Little is known about patterns of cooperative nest interactions within these supercolonies.…”