Behavioural and chemical evidence for multiple colonisation of the Argentine ant, Linepithema humile, in the Western Cape, South Africa

<p>Abstract</p> <p>Background</p> <p>The Argentine ant, <it>Linepithema humile</it>, 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.</p> <p>Results</p> <p>Both 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.</p> <p>Conclusions</p> <p>The 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.</p

“You are not always what you eat”: Diet did not override intrinsic nestmate recognition cues in Argentine ants from two supercolonies in South Africa

Nestmate recognition in ants is based on cuticular hydrocarbons (CHCs), which are heritable and may also be acquired from the environment (i.e. diet and nest environment). In Argentine ants (Linepithema humile), diet and a homogenous environment have been shown to affect nestmate recognition by altering the CHC profile and consequently intraspecific aggression. In our study, Argentine ants were collected from field nests representing two supercolonies in South Africa. Individuals were paired in aggression assays and their CHC profiles analysed. The same nests used in the aggression assays were maintained in the laboratory for five months on a shared diet of crickets and sugar water, in soil-free nests. We predicted that aggression between previously aggressive paired individuals from different nests would decrease over time through the homogenisation of CHCs as a consequence of the shared diet and similar nesting environment. Our data showed that ants maintained in the laboratory readily absorbed prey-derived hydrocarbons and experienced a loss in the number of cuticular compounds compared with their original CHC profiles. However, the changes in CHCs did not impair nestmate recognition with non-aggressive paired interactions maintained while previously aggressive paired interactions persisted. The persistence of aggression between previously aggressive pairs despite environmental homogeneity supports the notion that intrinsic nestmate recognition cues are not overridden by extrinsic cues in the recognition system of Argentine ants

Parasitic Cape honeybee workers, Apis mellifera capensis, evade policing

Relocation of the Cape honeybee, Apis mellifera capensis, by bee-keepers from southern to northern South Africa in 1990 has caused widespread death of managed African honeybee, A. m. scutellata, colonies. Apis mellifera capensis worker bees are able to lay diploid, female eggs without mating by means of automictic thelytoky (meiosis followed by fusion of two meiotic products to restore egg diploidy), whereas workers of other honeybee subspecies are able to lay only haploid, male eggs. The A. m. capensis workers, which are parasitizing and killing A. m. scutellata colonies in northern South Africa, are the asexual offspring of a single, original worker in which the small amount of genetic variation observed is due to crossing over during meiosis (P. Kryger, personal communication). Here we elucidate two principal mechanisms underlying this parasitism. Parasitic A. m. capensis workers activate their ovaries in host colonies that have a queen present (queenright colonies), and they lay eggs that evade being killed by other workers (worker policing)—the normal fate of worker-laid eggs in colonies with a queen. This unique parasitism by workers is an instance in which a society is unable to control the selfish actions of its members

Maternity of emergency queens in the Cape honey bee, Apis mellifera capensis

During reproductive swarming, some workers of the Cape honey bee, Apis mellifera capensis, lay eggs in queen cells, many of which are reared to maturity. However, it is unknown if workers are able to lay in queen cells immediately after queen loss during an episode of emergency queen rearing. In this study we experimentally de-queened colonies and determined the maternity of larvae and pupae that were reared as queens. This allowed us to determine how soon after queen loss workers contribute to the production of new queens. We were further interested to see if workers would preferentially raise new queens from queen-laid brood if this was introduced later. We performed our manipulations in two different settings: an apiary setting where colonies were situated close together and a more natural situation in which the colonies were well separated. This allowed us to determine how the vicinity of other colonies affects the presence of parasites. We found that workers do indeed contribute to queen cell production immediately after the loss of their queen, thus demonstrating that some workers either have activated ovaries even when their colony has a queen or are able to activate their ovaries extremely rapidly. Queen-laid brood introduced days after queen loss was ignored, showing that workers do not prefer to raise new queens from queen brood when given a choice. We also detected non-natal parasitism of queen cells in both settings. We therefore conclude that some A. m. capensis genotypes specialize in parasitizing queen cells.Centre of Excellence for Invasion Biolog

Breaking tradition with scientific learning

The original publication is available at http://www.sajs.co.za/Pathways to scientific teaching is a compilation of previously published, two-paged articles in Frontiers in ecology and the environment, a publication of the Ecological Society of America. In 2004, this publication instituted a new education section, entitled Pathways to scientific teaching, in response to a challenge given to professional societies to stress the need for reform in education. The idea behind this reform is that science should be taught as rigorously as it is practiced.Publishers' versio

Retraction

Editorial Expression of Concern:“Newrecords of a threatened lion population (Panthera leo) inaWest African national park”African Zoology is publishing an Editorial Expression of Concern regarding the following article:“New records of a threatened lion population (Panthera leo) in a West African national park” by Francesco Maria Angelici, Massimiliano Di Vittorio and Fabio Petrozzi, which appeared in African Zoology 47(2): 353–357, October 2012. In April 2014, concerns were expressed regarding the video footage complementing this article. As a result, the above article published in African Zoology, as well as the Letters to the Editor (African Zoology 49(1): 1–4, 2014), have been retracted and neither the electronic nor the print version of the article or letters should be cited.Carol Simon and Theresa WosslerEditors-in-ChiefAfrican Zoolog

Editorial: African Zoology reaches a milestone – a 50-year celebration

No Abstrac

Pheromone mimicry by Apis mellifera capensis social parasites leads to reproductive anarchy in host Apis mellifera scutellata colonies

Queen mandibular, tergal, tarsal and Dufour's gland secretions, as well as brood pheromones regulate worker reproduction in honeybees. In South Africa two contiguous populations of honeybees exist, Apis mellifera capensis and A. m. scutellata. Queenless A. m. capensis workers are reproductively distinct from workers of other races, in that they readily develop into pseudoqueens with rapid ovary and signal development. A. m. capensis queens are pheromonally competent in regulating reproduction in the resident workers. Recently however Cape honeybee workers have successfully invaded queenright A. m. scutellata colonies and simultaneously escaped reproductive suppression from the resident queen and brood. These “social parasites” rapidly develop into reproductives, lay acceptable eggs and mimic a series of queen pheromones. This pheromone mimicry by invading A. m. capensis workers causes a breakdown in reproductive regulation, resulting in reproductive anarchy