Abstract
BackgroundBiological invasions are recognized as a major cause of biodiversity decline and have considerable impact on the economy and human health. The African big-headed ant Pheidole megacephala is considered one of the world's most harmful invasive species.Methodology/Principal FindingsTo better understand its ecological and demographic features, we combined behavioural (aggression tests), chemical (quantitative and qualitative analyses of cuticular lipids) and genetic (mitochondrial divergence and polymorphism of DNA microsatellite markers) data obtained for eight populations in Cameroon. Molecular data revealed two cryptic species of P. megacephala, one inhabiting urban areas and the other rainforests. Urban populations belong to the same phylogenetic group than those introduced in Australia and in other parts of the world. Behavioural analyses show that the eight populations sampled make up four mutually aggressive supercolonies. The maximum distance between nests from the same supercolony was 49 km and the closest distance between two nests belonging to two different supercolonies was 46 m. The genetic data and chemical analyses confirmed the behavioural tests as all of the nests were correctly assigned to their supercolony. Genetic diversity appears significantly greater in Africa than in introduced populations in Australia; by contrast, urban and Australian populations are characterized by a higher chemical diversity than rainforest ones.Conclusions/SignificanceOverall, our study shows that populations of P. megacephala in Cameroon adopt a unicolonial social structure, like invasive populations in Australia. However, the size of the supercolonies appears several orders of magnitude smaller in Africa. This implies competition between African supercolonies and explains why they persist over evolutionary time scales.
Highlights
The recent increase in human activity and commerce has, intentionally or unintentionally, greatly contributed to the dispersal of exotic species and their introduction into new habitats
Sequences (Figure 2) reveals that Cameroonian populations of P. megacephala form two phylogenetic groups (P. megacephala var. 1 and P. megacephala var. 2) that evolved independently from a very long time. These two phylogenetic groups exactly match with the two ecological zones studied, P. megacephala var. 1 corresponding to the specimens collected in urban areas and P. megacephala var. 2 to those sampled in rainforest
Our genetic analyses show that mtDNA sequences of P. megacephala var. 1 and of Australian specimens belong to the same phylogenetic group
Summary
The recent increase in human activity and commerce has, intentionally or unintentionally, greatly contributed to the dispersal of exotic species and their introduction into new habitats. Some species’ overwhelming invasive success upsets the balance in the invaded ecosystems and constitutes an important threat to biodiversity [1] These biological invaders have a considerable impact on the economy and on public health [2]. Introduced populations usually suffer a dramatic reduction in genetic diversity due to bottleneck effects and genetic drift They may experience inbreeding depression leading to more recessive, deleterious traits. A rich and expanding body of literature has been produced to help to understand why some species become successful invaders and to decipher the processes involved in biological invasions [5,6,7,8,9]. The African big-headed ant Pheidole megacephala is considered one of the world’s most harmful invasive species
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