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.

Key evolutionary events associated with invasion success are traditionally thought to occur in the introduced, rather than the native range of species. In the invasive ant Wasmannia auropunctata, however, a shift in reproductive system has been demonstrated within the native range, from the sexual non-dominant populations of natural habitats to the clonal dominant populations of human-modified habitats. Because abiotic conditions of human- modified habitats are hotter and dryer, we performed lab experiments on workers from a set of native and introduced populations, to investigate whether these ecological and genetic transitions were accompanied by a change in thermotolerance and whether such changes occurred before establishment in the introduced range. Thermotolerance levels were higher in native populations from human-modified habitats than in native populations from natural habitats, but were similar in native and introduced populations from human-modified habitats. Differences in thermotolerance could not be accounted for by differences in body size. A scenario based on local adaptation in the native range before introduction in remote areas represents the most parsimonious hypothesis to account for the observed phenotypic pattern. These findings highlight the importance of human land use in explaining major contemporary evolutionary changes.

Diplopods (millipedes) are one of the important groups of terrestrial Arthropoda in tropical forest ecosystems. Despite their ecological importance, data on millipede populations are still scarce and outdated in Cameroon. The first comparative eco‐faunistic analysis is presented of two local populations of Diplopoda in two lowland rainforests (nearly primary and secondary) during 12 months (2015–2016) at the southern periphery of the Campo Ma'an National Park in southern Cameroon. The millipedes were collected using pitfall trapping and quadrat sampling, their diversity and distribution analyzed with the help of two diversity indexes and two nonparametric estimators. Overall, 27 species in eighteen genera, ten families and four orders were revealed in the two forests, yet each faunule was about equally rich (23 and 22 species in the primary and secondary forest, respectively) and peculiar (five and four species unique, respectively). The Odontopygidae was the most abundant family, which made up to 33% of the total species diversity. The most abundant species in both forests was Aporodesmus gabonicus (26.8% of occurrences). This study shows that despite the similarity in millipede species richness between both habitats, the species composition of all habitats was different. Some species occurred in two habitats whilst others were restricted to only one habitat.

The little fire ant, Wasmannia auropunctata, is native to Central America, but has been introduced into many parts of the world. We examined the current distribution of W. auropunctata in Cameroon, tested for aggression between workers from different parts of the country, and examined the genotypes of workers, queens, and males to evaluate the mating system. We found W. auropunctata at 36 sites in three provinces (Centre, East, and South). We found W. auropunctata only in humandisturbed habitats. Its spread appears to be primarily human mediated. Aggressive behaviour was almost non-existent between workers from different sites, indicating that there is only one supercolony in Cameroon. Our genetic analysis found that only one male/female pair of clones was introduced into Cameroon, probably from Gabon. No new male clonal lineage was identified, whereas new sexually derived female clonal lineages were noted. Apart from the genotype of the founding queen, which was well distributed but generally not dominant, a new clonal queen genotype emerged and was both omnipresent and dominant at most sites. These results may be useful in the development of management strategies.

The large pantropical millipede genus Stemmiulus, which currently encompasses more than 150 species, i.e. the bulk of the species diversity of the family Stemmiulidae and entire order Stemmiulida, is shown to comprise seven species in Cameroon, including three new ones: S. ongot Nzoko Fiemapong & VandenSpiegel, sp. n., S. uncus Nzoko Fiemapong & VandenSpiegel, sp. n., and S. mbalmayoensis Nzoko Fiemapong & VandenSpiegel, sp. n. In addition, S. beroni Mauriès, 1989, previously known only from the type locality in Nigeria, is recorded from Cameroon for the first time, also being redescribed based on new samples. A key is given to all species of the genus encountered in the country, based on male gonopodal conformation, except for S. camerunensis , which was described only from female and juvenile material.

According to Holway et al. (2002), six ants are recognized as the most widespread and damaging invasive species: Anoplopepis gracilipes (yellow crazy ant), Linepithelma humile (Argentine ant), Pheidole megacephala (African bigheaded ant), Solenopsis invicta (red imported fi re ant), Solenopsis geminata (tropical fi re ant) and Wasmannia auropunctata (little fi re ant). Wasmannia auropunctata Roger, 1893 is one of the most harmful invasive species in the world (Wetterer & Porter, 2003). Native to Central and South America, W. auropunctata has been introduced throughout the West Indies, Australia, Israel, Italy, Pacifi c islands groups and West Africa (Wetterer, 2013). In Cameroon, W. auropunctata was fi rst reported in cocoa plantations along the Kribi-Ebolowa road (de Miré, 1969). Since then, it has successfully spread into southern and eastern Cameroon (Tindo et al., 2012), where it has severely reduced the abundance and richness of native ant species (Mbenoun et al., 2017). The invasive success of exotic species can vary substantially over time from population explosions to population

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The large pantropical millipede genus Stemmiulus, which currently encompasses more than 150 species, i.e. the bulk of the species diversity of the family Stemmiulidae and entire order Stemmiulida, is shown to comprise seven species in Cameroon, including three new ones: S. ongot Nzoko Fiemapong & VandenSpiegel, sp. n., S. uncus Nzoko Fiemapong & VandenSpiegel, sp. n., and S. mbalmayoensis Nzoko Fiemapong & VandenSpiegel, sp. n. In addition, S. beroni Mauriès, 1989, previously known only from the type locality in Nigeria, is recorded from Cameroon for the first time, also being redescribed based on new samples. A key is given to all species of the genus encountered in the country, based on male gonopodal conformation, except for S. camerunensis (Silvestri, 1916), which was described only from female and juvenile material.