Maurice Tindo

Worldwide invasion by the little fire ant: routes of introduction and eco-evolutionary pathways

Biological invasions are generally thought to occur after human aided migration to a new range. However, human activities prior to migration may also play a role. We studied here the evolutionary genetics of introduced populations of the invasive ant Wasmannia auropunctata at a worldwide scale. Using microsatellite markers, we reconstructed the main routes of introduction of the species. We found three main routes of introduction, each of them strongly associated to human history and trading routes. We also demonstrate the overwhelming occurrence of male and female clonality in introduced populations of W. auropunctata, and suggest that this particular reproduction system is under selection in human‐modified habitats. Together with previous researches focused on native populations, our results suggest that invasive clonal populations may have evolved within human modified habitats in the native range, and spread further from there. The evolutionarily most parsimonious scenario for the emergence of invasive populations of the little fire ant might thus be a two‐step process. The W. auropunctata case illustrates the central role of humans in biological change, not only due to changes in migration patterns, but also in selective pressures over species.

Genetic Structure, Nestmate Recognition and Behaviour of Two Cryptic Species of the Invasive Big-Headed Ant Pheidole megacephala

Background Biological 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 worlds most harmful invasive species. Methodology/Principal Findings To 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/Significance Overall, 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.

Foraging activity and diet of the ant, Anoplolepis tenella Santschi (Hymenoptera: Formicidae), in southern Cameroon

Anoplolepis tenella is a ground-nesting ant of the tropical forest zone of Central Africa, commonly associated with African root and tuber scale, Stictococcus vayssierei Richard, an emerging cassava pest. Understanding the ants foraging activity and diet breadth is an important step towards developing control measures against S. vayssierei. The present study was carried out in cassava fields in Awae II and Mengomo, southern Cameroon, during the short wet and dry seasons of 2006. Foraging activity of A. tenella was continuous during the circadian cycle and showed four peaks of activity; two during the day and two at night at both localities and in both seasons. Activity was greater at night than during the day, and greater in the wet than in the dry season. During the day, activity was significantly positively correlated with relative humidity, and negatively correlated with air temperature. During the night, it was positively correlated with relative humidity but not with air temperature at both localities. The diet of A. tenella consisted of solid items, mainly live prey (63.3 %) but also dead prey (36.7 %) and sugary secretions collected from various hemipterans. Stictococcus vayssierei was the most commonly tended hemipteran (98.5 %). Continuous foraging activity, omnivory and especially association with hemipterans are factors that favour the numerical dominance of A. tenella in cassava fields.

Thermotolerance adaptation to human‐modified habitats occurs in the native range of the invasive ant Wasmannia auropunctata before long‐distance dispersal

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.

Behavioral role differentiation in the primitively eusocial waspBelonogaster juncea juncea (Hymenoptera: Vespidae)

With a view toward describing behavioral variability among individuals of the primitively eusocial speciesBelonogaster juncea juncea, we recorded the time-activity budget spent on five behavioral categories (foraging, building, feeding, inactivity, and reproduction) by 52 individuals belonging to four postemergence colonies. A principal-components analysis coupled with a hierarchical cluster analysis enabled us to discern four behavioral roles. The reproductive role is reserved to one individual (functional monogyny) and the workers’ role is differentiated into foragers, builders, and guards. The foragers are females that spend the most time (82.6% of their time) foraging, supplying the nest with prey load and liquid matter. The builders are individuals (with 41.5% of their time off the nest) that tend to bring pulp into the nest and then undertake building activities. The guards are those females that spend the most time (79.7% of their time) being inactive on the nest.

Current distribution and population dynamics of the little fire ant supercolony in Cameroon

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 human-disturbed 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.

Advantages of multiple foundress colonies in Belonogaster juncea juncea L.: greater survival and increased productivity

Abstract 1. The ecological hypothesis predicts that multiple foundress colonies of social wasps may have a better survival rate and produce more brood per capita than single foundress colonies. With the aim of verifying if these characteristics exist in the primitively eusocial wasp species Belonogaster juncea juncea (L.), we monitored 49 foundations, including 13 single and 36 multiple foundress colonies, in Cameroon.

Colony development and serial polygyny in the primitively eusocial wasp Belonogaster juncea juncea (Vespidae: Polistinae)

In Cameroon, the social ropalidiine wasp Belonogaster juncea juncea mostly selects human constructions for nesting, but nests installed in the shelter of large boulders were also noted. Nests were founded throughout the year by one female (25.5%) or by associations of two to eight females. Among the 49 colonies studied from foundation, 24 produced at least one adult, and only 5 produced males among the eight that succeeded in producing sexual individuals. After the first dominant female disappeared (died or abandoned the nest, from 77 to 196 days after foundation) the remaining females fought among themselves, leading to a drastic decrease in the total number of brood. They completely abandoned 22 of 24 surviving nests, over a mean colony cycle lasting about 7 months. Hence the colony and nesting cycles were congruent, illustrating that determinate nesting corresponds to the majority of the cases in this species. In the other two nests, some females remained on the nest and began a new colonial cycle illustrating semi-independence between colony and nesting cycles. Up to four successive cycles were completed in this way in the same nest, thus illustrating the phenomenon of serial polygyny (intermediate between determinate and indeterminate nesting cycles). Serial polygyny in independent founding polistine wasps, previously documented only once, has implications for studies attempting to identify factors involved in regulating the colony and nesting cycles in tropical social wasps.

Nest and brood recognition in Belonogaster juncea juncea (Hymenoptera Vespidae)

The nest-exchange technique was employed on colonies of Belonogaster juncea juncea to study the degree of nest and immature brood recognition in adults. In each experiment two nests, approximately at the same stage of development and found in the field, were exchanged and the behaviour of the females was recorded before and after their substitution. Checking the nests 24 hr after the exchange showed that all the experimental nests had been accepted by the alien females and that a portion of the eggs and immature larvae had been destroyed. It seems that just one female on each nest is responsible for destroying the immature brood. None of the behaviours performed by the females suggested that they applied secretion over the nest surface and immature brood. From the results of the experiment, it appears that a nest and brood recognition mechanism exists in this species, which is probably based on characteristic odours.

Behavioral Profiles Related to Dominance Hierarchy in Associated Foundresses of Belonogaster juncea juncea (F.) (Hymenoptera: Vespidae)

This study was conducted to examine the phenomenon of task partitioning among associations of foundresses of the primitively eusocial wasp Belonogaster juncea juncea (F.). The time–activity budget for five main behavioral categories (foraging, building, feeding, inactivity, and reproduction) for each foundress belonging to trigynic associations was recorded using the instantaneous scanning technique. After ranking the individuals on the basis of agonistic encounters, data were submitted to a canonical discriminant analysis. The results show behavioral differences between individuals of each rank. The proportion of time allocated to foraging behavior is a good rank index. The females of the first rank spent less time on foraging behavior and significantly more time (13.6% of their time) on reproductive behavior than females of other ranks. The females of the second rank also spent less time on foraging behavior and showed a tendency toward building behavior. The females of the third rank spent significantly more time (77.28% of their time) on foraging behavior. The behavioral profile of each foundress was therefore determined by its rank on the dominance scale.