Reproduction and recruitment in perennial colonies of the introduced wasp Vespula germanica

We investigated the genetic structure of perennial colonies of the yellowjacket wasp (Vespula germanica) in its introduced range in Australia and New Zealand. The nuclear genotypes of 712 gynes from 21 colonies, 147 workers from 5 colonies, and 81 males from 4 colonies were assayed at three polymorphic microsatellite loci. The mitochondrial haplotypes of all wasps also were determined for a 450-bp region of the mtDNA using double-stranded conformational polymorphism (DSCP) analysis. We found that multiple reproductives were needed to explain the genotypes of gynes, workers, and males in 7 of 21, 2 of 5, and 2 of 4 colonies, respectively, and that nestmate relatedness of these three castes equaled 0.42, 0.16, and 0.22, respectively. The mitochondrial data revealed that all individuals shared the same mtDNA haplotype in 20 of the 21 colonies. However, in one colony, gynes and workers displayed multiple mtDNA haplotypes, indicating that nonnestmate recruitment had occurred. Overall the genetic structure within the majority of perennial colonies conformed to expectations based on the biology of V. germanica and kin selection theory for polygyne colonies; multiple reproductives successfully produced offspring and were recruited into their natal nests, thereby maintaining relatively high relatedness between interacting individuals.     

Preference by Vespula germanica (Hymenoptera: Vespidae) for processed meats: implications for toxic baiting

The German yellowjacket, Vespula germanica (F.) (Hymenoptera: Vespidae), was introduced into Australia in 1959 and has established throughout southern Australia. In urban environments, V. germanica is frequently a nuisance pest at public gatherings and to homeowners. In native environments, it has the potential to pose a threat to native invertebrates. The current practice for controlling the wasps is nest destruction with pesticide. However, locating the nest(s) is not always practical or possible. Meat baits impregnated with an insecticide that foraging wasps cut and carry back to the nest offer a means of suppressing wasps where the nest sites are unknown. The success of meat baits depends on the attractiveness and acceptance of the meat to the wasp and the mode of action of the insecticide. Our objective was to determine wasp preference and acceptance of five processed meats: canned chicken or fish and freeze-dried chicken, fish, or kangaroo. We found that more wasps visited and took freeze-dried kangaroo and canned chicken than the other baits. Canned and freeze-dried fish were similarly preferred, and freeze-dried chicken was the least attractive and accepted by foraging wasps. Our findings demonstrate that wasps prefer some processed meats and hence take more loads back to the nest. By combining a suitable insecticide with a meat bait preferred by wasps, the likelihood of effective suppression of nuisance wasp populations should be increased.     

Genetics, behaviour and chemical recognition of the invading ant Pheidole megacephala

Introduced species often become ecologically dominant, displacing native species and posing a serious threat to ecosystem function and global biodiversity. Ants are among the most widespread and damaging alien species; introductions are often accompanied by population-level behavioural and genetic changes contributing to their success. We investigated the genetic structure, chemical profile and nestmate recognition in introduced populations of the invasive big-headed ant, Pheidole megacephala, in Australia. Behavioural analyses show that workers are not aggressive towards conspecifics from different nests, even at large geographical scales (up to 3000 km) and between populations encompassing a wide range of environmental conditions. By contrast, interactions with workers of other species invariably result in agonistic behaviours. Genetic analyses reveal that populations have low genetic diversity. No genetic differentiation occurs among nests of the same population; differentiation between populations, though significant, remains weak. Chemical analyses indicate that cuticular lipids are similar between colonies of a population, and that differentiation between populations is low. Altogether, these results indicate that the big-headed ant P. megacephala forms a large unicolonial population across northern/eastern Australia.     

Attraction of Vespula germanica (Hymenoptera: Vespidae) foragers by conspecific heads

The socialwasp Vespula germanica (F.) is a serious pest in many regions it has invaded. Control programs to reduce its populations are commonly based on the use of poison baits. These baits also attract nonpestiferous invertebrates and vertebrates. In this work we studied the attraction of V. germanica foragers by conspecific worker squashes, comparing the effect of head and abdomen squashes in wasps behavior. We found that head squashes attract V. germanica foragers, elicit landing and transportation to nests. Furthermore, the addition of squashed heads to a protein bait increased attraction. This could be an alternative to improve baiting programs.     

Prey Diets and Population-Densities of the Wasps

Prey collected by Vespula vulgaris and V. germanica were sampled by intercepting foragers returning to nests at two sites in scrubland-pasture near Hamilton. About 12% of returning foragers carried animal prey and 5% carried wood pulp. The remaining 83% carried no external load. The most common prey item for both species was Diptera, followed by Lepidoptera and Araneae (spiders). Even in similar habitats the two species collected different prey, with V. germanica collecting more Diptera and V. vulgaris more Lepidoptera. The prey changed slightly over time at both sites, V. germanica and V. vulgaris collected an estimated 1800 g and 600 g of prey nest-1 season-1 respectively. The wasps collected an estimated 75 000 prey loads ha-1 season-1 at Mystery Creek and 12 000 at Ruakura. This represents biomasses of 50 and 470 g ha-1, respectively, which are at least an order of magnitude lower than estimates of prey biomass for honeydew beech forest in parts of the South Island. The distribution of wasp nests was patchy however, and the biomass of prey collected exceeded 10 kg ha-1 in some places.     

Assessment of prey overlap between a native (Polistes humilis) and an introduced (Vespula germanica) social wasp using morphology and phylogenetic analyses of 16S rDNA

Abstract In newly invaded communities, interspecific competition is thought to play an important role in determining the success of the invader and its impact on the native community. In southern Australia, the native Polistes humilis was the predominant social wasp prior to the arrival of the exotic Vespula germanica (Hymenoptera: Vespidae). Both species forage for similar resources (water, pulp, carbohydrate and protein prey), and concerns have arisen about potential competition between them. The aim of this study was to identify the protein foods that these wasps feed on. As many prey items are masticated by these wasps to the degree that they cannot be identified using conventional means, morphological identification was complemented by sequencing fragments of the mitochondrial 16S rRNA gene. GenBank searches using blast and phylogenetic analyses were used to identify prey items to at least order level. The results were used to construct complete prey inventories for the two species. These indicate that while P. humilis is restricted to feeding on lepidopteran larvae, V. germanica collects a variety of prey of invertebrate and vertebrate origin. Calculated values of prey overlap between the two species are used to discuss the implications of V. germanica impacting on P. humilis. Results obtained are compared to those gained by solely 'conventional' methods, and the advantages of using DNA-based taxonomy in ecological studies are emphasized.     

Colony structure and nest characteristics of European wasps, Vespula germanica (F.) (Hymenoptera: Vespidae), in Victoria, Australia

Abstract European wasps, Vespula germanica , are common across southern and south-eastern Australia and have a negative impact upon urban areas, primary industries, and natural ecosystems. Aspects of colony structure and nest characteristics are examined for nests located in the ground and collected from urban and rural sites in Victoria during two summer−autumn field seasons (1996 and 2001). On average, nests were located 28 cm beneath the surface (range 5−58 cm). The average number of combs in the nest and the total area of the nests increased from early February to late May. In addition, the proportion of cells used to produce workers and different life stages (larvae, pupae) also varied throughout the season; being consistent with studies from New Zealand. No differences in colony structure or nest character­istics were detected between urban and rural nests.     

Geographic structuring into vicariant species-pairs in a wide-ranging,high-dispersal plant–insect mutualism: the case of <Emphasis Type="Italic">Ficus racemosa</Emphasis> and its pollinating wasps

Ficus and their mutualistic pollinating wasps provide a unique model to investigate joint diversification in a high dispersal system. We investigate genetic structuring in an extremely wide-ranging Ficus species, Ficus racemosa, and its pollinating wasp throughout their range, which extends from India to Australia. Our samples were structured into four large, vicariant populations of figs and wasps which may correspond to distinct (sub)species, located in India, China-Thailand, Borneo, and Australia. However, the genetically most divergent group was the Indian population for the figs and the China-Thailand population for the wasps, suggesting different evolutionary histories of populations. Molecular dating for the wasps shows that diversification of the pollinator clade is surprisingly old, beginning about 13.6 Ma. Data on both the host fig species and its pollinating wasps suggest that strong genetic flow within biogeographic groups over several hundreds of kilometers has limited genetic and morphological differentiation and, potentially, local adaptation. This is probably due to long-distance dispersal of pollinating wasps. The genetic clustering into large geographic units observed in F. racemosa and its pollinators is reminiscent of what can be observed in some other high-dispersal organisms characterized by morphology that varies little over huge distances. The implications of strong gene flow for diversification processes and adaptation to different ecological conditions in Ficus and their pollinating wasps are just beginning to emerge.     

RAPD variation in relation to population size and plant fitness in the rare Gentianella germanica (Gentianaceae)

We investigated the distribution of genetic variation and the relationship between population size and genetic variation in the rare plant Gentianella germanica using RAPD (random amplified polymorphic DNA) profiles. Plants for the analysis were grown from seeds sampled from 72 parent plants in 11 G. germanica populations of different size (40-5000 fruiting individuals). In large populations, seeds were sampled from parents in two spatially distinct subpopulations comparable in area to the total area covered by small populations. Analysis of molecular variance revealed significant genetic variation among populations (P <0.001), while genetic variation among subpopulations was marginally significant (P <0.06). Average molecular variance within subpopulations in large populations did not differ significantly from whole-population values. There was a positive correlation between genetic variation and population size (P <0.01). Genetic variation was also positively correlated with the number of seeds per plant in the field (P <0.02) and the number of flowers per planted seed in a common garden experiment (P <0.051). We conclude that gene flow among natural populations is very limited and that reduced plant fitness in small populations of G. germanica most likely has genetic causes. Management should aim to increase the size of small populations to minimize further loss of genetic variation. Because a large proportion of genetic variation is among populations, even small populations are worth preserving.     

Nestmate relatedness and population genetic structure of the Australian social crab spider Diaea ergandros (Araneae: Thomisidae)

We characterized the population genetic structure of the Australian social spider Diaea ergandros using polymorphic allozyme markers. Our main objectives were to understand the social organization of D. ergandros and discern patterns of gene flow across distantly separated geographical areas. Spiders were sampled from nests located within 100 m wide locales, which were distributed within larger 50 km wide regions. Our results indicated that nestmates could have been produced by a single mother and father in 88.9% of D. ergandros nests. The remainder of nests contained spiders that were probably produced by polyandrous females or were immigrants from foreign nests. Nestmate relatedness was relatively high (r = 0.44) and did not differ significantly between the sexes or among juvenile, subadult and adult life stages. We also discovered that D. ergandros populations were highly structured, with significant differentiation detected among locales (FLR = 0.23) and regions (FRT = 0.081). Spiders within locales were also substantially inbred (FIL = 0.15). Overall, our data show that significant population subdivision exists in D. ergandros populations, and we suggest that the poor dispersal ability of Diaea spiders can account for the observed genetic structure.     

Weather-Related Differences in Attractiveness of Protein Foods to

Low acceptance of protein baits by common (Vespula vulgaris) and German (V. germanica) wasps (Hymenoptera: Vespidae) occurred after rain in honeydew beech forest. This corresponded with a sharp decrease in the proportion of natural protein in the diet of V. vulgaris and V. germanica, and a reduction in the concentration of carbohydrate-rich honeydew in the crops of foraging wasps carrying liquid. The reduction of protein foraging most likely results from a change in the efficiency of foraging wasps at gathering high energy foods such as honeydew after rain, because rain reduces honeydew availability. Workers may therefore take longer to meet their own energy requirements before they can forage for protein to feed developing larvae.     

Flexible social organization and high incidence of drifting in the sweat bee, Halictus scabiosae

The very diverse social systems of sweat bees make them interesting models to study social evolution. Here we focus on the dispersal behaviour and social organization of Halictus scabiosae , a common yet poorly known species of Europe. By combining field observations and genetic data, we show that females have multiple reproductive strategies, which generates a large diversity in the social structure of nests. A detailed microsatellite analysis of 60 nests revealed that 55% of the nests contained the offspring of a single female, whereas the rest had more complex social structures, with three clear cases of multiple females reproducing in the same nest and frequent occurrence of unrelated individuals. Drifting among nests was surprisingly common, as 16% of the 122 nests in the overall sample and 44% of the nests with complex social structure contained females that had genotypes consistent with being full-sisters of females sampled in other nests of the population. Drifters originated from nests with an above-average productivity and were unrelated to their nestmates, suggesting that drifting might be a strategy to avoid competition among related females. The sex-specific comparison of genetic differentiation indicated that dispersal was male-biased, which would reinforce local resource competition among females. The pattern of genetic differentiation among populations was consistent with a dynamic process of patch colonization and extinction, as expected from the unstable, anthropogenic habitat of this species. Overall, our data show that H. scabiosae varies greatly in dispersal behaviour and social organization. The surprisingly high frequency of drifters echoes recent findings in wasps and bees, calling for further investigation of the adaptive basis of drifting in the social insects.     

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 world''s 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.     

Unicoloniality, recognition and genetic differentiation in a native Formica ant

Some ants have an extraordinary form of social organization, called unicoloniality, whereby individuals mix freely among physically separated nests. This mode of social organization has been primarily studied in introduced and invasive ant species, so that the recognition ability and genetic structure of ants forming unicolonial populations in their native range remain poorly known. We investigated the pattern of aggression and the genetic structure of six unicolonial populations of the ant Formica paralugubris at four hierarchical levels: within nests, among nests within the same population, among nests of populations within the Alps or Jura Mountains and among nests of the two mountain ranges. Ants within populations showed no aggressive behaviour, but recognized nonnestmates as shown by longer antennation bouts. Overall, the level of aggression increased with geographic and genetic distance but was always considerably lower than between species. No distinct behavioural supercolony boundaries were found. Our study provides evidence that unicoloniality can be maintained in noninvasive ants despite significant genetic differentiation and the ability to discriminate between nestmates and nonnestmates.     

Contrasting population genetic structure for workers and queens in the putatively unicolonial ant Formica exsecta

The theory of inclusive fitness provides a powerful explanation for reproductive altruism in social insects, whereby workers gain inclusive fitness benefit by rearing the brood of related queens. Some ant species, however, have unicolonial population structures where multiple nests, each containing numerous queens, are interconnected and individuals move freely between nests. In such cases, nestmate relatedness values may often be indistinguishable from zero, which is problematic for inclusive fitness-based explanations of reproductive altruism. We conducted a detailed population genetic study in the polygynous ant Formica exsecta, which has been suggested to form unicolonial populations in its native habitat. Analyses based on adult workers indeed confirmed a genetic structuring consistent with a unicolonial population structure. However, at the population level the genetic structuring inferred from worker pupae was not consistent with a unicolonial population structure, but rather suggested a multicolonial population structure of extended family-based nests. These contrasting patterns suggest limited queen dispersal and free adult worker dispersal. That workers indeed disperse as adults was confirmed by mark-recapture measures showing consistent worker movement between nests. Together, these findings describe a new form of social organization, which possibly also characterizes other ant species forming unicolonial populations in their native habitats. Moreover, the genetic analyses also revealed that while worker nestmate relatedness was indistinguishable from zero at a small geographical scale, it was significantly positive at the population level. This highlights the need to consider the relevant geographical scale when investigating the role of inclusive fitness as a selective force maintaining reproductive altruism.     

Abundance of wasps and prey consumption of paper wasps (Hymenoptera, Vespidae : Polistinae) in Northland, New Zealand

Polistine and vespine wasps were captured in Malaise traps in two fire-modified shrubland habitats of varying canopy height and composition at Lake Ohia, Northland, New Zealand. Prey consumption rates were calculated for the Asian paper wasp (Polistes chinensis antennalis) occupying these two areas of shrubland and a home garden in Whangarei, Northland. The sites were systematically searched for nests and wasp prey determined by intercepting foragers returning to nests. The Asian paper wasp predominated in the Malaise trap samples from the low- growing habitat while the German wasp (Vespula germanica) was more common in the taller vegetation type. The Asian paper wasp was more abundant than the German wasp in the samples in February and early March. Only four Australian paper wasps (Polistes humilis) and no common wasps (Vespula vulgaris) were caught. Asian paper wasps collected an estimated 15 000 prey loads per ha per season from one of the shrubland areas, and 478 000 prey loads per ha per season from the second area. These convert to estimates of 31 and 957 g per ha per season of invertebrate biomass removed by paper wasps from each habitat, respectively. The estimate for the garden site was 79 g per ha per season. Wasp nest densities varied between 20 and 210 nests per hectare. The biomass estimates are similar to average figures calculated for vespine wasps in scrubland and pasture. Both Asian paper wasps and Australian paper wasps preyed mainly on lepidopteran larvae. The cabbage white butterfly (Pieris rapae) was the most commonly collected species. Noctuid species were also well represented. Both male and female Asian paper wasps collected nectar in late March and early April.     

Genetic and behavioural evidence for a city-wide supercolony of the invasive Argentine ant Linepithema humile (Mayr) (Hymenoptera: Formicidae) in southeastern Australia

The success of invasive ants is frequently attributed to genetic and behavioural shifts in colony structure during or after introduction. The Argentine ant ( Linepithema humile ), a global invader, differs in colony genetic structure and behaviour between native populations in South America and introduced populations in Europe, Japan, New Zealand and North America. However, little is known about its colony structure in Australia. We investigated the genetic structure and behaviour of L. humile across Melbourne, Victoria by quantifying variation at four microsatellite loci and assaying intraspecific aggression at neighbourhood (30–200 m), fine (1–3.3 km) and regional (5–82 km) spatial scales. Hierarchical analyses across these scales revealed that most genetic variation occurred among workers within nests (∼98%). However, although low genetic differentiation occurred among workers between nests at the fine and regional scales (∼2%), negligible differentiation was detected among workers from neighbouring nests. Spatial genetic autocorrelation analysis confirmed that neighbouring nests were genetically more similar to each other. Lack of aggression within and across these scales supported the view that L. humile is unicolonial and forms a large supercolony across Melbourne. Comparisons of genetic structure of L. humile among single nests sampled from Adelaide, Brisbane, Hobart and Perth with Melbourne showed no greater levels of genetic differentiation or dissimilar spatial structure, suggesting an Australia-wide supercolony.     

Restricted dispersal and genetic diversity in populations of an endangered montane lizard (Eulamprus leuraensis,Scincidae)

Many alpine species are under threat from global climate change, as their geographic ranges become increasingly fragmented and unsuitable. Understanding rates and determinants of gene flow among such fragmented populations, over historical as well as recent timescales, can help to identify populations under threat. It is also important to clarify the degree to which loss of local populations reduces overall genetic diversity within the taxon. The endangered Blue Mountains Water Skink (Eulamprus leuraensis) is restricted to <40 small swamps in montane south‐eastern Australia. Our analyses of seven microsatellite loci of 241 animals from 13 populations show strong geographic structure, with major genetic divergence even between populations separated by <0.5 km. Dispersal between populations is scarce, and appears to involve mostly males. Our analyses suggest potential recent bottleneck events in all the identified populations, and lower genetic diversity and population size parameter at lower‐elevation sites than at higher‐elevation sites. Management of this endangered taxon thus needs to treat most populations separately, because of their genetic distinctiveness and low rates of genetic exchange.     

Population and Conservation Genetics in an Endangered Lemur, <Emphasis Type="Italic">Indri indri</Emphasis>, Across Three Forest Reserves in Madagascar

Population decline and fragmentation often lead to reduced genetic diversity and population differentiation. Habitat destruction throughout Madagascar has caused population decline and extinction of many endemic species. Lemur populations, including those of the largest extant lemur, Indri indri, have been fragmented into remaining forest patches. We assessed the level of genetic diversity in indri populations in three protected reserves by genotyping a total of 43 individuals at 17 microsatellite loci. Genetic diversity in terms of heterozygosity was high in all three reserves, with no differences between reserves. Population structure and F _ST analyses revealed Analamazaotra Forest Station and the Torotorofotsy Conservation Area, which are separated by ca. 18 km to be genetically differentiated from each other with some admixture. Betampona Strict Nature Reserve, which is separated from the other reserves by ca. 130 km, exhibited clear population genetic differentiation, with no signs of admixture with the other reserves. Our genetic diversity estimates are similar to those for other Indridae in similar habitats and may reflect past rather than current population processes, given that populations have declined recently. Our results suggest that Betampona may be genetically isolated and that it is important to maintain gene flow between remaining populations to prevent loss of genetic diversity for the future conservation of Indri indri.     

Genetic structure of introduced swamp buffalo subpopulations in tropical Australia

High densities of introduced herbivores can damage sensitive ecosystems, increase the risk of extinction of native biota, and host and spread disease. An essential step in managing large ‘feral’ animal populations is to quantify how they use habitats so that management interventions, such as culling, can be targeted to reduce densities and to minimize migration into areas from which animals have been removed. An effective method to quantify animal movements is by measuring landscape‐scale genetic population structure. We describe the genetic population structure of one of Australia's more destructive introduced mammals – the Asian swamp buffalo (Bubalus bubalis). We collected 524 skin samples from buffalo across their range in the Northern Territory of Australia. Allelic diversity in the Northern Territory population was low compared to those reported from populations in their native Asian habitats. The Australian population is tentatively made of three subpopulations; Melville Island, Eastern Arnhem and Central‐Western Arnhem populations. The Melville Island population is represented by a single cluster, while the Eastern Arnhem population has three clusters and the Central‐Western Arnhem population seven clusters. We found some support for isolation by distance across all the sampled populations, but little evidence for this relationship when comparing the two well‐mixed mainland meta‐populations. Despite their small founder populations and limited genetic variation, the persistence of buffalo in Australia has likely been aided by release from high predation, parasitism and disease typical of their native habitats.