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We compared the nesting success of a disturbance-dependent species, the Indigo Bunting ( Passerina cyanea), on different kinds of habitat edges in five sites (225 total nests) in southern Illinois from 1989 to 1993. Nest predation rates along agricultural and abrupt, permanent edges (e.g., wildlife openings, campgrounds) were nearly twice as high as rates along more gradual edges where plant succession was allowed to occur (e.g., treefalls, streamsides, gaps created by selective logging ). Levels of brood parasitism by Brown-headed Cowbirds ( Molothrus ater) varied significantly among sites and years, but not among edge types. Clutch sizes, however, were significantly smaller at agricultural edges where nest predation rates were also high, which suggests either decreased food availability or a population dominated by younger and/or lower-quality ( poor condition) birds. The results of this study illustrate the need to reevaluate management practices (e.g., wildlife openings) that are designed to promote populations of disturbance-dependent wildlife. Comparamos el exito de nidacion de una especie dependiente de perturbaciones Passerina cyanea, en diferentes tipos de habitat borde en cinco sitios (225 nidos en total) en el sur de Illinois de 1989 a 1993. La tasa de depredacion de nidos a lo largo de bordes agriculturales y bordes abruptos permanentes (e.g., areas silvestres abiertas y zonas de campamento) fueron dos veces mas altas que aquellas en bordes mas graduales donde la sucesion de pantas fue permitida (e.g., arboles caidos, bancos de arroyos y espacios abiertos creados por la tala selectiva). Niveles de parasitismo de nido por Molothrus ater variaron significativamente entre sitios y anos, pero no entre tipos de borde. De cualquier manera, el tamano de la nidada fue significativamente mas pequeno en bordes agriculturales donde la tasa de depredacion fue tambien alta, esto sugiere tanto una disminucion en la viabilidad de alimentos, como una poblacion dominada por aves jovenes y/o de baja calidad (pobre condicion). Los resultados de este estudio ilustran la necesidad de re-evaluar practicas de manejo (e.g., areas silvestres abiertas) que son disenadas para promover poblaciones de vida silvestre dependientes de disturbaciones.

SummaryContact pheromones in the form of cuticular hydrocarbons are widespread among insects. Eusocial insects present a special challenge for understanding the evolution of the cuticular hydrocarbon profile because this blend is responsible for multiple distinct roles such as nestmate recognition and signalling fertility status. This study investigates these two signalling roles of the hydrocarbon profile in the trap-jaw ant Odontomachus brunneus Patton. We demonstrate that the cuticular hydrocarbon profile is highly variable across populations and provide evidence that these differences are used for nestmate discrimination. Through manipulative experiments we also show that (Z)-9-nonacosene (Z9:C29) is used as a fertility signal and its role is conserved across populations. Our data demonstrate that both fertility and nestmate signalling influence the cuticular hydrocarbon profile and specifically the relative abundance of Z9:C29 on the cuticle of O. brunneus. Our study suggests that natural selection works on the cuticular chemical profile through multiple regulatory pathways, diversifying nestmate signals while conserving fertility signals.

Behaviour determines the rate at which invasive species spread, as well as the impact they have on natives. When behaviour varies between individuals (as it almost always does), then the mean behaviour is often less important than the extremes of behaviour. The rate at which a species spreads, for example, is governed primarily by the most extreme dispersers. Similarly, individuals of native species that are extreme in their behaviour may be more, or less, likely to suffer impact from a given invasive species. Thus, we argue, an understanding of behavioural variation is critical if we are to understand the long-term impacts of invasive species in a changing world.

Eusocial species exhibit pronounced division of labor, most notably between reproductive and non-reproductive castes, but also within non-reproductive castes via morphological specialization and temporal polyethism. For species with distinct worker and queen castes, age-related differences in behavior among workers (e.g. within-nest tasks versus foraging) appear to result from physiological changes such as decreased lipid content. However, we know little about how labor is divided among individuals in species that lack a distinct queen caste. In this study, we investigated how fat storage varied among individuals in a species of ant (Dinoponera australis) that lacks a distinct queen caste and in which all individuals are morphologically similar and capable of reproduction (totipotent at birth). We distinguish between two hypotheses, 1) all individuals are physiologically similar, consistent with the possibility that any non-reproductive may eventually become reproductive, and 2) non-reproductive individuals vary in stored fat, similar to highly eusocial species, where depletion is associated with foraging and non-reproductives have lower lipid stores than reproducing individuals. Our data support the latter hypothesis. Location in the nest, the probability of foraging, and foraging effort, were all associated with decreased fat storage.

Many arthropods engage in mutualisms in which they consume plant-based foods including nectar, extrafloral nectar, and honeydew. However, relatively little is known about the manner in which the specific macronutrients in these plant-based resources affect growth, especially for carnivorous arthropods. Using a combination of laboratory and field experiments, we tested (1) how plant-based foods, together with ad libitum insect prey, affect the growth of a carnivorous ant, Solenopsis invicta, and (2) which macronutrients in these resources (i.e., carbohydrates, amino acids, or both) contribute to higher colony growth. Access to honeydew increased the production of workers and brood in experimental colonies. This growth effect appeared to be due to carbohydrates alone as colonies provided with the carbohydrate component of artificial extrafloral nectar had greater worker and brood production compared to colonies deprived of carbohydrates. Surprisingly, amino acids only had a slight interactive effect on the proportion of a colony composed of brood and negatively affected worker survival. Diet choice in the laboratory and field matched performance in the laboratory with high recruitment to carbohydrate baits and only slight recruitment to amino acids. The strong, positive effects of carbohydrates on colony growth and the low cost of producing this macronutrient for plants and hemipterans may have aided the evolution of food-for-protection mutualisms and help explain why these interactions are so common in ants. In addition, greater access to plant-based resources in the introduced range of S. invicta may help to explain the high densities achieved by this species throughout the southeastern United States.

International audience; Arising from M. A. Nowak, C. E. Tarnita & E. O. Wilson 466, 1057-1062 (2010); Nowak et al. reply. Nowak et al. argue that inclusive fitness theory has been of little value in explaining the natural world, and that it has led to negligible progress in explaining the evolution of eusociality. However, we believe that their arguments are based upon a misunderstanding of evolutionary theory and a misrepresentation of the empirical literature. We will focus our comments on three general issues.

Ant-mediated seed dispersal may be a form of directed dispersal if collected seeds are placed in a favorable microhabitat (e.g., in or near an ant nest) that increases plant establishment, growth, and/or reproduction relative to random locations. We investigated whether the native ant community interacts with invasive leafy spurge (Euphorbia esula) in a manner consistent with predictions of the directed dispersal hypothesis. Resident ants quickly located and dispersed 60% of experimentally offered E. esula seeds. Additionally, 40% of seeds whose final deposition site was observed were either brought inside or placed on top of an ant nest. Seed removal was 100% when seeds were placed experimentally on foraging trails of mound-building Formica obscuripes, although the deposition site of these seeds is unknown. Natural density and above-ground biomass of E. esula were greater on Formica mound edges compared to random locations. However, seedling recruitment and establishment from experimentally planted E. esula seeds was not greater on mound edges than random locations 3 m from the mound. Soil from Formica mound edges was greater in available nitrogen and available phosphorus relative to random soil locations 3 m from the mound. These results suggest Formica ant mounds are favorable microhabitats for E. esula growth following seedling establishment, a likely consequence of nutrient limitation during plant growth. The results also indicate positive species interactions may play an important role in biological invasions.

Studies of food webs often employ stable isotopic approaches to infer trophic position and interaction strength without consideration of spatio-temporal variation in resource assimilation by constituent species. Using results from laboratory diet manipulations and monthly sampling of field populations, we illustrate how nitrogen isotopes may be used to quantify spatio-temporal variation in resource assimilation in ants. First, we determined nitrogen enrichment using a controlled laboratory experiment with the invasive Argentine ant (Linepithema humile). After 12 weeks, worker δ(15)N values from colonies fed an animal-based diet had δ(15)N values that were 5.51% greater compared to colonies fed a plant-based diet. The shift in δ(15)N values in response to the experimental diet occurred within 10 weeks. We next reared Argentine ant colonies with or without access to honeydew-producing aphids and found that after 8 weeks workers from colonies without access to aphids had δ(15)N values that were 6.31% larger compared to colonies with access to honeydew. Second, we sampled field populations over a 1-year period to quantify spatio-temporal variability in isotopic ratios of L. humile and those of a common native ant (Solenopsis xyloni). Samples from free-living colonies revealed that fluctuations in δ(15)N were 1.6-2.4‰ for L. humile and 1.8-2.9‰ for S. xyloni. Variation was also detected among L. humile castes: time averaged means of δ(15)N varied from 1.2 to 2.5‰ depending on the site, with δ(15)N values for queens ≥ workersbrood. The estimated trophic positions of L. humile and S. xyloni were similar within a site; however, trophic position for each species differed significantly at larger spatial scales. While stable isotopes are clearly useful for examining the trophic ecology of arthropod communities, our results suggest that caution is warranted when making ecological interpretations when stable isotope collections come from single time periods or life stages.

Tropical forest canopies house most of the globe's diversity, yet little is known about global patterns and drivers of canopy diversity. Here, we present models of ant species density, using climate, abundance and habitat (i.e. canopy versus litter) as predictors. Ant species density is positively associated with temperature and precipitation, and negatively (or non-significantly) associated with two metrics of seasonality, precipitation seasonality and temperature range. Ant species density was significantly higher in canopy samples, but this difference disappeared once abundance was considered. Thus, apparent differences in species density between canopy and litter samples are probably owing to differences in abundance–diversity relationships, and not differences in climate–diversity relationships. Thus, it appears that canopy and litter ant assemblages share a common abundance–diversity relationship influenced by similar but not identical climatic drivers.

Although many taxa show a latitudinal gradient in richness, the relationship between latitude and species richness is often asymmetrical between the northern and southern hemispheres. Here we examine the latitudinal pattern of species richness across 1003 local ant assemblages. We find latitudinal asymmetry, with southern hemisphere sites being more diverse than northern hemisphere sites. Most of this asymmetry could be explained statistically by differences in contemporary climate. Local ant species richness was positively associated with temperature, but negatively (although weakly) associated with temperature range and precipitation. After contemporary climate was accounted for, a modest difference in diversity between hemispheres persisted, suggesting that factors other than contemporary climate contributed to the hemispherical asymmetry. The most parsimonious explanation for this remaining asymmetry is that greater climate change since the Eocene in the northern than in the southern hemisphere has led to more extinctions in the northern hemisphere with consequent effects on local ant species richness. © 2009 Blackwell Publishing Ltd/CNRS.

A major challenge of invasion biology lies in the development of a predictive understanding of invasion processes. Attempts to identify the proximate causes of invasion success or to predict rates of spread seldom emphasize behavioral characteristics. Recent experimental work, however, illustrates that insight into the proximate causes of animal invasions often hinges on a careful assessment of behavioral mechanisms. For this reason, behavioral analyses should be more fully integrated into research on biological invasions. In addition to enhancing a general understanding of invasion processes, such approaches provide potentially underused opportunities for basic research in animal behavior.

Division of labour--individuals specializing in different activities--features prominently in the spectacular success of the social insects. Until recently, genetic and genomic analyses of division of labour were limited to just a few species. However, research on an ever-increasing number of species has provided new insight, from which we highlight two results. First, heritable influences on division of labour are more pervasive than previously imagined. Second, different forms of division of labour, in lineages in which eusociality has arisen independently, have evolved through changes in the regulation of highly conserved molecular pathways associated with several basic life-history traits, including nutrition, metabolism and reproduction.

Evolutionary co-option of existing structures for new functions is a powerful yet understudied mechanism for generating novelty. Trap-jaw ants of the predatory genus Odontomachus are capable of some of the fastest self-propelled appendage movements ever recorded; their devastating strikes are not only used to disable and capture prey, but produce enough force to launch the ants into the air. We tested four Odontomachus species in a variety of behavioral contexts to examine if their mandibles have been co-opted for an escape mechanism through ballistic propulsion. We found that nest proximity makes no difference in interactions with prey, but that prey size has a strong influence on the suite of behaviors employed by the ants. In trials involving a potential threat (another trap-jaw ant species), vertical jumps were significantly more common in ants acting as intruders than in residents (i.e. a dangerous context), while horizontal jumps occurred at the same rate in both contexts. Additionally, horizontal jump trajectories were heavily influenced by the angle at which the substrate was struck and appear to be under little control by the ant. We conclude that while horizontal jumps may be accidental side-effects of strikes against hard surfaces, vertical escape jumps are likely intentional defensive behaviors that have been co-opted from the original prey-gathering and food-processing functions of Odontomachus jaws.

We examined how dietary, social, and genetic factors affect individual size and caste in the Florida harvester ant Pogonomyrmex badius, which has three discrete female castes. The diet that a larva consumed, as indicated by delta(13)C, delta(15)N, and C:N, varied with caste. Both N content and estimated trophic position of dietary input was higher for major than for minor workers and was highest for gynes (reproductive females). The size and resources of a colony affected the size of only minor workers, not that of gynes and major workers. Approximately 19% of patrilines showed a bias in which female caste they produced. There were significant genetic effects on female size, and the average sizes of a major worker and a gyne produced by a patriline were correlated, but neither was correlated with minor worker size. Thus, genetic factors influence both caste and size within caste. We conclude that environmental, social, and genetic variation interact to create morphological and physiological variation among females in P. badius. However, the relative importance of each type of factor affecting caste determination is caste specific.

SUMMARYTrap-jaw ants of the genus Odontomachus produce remarkably fast predatory strikes. The closing mandibles of Odontomachus bauri, for example, can reach speeds of over 60 m s–1. They use these jaw strikes for both prey capture and locomotion – by striking hard surfaces, they can launch themselves into the air. We tested the hypothesis that morphological variation across the genus is correlated with differences in jaw speeds and accelerations. We video-recorded jaw-strikes at 70 000–100 000 frames s–1 to measure these parameters and to model force production. Differences in mean speeds ranged from 35.9±7.7 m s–1 for O. chelifer, to 48.8±8.9 m s–1 for O. clarus desertorum. Differences in species' accelerations and jaw sizes resulted in maximum strike forces in the largest ants (O. chelifer) that were four times those generated by the smallest ants (O. ruginodis). To evaluate phylogenetic effects and make statistically valid comparisons, we developed a phylogeny of all sampled Odontomachus species and seven outgroup species (19 species total) using four genetic loci. Jaw acceleration and jaw-scaling factors showed significant phylogenetic non-independence, whereas jaw speed and force did not. Independent contrast (IC) values were used to calculate scaling relationships for jaw length, jaw mass and body mass, which did not deviate significantly from isometry. IC regression of angular acceleration and body size show an inverse relationship, but combined with the isometric increase in jaw length and mass results in greater maximum strike forces for the largest Odontomachus species. Relatively small differences (3%) between IC and species-mean based models suggest that any deviation from isometry in species' force production may be the result of recent selective evolution, rather than deep phylogenetic signal.

Baker and Stebbins’s 1965 book The Genetics of Colonizing Species aimed to draw together scientists from a variety of disciplines to provide a conceptual framework for the study of species introductions. A goal of their volume was to examine how studies on biological invasions could be used to provide insight into basic research questions as well as to develop practical strategies for control. In this article, we attempt to follow the goals of Baker and Stebbins by reviewing work on the genetics and behavior of a widespread colonizing species, the Argentine ant (Linepithema humile). Specifically, we examine the evolutionary changes that have taken place as a result of this species being introduced into new environments and synthesize recent research on Argentine ants from the perspective of population genetics, recognition systems, and the mechanisms that may underlie their ecological success.

Background Despite the economic and ecological importance of ants, genomic tools for this family (Formicidae) remain woefully scarce. Knowledge of genome size, for example, is a useful and necessary prerequisite for the development of many genomic resources, yet it has been reported for only one ant species (Solenopsis invicta), and the two published estimates for this species differ by 146.7 Mb (0.15 pg). Results Here, we report the genome size for 40 species of ants distributed across 10 of the 20 currently recognized subfamilies, thus making Formicidae the 4th most surveyed insect family and elevating the Hymenoptera to the 5th most surveyed insect order. Our analysis spans much of the ant phylogeny, from the less derived Amblyoponinae and Ponerinae to the more derived Myrmicinae, Formicinae and Dolichoderinae. We include a number of interesting and important taxa, including the invasive Argentine ant (Linepithema humile), Neotropical army ants (genera Eciton and Labidus), trapjaw ants (Odontomachus), fungus-growing ants (Apterostigma, Atta and Sericomyrmex), harvester ants (Messor, Pheidole and Pogonomyrmex), carpenter ants (Camponotus), a fire ant (Solenopsis), and a bulldog ant (Myrmecia). Our results show that ants possess small genomes relative to most other insects, yet genome size varies three-fold across this insect family. Moreover, our data suggest that two whole-genome duplications may have occurred in the ancestors of the modern Ectatomma and Apterostigma. Although some previous studies of other taxa have revealed a relationship between genome size and body size, our phylogenetically-controlled analysis of this correlation did not reveal a significant relationship. Conclusion This is the first analysis of genome size in ants (Formicidae) and the first across multiple species of social insects. We show that genome size is a variable trait that can evolve gradually over long time spans, as well as rapidly, through processes that may include occasional whole-genome duplication. The small genome sizes of ants, combined with their ecological, evolutionary and agricultural importance, suggest that some of these species may be good candidates for future whole-genome sequencing projects.

A major challenge of invasion biology is the development of a predictive framework that prevents new invasions. This is inherently difficult because different biological characteristics are important at the different stages of invasion: opportunity/transport, establishment and spread. Here, we draw from recent research on a variety of taxa to examine the evolutionary causes and consequences of biological invasions. The process of introduction may favour species with characteristics that promote success in highly disturbed, human-dominated landscapes, thus exerting novel forms of selection on introduced populations. Moreover, evidence is accumulating that multiple introductions can often be critical to the successful establishment and spread of introduced species, as they may be important sources of genetic variation necessary for adaptation in new environments or may permit the introduction of novel traits. Thus, not only should the introduction of new species be prevented, but substantial effort should also be directed to preventing the secondary introduction of previously established species (and even movement of individuals among introduced populations). Modern molecular techniques can take advantage of genetic changes postintroduction to determine the source of introduced populations and their vectors of spread, and to elucidate the mechanisms of success of some invasive species. Moreover, the growing availability of genomic tools will permit the identification of underlying genetic causes of invasive success.

Although the ecological effects of invasions often become obvious soon after introduced species become established, more gradual effects may take years to manifest and can thus require long-term data for quantification. We analyzed an 8-year record of stable isotope data on Argentine ants ( Linepithema humile ) from southern California to infer how the trophic position of this widespread invasive species changes over time as native ant species are displaced. We couple this longitudinal analysis with a biregional comparison of stable isotope data (δ 15 N) on ants from Argentina (native range) and California (introduced range) to quantify ( i ) how the trophic position of L. humile differs between native and introduced populations, and ( ii ) how relative trophic position as estimated by δ 15 N values of Argentine ants compare with those of other ants at the same site. Both long-term and biregional comparisons indicate that the Argentine ant's relative trophic position is reduced at sites with a longer history of occupation. Over the course of 8 years, the relative trophic position of L. humile remained high at the leading edge of an invasion front but declined, on average, behind the front as native ants disappeared. Relative to native populations, where L. humile is among the most carnivorous of ants, Argentine ants from California occupied lower trophic positions. These results support the hypothesis that Argentine ants shift their diet after establishment as a result of resource depletion and increasing reliance on plant-based resources, especially honeydew-producing Hemiptera. Our results demonstrate the value of long-term and biregional data in uncovering ecological effects of invasions.

An understanding of why introduced species achieve ecological success in novel environments often requires information about the factors that limit the abundance of these taxa in their native ranges. Although numerous recent studies have evaluated the importance of natural enemies in this context, relatively few have examined how ecological success may result from differences in the magnitude of interference competition between communities in the native and introduced ranges of nonnative species. Here we examine how native-range competitive environments may relate to invasion success for two important invasive species, the red imported fire ant (Solenopsis invicta) and the Argentine ant (Linepithema humile), in a region of native-range sympatry. At two study sites in northern Argentina, we used stable-isotope analysis, a variety of observational approaches, and two different reciprocal removal experiments to test (1) whether S. invicta competes asymmetrically with L. humile (as suggested by the 20th century pattern of replacement in the southeastern United States) and (2) the extent to which these two species achieve behavioral and numerical dominance. Stable-isotope analysis and activity surveys indicated that S. invicta and L. humile are both omnivores and forage during broadly overlapping portions of the diel cycle. Short-term removal experiments at baits revealed no competitive asymmetry between S. invicta and L. humile. Longer-term colony removal experiments illustrated that S. invicta and L. humile experience an approximately equal competitive release upon removal of the other. Our results indicate that neither S. invicta nor L. humile achieves the same degree of behavioral or ecological dominance where they co-occur in native populations as they do in areas where either is common in their introduced range. These results strongly suggest that interspecific competition is an important limiting factor for both S. invicta and L. humile in South America.

Some species of ants possess an unusual form of social organization in which aggression among nests is absent. This type of social organization, called unicoloniality, has been studied in only a handful of species and its evolutionary origins remain unclear. To date, no study has examined behavioural and genetic patterns at points of contact between the massive supercolonies that characterize unicoloniality. Since interactions at territory boundaries influence the costs of aggression and the likelihood of gene flow, such data may illuminate how supercolonies are formed and maintained. Here we provide field data on intraspecific territoriality for a widespread and invasive unicolonial social insect, the Argentine ant (Linepithema humile). We observed abrupt and well-defined behavioural boundaries at 16 contact zones between three different pairs of supercolonies. We visited nine of these zones weekly during a six-month period and observed consistent and intense intercolony aggression that resulted in variable, but often large, levels of worker mortality. Microsatellite variation along six transects across territory borders showed that F(ST) values were lower within supercolonies (0.08 +/- 0.01 (mean +/- SE)) than between supercolonies (0.29 +/- 0.01) and that this disparity was especially strong right at territory borders, despite direct and prolonged contact between the supercolonies. Matrix correspondence tests confirmed that levels of aggression and genetic differentiation were significantly correlated, but no relationship existed between geographic distance and either intraspecific aggression or genetic differentiation. Patterns of F(ST) variation indicated high levels of gene flow within supercolonies, but little to no gene flow between them. Overall, these findings are inconsistent with a model of relaxed ecological constraints leading to colony fusion and suggest that environmentally derived cues are not the prime determined of nestmate recognition in field populations of Argentine ants.

Ce travail résulte de la collaboration de très nombreux chercheurs. Seuls les auteurs de la rubrique Physical and Genetic Mapping sont cités explicitement.; Here we report the genome sequence of the honeybee Apis mellifera, a key model for social behaviour and essential to global ecology through pollination. Compared with other sequenced insect genomes, the A. mellifera genome has high A1T and CpG contents, lacks major transposon families, evolves more slowly, and is more similar to vertebrates for circadian rhythm, RNA interference and DNA methylation genes, among others. Furthermore, A.mellifera has fewer genes for innate immunity, detoxification enzymes, cuticle-forming proteins and gustatory receptors, more genes for odorant receptors, and novel genes for nectar and pollen utilization, consistent with its ecology and social organization. Compared to Drosophila, genes in early developmental pathways differ in Apis, whereas similarities exist for functions that differ markedly, such as sex determination, brain function and behaviour. Population genetics suggests a novel African origin for the species A.mellifera and insights into whether Africanized bees spread throughout the New World via hybridization or displacement

The success of some invasive species may depend on phenotypic changes that occur following introduction. In Argentine ants (Linepithema humile) introduced populations typically lack intraspecific aggression, but native populations display such behavior commonly. We employ three approaches to examine how this behavioral shift might influence interspecific competitive ability. In a laboratory experiment, we reared colonies of Forelius mccooki with pairs of Argentine ant colonies that either did or did not exhibit intraspecific aggression. F. mccooki reared with intraspecifically non-aggressive pairs of Argentine ants produced fewer eggs, foraged less actively, and supported fewer living workers than those reared with intraspecifically aggressive pairs. At natural contact zones between competing colonies of L. humile and F. mccooki, the introduction of experimental Argentine ant colonies that fought with conspecific field colonies caused L. humile to abandon baits in the presence of F. mccooki, whereas the introduction of colonies that did not fight with field colonies of Argentine ants resulted in L. humile retaining possession of baits. Additional evidence for the potential importance of colony- structure variation comes from the Argentine ant's native range. At a site along the Rio de la Plata in Argentina, we found an inverse relationship between ant richness and density of L. humile (apparently a function of local differences in colony structure) in two different years of sampling.

Moffett provides a very thorough review of the ‘‘supercolony’’ concept, focusing on the biology of the Argentine ant (Linepithema humile). The term supercolony is being used more and more frequently in the social insect literature, however, not always to describe the same colony structure. Despite invoking an almost science fiction-like quality, we agree with Moffett that the concept of the supercolony has been valuable, providing considerable insight from both an ecological and an evolutionary perspective. Ecologically, the term supercolony is often used to describe a polydomous colony that occupies such a large number of nests that it is impossible for all members of the colony to interact in their lifetime (Pedersen et al. 2006). That is, the society occupies many nest sites over such a large area that queens and workers who live on one side of the supercolony will never meet individuals from the other side. As Moffett points out, this is likely true for many social insects, even those that occupy relatively few nest sites over smaller areas. Moffett suggests that we restrict the definition of supercolony to societies with at least 1 million workers. However, this seems a bit arbitrary; a number of ant species are known to have more than 1 million workers yet occupy a single nest site. Are these supercolonies in the same sense that a spatially extensive polydomous Argentine ant colony is? Species that form supercolonies are also often ecologically dominant where they occur, both outcompeting other species for resources and overwhelming species through numerical superiority (Holway et al. 2002). However, as pointed out by Holldobler and Wilson (1977), research is still needed to determine if ants become ecologically dominant because they form supercolonies or if ecologically dominant ants monopolize resources and subsequently form supercolonies as a result. From an evolutionary perspective, a supercolony can be defined as the aggregation of ants across many nests that share a common genotype (usually inferred using microsatellites or mitochondrial DNA) and phenotype (e.g., cuticular hydrocarbon profile). This is likely due to having a shared common ancestry. Subsequently, this approach has been used to examine the source and introduction history of invasive ants. Recent holistic work combining behavior, chemistry, and genetics has provided incredible insight into the worldwide spread of Argentine ants (Wilgenburg et al. 2010), and supercolony identity has been used to infer recent exchange of ants between different introduced populations (Tsutsui et al. 2001; Corin et al. 2007; Sunamura et al. 2009; Vogel et al. 2010; Suhr et al. 2011). As Moffett points out, genetic work on both native and introduced populations of Argentine ants suggests little to know gene flow among supercolonies. However, we disagree that each supercolony should be considered its own species (much as each individual is not considered its own species in clonal organisms). More work is needed to determine the spatial extent of gene flow in species that form supercolonies. We agree with Moffett that we need to move past semantic arguments when discussing supercolonies. However, we believe that both ecological and evolutionary examinations of supercolonies need to be conducted from the perspective of the population. A population can be defined as a group of colonies that have the potential to exchange genes or compete for resources. A population can therefore have many colonies, even many supercolonies. However, the term unicolonial, which is often considered synonymous with supercolony (Pedersen et al. 2006), should be restricted to describe situations in which the entire population consists of only one supercolony (a ‘‘unicolonial population’’ Holldobler and Wilson 1977; Suarez et al. 2008). Research is still clearly needed on the biology of species that form supercolonies as many unanswered questions remain. For example, how do supercolonies arise and how long do they last? How much variation in social parameters exists in native populations of species that can form supercolonies (e.g., colony size, queen number, intravs. intercolony genetic diversity, gene flow among colonies)? Is there conflict over reproduction within supercolonies or are they as harmonious as Moffett implies? Over what spatial scales are food and information exchanged (Heller et al. 2008)? These last 2 questions in particular address whether or not supercolonies are effectively made up of aggregations of smaller colonies. Despite being one of the best-studied social insects, we still know surprisingly little about the biology of Argentine ants, particularly in their native range. From an evolutionary perspective, we often know even less about species closely related to those that form supercolonies. For example, what characteristics are shared among sibling species in the humile complex or are unique to the widespread L. humile?

We are pleased that McGlynn agrees with the main point of our TREE Perspective article1xHolway, D.A. and Suarez, A.V. Trends Ecol. Evol. 1999; 14: 328–330Abstract | Full Text | Full Text PDF | PubMed | Scopus (213)See all References1, in which we argued that a full understanding of the success of animal invasions often hinges on a careful analysis of behavioral mechanisms.McGlynn takes issue with our statement that ‘… detailed studies of other highly invasive ant species … have yet to be done’. This is taken out of context. Other highly invasive ant species have been studied; however, in our Perspective article we acknowledge the value of detailed behavioral studies, specifically those that compare introduced with native populations2xRoss, K.G. and Keller, L. Annu. Rev. Ecol. Syst. 1995; 26: 631–656CrossrefSee all References, 3xRoss, K.G., Vargo, E.L., and Keller, L. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 3021–3025Crossref | PubMed | Scopus (114)See all References, 4xSuarez, A.V. et al. Biol. Invasions. 1999; 1: 43–53CrossrefSee all References. His statement that ‘… three other significant global invaders are known quite well’, is not supported by his citations, which focus primarily on introduced populations or do not address mechanisms explaining invasion success.Our point is well illustrated by McGlynn’s own example of a ‘well studied’ species, Pheidole megacephala. Although P. megacephala is a widespread invasive species5xSee all References5, little is known about the mechanisms underlying its ecological success or whether differences in social structure exist between native and introduced populations. This uncertainty is illustrated by McGlynn’s own statement: ‘… it is likely that P. megacephala is unicolonial wherever it is native’.In addition, McGlynn makes several unqualified statements about the red imported fire ant (Solenopsis invicta). First, S. invicta occurs in two social forms in its introduced range; the widespread monogyne form is multicolonial, monogynous, and exhibits pronounced intraspecific aggression2xRoss, K.G. and Keller, L. Annu. Rev. Ecol. Syst. 1995; 26: 631–656CrossrefSee all References, 6xTschinkel, W.R. BioScience. 1998; 48: 593–605CrossrefSee all References. Second, although S. invicta and Linepithema humile have undergone behavioral shifts following introduction, McGlynn’s statement that traits such as polygyny are absent from native populations is incorrect2xRoss, K.G. and Keller, L. Annu. Rev. Ecol. Syst. 1995; 26: 631–656CrossrefSee all References, 3xRoss, K.G., Vargo, E.L., and Keller, L. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 3021–3025Crossref | PubMed | Scopus (114)See all References.

Despite the innumerable ecological problems and large economic costs associated with biological invasions, the proximate causes of invasion success are often poorly understood. Here, evidence is provided that reduced intraspecific aggression and the concomitant abandonment of territorial behavior unique to introduced populations of the Argentine ant contribute to the elevated population densities directly responsible for its widespread success as an invader. In the laboratory, nonaggressive pairs of colonies experienced lower mortality and greater foraging activity relative to aggressive pairs. These differences translated into higher rates of resource retrieval, greater brood production, and larger worker populations.

Background The unintentional transport of species as a result of human activities has reached unprecedented rates. Once established, introduced species can be nearly impossible to eradicate. It is therefore essential to identify and monitor locations where invaders are most likely to establish new populations. Despite the obvious value of early detection, how does an agency identify areas that are most vulnerable to new invaders? Here we propose a novel approach by using the “first detection location” (FDL) of introduced species in China to quantify characteristics of areas where introduced species are first reported. Methodology/Principal Findings We obtained FDLs for 166 species (primarily agricultural and forestry pests) that were unintentionally introduced into China prior to 2008 from literature searches. The spatial pattern and determinants of FDLs were examined at the provincial level. The spatial pattern of FDLs varied among provinces with more commerce and trade and economically developed provinces in coastal regions having more FDLs than interior provinces. For example, 74.6% of FDLs were distributed in coastal regions despite that they only cover 15.6% of the total area in China. Variables that may be indicators of “introduction pressure” (e.g. the amount of received commerce) had an overwhelming effect on the number of FDLs in each province (R2 = 0.760). Conclusions/Significance Our results suggest that “introduction pressure” may be one of the most important factors that determine the locations where newly-introduced species are first detected, and that open and developed provinces in China should be prioritized when developing monitoring programs that focus on locating and managing new introductions. Our study illustrates that FDL approaches can contribute to the study and management of biological invasions not only for China but also for elsewhere.

Many museums and academic institutions maintain first-rate collections of biological materials, ranging from preserved whole organisms to DNA libraries and cell lines. These biological collections make innumerable contributions to science and society in areas as divergent as homeland secu- rity ,p ublic health and safety, monitoring of environmental change, and traditional taxonomy and systematics. Moreover, these collections save governments and taxpayers many millions of dollars each year by effectively guiding government spending, preventing catastrophic events in public health and safety, eliminating redundancy, and securing natural and agricultural resources. However, these contributions are widely underappre- ciated by the public and by policymakers, resulting in insufficient financial support for maintenance and improvement of biological collections.

Nature published a paper last year claiming that transgenic DNA had become genetically incorporated into traditional maize in Mexico. A debate ensued ...

When invasive species establish in new environments, they may disrupt existing or create new interactions with resident species. Understanding of the functioning of invaded ecosystems will benefit from careful investigation of resulting species-level interactions. We manipulated ant visitation to compare how invasive ant mutualisms affect two common plants, one native and one invasive, on a sub-tropical Indian Ocean island. Technomyrmex albipes, an introduced species, was the most common and abundant ant visitor to the plants. T. albipes were attracted to extrafloral nectaries on the invasive tree (Leucaenaleucocephala) and deterred the plant’s primary herbivore, the Leucaena psyllid (Heteropsylla cubana). Ant exclusion from L. leucocephala resulted in decreased plant growth and seed production by 22% and 35%, respectively. In contrast, on the native shrub (Scaevola taccada), T. albipes frequently tended sap-sucking hemipterans, and ant exclusion resulted in 30% and 23% increases in growth and fruit production, respectively. Stable isotope analysis confirmed the more predacious and herbivorous diets of T. albipes on the invasive and native plants, respectively. Thus the ants’ interactions protect the invasive plant from its main herbivore while also exacerbating the effects of herbivores on the native plant. Ultimately, the negative effects on the native plant and positive effects on the invasive plant may work in concert to facilitate invasion by the invasive plant. Our findings underscore the importance of investigating facilitative interactions in a community context and the multiple and diverse interactions shaping novel ecosystems.