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Once established in new areas, introduced species may exhibit changes in their biology due to phenotypic plasticity, novel selection pressures and genetic drift. Moreover, the introduction process itself has been hypothesised to act as a selective filter for traits that promote invasiveness. We tested the hypothesis that behaviours thought to promote invasiveness���such as increased foraging activity and aggression���are selected for during invasion by comparing traits among native and introduced populations of the widespread Argentine ant (Linepithema humile). We studied Argentine ant populations in the native range in Argentina and in three invaded regions along an introduction pathway: California, Australia and New Zealand. In each region, we set up 32 experimental colonies to measure foraging activity and interspecific aggression in a subset of the study regions. These colonies were subject to experimental manipulation of carbohydrate availability and octopamine, a biogenic amine known to modulate behaviour in insects, to measure variation in behavioural plasticity. We found variation in foraging activity among populations, but this variation was not consistent with selection on behaviour in relation to the invasion process. We found that colonies with limited access to carbohydrates exhibited unchanged exploratory behaviour, but higher exploitation activity and lower aggression. Colonies given octopamine consistently increased foraging behaviour (both exploration and exploitation), as well as aggression when also sugar-deprived. There was no difference in the degree of behavioural response to our experimental treatments along the introduction pathway. We did not find support for selection of behavioural traits associated with invasiveness along the Argentine ant's introduction pathway or clear evidence for an association between the introduction process and variation in behavioural plasticity. These results indicate that mechanisms promote behavioural variation in a similar fashion both in native and introduced ranges. Our results challenge the assumption that introduced populations always perform better in key behavioural traits hypothesised to be associated with invasion success.

Author(s): Seltmann, Katja; Allen, Julie; Brown, Brian V.; Carper, Adrian; Engel, Michael S.; Franz, Nico; Gilbert, Edward; Grinter, Chris; Gonzalez, Victor H.; Horsley, Pam; Lee, Sangmi; Maier, Crystal; Miko, Istvan; Morris, Paul; Oboyski, Peter; Pierce, Naomi E.; Poelen, Jorrit; Scott, Virginia L.; Smith, Mark; Talamas, Elijah J.; Tsutsui, Neil D.; Tuker, Erika | Abstract: While bees are critical to sustaining a large proportion of global food production, as well as pollinating both wild and cultivated plants, they are decreasing in both numbers and diversity. Our understanding of the factors driving these declines is limited, in part, because we lack sufficient data on the distribution of bee species to predict changes in their geographic range under climate change scenarios. Additionally lacking is adequate data on the behavioral and anatomical traits that may make bees either vulnerable or resilient to human-induced environmental changes, such as habitat loss and climate change. Fortunately, a wealth of associated attributes can be extracted from the specimens deposited in natural history collections for over 100 years.Extending Anthophila Research Through Image and Trait Digitization (Big-Bee)nis a newly funded US National Science Foundation Advancing Digitization of Biodiversity Collections project. Over the course of three years, we will create over one million high-resolution 2D and 3D images of bee specimens (Fig.n1), representing over 5,000 worldwide bee species, including most of the major pollinating species. We will also develop tools to measure bee traits from images and generate comprehensive bee trait and image datasets to measure changes through time. The Big-Bee network of participating institutions includes 13 US institutions (Fig.n2) and partnerships with US government agencies. We will develop novel mechanisms for sharing image datasets and datasets of bee traits that will be available through an open,nSymbiota-Lightn(Gilbert et al. 2020) data portal called the Bee Library. In addition, biotic interaction and speciesnassociationndata will be shared vianGlobal Biotic Interactionsn(Poelen et al. 2014). ThenBig-Bee projectnwill engage the public in research through community science via crowdsourcing trait measurements and data transcription from images usingnNotes from Naturen(Hill et al. 2012). Training and professional development for natural history collection staff, researchers, and university students in data science will be provided through the creation and implementation of workshops focusing on bee traits and species identification. We are also planning a short, artistic college radio segment called "the Buzz" to get people excited about bees, biodiversity, and the wonders of our natural world.This poster was prepared for TDWG 2021 virtual conference.

© 2018 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd. Host–parasite associations facilitate the action of reciprocal selection and can drive rapid evolutionary change. When multiple host species are available to a single parasite, parallel specialization on different hosts may promote the action of diversifying natural selection and divergence via host race formation. Here, we examine a population of the kidnapper ant (Polyergus mexicanus) that is an obligate social parasite of three sympatric ant species: Formica accreta, F. argentea, and F. subaenescens (formerly F. fusca). Behavioral and ecological observations of P. mexicanus have shown that individual colonies parasitize only one species of host and that new Polyergus queens maintain host fidelity when establishing new colonies. To successfully adapt to a particular host, Polyergus ants may mimic or camouflage themselves with the species-specific chemical cues (cuticular hydrocarbons) that their hosts use to ascertain colony membership. To investigate the extent of host specialization, we collected both genetic and chemical data from P. mexicanus that parasitize each of the three different Formica species in sympatry. We show that host-associated genetic structure exists for both maternally inherited mitochondrial DNA data and biparentally inherited microsatellite markers. We also show that P. mexicanus can be distinguished by chemical profile according to host due to partial matching with their host. Our results support the hypothesis that host race formation is occurring among lineages of P. mexicanus that use different Formica hosts. Thus, this system may represent a promising model for illuminating the early steps of divergence, accumulation of reproductive isolation, and speciation.

© The Author(s) 2018. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. The western honey bee, Apis mellifera, is an enormously influential pollinator in both natural and managed ecosystems. In North America, this species has been introduced numerous times from a variety of different source populations in Europe and Africa. Since then, feral populations have expanded into many different environments across their broad introduced range. Here, we used whole genome sequencing of historical museum specimens and newly collected modern populations from California (USA) to analyze the impact of demography and selection on introduced populations during the past 105 years. We find that populations from both northern and southern California exhibit pronounced genetic changes, but have changed in different ways. In northern populations, honey bees underwent a substantial shift from western European to eastern European ancestry since the 1960s, whereas southern populations are dominated by the introgression of Africanized genomes during the past two decades. Additionally, we identify an isolated island population that has experienced comparatively little change over a large time span. Fine-scale comparison of different populations and time points also revealed SNPs that differ in frequency, highlighting a number of genes that may be important for recent adaptations in these introduced populations.

Ecological impacts associated with ant introductions have received considerable attention, but most studies that report on these impacts contrast species assemblages between invaded and uninvaded sites. Given the low inferential power of this type of space-for-time comparison, alternative approaches are needed to evaluate claims that ant invasions drive native species loss. Here, we use long-term data sets from two different Argentine ant eradication programs on the California Channel Islands to examine how the richness and composition of native ant assemblages change before and after invasion (but prior to the initiation of treatments). At four different sites on two different islands, pre-invasion native ant assemblages closely resembled those at uninvaded (control) sites in terms of species richness, species composition, and the presence of multiple indicator species. Invader arrival coincided with large (> 75%) and rapid (within 1year) declines in species richness, shifts in species composition, and the loss of indicator species. These impacts will hopefully be reversed by the recolonization of formerly invaded areas by native ant species following Argentine ant treatment, and long-term studies of native ant recovery at these sites are ongoing. Unchecked spread of the Argentine ant on other islands in this archipelago, however, poses a grave threat to native ants, which include a number of endemic taxa.

Chemical recognition systems are crucial for maintaining the unity of social insect colonies. It has been proposed that colonies form a common chemical signature, called the gestalt odor, which is used to distinguish colony members and non-members. This chemical integration is achieved actively through social interactions such as trophallaxis and allogrooming, or passively such as through exposure to common nest material. When colonies are infiltrated by social parasites, the intruders often use some form of chemical mimicry. However, it is not always clear how this chemical mimicry is accomplished. Here, we used a three-species nesting symbiosis to test the differences in chemical integration of mutualistic (parabiotic) and parasitic ant species. We found that the parasite (Solenopsis picea) obtains chemical cues from both of the two parabiotic host ant species. However, the two parabiotic species (Crematogaster levior and Camponotus femoratus) maintain species-specific cues, and do not acquire compounds from the other species. Our findings suggest that there is a fundamental difference in how social mutualists and social parasites use chemicals to integrate themselves into colonies.

Climate change is a serious threat to biodiversity; it is therefore important to understand how animals will react to this stress. Ectotherms, such as ants, are especially sensitive to the climate as the environmental temperature influences myriad aspects of their biology, from optimal foraging time to developmental rate. In this study, we conducted an RNA-seq analysis to identify stress-induced genes in the winter ant (Prenolepis imparis). We quantified gene expression during heat and cold stress relative to a control temperature. From each of our conditions, we sequenced the transcriptome of three individuals. Our de novo assembly included 13,324 contigs that were annotated against the nr and SwissProt databases. We performed gene ontology and enrichment analyses to gain insight into the physiological processes involved in the stress response. We identified a total of 643 differentially expressed genes across both treatments. Of these, only seven genes were differentially expressed in the cold-stressed ants, which could indicate that the temperature we chose for trials did not induce a strong stress response, perhaps due to the cold adaptations of this species. Conversely, we found a strong response to heat: 426 upregulated genes and 210 downregulated genes. Of these, ten were expressed at a greater than ten-fold change relative to the control. The transcripts we could identify included those encoding for protein folding genes, heat shock proteins, histones, and Ca2+ ion transport. One of these transcripts, hsc70-4L was found to be under positive selection. We also characterized the functional categories of differentially expressed genes. These candidate genes may be functionally conserved and relevant for related species that will deal with rapid climate change.

The evolution of pre-zygotic reproductive isolation is a key step in the process of speciation. In many organisms, particularly insects, chemical labels are used as pheromones for species-specific mate recognition. Although an enormous body of knowledge exists regarding the patterns of pheromone chemical ecology, much less is known about the evolutionary processes that underlie the origin of new mating pheromones. Here, we examine case studies that have illuminated the origins of species-specific mating pheromones and suggest future directions for productive research. This article is part of the theme issue ‘Signal detection theory in recognition systems: from evolving models to experimental tests’.

Author(s): Felden, A; Paris, C; Chapple, DG; Suarez, AV; Tsutsui, ND; Lester, PJ; Gruber, MAM | Abstract: Biological invasions can be influenced by trait variation in the invader, such as behavioural traits and ecological factors, such as variation in pathogen pressure. High-throughput nucleotide sequencing has increased our capacity to investigate the genomic basis of the functional changes associated with biological invasions. Here, we used RNA-sequencing in Argentina and California, Australia and New Zealand to investigate if native and introduced Argentine ant populations were characterised by distinct transcriptomic signatures. We focused our analysis on viral pressure and immunity, as well as genes associated with biogenic amines known to modulate key behaviour in social insects. Using a combination of differential expression analysis, gene co-expression network analysis and candidate gene approach, we show that native and introduced populations have distinct transcriptomic signatures. Genes associated with biogenic amines were overall up-regulated in the native range compared to introduced populations. Although we found no significant variation in overall viral loads amongst regions for viruses known to infect Argentine ants, viral diversity was lower in most of the introduced range which was interestingly associated with down-regulation of the RNAi immune pathway, primarily directed against viruses. Altogether, our data show that Argentine ant populations exhibit range-specific transcriptomic signatures, perhaps reflecting regional adaptations that may contribute to the ecological success of introduced populations.

Cuticular hydrocarbons (CHCs), the dominant fraction of the insects' epicuticle and the primary barrier to desiccation, form the basis for a wide range of chemical signaling systems. In eusocial insects, CHCs are key mediators of nestmate recognition, and colony identity appears to be maintained through a uniform CHC profile. In the unicolonial Argentine ant Linepithema humile, an unparalleled invasive expansion has led to vast supercolonies whose nestmates can still recognize each other across thousands of miles. CHC profiles are expected to display considerable variation as they adapt to fundamentally differing environmental conditions across the Argentine ant's expanded range, yet this variation would largely conflict with the vastly extended nestmate recognition based on CHC uniformity. To shed light on these seemingly contradictory selective pressures, we attempt to decipher which CHC classes enable adaptation to such a wide array of environmental conditions and contrast them with the overall CHC profile uniformity postulated to maintain nestmate recognition. n-Alkanes and n-alkenes showed the largest adaptability to environmental conditions most closely associated with desiccation, pointing at their function for water-proofing. Trimethyl alkanes, on the other hand, were reduced in environments associated with higher desiccation stress. However, CHC patterns correlated with environmental conditions were largely overriden when taking overall CHC variation across the expanded range of L. humile into account, resulting in conserved colony-specific CHC signatures. This delivers intriguing insights into the hierarchy of CHC functionality integrating both adaptation to a wide array of different climatic conditions and the maintenance of a universally accepted chemical profile.

A central goal of ecology is to understand the mechanisms behind variation in the abundance of species. Food web theory predicts higher biomass for animals at lower trophic levels. However, some high trophic level species may reach great abundance via highly efficient foraging behaviors. We evaluated ecological and behavioral traits of the giant tropical ant Dinoponera australis related to these mechanisms. We determined its distribution and abundance, documented its foraging behavior, and measured its trophic position in a population at P.N. Iguazu, Argentina. We report that D. australis colonies are overdispersed, and the species reaches a wet biomass of more than 2.5 kg/ha at this site. Dinoponera australis foraging behavior is characterized by route fidelity of individual workers, with different individuals specializing on different areas around the nest. Finally, stable isotopic evidence and direct observation suggest these ants are among the top predators in this terrestrial invertebrate community. We interpret our findings in the context of how the behavior of an abundant top predator creates an exception to the usual trade-off between biomass and trophic level. Together these data provide insight into the biology of one of the world's largest ants and why they may be able to attain such high densities where they occur. © 2014 The Association for Tropical Biology and Conservation.

Myrmecophiles (i.e. organisms that associate with ants) use a variety of ecological niches and employ different strategies to survive encounters with ants. Because ants are typically excellent defenders, myrmecophiles may choose moments of weakness to take advantage of their ant associates. This hypothesis was studied in the rove beetle, Myrmedonota xipe , which associates with Azteca sericeasur ants in the presence of parasitoid flies. A combination of laboratory and field experiments show that M. xipe beetles selectively locate and prey upon parasitized ants. These parasitized ants are less aggressive towards beetles than healthy ants, allowing beetles to eat the parasitized ants alive without interruption. Moreover, behavioural assays and chemical analysis reveal that M. xipe are attracted to the ant's alarm pheromone, the same secretion used by the phorid fly parasitoids in host location. This strategy allows beetles access to an abundant but otherwise inaccessible resource, as A. sericeasur ants are typically highly aggressive. These results are the first, to our knowledge, to demonstrate a predator sharing cues with a parasitoid to gain access to an otherwise unavailable prey item. Furthermore, this work highlights the importance of studying ant–myrmecophile interactions beyond just their pairwise context.

Ants are some of the most abundant and familiar animals on Earth, and they play vital roles in most terrestrial ecosystems. Although all ants are eusocial, and display a variety of complex and fascinating behaviors, few genomic resources exist for them. Here, we report the draft genome sequence of a particularly widespread and well-studied species, the invasive Argentine ant ( Linepithema humile ), which was accomplished using a combination of 454 (Roche) and Illumina sequencing and community-based funding rather than federal grant support. Manual annotation of >1,000 genes from a variety of different gene families and functional classes reveals unique features of the Argentine ant's biology, as well as similarities to Apis mellifera and Nasonia vitripennis . Distinctive features of the Argentine ant genome include remarkable expansions of gustatory (116 genes) and odorant receptors (367 genes), an abundance of cytochrome P450 genes (>110), lineage-specific expansions of yellow/major royal jelly proteins and desaturases, and complete CpG DNA methylation and RNAi toolkits. The Argentine ant genome contains fewer immune genes than Drosophila and Tribolium , which may reflect the prominent role played by behavioral and chemical suppression of pathogens. Analysis of the ratio of observed to expected CpG nucleotides for genes in the reproductive development and apoptosis pathways suggests higher levels of methylation than in the genome overall. The resources provided by this genome sequence will offer an abundance of tools for researchers seeking to illuminate the fascinating biology of this emerging model organism.

© 2016, Springer Science+Business Media New York. Parasitoids often use complex cues to identify suitable hosts in their environment. Phorid fly parasitoids that develop on one or a few host species often use multiple cues, ranging from general to highly specific, to home in on an appropriate host. Here, we describe the hierarchy of cues that Pseudacteon phorid flies use to identify Azteca ant hosts. We show, through behavioral observations in the field, that phorid flies are attracted to two cryptic Azteca species, but only attack Azteca sericeasur (Hymenoptera: Formicidae: Dolichoderinae). To test whether the phorid flies use cuticular hydrocarbons (CHCs) to distinguish between the two Azteca taxa, we first documented and compared cuticular hydrocarbons of the two Azteca taxa using gas chromatography/mass spectrometry. Then, using cuticular hydrocarbon-transfer experiments with live ants, we characterized the cuticular hydrocarbons of A. sericeasur as a short-range, host location cue used by P. lasciniosus (Diptera: Phoridae) to locate the ants.

Early work on the setting of acceptance thresholds fornestmate recognition suggested that an overlap betweenthe odor templates used by different colonies could lead toa tradeoff between accepting nestmates and rejecting non-nestmates (Reeve 1989). In a recent paper, we pointed outan alternative approach to this problem (Johnson et al.2011). We started with a literature review that suggests thatrejection of nestmates is exceedingly rare in ants, although itdoes seem to occur in bees and wasps. Hence, ants do notseem to need to reject their own nestmates in order toexclude non-nestmates. Following this literature review,we suggested that if social insects are using gestalt mecha-nisms to generate a template of acceptable odors (reviewedby Tsutsui 2004; Martin and Drijfhout 2009), then theconcept of overlap between the cues used by different col-onies might be of little utility. The relevant question is ratherone of errors due to limited sensory acuity. We then inter-preted the rejection errors of bees from this perspective andshowed that per encounter rejection rates may be part of amore accurate colony level collective decision-makingprocess. Essentially, per encounter rejection rates can am-plify over many encounters to a more accurate level ofrecognition than would be the case for a single interaction.Couvillon et al. (2011), in their commentary on this work,argue that our results are based on false assumptions. Wedisagree. Couvillon et al. raise three issues with our work, towhich we respond below.Couvillon et al. (2011) argue that we did not considerprevious work on individual-level responses by guards(Couvillon et al. 2008). They further suggest that this workon individual-level responses undermines our model. Werecognize that individual social insects can change theirbehaviors in response to threats, and we have recentlypublished research on exactly this topic (van Wilgenburgetal. 2010).However,the roleof collective decision-makinghas been largely overlooked in the field of nestmate recog-nition, and the explicit goal of Johnson et al. was to explorethe nature and efficacy of such systems. Ultimately, thestringency of nestmate recognition is likely regulated byboth individual-level changes and collective responses, asthe two are not mutually exclusive.Nevertheless, the study highlighted by Couvillon et al.(2008) suffers from a number of shortcomings, rendering itsoverall conclusions about honey bee nestmate recognitiondubious. In their experiment, Couvillon et al. (2008) put afeeder dish in the entrance of one colony in an apiary underthe assumption that this will cause that colony to go out androb its neighbors. They inform us that they subsequentlyrecorded a 10-fold increase in fights at the entrances of theirstudy colonies along with a 20% increase in guard numbers.They then point out that the overall increase in defensive-ness that they recorded was completely accounted for by anindividual level response by guards who decreased theiracceptance rates. What Couvillon et al. have not mentionedin their commentary are the actual numbers involved. The

Social insects rank among the most abundant and influential terrestrial organisms. The key to their success is their ability to form tightly knit social groups that perform work cooperatively, and effectively exclude non-members from the colony. An extensive body of research, both empirical and theoretical, has explored how optimal acceptance thresholds could evolve in individuals, driven by the twin costs of inappropriately rejecting true nestmates and erroneously accepting individuals from foreign colonies. Here, in contrast, we use agent-based modeling to show that strong nestmate recognition by individuals is often unnecessary. Instead, highly effective nestmate recognition can arise as a colony-level property from a collective of individually poor recognizers. Essentially, although an intruder can get by one defender when their odor cues are similar, it is nearly impossible to get past many defenders if there is the slightest difference in cues. The results of our models match observed rejection rates in studies of ants, wasps, and bees. We also show that previous research in support of the optimal threshold theory approach to the problem of nestmate recognition can be alternatively viewed as evidence in favor of the collective formation of a selectively permeable barrier that allows in nestmates (at a significant cost) while rejecting non-nestmates. Finally, this work shows that nestmate recognition has a stronger task allocation component than previously thought, as colonies can nearly always achieve perfect nestmate recognition if it is cost effective for them to do so at the colony level. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00265-010-1094-x) contains supplementary material, which is available to authorized users.

Male orchid bees collect volatiles, from both floral and non-floral sources, that they expose as pheromone analogues (perfumes) during courtship display. The chemical profile of these perfumes, which includes terpenes and aromatic compounds, is both species-specific and divergent among closely related lineages. Thus, fragrance composition is thought to play an important role in prezygotic reproductive isolation in euglossine bees. However, because orchid bees acquire fragrances entirely from exogenous sources, the chemical composition of male perfumes is prone to variation due to environmental heterogeneity across habitats. We used Gas Chromatography/Mass Spectrometry (GC/MS) to characterize the perfumes of 114 individuals of the green orchid bee (Euglossa aff. viridissima) sampled from five native populations in Mesoamerica and two naturalized populations in the southeastern United States. We recorded a total of 292 fragrance compounds from hind-leg extracts, and found that overall perfume composition was different for each population. We detected a pronounced chemical dissimilarity between native (Mesoamerica) and naturalized (U.S.) populations that was driven both by proportional differences of common compounds as well as the presence of a few chemicals unique to each population group. Despite these differences, our data also revealed remarkable qualitative consistency in the presence of several major fragrance compounds across distant populations from dissimilar habitats. In addition, we demonstrate that naturalized bees are attracted to and collect large quantities of triclopyr 2-butoxyethyl ester, the active ingredient of several commercially available herbicides. By comparing incidence values and consistency indices across populations, we identify putative functional compounds that may play an important role in courtship signaling in this species of orchid bee. Electronic supplementary material The online version of this article (doi:10.1007/s10886-010-9821-3) contains supplementary material, which is available to authorized users.

The early phases of biological invasions are poorly understood. In particular, during the introduction, establishment, and possible lag phases, it is unclear to what extent evolution must take place for an introduced species to transition from established to expanding. In this study, we highlight three disparate data sources that can provide insights into evolutionary processes associated with invasion success: biological control organisms, horticultural introductions, and natural history collections. All three data sources potentially provide introduction dates, information about source populations, and genetic and morphological samples at different time points along the invasion trajectory that can be used to investigate preadaptation and evolution during the invasion process, including immediately after introduction and before invasive expansion. For all three data sources, we explore where the data are held, their quality, and their accessibility. We argue that these sources could find widespread use with a few additional pieces of data, such as voucher specimens collected at certain critical time points during biocontrol agent quarantine, rearing, and release and also for horticultural imports, neither of which are currently done consistently. In addition, public access to collected information must become available on centralized databases to increase its utility in ecological and evolutionary research.

Ants are among the most damaging invasive species, and their success frequently arises from the widespread cooperation displayed by introduced populations, often across hundreds of kilometers. Previous studies of the invasive Argentine ant (Linepithema humile) have shown that introduced populations on different continents each contain a single, vast supercolony and, occasionally, smaller secondary colonies. Here, we perform inter-continental behavioral analyses among supercolonies in North America, Europe, Asia, Hawaii, New Zealand and Australia and show that these far-flung supercolonies also recognize and accept each other as if members of a single, globally distributed supercolony. Furthermore, populations also possess similar genetic and chemical profiles. However, these ants do show aggression toward ants from South Africa and the smaller secondary colonies that occur in Hawaii and California. Thus, the largest and most dominant introduced populations are likely descended from the same ancestral colony and, despite having been established more than 100 years ago, have diverged very little. This apparent evolutionary stasis is surprising because, in other species, some of the most rapid rates of evolutionary change have occurred in introduced populations. Given the spatial extent of the Argentine ant society we report here, there can be little doubt that this intercontinental supercolony represents the most populous known animal society.

In recent decades, a growing number of studies have addressed connections between ecological and evolutionary concepts in biologic invasions. These connections may be crucial for understanding the processes underlying invaders’ success. However, the extent to which scientists have worked on the integration of the ecology and evolution of invasive plants is poorly documented, as few attempts have been made to evaluate these efforts in invasion biology research. Such analysis can facilitate recognize well-documented relationships and identify gaps in our knowledge. In this study, we used a network-based method for visualizing the connections between major aspects of ecology and evolution in the primary research literature. Using the family Poaceae as an example, we show that ecological concepts were more studied and better interconnected than were evolutionary concepts. Several possible connections were not documented at all, representing knowledge gaps between ecology and evolution of invaders. Among knowledge gaps, the concepts of plasticity, gene flow, epigenetics and human influence were particularly under-connected. We discuss five possible research avenues to better understand the relationships between ecology and evolution in the success of Poaceae, and of alien plants in general.

All animals interact with conspecifics during their life, and nearly all also display some form of aggression. An enduring challenge, however, is to understand how the experiences of an individual animal influence its later behaviours. Several studies have shown that prior winning experience increases the probability of initiating fights in later encounters. Using behavioural assays in the laboratory, we provide evidence that, in Argentine ants ( Linepithema humile ), the mere exposure to an opponent, without the encounter escalating to a fight, also increases the probability that it will display aggression in later encounters. Argentine ant workers differ in their propensity to attack non-colonymates, with some ants repeatedly aggressive and others consistently more docile. Although 78 per cent of the workers were consistent in their behaviour from one encounter to the next, workers that did change their behaviour after an encounter with a non-colonymate more often changed from non-aggressive to aggressive, rather than the reverse. Surprisingly, a single encounter with a non-colonymate increased a worker's propensity to fight in encounters up to a week later. An encounter with a non-colonymate also increased the probability that a worker would attack ants from a colony that it had not previously encountered. Thus, these interactions lowered the overall aggression threshold, rather than stimulating a specific aggressive response to a particular foreign colony. Finally, our data suggest that aggression towards non-colonymates increases with age.

Ants are some of the most abundant and ecologically successful terrestrial organisms, and invasive ants rank among the most damaging invasive species. The Argentine ant is a particularly well-studied invader, in part because of the extreme social structure of introduced populations, known as unicoloniality. Unicolonial ants form geographically vast supercolonies, within which territorial behaviour and intraspecific aggression are absent. Because the extreme social structure of introduced populations arises from the widespread acceptance of conspecifics, understanding how this colonymate recognition occurs is key to explaining their success as invaders. Here, we present analyses of Argentine ant recognition cues (cuticular hydrocarbons) and population genetic characteristics from 25 sites across four continents and the Hawaiian Islands. By examining both hydrocarbon profiles and microsatellite genotypes in the same individual ants, we show that native and introduced populations differ in several respects. Both individual workers and groups of nestmates in the introduced range possess less diverse chemical profiles than ants in the native range. As previous studies have reported, we also find that introduced populations possess much lower levels of genetic diversity than populations in the native range. Interestingly, the largest supercolonies on several continents are strikingly similar to each other, suggesting that they arose from a shared introduction pathway. This high similarity suggests that these geographically far-flung ants may still recognize and accept each other as colonymates, thus representing distant nodes of a single, widely distributed supercolony. These findings shed light on the behaviour and sociality of these unicolonial invaders, and pose new questions about the history and origins of introduced populations.

Liquid ant baits are an alternative to broad-spectrum insecticide sprays conventionally used to control Argentine ants. We review the development of liquid ant baits, which capitalize on the ants' sugar-feeding requirements and social structure to deliver small doses of toxicant throughout the colony. The ant bait program described here, developed for commercial vineyards, also has the potential to facilitate the use of biological controls for mealybug and scale pests. The implementation of an Argentine ant bait program will enable grape growers to target other pests more selectively with insecticides, further contributing to their sustainable viticulture practices.

This work describes the annual and daily activity patterns of two parasitoid fly communities of the fire ant Solenopsis invicta (Hymenoptera: Formicidae) in their native range in Argentina. Pseudacteon (Diptera: Phoridae) flies were censused monthly for 1 yr at two sites in northwestern Corrientes province. Additionally, parasitism rates of S. invicta colonies naturally attacked in the field by Pseudacteon flies are reported for the first time from its native habitat. In total, 4,528 flies (86.3% females) of eight Pseudacteon species were collected attacking ants in the field. Pseudacteon litoralis Borgmeier and Pseudacteon nocens Borgmeier represented 71-79% of female flies censused in both sites. Most species were active throughout the year, although abundances were variable over time and between sites. The highest occurrence peaks of flies were recorded in spring, whereas the lowest occurrence was in summer. Fly abundance was higher close to dusk, whereas species diversity was highest at midday. Relationships among species were established based on their activity patterns and genetic proximity. The presence and abundance of four species were explained by climatic variables, whereas two species may have inherited similar circadian rhythms from a common ancestor. Overall, the parasitism rate by the nine species recorded was very low (0.24%). The highest percentage of parasitized workers was found in spring (0.5%) and occurred within the most complex habitat (gallery forest). The highest parasitism rate per site and colony was also for this habitat in spring (1.16 and 2.81%, respectively). The highest rates of emergence were recorded for Pseudacteon nudicornis Borgmeier.

Argentine ants (Linepithema humile) in their native South American range, like most other ant species, form spatially restricted colonies that display high levels of aggression toward other such colonies. In their introduced range, Argentine ants are unicolonial and form massive supercolonies composed of numerous nests among which territorial boundaries are absent. Here we examine the role of cuticular hydrocarbons (CHCs) in nestmate recognition of this highly damaging invasive ant using three supercolonies from its introduced range. We conducted behavioral assays to test the response of Argentine ants to workers treated with colonymate or non-colonymate CHCs. Additionally, we quantified the amount of hydrocarbons transferred to individual ants and performed gas chromatography-mass spectrometry (GC/MS) to qualitatively characterize our manipulation of CHC profiles. The GC/MS data revealed marked differences in the hydrocarbon profiles across supercolonies and indicated that our treatment effectively masked the original chemical profile of the treated ants with the profile belonging to the foreign individuals. We found that individual workers treated with foreign CHCs were aggressively rejected by their colonymates and this behavior appears to be concentration-dependent: larger quantities of foreign CHCs triggered higher levels of aggression. Moreover, this response was not simply due to an increase in the amount of CHCs applied to the cuticle since treatment with high concentrations of nestmate CHCs did not trigger aggression.The results of this study bolster the findings of previous studies on social insects that have implicated CHCs as nestmate recognition cues and provide insight into the mechanisms of nestmate recognition in the invasive Argentine ant.

Twenty-two species of Pseudacteon flies (Diptera: Phoridae) are known to attack fire ants (Solenopsis spp.) in Argentina, Brazil, Bolivia, and Paraguay, but none are known in Chile. Surveys were conducted in central Chile and at similar latitudes in western Argentina to detect the presence of fire ants and parasitoid flies and to determine their relationship. Flies and fire ants were much more common and abundant in Argentina. In total, 100 colonies of four fire ant species were found at 63.6% of the sites surveyed. In contrast, only six colonies of one species, Solenopsis gayi (Spinola), were found at 4.7% of the sites surveyed in Chile. Our survey includes the first record of five parasitic fly species in central western Argentina and a new host, Solenopsis quinquecuspis Forel. The large form of Pseudacteon obtusus Borgmeier was found attacking S. gayi in Chile, which is the first record in that country, and the first record on this host species. The southern-most and western-most records were established for fire ant-decapitating flies. Mitochondrial DNA (mtDNA) indicates that S. gayi is genetically closer to the Argentine fire ants (saevissima-group) than the North American S. geminata-group. However, S. gayi venom alkaloid composition is similar to S. geminata-group, whereas cuticular hydrocarbon composition has characteristics of both groups. Analysis of mtDNA from the collected flies supports the monophyly of P. obtusus and suggests that the Chilean population is similar to populations in eastern Argentina. The presence of P. obtusus in Chile could be explained by immigrant parasitized fire ant species from Argentina or by an accidental introduction.

Complex recognition systems underlie the social organization of many organisms. In social insects the acceptance of other individuals as nestmates can involve a variety of different cues, but the relative importance of these cues can change in relation to the fitness costs of accepting or rejecting other individuals. In this study we investigate the mechanisms that underlie recognition behaviour in Argentine ants (Linepithema humile). Introduced populations of Argentine ants are characterized by a social structure known as unicoloniality where intraspecific aggression is absent over large distances resulting in the formation of expansive supercolonies. Recent research has identified sites where multiple, mutually aggressive supercolonies co-occur allowing an examination of Argentine ant behaviour at territorial boundaries. We found that workers from different supercolonies always interact aggressively with one another, but that neighbours from different colonies (i.e., workers from nests located in the immediate vicinity of territory borders) consistently exhibited higher levels of aggression compared to those displayed by non-neighbours from different colonies (i.e., workers from nests located far enough away from a territory border so that interactions are unlikely). This difference in the level of aggression displayed between neighbours and between non-neighbours from different supercolonies cannot be explained by differences in relatedness or genetic similarity. Instead our findings suggest that direct contact between mutually antagonistic colonies is sufficient to elevate aggression. A laboratory experiment in which we manipulated the extent to which colonies with no prior history of contact could interact with one another, revealed that aggression increased after colonies were permitted to interact, but dropped after connections between colonies were severed. Moreover, the mere presence of an aggressive supercolony was sufficient to elicit elevated aggression. Overall these patterns are opposite to the “dear enemy” phenomenon and could be the result of the intense territorial aggression exhibited by established supercolonies of this species.

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 FST 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 FST 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.

We characterized Apis mellifera in both native and introduced ranges using 1136 single-nucleotide polymorphisms genotyped in 341 individuals. Our results indicate that A. mellifera originated in Africa and expanded into Eurasia at least twice, resulting in populations in eastern and western Europe that are geographically close but genetically distant. A third expansion in the New World has involved the near-replacement of previously introduced “European” honey bees by descendants of more recently introduced A. m. scutellata (“African” or “killer” bees). Our analyses of spatial transects and temporal series in the New World revealed differential replacement of alleles derived from eastern versus western Europe, with admixture evident in all individuals.

Cooperative social groups rely on the ability to distinguish members from nonmembers. Accordingly, social insects have evolved a variety of systems that allow discrimination of nest mates from non‐nest mates. In this study, we show that experience can modify patterns of intraspecific aggression in Argentine ants (Linepithema humile). In laboratory experiments, we found that aggression between colonies was often asymmetrical, but in all five cases, this asymmetry shifted to symmetrical aggression after contact with a hostile colony. Moreover, in the field, aggression between workers collected from colony borders was symmetrical, whereas polarized aggression occurred between workers collected 500 m away from colony borders. Coinciding with this shift in aggression symmetry, we also observed an increase in both the overall level of aggression and the frequency of aggression in both the field and laboratory bioassays. We found little evidence for colony-level competitive asymmetries stemming from polarities in aggression at the worker level, either in the laboratory or in the field. These results illustrate that recognition systems in Argentine ants are surprisingly dynamic and provide experimental evidence for how recognition can be adjusted in response to specific circumstances—in this case the presence of intraspecific competitors. Key words: aggression symmetry, intraspecific competition, invasive species, nest-mate recognition, unicoloniality. [Behav Ecol]

Ants are among the most widespread and damaging of introduced species. Many invasive ants share a suite of characteristics that facilitate their introduction, establishment, and subsequent range expan- sion. One feature of particular importance is the ability to form numerically large, ecologically dominant col- onies. We review the population biology of invasive ants, focusing on the role of sociality and colony struc- ture in their success. Specifically, we considered different hypotheses that have been proposed for the observed transitions in social structure of the two most well-studied ant invaders, the Argentine ant ( Linepithema hu- mile ) and the red imported fire ant ( Solenopsis invicta ). In both species, genetic changes during or subsequent to introduction have led to alterations in social behavior and colony structure; these, in turn, have promoted the invasive success of introduced populations. Although many other invasive ant species appear to have sim- ilar forms of social organization, little is known about the basic population biology of these species.

The evolution and persistence of cooperative social units depends on the ability to distinguish group members from nonmembers. The precision of discrimination, in turn, relies on variation in the labels that individuals use to recognize group members. However, this same variation can be selected against if individuals that are rejected as nonmembers incur a high cost. Here we provide evidence that selection against individuals from genetically diverse groups has contributed to the formation of the unicolonial colony structure that characterizes introduced populations of the invasive Argentine ant ( Linepithema humile ). Studies in both the laboratory and the field showed that individuals from less genetically diverse colonies attack individuals from more diverse colonies and that attackers survived agonistic encounters more than six times as often as recipients of aggression. This selection, in concert with reductions in genetic diversity after a founder event, likely creates a barrier to the establishment of new, genetically diverse introductions from the native range and may reduce genetic diversity within established populations in the introduced range.

The Argentine ant, Linepithema humile, is a widespread invasive species characterized by reduced intraspecific aggression within introduced populations. To illuminate the mechanisms underlying nestmate recognition in Argentine ants, we studied the spatial and temporal fidelity of intraspecific aggression in an introduced population of Argentine ants within which intraspecific aggression does occur. We quantified variation in the presence or absence of intraspecific aggression among nests over time both in the field and under controlled laboratory conditions to gain insight into the role of environmental factors as determinants of nestmate discriminatory ability. In addition, we compared levels of intraspecific aggression between nest pairs to the similarity of their cuticular hydrocarbons to determine the potential role of these compounds as labels for nestmate discrimination. In both field and laboratory comparisons, nest pairs behaved in a consistent manner throughout the course of the experiment: pairs that fought did so for an entire year, and pairs that did not fight remained nonaggressive. Moreover, we found a negative relationship between cuticular hydrocarbon similarity and the degree of aggression between nests, suggesting that these hydrocarbons play a role in nestmate discriminatory ability. In contrast to the prevailing pattern, ants from one site showed a marked change in behaviour during the course of this study. A concomitant change was also seen in the cuticular hydrocarbon profiles of ants from this site.

▪ Abstract Invasions by non-native ants are an ecologically destructive phenomenon affecting both continental and island ecosystems throughout the world. Invasive ants often become highly abundant in their introduced range and can outnumber native ants. These numerical disparities underlie the competitive asymmetry between invasive ants and native ants and result from a complex interplay of behavioral, ecological, and genetic factors. Reductions in the diversity and abundance of native ants resulting from ant invasions give rise to a variety of direct and indirect effects on non-ant taxa. Invasive ants compete with and prey upon a diversity of other organisms, including some vertebrates, and may enter into or disrupt mutualistic interactions with numerous plants and other insects. Experimental studies and research focused on the native range ecology of invasive ants will be especially valuable contributions to this field of study.

The Argentine ant (Linepithema humile) is a damaging invasive species that has become established in many Mediterranean-type ecosystems worldwide. To identify likely sources of introduced populations we examined the relationships among native Linepithema populations from Argentina and Brazil and introduced populations of L. humile using mitochondrial cytochrome b sequence data and nuclear microsatellite allele frequencies. The mitochondrial phylogeny revealed that the populations in Brazil were only distantly related to both the introduced populations and the native populations in Argentina, and confirmed that populations in Brazil, previously identified as L. humile, are likely a different species. The microsatellite-based analysis provided resolution among native and introduced populations of L. humile that could not be resolved using the mitochondrial sequences. In the native range, colonies that were geographically close to one another tended to be genetically similar, whereas more distant colonies were genetically different. Most samples from the introduced range were genetically similar, although some exceptions were noted. Most introduced populations were similar to native populations from the southern Rio Parana and were particularly similar to a population from Rosario, Argentina. These findings implicate populations from the southern Rio Parana as the most likely source of introduced populations. Moreover, these data suggest that current efforts to identify natural enemies of the Argentine ant for biological control should focus on native populations in the southern Rio Parana watershed.

Despite the severe ecological and economic damage caused by introduced species, factors that allow invaders to become successful often remain elusive. Of invasive taxa, ants are among the most widespread and harmful. Highly invasive ants are often unicolonial, forming supercolonies in which workers and queens mix freely among physically separate nests. By reducing costs associated with territoriality, unicolonial species can attain high worker densities, allowing them to achieve interspecific dominance. Here we examine the behavior and population genetics of the invasive Argentine ant (Linepithema humile) in its native and introduced ranges, and we provide a mechanism to explain its success as an invader. Using microsatellite markers, we show that a population bottleneck has reduced the genetic diversity of introduced populations. This loss is associated with reduced intraspecific aggression among spatially separate nests, and leads to the formation of interspecifically dominant supercolonies. In contrast, native populations are more genetically variable and exhibit pronounced intraspecific aggression. Although reductions in genetic diversity are generally considered detrimental, these findings provide an example of how a genetic bottleneck can lead to widespread ecological success. In addition, these results provide insights into the origin and evolution of unicoloniality, which is often considered a challenge to kin selection theory.

In this paper, we examine the hypothesis that reduced intraspecific aggression underlies the competitive prowess of Argentine ants in their introduced range. Specifically, we test three predictions of this hypothesis by comparing the genetic diversity, behavior, and ecology of Argentine ants in their native range to introduced populations. Differences between native and introduced populations of Argentine ants were consistent with our predictions. Introduced populations of the Argentine ant appear to have experienced a population bottleneck at the time of

Genomes of eusocial insects code for dramatic examples of phenotypic plasticity and social organization. We compared the genomes of seven ants, the honeybee, and various solitary insects to examine whether eusocial lineages share distinct features of genomic organization. Each ant lineage contains ∼4000 novel genes, but only 64 of these genes are conserved among all seven ants. Many gene families have been expanded in ants, notably those involved in chemical communication (e.g., desaturases and odorant receptors). Alignment of the ant genomes revealed reduced purifying selection compared with Drosophila without significantly reduced synteny. Correspondingly, ant genomes exhibit dramatic divergence of noncoding regulatory elements; however, extant conserved regions are enriched for novel noncoding RNAs and transcription factor–binding sites. Comparison of orthologous gene promoters between eusocial and solitary species revealed significant regulatory evolution in both cis (e.g., Creb) and trans (e.g., fork head) for nearly 2000 genes, many of which exhibit phenotypic plasticity. Our results emphasize that genomic changes can occur remarkably fast in ants, because two recently diverged leaf-cutter ant species exhibit faster accumulation of species-specific genes and greater divergence in regulatory elements compared with other ants or Drosophila. Thus, while the “socio-genomes” of ants and the honeybee are broadly characterized by a pervasive pattern of divergence in gene composition and regulation, they preserve lineage-specific regulatory features linked to eusociality. We propose that changes in gene regulation played a key role in the origins of insect eusociality, whereas changes in gene composition were more relevant for lineage-specific eusocial adaptations.

The worldwide resurgence of bed bugs has recently created urban pest challenges in California. Regardless of information source — newspaper, Internet, television, university or government — the message is the same: bed bugs are back, and with a vengeance. Until recently, the pest's longstanding rarity and a historical reliance on pesticide-based management have not encouraged research and public education to develop and make available current information on bed bug biology, detection and control. UC is currently directing comprehensive, collaborative programs of research and education to combat this emerging nuisance and public health threat. Laboratory and field tests were conducted by UC researchers on several commercial bed bug monitors and confirm that additional research is needed to improve the performance of existing monitors and to develop new ones.

Social organisms rank among the most abundant and ecologically dominant species on Earth, in part due to exclusive recognition systems that allow cooperators to be distinguished from exploiters. Exploiters, such as social parasites, manipulate their hosts’ recognition systems, whereas cooperators are expected to minimize interference with their partner’s recognition abilities. Despite our wealth of knowledge about recognition in single-species social nests, less is known of the recognition systems in multi-species nests, particularly involving cooperators. One uncommon type of nesting symbiosis, called parabiosis, involves two species of ants sharing a nest and foraging trails in ostensible cooperation. Here, we investigated recognition cues (cuticular hydrocarbons) and recognition behaviors in the parabiotic mixed-species ant nests of Camponotus femoratus and Crematogaster levior in North-Eastern Amazonia. We found two sympatric, cryptic Cr. levior chemotypes in the population, with one type in each parabiotic colony. Although they share a nest, very few hydrocarbons were shared between Ca. femoratus and either Cr. levior chemotype. The Ca. femoratus hydrocarbons were also unusually long–chained branched alkenes and dienes, compounds not commonly found amongst ants. Despite minimal overlap in hydrocarbon profile, there was evidence of potential interspecific nestmate recognition –Cr. levior ants were more aggressive toward Ca. femoratus non-nestmates than Ca. femoratus nestmates. In contrast to the prediction that sharing a nest could weaken conspecific recognition, each parabiotic species also maintains its own aggressive recognition behaviors to exclude conspecific non-nestmates. This suggests that, despite cohabitation, parabiotic ants maintain their own species-specific colony odors and recognition mechanisms. It is possible that such social symbioses are enabled by the two species each using their own separate recognition cues, and that interspecific nestmate recognition may enable this multi-species cooperative nesting.

Most flowering plants establish mutualistic associations with insect pollinators to facilitate sexual reproduction. However, the evolutionary processes that gave rise to these associations remain poorly understood. We reconstructed the times of divergence, diversification patterns, and interaction networks of a diverse group of specialized orchids and their bee pollinators. In contrast to a scenario of coevolution by race formation, we show that fragrance-producing orchids originated at least three times independently after their fragrance-collecting bee mutualists. Whereas orchid diversification has apparently tracked the diversification of orchids’ bee pollinators, bees appear to have depended on the diverse chemical environment of neotropical forests. We corroborated this apparent asymmetrical dependency by simulating co-extinction cascades in real interaction networks that lacked reciprocal specialization. These results suggest that the diversification of insect-pollinated angiosperms may have been facilitated by the exploitation of preexisting sensory biases of insect pollinators.