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1. Interspecific trade-offs are thought to facilitate coexistence between species at small spatial scales. The discovery-dominance trade-off, analogous to a competition-colonisation trade-off, is considered an important structuring mechanism in ant ecology. A trade-off between species' ability to discover food resources and to dominate them may explain how so many species apparently dependent on similar resources can coexist. 2. The discovery-dominance trade-off is thought to be broken by invasive species in enemy-free space or territorial species whose activity is fuelled by domination of carbohydrate resources. It may also be mediated by factors such as temperature and habitat structure. 3. We investigate the generality and form of the discovery-dominance relationship in an experiment using habitats of contrasting complexity across three continents. In addition, to assess how widespread the discovery-dominance trade-off is, we conducted a systematic review combining all empirical studies (published and from our experiment). 4. From our own fieldwork and meta-analyses of available studies, we find surprisingly little empirical support for the trade-off, with results indicating that mean effect sizes were either not significantly different from 0 or significantly positive. The trade-off was only detected in studies with parasitoids present. Additionally, experimental data from simple and complex habitats within each continent suggest that simple habitats may facilitate both food resource discovery and dominance. 5. We conclude that the discovery-dominance trade-off is the exception, rather than the rule. Instead, these abilities were commonly correlated. Real food resources provide many axes along which partitioning may occur, and discovery-dominance trade-offs are not a prerequisite for coexistence.

It is unclear why some species become successful invaders whilst others fail, and whether invasive success depends on pre-adaptations already present in the native range or on characters evolving de-novo after introduction. Ants are among the worst invasive pests, with Lasius neglectus and its rapid spread through Europe and Asia as the most recent example of a pest ant that may become a global problem. Here, we present the first integrated study on behavior, morphology, population genetics, chemical recognition and parasite load of L. neglectus and its non-invasive sister species L. turcicus. We find that L. neglectus expresses the same supercolonial syndrome as other invasive ants, a social system that is characterized by mating without dispersal and large networks of cooperating nests rather than smaller mutually hostile colonies. We conclude that the invasive success of L. neglectus relies on a combination of parasite-release following introduction and pre-adaptations in mating system, body-size, queen number and recognition efficiency that evolved long before introduction. Our results challenge the notion that supercolonial organization is an inevitable consequence of low genetic variation for chemical recognition cues in small invasive founder populations. We infer that low variation and limited volatility in cuticular hydrocarbon profiles already existed in the native range in combination with low dispersal and a highly viscous population structure. Human transport to relatively disturbed urban areas thus became the decisive factor to induce parasite release, a well established general promoter of invasiveness in non-social animals and plants, but understudied in invasive social insects.

Early Eocene land bridges allowed numerous plant and animal species to cross between Europe and North America via the Arctic. While many species suited to prevailing cool Arctic climates would have been able to cross throughout much of this period, others would have found dispersal opportunities only during limited intervals when their requirements for higher temperatures were met. Here, we present Titanomyrma lubei gen. et sp. nov. from Wyoming, USA, a new giant (greater than 5 cm long) formiciine ant from the early Eocene (approx. 49.5 Ma) Green River Formation. We show that the extinct ant subfamily Formiciinae is only known from localities with an estimated mean annual temperature of about 20°C or greater, consistent with the tropical ranges of almost all of the largest living ant species. This is, to our knowledge, the first known formiciine of gigantic size in the Western Hemisphere and the first reported cross-Arctic dispersal by a thermophilic insect group. This implies intercontinental migration during one or more brief high-temperature episodes (hyperthermals) sometime between the latest Palaeocene establishment of intercontinental land connections and the presence of giant formiciines in Europe and North America by the early middle Eocene.

The range of hosts exploited by a parasite is determined by several factors, including host availability, infectivity and exploitability. Each of these can be the target of natural selection on both host and parasite, which will determine the local outcome of interactions, and potentially lead to coevolution. However, geographical variation in host use and specificity has rarely been investigated. Maculinea (=Phengaris) butterflies are brood parasites of Myrmica ants that are patchily distributed across the Palæarctic and have been studied extensively in Europe. Here, we review the published records of ant host use by the European Maculinea species, as well as providing new host ant records for more than 100 sites across Europe. This comprehensive survey demonstrates that while all but one of the Myrmica species found on Maculinea sites have been recorded as hosts, the most common is often disproportionately highly exploited. Host sharing and host switching are both relatively common, but there is evidence of specialization at many sites, which varies among Maculinea species. We show that most Maculinea display the features expected for coevolution to occur in a geographic mosaic, which has probably allowed these rare butterflies to persist in Europe. This article is part of the theme issue ‘The coevolutionary biology of brood parasitism: from mechanism to pattern’.

Globally threatened butterflies have prompted research-based approaches to insect conservation. Here, we describe the reversal of the decline of Maculinea arion (Large Blue), a charismatic specialist whose larvae parasitize Myrmica ant societies. M. arion larvae were more specialized than had previously been recognized, being adapted to a single host-ant species that inhabits a narrow niche in grassland. Inconspicuous changes in grazing and vegetation structure caused host ants to be replaced by similar but unsuitable congeners, explaining the extinction of European Maculinea populations. Once this problem was identified, UK ecosystems were perturbed appropriately, validating models predicting the recovery and subsequent dynamics of the butterfly and ants at 78 sites. The successful identification and reversal of the problem provides a paradigm for other insect conservation projects.

Surime, considered the most forested country in the world, is home to a variety of Amazonian communities, both of Amerindian and African (Maroon) descent. The shifting cultivation that was required by their Amazonian environment has over the past centuries led to the emergence of intricate schemes to effectively mage common land resources. As this contribution shows, leafcutter ants have importantly served human communities by increasing and indicating levels of soil fertility and recommending the pace of shifting from one plot to the next. Over the past century, extractive activities (gold, bauxite and hydroelectricity) have set in motion a still ongoing process of ‘enclosing’ Surime’s Amazonian space. Ant eradication programmes implemented in the 1940s and 50s by the Agricultural Research Centre of Surime departed from a profoundly racialized belief in “essential” characteristics of different Amazonian communities. This contribution argues that ant–human coexistence became an instrumental argument to showcase the alleged ‘primitivity’, ‘ecological destructiveness’ or even the ‘parasitic ture’ of certain Amazonian communities, which aided in their margilization and eventual resettlement.

The major factors explaining ecological variation in plants have been widely discussed over the last decade thanks to numerous studies that have examined the covariation that exists between pairs of traits. However, multivariate relationships among traits remain poorly characterized in animals. In this study, we aimed to identify the main multivariate trait dimensions that explain variance in important functional traits related to resource exploitation in ants. To this end, we created a large ant trait database. This database includes information on 11 traits that are important in ant resource exploitation; data were obtained for 150 European species found in different biomes. First, we examined the pairwise correlations between the traits included in the database. Second, we used multivariate analyses to identify potential trait dimensions. Our study shows that, to a great extent, resource exploitation strategies align along two main trait dimensions. The first dimension emerged in both the overall and group-specific analyses, where it accounted for the same pairwise trait correlations. The second dimension was more variable, as species were grouped by levels of taxonomy, habitat, and climate. These two dimensions included most of the significant pairwise trait correlations, thus highlighting that complementarity, but also redundancy, exists among different pairs of traits. The first dimension was associated with behavioral dominance: dominance was associated with large colony size, presence of multiple nests per colony, worker polymorphism, and a collective foraging strategy. The second dimension was associated with resource partitioning along dietary and microhabitat lines: it ranged from species that consume liquid foods, engage in group foraging, and mainly nest in the vegetation to species that consume insects and seeds, engage in individual foraging, and demonstrate strictly diurnal activity. Our findings establish a proficient ecological trait-based animal research that minimizes the number of traits to be measured while maximizing the number of relevant trait dimensions. Overall, resource exploitation in animals might be framed by behavioral dominance, foraging strategy, diet, and nesting habitat; the position of animal species within this trait space could provide relevant information about their distribution and abundance, for today as well as under future global change scenarios.

Two of the world’s most invasive ants, Linepithema humile and Lasius neglectus, are destined to overlap in range as they continue to spread throughout Europe. Although L. humile arrived first, and is therefore more numerically abundant, L. neglectus is the more behaviorally dominant of the two. We performed lab trials to determine whether L. humile could use numerical abundance to overcome the behavioral dominance of L. neglectus and whether the ants’ behavioral patterns shifted when the species co-occurred. We found that L. neglectus was more aggressive when less abundant, whereas the opposite was true of L. humile. When L. neglectus was outnumbered, it employed aggressive behaviors, such as biting or chemical attacks, more frequently than L. humile; it also utilized a behavioral sequence that included mandible opening and biting. Our results for these species support the hypothesis that species modulate their behavior towards competitors, which facilitates the understanding of how multiple invasive ant species can co-occur in a given area. Moreover, our study shows that the co-occurrence of invasive species could result from the use of two strategies: (1) the Bourgeois strategy, in which aggressiveness changes based on numerical dominance and (2) the dear-enemy strategy, in which aggressiveness is reduced when competitors co-occur. Since these strategies may lead to territory partitioning, we suggest that the behavioral flexibility displayed by both species when they overlap may allow local co-occurrence and increase their likelihood of co-occurrence during their range expansion in Europe, which could have a negative cumulative impact on invaded areas.

Some ants have an extraordinary social organization, called unicoloniality, whereby individuals mix freely among physically separated nests. This type of social organization is not only a key attribute responsible for the ecological domination of these ants, but also an evolutionary paradox and a potential problem for kin selection theory because relatedness between nest mates is effectively zero. The introduction of the Argentine ant in Europe was apparently accompanied by a dramatic loss of inter-nest aggression and the formation of two immense supercolonies (which effectively are two unicolonial populations). Introduced populations experienced only limited loss of genetic diversity at neutral markers, indicating that the breakdown of recognition ability is unlikely to be merely due to a genetic bottleneck. Rather, we suggest that a \"genetic cleansing\" of recognition cues occurred after introduction. Indeed workers of the same supercolony are never aggressive to each other despite the large geographical distance and considerable genetic differentiation between sampling sites. By contrast, aggression is invariably extremely high between the two supercolonies, indicating that they have become fixed for different recognition alleles. The main supercolony, which ranges over 6,000 km from Italy to the Spanish Atlantic coast, effectively forms the largest cooperative unit ever recorded.