Prolonged faunal turnover in earliest ants revealed by North American Cretaceous amber.

All ∼14,000 extant ant species descended from the same common ancestor, which lived ∼140-120 million years ago (Ma).1,2 While modern ants began to diversify in the Cretaceous, recent fossil evidence has demonstrated that older lineages concomitantly occupied the same ancient ecosystems.3 These early-diverging ant lineages, or stem ants, left no modern descendants; however, they dominated the fossil record throughout the Cretaceous until their ultimate extinction sometime around the K-Pg boundary. Even as stem ant lineages appear to be diverse and abundant throughout the Cretaceous, the extent of their longevity in the fossil record and circumstances contributing to their extinction remain unknown.3 Here we report the youngest stem ants, preserved in ∼77 Ma Cretaceous amber from North Carolina, which illustrate unexpected morphological stability and lineage persistence in this enigmatic group, rivaling the longevity of contemporary ants. Through phylogenetic reconstruction and morphometric analyses, we find evidence that total taxic turnover in ants was not accompanied by a fundamental morphological shift, in contrast to other analogous stem extinctions such as theropod dinosaurs. While stem taxa showed broad morphological variation, high-density ant morphospace remained relatively constant through the last 100 million years, detailing a parallel, but temporally staggered, evolutionary history of modern and stem ants.

Riqueza y diversidad de hormigas (Hymenoptera: Formicidae) según uso de suelo en dos paisajes agroforestales de Colombia / Richness and diversity of ants (Hymenoptera: Formicidae) according to land use in two agroforestry landscapes of Colombia

Introducción: Las hormigas cumplen funciones ecológicas importantes en muchos ecosistemas, y son altamente sensibles a los cambios en el uso del suelo. Sin embargo, la respuesta ante estos cambios está poco documentada, a grandes escalas espaciales y en distintos usos de suelo, en ecosistemas poco estudiados como la Serranía del Perijá. Objetivo: Analizar la riqueza, diversidad y composición de las comunidades de hormigas en cuatro usos de suelo de dos paisajes agroforestales de la Serranía del Perijá, Cesar, Colombia. Métodos: En dos paisajes agroforestales (compensación y no compensación) se delimitaron dos ventanas de muestreo de 4 × 4 km. Dentro de cada ventana y paisaje se escogieron cuatro usos de suelo: bosques, sistemas agroforestales de café, regeneración natural y pastizales, en los cuales se aplicaron dos métodos de captura: trampas Pitfall y sacos Winkler. Se midieron seis variables ambientales: cobertura de dosel, altura de la hojarasca, densidad aparente, temperatura, humedad y dureza del suelo. El esfuerzo de muestreo fueron 384 trampas Pitfall y 192 m2 de extracción de hojarasca. El trabajo de campo se realizó entre febrero y marzo de 2021. Resultados: Las hormigas mostraron alta sensibilidad a los cambios en el uso del suelo. La diversidad y riqueza de especies disminuyó en los usos de suelo con menor cobertura vegetal natural, como los pastizales; mientras que los bosques, en ambos paisajes, conservaron la mayor riqueza de especies. La cobertura de dosel y la disponibilidad de hojarasca fueron los parámetros ambientales que favorecieron la diversidad y riqueza de las comunidades de hormigas en todos los usos de suelo. No se encontraron diferencias entre la composición de hormigas de los dos paisajes estudiados. Conclusiones: Las hormigas responden a los cambios de uso de suelo y en particular a la cobertura vegetal. Se confirmó nuestra hipótesis puesto que los usos de suelo con alta cobertura vegetal fueron los hábitats con mayor riqueza y diversidad de hormigas. La heterogeneidad ambiental, producto de la dinámica de transformación de los paisajes es un elemento que debe considerarse en futuras investigaciones.

Introduction: Ants fulfill important ecological functions in many ecosystems and are highly sensitive to changes in land use. However, the response to these changes is poorly documented, at large spatial scales and in different land uses, in poorly studied ecosystems such as the Serranía del Perijá. Objective: To analyze the richness, diversity, and composition of ant communities in four land uses of two agroforestry landscapes of the Serranía del Perijá, Cesar, Colombia. Methods: Two sampling windows of 4 × 4 km were delimited in two agroforestry landscapes (compensation and non-compensation). In each window and landscape four land uses were chosen: forests, coffee agroforestry systems, natural regeneration and pastures, in which two trapping methods were applied: Pitfall traps and Winkler bags. Six environmental variables were measured: canopy cover, leaf litter height, bulk density, temperature, humidity and soil hardness. The sampling effort was 384 Pitfall traps and 192 m2 of leaf litter extraction. The fieldwork was conducted between February and March 2021. Results: Ants showed high sensitivity to changes in land use. Species diversity and richness decreased in land uses with less natural vegetation cover, such as pastures; while forests, in both landscapes, retained the highest species richness. Canopy cover and leaf litter availability were the environmental parameters that favored the diversity and richness of ant communities in all land uses. No differences were found between the ant composition of the two landscapes studied. Conclusions: Ants respond to changes in land use, particularly to vegetation cover. Our hypothesis was confirmed since land uses with high vegetation cover were the habitats with the greatest richness and diversity of ants. Environmental heterogeneity, a product of the dynamics of landscape transformation, is an element that should be considered in future research.

Cold comfort: metabolic rate and tolerance to low temperatures predict latitudinal distribution in ants.

Metabolic compensation has been proposed as a mean for ectotherms to cope with colder climates. For example, under the metabolic cold adaptation and the metabolic homeostasis hypotheses (MCA and MHH), it has been formulated that cold-adapted ectotherms should display both higher (MCA) and more thermally sensitive (MHH) metabolic rates (MRs) at lower temperatures. However, whether such compensation can truly be associated with distribution, and whether it interplays with cold tolerance to predict species' climatic niches, remains largely unclear despite broad ecological implications thereof. Here, we teased apart the relationship between MRs, cold tolerance and distribution, to test the MCA/MHH among 13 European ant species. We report clear metabolic compensation effects, consistent with the MCA and MHH, where MR parameters strongly correlated with latitude and climatic factors across species' distributions. The combination of both cold tolerance and MRs further upheld the best predictions of species' environmental temperatures and limits of northernmost distribution. To our knowledge, this is the first study showing that the association of metabolic data with cold tolerance supports better predictive models of species' climate and distribution in social insects than models including cold tolerance alone. These results also highlight that adaptation to higher latitudes in ants involved adjustments of both cold tolerance and MRs, to allow this extremely successful group of insects to thrive under colder climates.

Ant diversity (Hymenoptera: Formicidae) in Turvo State Park, municipality of Derrubadas, state of Rio Grande do Sul, Brazil / Diversidade de formigas (Hymenoptera: Formicidae) no Parque Estadual do Turvo, Derrubadas, Rio Grande do Sul, Brasil

The knowledge of ant assemblages that occurs in Conservation Units in the Atlantic Forest domain is a priority, considering the number of endemic species and the impacts that this biome has been suffering. The aim of this study was to evaluate ant assemblages in the Turvo State Park, which is the largest conservation unit in the State of Rio Grande do Sul and presents an important role on biodiversity protection. Two samplings were conducted in 2019, one in the summer (January) and the other in the spring (November and December), at five sites 2 km apart, with pitfall traps (soil and canopy), sardine baits, glucose, beating net, sweeping net and manual collection. We sampled 121 species in the summer and 120 in the spring, totaling 163 ant species. A total of 78 species (47.8%) occurred in both sampling seasons. The richest genera in the study were Camponotus (S = 30), Pheidole (S = 23) and Linepithema (S = 11). Seventeen species were recorded for the first time for Rio Grande do Sul state. The results indicate that this is one of the most species-rich assemblages of ants ever surveyed in a conservation unit in southern Brazil. The study highlights the importance of Conservation Units as protected environments against habitat loss for ant biodiversity. The results of this study contribute to myrmecofauna knowledge and serve as a basis for environmental impact studies, management plans and conservation of Atlantic Forest remnants.

O conhecimento das assembleias de formigas que ocorrem em Unidades de Conservação no domínio Mata Atlântica é prioritário, considerando-se o número de espécies endêmicas e os impactos que este bioma vem sofrendo. O objetivo desse trabalho foi caracterizar a assembleia de formigas que ocorre no Parque Estadual do Turvo, a maior unidade de conservação do Rio Grande do Sul que se destaca pelo seu papel na proteção da biodiversidade da Mata Atlântica austral. Foram realizadas duas amostragens no ano de 2019, uma no verão (janeiro) e a outra na primavera (novembro e dezembro), em cinco pontos distantes 2 km entre si, com armadilhas pitfall (solo e dossel), iscas de sardinha, iscas de glicose, guarda-chuva entomológico, rede de varredura e coleta manual. A riqueza amostrada no verão foi de 121 e na primavera de 120, totalizando 163 espécies. Ao todo, 78 espécies (47,8%) ocorreram concomitantemente nas duas amostragens. Os gêneros mais ricos foram Camponotus (S=30), Pheidole (S=23) e Linepithema (S=11). Dezessete espécies foram registradas pela primeira vez para o estado do Rio Grande do Sul. Os resultados se constituem em uma das mais ricas assembleias de formigas já inventariadas em uma unidade de conservação na região sul do Brasil. O estudo destaca a importância das Unidades de Conservação como ambientes protegidos contra a perda de habitat para a biodiversidade de formigas. Os resultados deste estudo contribuem para o conhecimento da mirmecofauna e servem como base para estudos de impacto ambiental, planos de manejo e conservação de remanescentes da Mata Atlântica.

Nest architecture and colony composition in two populations of Ectatomma ruidum sp. 2 (E. ruidum species complex) in southwestern Colombia.

Nest architecture plays a fundamental role in the adaptation of ants to their habitat, favoring the action of economically important species. Ectatomma ruidum sp. 2 (ruidum species complex) is a biological control agent in Neotropical agroecosystems, exhibiting high bioturbation impact due to high nest densities. The architecture and composition of 152 nests were studied in two Andean populations of southwestern Colombia, 24 of them being cast using the paraffin wax technique. Nest entrance was a single, circular, 4 mm hole at ground level, without any special external structure, connected to a single vertical tunnel communicating with successive half ellipsoidal chambers. Nests were extremely shallow (depth range: 28.7-35.4 cm), with an average of six chambers and an overall volume of 92.2 cm3 per nest. The deeper the chamber, the smaller its volume. Nest building was independent of plants or roots, and no surface or underground physical connections were found between neighboring nests. Few nests possessed a queen, and neither ergatoids nor microgynes were recorded. Despite significant interactions between localities and the number of both males and workers, queen presence had an overall highly positive effect on the number of workers and larvae and a negative one on the number of gynes. Overall, the studied Colombian populations of E. ruidum sp. 2 retained the simple nest structure described for other species of this species complex and for colonies of the same species from other geographical areas, though they constrasted in their extreme shallowness. Our data suggest that E. ruidum sp. 2, at the local level, does not follow the usual monodomic pattern of this species with facultative polygyny but, rather, has a polydomic pattern with monogyny, perhaps related to the extreme shallowness of the nests due to soil structure, which could significantly enhance the queen's reproductive inhibition previously reported for this species.

Ants of the State of Par, Brazil: a historical and comprehensive dataset of a key biodiversity hotspot in the Amazon Basin.

The state of Par in northern Brazil is located entirely within the Amazon Basin and harbors a great diversity of landscape and vegetation types that support high levels of biodiversity. Here, we provide a comprehensive inventory of ant species and their distribution in Par. This regional list is based on an extensive review of species records from published and unpublished sources covering a period of 134 years (18862020) and includes the five most representative ant collections in Brazil. In total, we documented 12 subfamilies, 90 genera and 753 ant species, including 97 species recorded for the first time in Par and 12 species newly reported in Brazil. Sampling effort across the state is highly uneven, and most records may be associated with research areas near the state capital, mining areas, hydroelectric dams, and research field stations run by the state or universities. In addition, our results suggest a strong bias in ant collection in Par in terms of proximity of sampled sites to access routes, such as roads and rivers. We also found that species records were highly unevenly distributed based on areas of endemism within the Amazon, vegetation type, and protected areas within the state. Ant surveys are still lacking from most protected areas of Par, and further sampling is urgently needed in view of the current trend of expansion of major infrastructure projects and natural resource harvesting within protected areas of Par. Our database represents an extremely valuable and rich source of information for further studies on ant biodiversity and conservation in the Amazon Basin.

Possible impacts of the predominant Bacillus bacteria on the Ophiocordyceps unilateralis s. l. in its infected ant cadavers.

Animal hosts infected and killed by parasitoid fungi become nutrient-rich cadavers for saprophytes. Bacteria adapted to colonization of parasitoid fungi can be selected and can predominate in the cadavers, actions that consequently impact the fitness of the parasitoid fungi. In Taiwan, the zombie fungus, Ophiocordyceps unilateralis sensu lato (Clavicipitaceae: Hypocreales), was found to parasitize eight ant species, with preference for a principal host, Polyrhachis moesta. In this study, ant cadavers grew a fungal stroma that was predominated by Bacillus cereus/thuringiensis. The bacterial diversity in the principal ant host was found to be lower than the bacterial diversity in alternative hosts, a situation that might enhance the impact of B. cereus/thuringiensis on the sympatric fungus. The B. cereus/thuringiensis isolates from fungal stroma displayed higher resistance to a specific naphthoquinone (plumbagin) than sympatric bacteria from the environment. Naphthoquinones are known to be produced by O. unilateralis s. l., and hence the resistance displayed by B. cereus/thuringiensis isolates to these compounds suggests an advantage to B. cereus/thuringiensis to grow in the ant cadaver. Bacteria proliferating in the ant cadaver inevitably compete for resources with the fungus. However, the B. cereus/thuringiensis isolates displayed in vitro capabilities of hemolysis, production of hydrolytic enzymes, and antagonistic effects to co-cultured nematodes and entomopathogenic fungi. Thus, co-infection with B. cereus/thuringiensis offers potential benefits to the zombie fungus in killing the host under favorable conditions for reproduction, digesting the host tissue, and protecting the cadaver from being taken over by other consumers. With these potential benefits, the synergistic effect of B. cereus/thuringiensis on O. unilateralis infection is noteworthy given the competitive relationship of these two organisms sharing the same resource.

Functional composition of ant assemblages in habitat islands is driven by habitat factors and landscape composition.

Fragmented natural habitats within human-transformed landscapes play a key role in preserving biodiversity. Ants as keystone species are essential elements of terrestrial ecosystems; thus, it is important to understand the factors influencing their presence. In a large-scale multi-site study, we surveyed ant assemblages using sweep netting and D-vac sampling on 158 ancient burial mounds preserving grassland habitats in agricultural landscapes in East-Hungary. We asked the following questions: (1) How do habitat factors and landscape composition affect species richness and functional diversity of ants? (2) Which ant traits are affected by habitat factors and landscape composition? Despite their small sizes, mounds as permanent and relatively undisturbed landscape elements could provide safe havens for diverse ant assemblages even in transformed agricultural landscapes. The complex habitat structure of wooded mounds supported high species and functional diversity of ant assemblages. Ant species on wooded mounds had small or medium-sized colonies, enabling the co-existence of more species. The effect of landscape composition on ant assemblages was mediated by habitat factors: steep slopes buffered the negative effect of the cropland matrix and enabled higher ant diversity.

Description of two new species of ants of the genus Myrmecina Curtis, 1829 (Hymenoptera: Formicidae: Myrmicinae) from the Eastern Himalayas.

Two new species of the ant genus Myrmecina Curtis, 1829, M. bawai sp. nov. and M. reticulata sp. nov., are described and illustrated based on the worker caste from Mizoram, Northeast India. The genus is reported for the first time from Mizoram, the Indian state with the highest percentage of forest cover. A key to the Indian fauna of Myrmecina is also provided based on the worker caste.

First record of the myrmicine ant genus Syllophopsis Santschi, 1915 (Hymenoptera: Formicidae) from India with description of a new species.

Here we describe and illustrate Syllophopsis peetersi sp. nov. from Silent Valley National Park, a biodiversity hotspot region of the Western Ghats of India. The discovery also marks a first native report of the genus from the Indian subcontinent. Scanning Electron Microscopy (SEM) analysis was carried out to elucidate the general morphology and sensilla of the new species. The new species is similar to congeners from Madagascar, but with larger differences from species that occur elsewhere.

Myrmecotypus haddadi sp. nov.-a new species of ant resembling sac spider from the Bolivian orocline (Araneae: Corinnidae: Castianeirinae).

A new species of ant resembling sac spider of the subfamily Castianeirinae, Myrmecotypus haddadi sp. nov. is described from the Sub-Andean area at the Bolivian orocline. The species was collected from low herbaceous vegetation along the edges of the Chiquitano and Cerradao forest.

Patterns of Ant Diversity in the Natural Grasslands of Southern Brazil.

In the south of Brazil, grasslands are naturally widespread over two different biomes, the Pampa in the southernmost region and within the Atlantic Forest in the northern portions. The natural grasslands of the state of Paraná comprise a very particular physiognomy composed of two distinct formations: the Campos Gerais and the grasslands of the southwest. The first is located in the edge of the second plateau of Paraná state, comprising a great diversity of environments. The grasslands of the southwest are more homogeneous, with a continuous herbaceous stratum dominating the landscape. In this context, the aim of this study was to evaluate the patterns of species richness and composition of ants, an ecologically prominent group, along the natural grasslands of Paraná. We also intended to compare the faunal similarity between the two different grassland formations. For that, four different Conservation Unities were sampled along a latitudinal gradient. A remarkable total of 245 ant species was recorded, and the results indicate that species richness decreases as latitude increases along the grasslands of Paraná. There were clear differences in species composition between these two grasslands formations, given the significative number of endemic species in each of these two grassland formations. Ten species were recorded for the first time in the state of Paraná, of which three also for the first time in the Southern Region of Brazil. Overall, our study contributes to a better understanding about the diversity and composition of ant communities in subtropical grasslands.

Relaxed selection underlies genome erosion in socially parasitic ant species.

Inquiline ants are highly specialized and obligate social parasites that infiltrate and exploit colonies of closely related species. They have evolved many times convergently, are often evolutionarily young lineages, and are almost invariably rare. Focusing on the leaf-cutting ant genus Acromyrmex, we compared genomes of three inquiline social parasites with their free-living, closely-related hosts. The social parasite genomes show distinct signatures of erosion compared to the host lineages, as a consequence of relaxed selective constraints on traits associated with cooperative ant colony life and of inquilines having very small effective population sizes. We find parallel gene losses, particularly in olfactory receptors, consistent with inquiline species having highly reduced social behavioral repertoires. Many of the genomic changes that we uncover resemble those observed in the genomes of obligate non-social parasites and intracellular endosymbionts that branched off into highly specialized, host-dependent niches.

The basitarsal sulcus gland, a novel exocrine structure in ants.

The basitarsus of the mid- and/or hindlegs of several Amblyoponinae ants shows a deep longitudinal groove or sulcus on its anterior face in workers and queens. Histological examination reveals this sulcus is associated with a conspicuous novel epithelial gland, which brings the number of exocrine glands in the legs of ants to 25. The ultrastructural characteristics of the gland show the presence of a well-developed smooth endoplasmic reticulum. This is indicative for the elaboration of a non-proteinaceous and thus possibly pheromonal secretion. Behavioural observations show that this secretion is collected by the tarsomeres and spread onto the brood and nest, suggesting a role in nestmate recognition. A similar basitarsal sulcus gland was also found in Nothomyrmecia, Paraponera and Tetraponera, which represents both a wide phylogenetic and ecological distribution, as it includes arboreal, ground-dwelling as well as subterranean taxa.

Influence of Urban Landscape on Ants and Spiders Richness and Composition in Forests.

As large amounts of natural environments are lost due to urbanization, the role of remnant native vegetation in the preservation of biodiversity has become even more significant. Remnant native forest patches are essential refugia for flora and fauna and are crucial for the maintenance of ecosystem processes in urbanized landscapes. We evaluated the influence of landscape structure on ants and spiders associated with Atlantic Forest remnants in urban landscapes. We sampled 14 forest areas in the Metropolitan Region of Salvador and tested the effect of the landscapes' proportion of forest cover, mean landscape isolation, and mean landscape shape complexity on the taxonomic and functional richness and the community composition of both groups. The species collected were classified into functional groups based on behavioral attributes and environmental preferences. Overall, there were strong adverse effects of forest loss, decreased connectivity, and an increase in edge effects associated with the mean shape complexity of the forest remnants. However, the spiders responded to all three landscape structure characteristics whereas the ants only responded to the landscape mean shape complexity. Our findings indicate that the maintenance of urban forest habitats is essential for the conservation of biodiversity in the Metropolitan Region of Salvador and the preservation of ecological functions performed by species within the forest areas.

Taxonomic revision of Madagascan species of the Pheidole fervens species-group (Hymenoptera, Formicidae).

Madagascar, one of the top megadiversity regions, hosts one of the highest numbers of endemic and threatened organisms on earth. One of the most spectacular examples of ant radiation on the island has occurred in the hyperdiverse genus Pheidole. To this date, there are 117 described Madagascan Pheidole divided into 16 species-groups, and 97% of them are endemic to the island. Only two of these species-groups contain widely distributed invasive species in addition to native, endemic taxa: megacephala, and fervens species-groups. Here we revise the fervens species-group and discuss updated distribution records of its introduced members on Madagascar. We recognize six species belonging to this group, including five new to science: Pheidole ampangabe sp. nov., P. arivo sp. nov., P. comosa sp. nov., P. indica Mayr, P. mamirapiratra sp. nov., and P. mena sp. nov. Detailed descriptions are supplemented with measurements, diagnoses, identification key, high-resolution images for major and minor worker, and comments on distribution and biology.

Comprehensive phylogeny of Myrmecocystus honey ants highlights cryptic diversity and infers evolution during aridification of the American Southwest.

The New World ant genus Myrmecocystus Wesmael, 1838 (Formicidae: Formicinae: Lasiini) is endemic to arid and semi-arid habitats of the western United States and Mexico. Several intriguing life history traits have been described for the genus, the best-known of which are replete workers, that store liquified food in their largely expanded crops and are colloquially referred to as "honeypots". Despite their interesting biology and ecological importance for arid ecosystems, the evolutionary history of Myrmecocystus ants is largely unknown and the current taxonomy presents an unsatisfactory systematic framework. We use ultraconserved elements to infer the evolutionary history of Myrmecocystus ants and provide a comprehensive, dated phylogenetic framework that clarifies the molecular systematics within the genus with high statistical support, reveals cryptic diversity, and reconstructs ancestral foraging activity. Using maximum likelihood, Bayesian and species tree approaches on a data set of 134 ingroup specimens (including samples from natural history collections and type material), we recover largely identical topologies that leave the position of only few clades uncertain and cover the intra- and interspecific variation of 28 of the 29 described and six undescribed species. In addition to traditional support values, such as bootstrap and posterior probability, we quantify genealogical concordance to estimate the effects of conflicting evolutionary histories on phylogenetic inference. Our analyses reveal that the current taxonomic classification of the genus is inconsistent with the molecular phylogenetic inference, and we identify cryptic diversity in seven species. Divergence dating suggests that the split between Myrmecocystus and its sister taxon Lasius occurred in the early Miocene. Crown group Myrmecocystus started diversifying about 14.08 Ma ago when the gradual aridification of the southwestern United States and northern Mexico led to formation of the American deserts and to adaptive radiations of many desert taxa.