Evolutionary déjà vu? A case of convergent evolution in an ant-plant association.

Obligatory ant-plant symbioses often appear to be single evolutionary shifts within particular ant lineages; however, convergence can be revealed once natural history observations are complemented with molecular phylogenetics. Here, we describe a remarkable example of convergent evolution in an ant-plant symbiotic system. Exclusively arboreal, Myrmelachista species can be generalized opportunists nesting in several plant species or obligately symbiotic, live-stem nesters of a narrow set of plant species. Instances of specialization within Myrmelachista are known from northern South America and throughout Middle America. In Middle America, a diverse radiation of specialists occupies understory treelets of lowland rainforests. The morphological and behavioural uniformity of specialists suggests that they form a monophyletic assemblage, diversifying after a single origin of specialization. Using ultraconserved element phylogenomics and ancestral state reconstructions, we show that shifts from opportunistic to obligately symbiotic evolved independently in South and Middle America. Furthermore, our analyses support a remarkable case of convergence within the Middle American radiation, with two independently evolved specialist clades, arising nearly simultaneously from putative opportunistic ancestors during the late Pliocene. This repeated evolution of a complex phenotype suggests similar mechanisms behind trait shifts from opportunists to specialists, generating further questions about the selective forces driving specialization.

The global distribution of known and undiscovered ant biodiversity.

Invertebrates constitute the majority of animal species and are critical for ecosystem functioning and services. Nonetheless, global invertebrate biodiversity patterns and their congruences with vertebrates remain largely unknown. We resolve the first high-resolution (~20-km) global diversity map for a major invertebrate clade, ants, using biodiversity informatics, range modeling, and machine learning to synthesize existing knowledge and predict the distribution of undiscovered diversity. We find that ants and different vertebrate groups have distinct features in their patterns of richness and rarity, underscoring the need to consider a diversity of taxa in conservation. However, despite their phylogenetic and physiological divergence, ant distributions are not highly anomalous relative to variation among vertebrate clades. Furthermore, our models predict that rarity centers largely overlap (78%), suggesting that general forces shape endemism patterns across taxa. This raises confidence that conservation of areas important for small-ranged vertebrates will benefit invertebrates while providing a "treasure map" to guide future discovery.

Functional innovation promotes diversification of form in the evolution of an ultrafast trap-jaw mechanism in ants.

Evolutionary innovations underlie the rise of diversity and complexity-the 2 long-term trends in the history of life. How does natural selection redesign multiple interacting parts to achieve a new emergent function? We investigated the evolution of a biomechanical innovation, the latch-spring mechanism of trap-jaw ants, to address 2 outstanding evolutionary problems: how form and function change in a system during the evolution of new complex traits, and whether such innovations and the diversity they beget are repeatable in time and space. Using a new phylogenetic reconstruction of 470 species, and X-ray microtomography and high-speed videography of representative taxa, we found the trap-jaw mechanism evolved independently 7 to 10 times in a single ant genus (Strumigenys), resulting in the repeated evolution of diverse forms on different continents. The trap mechanism facilitates a 6 to 7 order of magnitude greater mandible acceleration relative to simpler ancestors, currently the fastest recorded acceleration of a resettable animal movement. We found that most morphological diversification occurred after evolution of latch-spring mechanisms, which evolved via minor realignments of mouthpart structures. This finding, whereby incremental changes in form lead to a change of function, followed by large morphological reorganization around the new function, provides a model for understanding the evolution of complex biomechanical traits, as well as insights into why such innovations often happen repeatedly.

Pheidole (Hymenoptera, Formicidae) of Middle American Wet Forest.

The ant genus Pheidole is a highly diverse lineage of ants that are dominant elements of tropical and subtropical ecosystems throughout the world. Biodiversity inventory projects in Middle American wet forests (southern Mexico to Costa Rica, lowland rainforest to high montane forest) allow an improved taxonomy of the genus in this region. An identification guide to 234 species in the region is provided, using a "bird guide" approach. Species are arranged in order of minor worker head width and scape length, and each species has a fixed layout that includes habitat and microhabitat information, standard views (minor lateral, minor face, major face), and a distribution map. The following new synonyms are proposed: biconstricta Mayr 1870 (= inermis Mayr 1870), carapuna Mann 1916 (= tristicula Wilson 2003), fimbriata Roger 1863 (= soesilae Makhan 2007), insipida Forel 1899 (= fariasana Wilson 2003, mooreorum Wilson 2003), longiscapa Forel 1901 (= cocciphaga Borgmeier 1934), plebecula Forel 1899 (= perdiligens Wilson 2003, texticeps Wilson 2003), nitidicollis Emery 1896 (= chalcoides Wilson 2003), nubicola Wilson 2003 (= cielana Wilson 2003, petrensis Wilson 2003), simonsi Wilson 2003 (= arctos Wilson 2003, gangamon Wilson 2003, thrasys Wilson 2003), striaticeps Mayr 1870 (= chloe Forel 1908), transversostriata Mayr 1887 (= scalaris Wilson 2003), vafra Santschi 1923 (= laticornis Wilson 2003). The following 57 new species are described: ajaxigibba, andersoni, angustinigra, atitlana, balatro, belonorte, besalon, bicornisculpta, brownampla, cahui, caliginosa, carinitida, corniclypeus, costaricensis, cusuco, depressinoda, eosimilis, familiaparra, fincanaranjo, hansoni, hectornitida, hitoy, huarache, imbrilis, indagarama, kasparii, kelainos, lagunculiminor, lamancha, laselvoides, lineafrons, luteagossamer, machaquila, marmor, moskitia, muralla, musacolor, musinermis, natalie, nephele, obturaculum, passivaeferox, perissothrix, platyscapa, probolonotum, rima, rogeripolita, savegre, sensipelada, sepultura, tapanti, tikal, tinamu, tsontekonwei, tuculutan, xiloa, zannia.

A global database of ant species abundances.

What forces structure ecological assemblages? A key limitation to general insights about assemblage structure is the availability of data that are collected at a small spatial grain (local assemblages) and a large spatial extent (global coverage). Here, we present published and unpublished data from 51 ,388 ant abundance and occurrence records of more than 2,693 species and 7,953 morphospecies from local assemblages collected at 4,212 locations around the world. Ants were selected because they are diverse and abundant globally, comprise a large fraction of animal biomass in most terrestrial communities, and are key contributors to a range of ecosystem functions. Data were collected between 1949 and 2014, and include, for each geo-referenced sampling site, both the identity of the ants collected and details of sampling design, habitat type, and degree of disturbance. The aim of compiling this data set was to provide comprehensive species abundance data in order to test relationships between assemblage structure and environmental and biogeographic factors. Data were collected using a variety of standardized methods, such as pitfall and Winkler traps, and will be valuable for studies investigating large-scale forces structuring local assemblages. Understanding such relationships is particularly critical under current rates of global change. We encourage authors holding additional data on systematically collected ant assemblages, especially those in dry and cold, and remote areas, to contact us and contribute their data to this growing data set.

Midpoint attractors and species richness: Modelling the interaction between environmental drivers and geometric constraints.

We introduce a novel framework for conceptualising, quantifying and unifying discordant patterns of species richness along geographical gradients. While not itself explicitly mechanistic, this approach offers a path towards understanding mechanisms. In this study, we focused on the diverse patterns of species richness on mountainsides. We conjectured that elevational range midpoints of species may be drawn towards a single midpoint attractor - a unimodal gradient of environmental favourability. The midpoint attractor interacts with geometric constraints imposed by sea level and the mountaintop to produce taxon-specific patterns of species richness. We developed a Bayesian simulation model to estimate the location and strength of the midpoint attractor from species occurrence data sampled along mountainsides. We also constructed midpoint predictor models to test whether environmental variables could directly account for the observed patterns of species range midpoints. We challenged these models with 16 elevational data sets, comprising 4500 species of insects, vertebrates and plants. The midpoint predictor models generally failed to predict the pattern of species midpoints. In contrast, the midpoint attractor model closely reproduced empirical spatial patterns of species richness and range midpoints. Gradients of environmental favourability, subject to geometric constraints, may parsimoniously account for elevational and other patterns of species richness.

Climate mediates the effects of disturbance on ant assemblage structure.

Many studies have focused on the impacts of climate change on biological assemblages, yet little is known about how climate interacts with other major anthropogenic influences on biodiversity, such as habitat disturbance. Using a unique global database of 1128 local ant assemblages, we examined whether climate mediates the effects of habitat disturbance on assemblage structure at a global scale. Species richness and evenness were associated positively with temperature, and negatively with disturbance. However, the interaction among temperature, precipitation and disturbance shaped species richness and evenness. The effect was manifested through a failure of species richness to increase substantially with temperature in transformed habitats at low precipitation. At low precipitation levels, evenness increased with temperature in undisturbed sites, peaked at medium temperatures in disturbed sites and remained low in transformed sites. In warmer climates with lower rainfall, the effects of increasing disturbance on species richness and evenness were akin to decreases in temperature of up to 9°C. Anthropogenic disturbance and ongoing climate change may interact in complicated ways to shape the structure of assemblages, with hot, arid environments likely to be at greatest risk.

Alkaloid venom weaponry of three Megalomyrmex thief ants and the behavioral response of Cyphomyrmex costatus host ants.

Social parasites exploit other societies by invading and stealing resources. Some enter protected nests using offensive chemical weaponry made from alkaloid-based venom. We characterized the venoms of three Megalomyrmex thief ant species (M. mondabora, M. mondaboroides, and M. silvestrii) that parasitize the fungus-growing ants, and developed an ethogram to describe host ant reactions to raiding M. mondaboroides and M. silvestrii parasites. We compared piperidine, pyrrolidine, and pyrolizidine venom alkaloid structures with synthetic samples from previous studies, and describe the novel stereochemistry of trans 2-hexyl-5-[8-oxononyl]-pyrrolidine (3) from M. mondabora. We showed that workers of Cyphomyrmex costatus, the host of M. mondaboroides and M. silvestrii, react to a sting by Megalomyrmex parasites mainly with submissive behavior, playing dead or retreating. Host submission also followed brief antennal contact. The behavior of C. costatus ants observed in this study was similar to that of Cyphomyrmex cornutus, host of M. mondabora, suggesting that the alkaloidal venoms with pyrrolidines from M. mondabora, piperidines from M. mondaboroides, and pyrolizidines from M. silvestrii may function similarly as appeasement and repellent allomones against host ants, despite their different chemical structure. With the use of these chemical weapons, the Megalomyrmex thief ants are met with little host resistance and easily exploit host colony resources.

How ants drop out: ant abundance on tropical mountains.

In tropical wet forests, ants are a large proportion of the animal biomass, but the factors determining abundance are not well understood. We characterized ant abundance in the litter layer of 41 mature wet forest sites spread throughout Central America (Chiapas, Guatemala, Honduras, Nicaragua, and Costa Rica) and examined the impact of elevation (as a proxy for temperature) and community species richness. Sites were intentionally chosen to minimize variation in precipitation and seasonality. From sea level to 1500 m ant abundance very gradually declined, community richness declined more rapidly than abundance, and the local frequency of the locally most common species increased. These results suggest that within this elevational zone, density compensation is acting, maintaining high ant abundance as richness declines. In contrast, in sites above 1500 m, ant abundance dropped abruptly to much lower levels. Among these high montane sites, community richness explained much more of the variation in abundance than elevation, and there was no evidence of density compensation. The relative stability of abundance below 1500 m may be caused by opposing effects of temperature on productivity and metabolism. Lower temperatures may decrease productivity and thus the amount of food available for consumers, but slower metabolisms of consumers may allow maintenance of higher biomass at lower resource supply rates. Ant communities at these lower elevations may be highly interactive, the result of continuous habitat presence over geological time. High montane sites may be ephemeral in geological time, resulting in non-interactive communities dominated by historical and stochastic processes. Abundance in these sites may be determined by the number of species that manage to colonize and/or avoid extinction on mountaintops.

Thermal-safety margins and the necessity of thermoregulatory behavior across latitude and elevation.

Physiological thermal-tolerance limits of terrestrial ectotherms often exceed local air temperatures, implying a high degree of thermal safety (an excess of warm or cold thermal tolerance). However, air temperatures can be very different from the equilibrium body temperature of an individual ectotherm. Here, we compile thermal-tolerance limits of ectotherms across a wide range of latitudes and elevations and compare these thermal limits both to air and to operative body temperatures (theoretically equilibrated body temperatures) of small ectothermic animals during the warmest and coldest times of the year. We show that extreme operative body temperatures in exposed habitats match or exceed the physiological thermal limits of most ectotherms. Therefore, contrary to previous findings using air temperatures, most ectotherms do not have a physiological thermal-safety margin. They must therefore rely on behavior to avoid overheating during the warmest times, especially in the lowland tropics. Likewise, species living at temperate latitudes and in alpine habitats must retreat to avoid lethal cold exposure. Behavioral plasticity of habitat use and the energetic consequences of thermal retreats are therefore critical aspects of species' vulnerability to climate warming and extreme events.

A revision of the ant genus Octostruma Forel 1912 (Hymenoptera, Formicidae).

The ant genus Octostruma is restricted to the Neotropics, where it is an inhabitant of forest leaf litter and soil. The genus is reviewed, with an emphasis on the fauna of the MesoAmerican corridor. A total of 34 species are recognized, of which 19 are described as new. A key to species is provided, and the following new species are described: O. ascrobicula Long-ino, sp. nov., O. ascrobis Longino, sp. nov., O. convallis Longino, sp. nov., O. convallisur Longino, sp. nov., O. cyrtino-tum Longino, sp. nov., O. excertirugis Longino, sp. nov., O. gymnogon Longino, sp. nov., O. gymnosoma Longino, sp. nov., O. leptoceps Longino, sp. nov., O. limbifrons Longino, sp. nov., O. megabalzani Longino, sp. nov., O. montanis Longino, sp. nov., O. obtusidens Longino, sp. nov., O. pexidorsum Longino, sp. nov., O. planities Longino, sp. nov., O. schusteri Longino, sp. nov., O. triquetrilabrum Longino, sp. nov., O. triangulabrum Longino, sp. nov., and O. trithrix Longino, sp. nov. Octostruma lutzi (Wheeler) and O. amrishi (Makhan) are removed from synonymy with O. balzani (Emery). Queens are newly associated with workers for O. amrishi (Makhan), O. rugiferoides Brown & Kempf, and O. wheeleri (Mann).

New species of Central American Rhopalothrix Mayr, 1870 (Hymenoptera, Formicidae).

The ant genus Rhopalothrix is a rare inhabitant of wet forest leaf litter and soil. We propose a monophyletic R. isthmica clade that is restricted to the Neotropics, contains most of the species in the genus, and has its center of abundance and diversity in Central America. Thirteen species are recognized in the R. isthmica clade, of which eight are described as new and three are redescribed. A key to species in the R. isthmica clade is provided, and the following eight new species are described: R. andersoni Longino & Boudinot, sp. nov., R. apertor Longino & Boudinot, sp. nov., R. atitlanica Longino & Boudinot, sp. nov., R. megisthmica Longino & Boudinot, sp. nov., R. nubilosa Longino & Boudinot, sp. nov., R. subspatulata Longino & Boudinot, sp. nov., R. therion Longino & Boudinot, sp. nov., and R. triumphalis Longino & Boudinot, sp. nov.. Queens are newly associated with workers for three Central American species. New synonymy is proposed for Rhopalothrix plaumanni Brown & Kempf, 1960 = R. acutipilis Kempf, 1962, syn. nov.

A review of the Central American and Caribbean species of the ant genus Eurhopalothrix Brown and Kempf, 1961 (Hymenoptera, Formicidae), with a key to New World species.

The ant genus Eurhopalothrix occurs throughout the Neotropics and Australasian tropics, where it is an inhabitant of forest leaf litter and soil. The New World species are reviewed, with an emphasis on the fauna of the MesoAmerican corridor and the Caribbean. Previously unappreciated characters of mandibular dentition and labrum shape vary dramatically among species and species groups. A total of 28 New World species are recognized, of which 14 are described as new. A key to workers of all New World species is provided. Eurhopalothrix procera is reported for the first time in the New World. The following new species are described: E. cimu Longino, sp. nov., E. circumcapillum Longino, sp. nov., E. guadeloupensis Longino, sp. nov., E. hunhau Longino, sp. nov., E. mabuya Longino, sp. nov., E. machaquila Longino, sp. nov., E. megalops Longino, sp. nov., E. ortizae Longino, sp. nov., E. oscillum Longino, sp. nov., E. semicapillum Longino, sp. nov., E. sepultura Longino, sp. nov., E. vulcan Longino, sp. nov., E. xibalba Longino, sp. nov., and E. zipacna Longino. sn. nov. Eurhopalothrix schmidti (Menozzi) is removed from synonymy with E. gravis (Mann).

Unprecedented ichneumonid parasitoid wasp diversity in tropical forests.

The megadiverse parasitoid wasp family Ichneumonidae (Hymenoptera) is classically considered an exception to the extensively studied latitudinal diversity gradient: the majority of ichneumonid species are described from temperate regions. The gradient has been hypothesized to be dependent on the biology of the wasps, but recently questions of sampling and description biases have been raised. Here, we show with primary data that the species richness of Ichneumonidae is markedly underestimated in tropical areas and that latitudinal diversity patterns in the family remain uncharacterized. We discovered a startling 177 likely undescribed orthocentrine species with relatively low sampling effort in the forests of Central America and Amazonian Ecuador, over three times the previously known orthocentrine diversity in the world's tropics. Species accumulation curves reveal that we are just beginning to unveil the true extent of tropical orthocentrine diversity. We also found evidence for cryptic species; our DNA analysis revealed additional species not easily distinguishable using morphological characteristics. The difficulty in establishing species richness patterns of Ichneumonidae probably follows from the relative lack of taxonomic expertise and the low density of ichneumonid species throughout the landscape.

Three new species and reassessment of the rare Neotropical ant genus Leptanilloides (Hymenoptera, Formicidae, Leptanilloidinae).

We describe three new species of the Neotropical ant genus Leptanilloides: Leptanilloides gracilissp. n. based on workers from Mexico and Guatemala, Leptanilloides erinyssp. n. based on workers and a gyne from Ecuador, and Leptanilloides femoralissp. n. based on workers from Venezuela. The description of Leptanilloides gracilis is a northern extension of the known range of the genus, now numbering eleven described species. We also describe and discuss three unassociated male morphotypes from Central America. We report the occurrence of a metatibial gland in Leptanilloides and a fused promesonotal connection (suture) in some species. We provide a modified, detailed diagnosis of the genus and a revised key to the worker caste of the known species.

DNA barcoding and morphology reveal two common species in one: Pimpla molesta stat. rev. separated from P. croceipes (Hymenoptera, Ichneumonidae).

Correct species identification is the basis of ecological studies. Nevertheless, morphological examination alone may not be enough to tell species apart. Here, our integrated molecular and morphological studies demonstrate that the relatively widespread and common neotropical parasitoid wasp Pimpla croceipes Cresson, 1874 (Hymenoptera: Ichneumonidae: Pimplinae) actually consists of two distinct species. The name Pimpla molesta (Smith, 1879), stat. rev. is available for the second species. The two species were identified by DNA barcoding and minor differences in morphology and colouration. Our results support the previous notions that DNA barcoding can complement morphological identification and aid the discovery of cryptic species complexes.

Canopy and litter ant assemblages share similar climate-species density relationships.

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

Climatic drivers of hemispheric asymmetry in global patterns of ant species richness.

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