An ant genus-group (Prenolepis) illuminates the biogeography and drivers of insect diversification in the Indo-Pacific.

The Malay Archipelago and the tropical South Pacific (hereafter the Indo-Pacific region) are considered biodiversity hotspots, yet a general understanding of the origins and diversification of species-rich groups in the region remains elusive. We aimed to test hypotheses for the evolutionary processes driving insect species diversity in the Indo-Pacific using a higher-level and comprehensive phylogenetic hypothesis for an ant clade consisting of seven genera. We estimated divergence times and reconstructed the biogeographical history of ant species in the Prenolepis genus-group (Formicidae: Formicinae: Lasiini). We used a fossil-calibrated phylogeny to infer ancestral geographical ranges utilizing a biogeographic model that includes founder-event speciation. Ancestral state reconstructions of the ants' ecological preferences, and diversification rates were estimated for selected Indo-Pacific clades. Overall, we report that faunal interchange between Asia and Australia has occurred since at least 20-25 Ma, and early dispersal to the Fijian Basin happened during the early and mid-Miocene (ca. 10-20 Ma). Differences in diversification rates across Indo-Pacific clades may be related to ecological preference breadth, which in turn may have facilitated geographical range expansions. Ancient dispersal routes suggested by our results agree with the palaeogeography of the region. For this particular group of ants, the rapid orogenesis in New Guinea and possibly subsequent ecological shifts may have promoted their rapid diversification and widespread distribution across the Indo-Pacific.

Biogeography of mutualistic fungi cultivated by leafcutter ants.

Leafcutter ants propagate co-evolving fungi for food. The nearly 50 species of leafcutter ants (Atta, Acromyrmex) range from Argentina to the United States, with the greatest species diversity in southern South America. We elucidate the biogeography of fungi cultivated by leafcutter ants using DNA sequence and microsatellite-marker analyses of 474 cultivars collected across the leafcutter range. Fungal cultivars belong to two clades (Clade-A and Clade-B). The dominant and widespread Clade-A cultivars form three genotype clusters, with their relative prevalence corresponding to southern South America, northern South America, Central and North America. Admixture between Clade-A populations supports genetic exchange within a single species, Leucocoprinus gongylophorus. Some leafcutter species that cut grass as fungicultural substrate are specialized to cultivate Clade-B fungi, whereas leafcutters preferring dicot plants appear specialized on Clade-A fungi. Cultivar sharing between sympatric leafcutter species occurs frequently such that cultivars of Atta are not distinct from those of Acromyrmex. Leafcutters specialized on Clade-B fungi occur only in South America. Diversity of Clade-A fungi is greatest in South America, but minimal in Central and North America. Maximum cultivar diversity in South America is predicted by the Kusnezov-Fowler hypothesis that leafcutter ants originated in subtropical South America and only dicot-specialized leafcutter ants migrated out of South America, but the cultivar diversity becomes also compatible with a recently proposed hypothesis of a Central American origin by postulating that leafcutter ants acquired novel cultivars many times from other nonleafcutter fungus-growing ants during their migrations from Central America across South America. We evaluate these biogeographic hypotheses in the light of estimated dates for the origins of leafcutter ants and their cultivars.

Phylogenomics, biogeography and diversification of obligate mealybug-tending ants in the genus Acropyga.

Acropyga ants are a widespread clade of small subterranean formicines that live in obligate symbiotic associations with root mealybugs. We generated a data set of 944 loci of ultraconserved elements (UCEs) to reconstruct the phylogeny of 41 representatives of 23 Acropyga species using both concatenation and species-tree approaches. We investigated the biogeographic history of the genus through divergence dating analyses and ancestral range reconstructions. We also explored the evolution of the Acropyga-mealybug mutualism using ancestral state reconstruction methods. We recovered a highly supported species phylogeny for Acropyga with both concatenation and species-tree analyses. The age for crown-group Acropyga is estimated to be around 30Ma. The geographic origin of the genus remains uncertain, although phylogenetic affinities within the subfamily Formicinae point to a Paleotropical ancestor. Two main Acropyga lineages are recovered with mutually exclusive distributions in the Old World and New World. Within the Old World clade, a Palearctic and African lineage is suggested as sister to the remaining species. Ancestral state reconstructions indicate that Old World species have diversified mainly in close association with xenococcines from the genus Eumyrmococcus, although present-day associations also involve other mealybug genera. In contrast, New World Acropyga predominantly evolved with Neochavesia until a recent (10-15Ma) switch to rhizoecid mealybug partners (genus Rhizoecus). The striking mandibular variation in Acropyga evolved most likely from a 5-toothed ancestor. Our results provide an initial evolutionary framework for extended investigations of potential co-evolutionary interactions between these ants and their mealybug partners.

Ants and the fossil record.

The dominance of ants in the terrestrial biosphere has few equals among animals today, but this was not always the case. The oldest ants appear in the fossil record 100 million years ago, but given the scarcity of their fossils, it is presumed they were relatively minor components of Mesozoic insect life. The ant fossil record consists of two primary types of fossils, each with inherent biases: as imprints in rock and as inclusions in fossilized resins (amber). New imaging technology allows ancient ant fossils to be examined in ways never before possible. This is particularly helpful because it can be difficult to distinguish true ants from non-ants in Mesozoic fossils. Fossil discoveries continue to inform our understanding of ancient ant morphological diversity, as well as provide insights into their paleobiology.

Trophobiosis between a new species of Acropyga (Hymenoptera, Formicidae) and new Neochavesia (Hemiptera, Xenococcidae) from Peru, and establishment of the Acropygasmithii species-group.

We describe a new pair of trophobiotic partners from the ant genus Acropyga and the root mealybug genus Neochavesia. A recent field study on Acropyga ants and associated root mealybugs, conducted in the Peruvian Amazon, led to the discovery of Acropygamanuense LaPolla & Schneider, sp. nov. and its root mealybug symbiont Neochavesiapodexuta Schneider & LaPolla, sp. nov. The new root mealybug belongs to the family Xenococcidae, whose members are all obligate associates of Acropyga ants. Providing joint descriptions of new mutualist partners in the same article is a novel approach for this system, and it offers benefits to the ongoing study of mutualism and patterns of association among these symbiotic ants and scales. Here, we also begin to revise the species-group composition of Acropyga by establishing the smithii species-group, and we provide updated information to aid in identifying the new ant species and root mealybug species.

A Neotropical complex of Ripersiella species (Hemiptera, Coccomorpha, Rhizoecidae) collected from the nests of Acropyga ants (Hymenoptera, Formicidae).

We describe five new Neotropical species of Ripersiella living in association with Acropyga ants: R.campensis sp. nov., R.illicians sp. nov., R.montanae sp. nov., R.pediandensis sp. nov., and R.telalia sp. nov. We also redescribe R.andensis and R.colombiensis based on type specimens and other collections. Together, these seven species form a morphologically similar group that we informally refer to as the andensis-complex of Ripersiella. All members of the andensis-complex are confirmed or are speculated to be mutualists of Acropyga ants. We discuss the implications of these associations and provide an identification key to the Neotropical species of Ripersiella that are lacking bitubular cerores, including the new species.

Distinguishing Symbiotic Partners of Acropyga Ants from Free-Living Soil Inhabitants.

The fruitful study of associations between ants and scale insects yields insight into the mechanisms that shape these symbioses. Field collections provide the basic information linking partnered species, and as such it is critical that collection techniques from the field reflect true species-to-species partnerships in the published literature. It is equally critical that such practices limit the potential for mistaking free-living "neighbors" for symbiotic partners and publishing erroneous associations. This article describes a protocol for collecting subterranean scale insects and associated Acropyga Roger ants, which relies upon the activity of worker ants to sort and distinguish symbionts from free-living scale insects that happen to live near the colony. By collecting samples of ants and scales into nest boxes and allowing a resting period of several hours, worker ants will gather symbiotic partners into dense, protected clusters in which symbionts are actively tended. Free-living scale insects neighboring the colony can be collected from soil along with colony samples, but these free-living individuals are excluded from protective clusters and ignored by workers. Following confirmation of ant attendance, true symbiotic partners can be confidently collected, preserved, and recorded for future study. We illustrate the value of employing this collection protocol using a case study from Peru.

Trophobiosis between a new species of Williamsrhizoecus (Hemiptera: Coccomorpha: Rhizoecidae) and Acropyga silvestrii (Hymenoptera: Formicidae) in Tanzania.

A new myrmecophilous species of root mealybug, Williamsrhizoecus udzungwensis sp. n., is described from individuals found living within a nest of Acropyga silvestrii in the Udzungwa Mountains of Tanzania. Acropyga ants are highly specialized, obligate associates of scale insects, typically members of the scale family Xenococcidae. Acropyga are best known for vertically transmitting trophobiotic partners during their nuptial flights and for housing them within brood chambers. This article presents the first record of trophobiosis between a species of Williamsrhizoecus and Acropyga, and only the second record of an association between Acropyga and rhizoecids in the Old World. This discovery contributes important information about the few species of Rhizoecidae confirmed to engage in these unique symbioses, each putatively the result of a past horizontal transmission event from a xenococcid to a rhizoecid lineage. Included is a discussion on the diagnosis of Williamsrhizoecus and an updated key to the species.

Nylanderia of the World Part III: Nylanderia in the West Indies.

The diversity of the formicine ant genus Nylanderia is currently underestimated and largely undescribed. This includes the faunas of tropical regions where species richness is typically high. Here, the taxonomy of the West Indian Nylanderia fauna is revised for the first time. Fourteen new species are described, bringing the total number of species known from the region to 22. The new species are: N. bibadia, sp. nov., N. caerula, sp. nov., N. coveri, sp. nov., N. disatra, sp. nov., N. esperanza, sp. nov., N. fuscaspecula, sp. nov., N. lucayana, sp. nov., N. metacista, sp. nov., N. pini, sp. nov., N. semitincta, sp. nov., N. sierra, sp. nov., N. wardi, sp. nov., N. xestonota, sp. nov., and N. zaminyops, sp. nov. There are several introduced species in the region including the globally widespread Old World species N. bourbonica. Other introduced species are N. fulva, N. pubens, N. guatemalensis, and N. steinheili. The following new synonyms are proposed: fulva Mayr 1862 (= fulva cubana Santschi 1930); steinheili Forel 1893 (= steinheili minuta Forel 1893). An identification key is provided for the workers of Nylanderia found in the West Indies. Photomontage images are provided for the worker of each species and when available photomontage and SEM images are provided for males. This work represents another step forward in understanding the diversity of this widespread and commonly encountered ant genus.

Two new Prenolepis species (Hymenoptera: Formicidae) from Indomalaya and Australasia, with a redescription of P. dugasi from Vietnam.

Prenolepis is a lineage of formicine ants with its center of diversity in the Old World tropics. Three more Prenolepis species are added to the Indomalayan and Australasian fauna and another is synonymized, bringing the total number of Prenolepis species worldwide to 19. Two new species are described: P. nepalensis from Nepal and P. lakekamu from Papua New Guinea, the latter being the first in the genus east of Wallace's Line. Additionally, P. dugasi Forel (comb. rev.) from Vietnam is transferred from Nylanderia and redescribed. Based on morphology, each of the three species appears to be most closely-related to other species found predominantly in or nearest to their respective bioregions: P. nepalensis most resembles P. darlena, P. fisheri, and P. fustinoda; P. lakekamu bears strongest resemblance to P. jacobsoni, P. jerdoni, and P. subopaca; and P. dugasi most resembles P. melanogaster. Descriptions, illustrations and images are provided for all three species. One new synonymy is proposed: P. angulinoda Chen Zhou 2018 = P. fustinoda Williams LaPolla 2016. An updated key for workers of all extant Prenolepis species is also included.

Phylogenetic position of the ant genus Acropyga Roger (Hymenoptera: Formicidae) and the evolution of trophophoresy.

Trophophoresy is exhibited in two ant genera: Acropyga (Formicinae), in which all 37 species are thought to be trophophoretic, and Tetraponera (Pseudomyrmecinae), in which it has been observed in only one species, T. binghami. This study analyses a dataset comprised of both morphological and molecular (D2 region of 28S rRNA and EF1-alpha) data. Evidence is presented in favor of Acropyga being monophyletic, hence trophophoresy has evolved only once within the Formicinae and twice within the ants overall. The data further suggests that Acropyga belongs within a clade containing Anoplolepis, Aphomomyrmex, and Petalomyrmex. Aphomomyrmex and Petalomyrmex were found to be the sister group to Acropyga. The results indicate that the Lasiini and Plagiolepidini are not monophyletic and are in need of reexamination. Given the extant pantropical distribution of Acropyga it is speculated that Acropyga maybe of Gondwanan origin and that trophobiosis was the first form of agriculture to evolve in the ants.

Taxonomic revision and phylogeny of the ant genus Prenolepis (Hymenoptera: Formicidae).

The formicine ant genus Prenolepis is here revised for the first time. Thirteen extant species are recognized of which four are described as new. A key for the worker caste is provided, and the worker of each species is imaged, with males and queens imaged in species where they are known. Worker-based characters were used to construct a species-level phylogeny of Prenolepis. Both maximum parsimony and Bayesian inference methods were used for the phylogenetic analyses. A morphological diagnosis for the genus is provided, with a discussion of useful morphological characters for separating Prenolepis from other genera in the Prenolepis genus-group. Major taxonomic changes are proposed. The new species are: P. darlena, P. fustinoda, P. mediops, and P. shanialena. Prenolepis jerdoni subopaca is elevated to full species. Three species are excluded from Prenolepis and transferred to Nylanderia and Paratrechina as new combinations: N. emmae, N. flaviabdominis, and P. umbra. Two species are excluded from Paratrechina and transferred to Nylanderia and Paraparatrechina as new combinations: N. guanyin and P. kongming. One species, Z. darlingtoni, is excluded from Nylanderia and transferred to Zatania as a new combination. Several synonyms are proposed: Prenolepis sphingthoraxa = Nylanderia flaviabdominis; P. imparis arizonica, P. imparis colimana, P. imparis coloradensis, and P. imparis veracruzensis = P. imparis; P. melanogaster carinifrons and P. nigriflagella = P. melanogaster; P. longiventris and P. magnocula = P. naoroji; and P. septemdenta = Nylanderia opisopthalmia.

Nylanderia deceptrix sp. n., a new species of obligately socially parasitic formicine ant (Hymenoptera, Formicidae).

Obligately socially parasitic ants are social parasites that typically lack the sterile worker caste, and depend on the host species for survival and brood care. The genus Nylanderia has over 130 described species and subspecies, none of which, until this study, were known social parasites. Here we describe the first social parasite known in the genus, Nylanderia deceptrix. Aspects of the biology of the host species, Nylanderia parvula (Mayr 1870), and Nylanderia deceptrix are examined. The data from both the host and the parasite species are combined to better understand the host-parasite relationship.

Isolation and characterization of Nylanderia fulva virus 1, a positive-sense, single-stranded RNA virus infecting the tawny crazy ant, Nylanderia fulva.

We report the discovery of Nylanderia fulva virus 1 (NfV-1), the first virus identified and characterized from the ant, Nylanderia fulva. The NfV-1 genome (GenBank accession KX024775) is 10,881 nucleotides in length, encoding one large open reading frame (ORF). Helicase, protease, RNA-dependent RNA polymerase, and jelly-roll capsid protein domains were recognized within the polyprotein. Phylogenetic analysis placed NfV-1 in an unclassified clade of viruses. Electron microscopic examination of negatively stained samples revealed particles with icosahedral symmetry with a diameter of 28.7±1.1nm. The virus was detected by RT-PCR in larval, pupal, worker and queen developmental stages. However, the replicative strand of NfV-1 was only detected in larvae. Vertical transmission did not appear to occur, but horizontal transmission was facile. The inter-colonial field prevalence of NfV-1 was 52±35% with some local infections reaching 100%. NfV-1 was not detected in limited samples of other Nylanderia species or closely related ant species.

Evidence of niche shift and global invasion potential of the Tawny Crazy ant, Nylanderia fulva.

Analysis of an invasive species' niche shift between native and introduced ranges, along with potential distribution maps, can provide valuable information about its invasive potential. The tawny crazy ant, Nylanderia fulva, is a rapidly emerging and economically important invasive species in the southern United States. It is originally from east-central South America and has also invaded Colombia and the Caribbean Islands. Our objectives were to generate a global potential distribution map for N. fulva, identify important climatic drivers associated with its current distribution, and test whether N. fulva's realized climatic niche has shifted across its invasive range. We used MaxEnt niche model to map the potential distribution of N. fulva using its native and invaded range occurrences and climatic variables. We used principal component analysis methods for investigating potential shifts in the realized climatic niche of N. fulva during invasion. We found strong evidence for a shift in the realized climatic niche of N. fulva across its invasive range. Our models predicted potentially suitable habitat for N. fulva in the United States and other parts of the world. Our analyses suggest that the majority of observed occurrences of N. fulva in the United States represent stabilizing populations. Mean diurnal range in temperature, degree days at ≥10°C, and precipitation of driest quarter were the most important variables associated with N. fulva distribution. The climatic niche expansion demonstrated in our study may suggest significant plasticity in the ability of N. fulva to survive in areas with diverse temperature ranges shown by its tolerance for environmental conditions in the southern United States, Caribbean Islands, and Colombia. The risk maps produced in this study can be useful in preventing N. fulva's future spread, and in managing and monitoring currently infested areas.

Then there were five: a reexamination of the ant genus Paratrechina (Hymenoptera, Formicidae).

The ant genus Paratrechina is reexamined based on the discovery of two new species from Madagascar (P. ankarana sp. n. and P. antsingy sp. n.). Paratrechina kohli, a species known from central Africa, is transferred to Paratrechina from Prenolepis based on a new morphological interpretation of the genus and an updated morphological diagnosis of the genus is provided. This means that other than the widespread P. longicornis, whose origins remain uncertain, all Paratrechina are restricted either to the Afrotropical or Malagasy regions. It would also appear that of the five Paratrechina species now known, three are from dry forest habitats. With this reexamination of the genus, the possible origins of P. longicornis are discussed. A key to the genera of the Prenolepis genus-group is provided, as is a key to the workers of Paratrechina. In addition, we also designate a lectotype for Paratrechina kohli.

Two new Paraparatrechina (Hymenoptera, Formicidae) species from the Seychelles, with notes on the hypogaeic weissi species-group.

Recent survey work in the Seychelles has revealed two new species of Paraparatrechina that are here described: P. illusio sp. n. and P. luminella sp. n. A revised key to the workers of Paraparatrechina for the Afrotropical and Malagasy regions is provided. The taxonomy of the hypogaeic weissi species-group is also reviewed in light of recent field collections. The species P. sordida is revived from synonymy and given new status (as a full species) and a discussion of the morphologically peculiar species-group is provided. With the description of the two species and the removal of another species from weissi synonomy there are now 16 Paraparatrechina species known from the Afrotropical and Malagasy regions.

The importance of using multiple approaches for identifying emerging invasive species: the case of the Rasberry Crazy Ant in the United States.

In the past decade, Houston, Texas has been virtually overrun by an unidentified ant species, the sudden appearance and enormous population sizes and densities of which have received national media attention. The Rasberry Crazy Ant, as it has become known due to its uncertain species status, has since spread to neighboring states and is still a major concern to pest control officials. Previous attempts at identifying this species have resulted in widely different conclusions in regards to its native range, source, and biology. We identify this highly invasive pest species as Nylanderia fulva (Mayr) using morphometric data measured from 14 characters, molecular sequence data consisting of 4,669 aligned nucleotide sites from six independent loci and comparison with type specimens. This identification will allow for the study and control of this emerging pest species to proceed unencumbered by taxonomic uncertainty. We also show that N. fulva has a much wider distribution than previously thought and has most likely invaded all of the Gulf Coast states.

Why weight?

Whether phylogenetic data should be differentially or equally weighted is currently debated. Further, if differential weighting is to be explored, there is no consensus among investigators as to which weighting scheme is most appropriate. Mitochondrial genome data offer a powerful tool in assessment of differential weighting schemes because taxa can be selected from which a highly corroborated phylogeny is available (so that accuracy can be assessed), and it can be assumed that different data partitions share the same history (so that gene-sorting issues are not so problematic). Using mitochondrial data from 17 mammalian genomes, we evaluated the most commonly used weighting schemes, such as successive weighting, transversion weighting, codon-based weighting, and amino acid coding, and compared them to more complex weighting schemes including a 6-parameter weighting, pseudoreplicate reweighting, and tri-level weighting. We found that the most commonly used weighting schemes perform the worst with these data. Some of the more complex schemes perform well, however, none of them is consistently superior. These results support ones biases; if one has a predilection to avoid differential weighting, these data support equally weighted parsimony and maximum likelihood. Others might be encouraged by these results to try weighting as a form of data exploration.