Turning one into five: Integrative taxonomy uncovers complex evolution of cryptic species in the harvester ant Messor “structor”

Co-habiting ants and silverfish display a converging feeding ecology

BACKGROUND

Various animal taxa have specialized to living with social hosts. Depending on their level of specialization, these symbiotic animals are characterized by distinct behavioural, chemical, and morphological traits that enable close heterospecific interactions. Despite its functional importance, our understanding of the feeding ecology of animals living with social hosts remains limited. We examined how host specialization of silverfish co-habiting with ants affects several components of their feeding ecology. We combined stable isotope profiling, feeding assays, phylogenetic reconstruction, and microbial community characterization of the Neoasterolepisma silverfish genus and a wider nicoletiid and lepismatid silverfish panel where divergent myrmecophilous lifestyles are observed.

RESULTS

Stable isotope profiling (δ13C and δ15N) showed that the isotopic niches of granivorous Messor ants and Messor-specialized Neoasterolepisma exhibit a remarkable overlap within an ant nest. Trophic experiments and gut dissections further supported that these specialized Neoasterolepisma silverfish transitioned to a diet that includes plant seeds. In contrast, the isotopic niches of generalist Neoasterolepisma silverfish and generalist nicoletiid silverfish were clearly different from their ant hosts within the shared nest environment. The impact of the myrmecophilous lifestyle on feeding ecology was also evident in the internal silverfish microbiome. Compared to generalists, Messor-specialists exhibited a higher bacterial density and a higher proportion of heterofermentative lactic acid bacteria. Moreover, the nest environment explained the infection profile (or the 16S rRNA genotypes) of Weissella bacteria in Messor-specialized silverfish and the ant hosts.

CONCLUSIONS

Together, we show that social hosts are important determinants for the feeding ecology of symbiotic animals and can induce diet convergence.

Analysis of Whole-Genome as a Novel Strategy for Animal Species Identification

Survival crises stalk many animals, especially endangered and rare animals. Accurate species identification plays a pivotal role in animal resource conservation. In this study, we developed an animal species identification method called Analysis of whole-GEnome (AGE), which identifies species by finding species-specific sequences through bioinformatics analysis of the whole genome and subsequently recognizing these sequences using experimental technologies. To clearly demonstrate the AGE method, Cervus nippon, a well-known endangered species, and a closely related species, Cervus elaphus, were set as model species, without and with published genomes, respectively. By analyzing the whole genomes of C. nippon and C. elaphus, which were obtained through next-generation sequencing and online databases, we built specific sequence databases containing 7,670,140 and 570,981 sequences, respectively. Then, the species specificities of the sequences were confirmed experimentally using Sanger sequencing and the CRISPR-Cas12a system. Moreover, for 11 fresh animal samples and 35 commercially available products, our results were in complete agreement with those of other authoritative identification methods, demonstrating AGE's precision and potential application. Notably, AGE found a mixture in the 35 commercially available products and successfully identified it. This study broadens the horizons of species identification using the whole genome and sheds light on the potential of AGE for conserving animal resources.

Nomenclatural changes on some Mediterranean Aphaenogaster Mayr, 1853 taxa (Hymenoptera, Formicidae)

The ant genus Aphaenogaster Mayr, 1853 is especially diverse in the West-Palearctic region, where its taxonomy is still problematic for several groups. Among other issues, there is a redundancy of valid taxa compared to the number of species whose validity is currently sustained by any evidence. Names that do not represent taxa with clearly defined identities complicate specimen identification and add confusion to biodiversity databases and checklists. Based on a review of the available literature information on several taxa, and the study of both type and non-type material, the following taxonomic changes are proposed: i) A. mauritanica Dalla Torre, 1893 should be considered a senior synonym of A. gibbosa homonyma Emery, 1921 syn. nov. and of A. foreli Cagniant, 1996 syn. nov. (the Maghrebian populations of the pallida group hitherto considered to represent A. foreli should be attributed to A. dulcineae Emery, 1924); ii) A. pallida (Nylander, 1849) should be considered a senior synonym of A. leveillei Emery, 1881 syn. nov. and of A. leveillei laurenti Santschi, 1939 syn. nov.; iii) A. sangiorgii (Emery, 1901) should be considered a senior synonym of A. finzii Müller, 1921 syn. nov. and A. radchenkoi Kiran & Tezcan, 2008 syn. nov.; iv) A. sardoa Mayr, 1853 should be considered a senior synonym of A. sardoa ujhelyii Szabó, 1910 syn. nov. and A. sardoa anoemica Santschi, 1910 syn. nov.; v) A. subterraneosplendida André, 1883 should be considered a senior synonym of A. sicula Emery, 1908 syn. nov.; vi) A. subterraneoides Emery, 1881 should be considered a senior synonym of A. subterraneoides armeniaca Arnol'di, 1968 syn. nov. These changes will reduce the gap between nomenclature and actual understanding of species diversity, while synonymized names may be resurrected if supporting evidence is discovered.

Phylogenomic inference and demographic model selection suggest peripatric separation of the cryptic steppe ant species Plagiolepis pyrenaica stat. rev

The ant Plagiolepis taurica Santschi, 1920 (Hymenoptera, Formicidae) is a typical species of the Eurasian steppes, a large grassland dominated biome that stretches continuously from Central Asia to Eastern Europe and is represented by disjunct outposts also in Central and Western Europe. The extent of this biome has been influenced by the Pleistocene climate, and steppes expanded recurrently during cold stages and contracted in warm stages. Consequently, stenotopic steppe species such as P. taurica repeatedly went through periods of demographic expansion and severe isolation. Here, we explore the impact of these dynamics on the genetic diversification within P. taurica. Delimitation of P. taurica from other Plagiolepis species has been unclear since its initial description, which raised questions on both its classification and its spatiotemporal diversification early on. We re-evaluate species limits and explore underlying mechanisms driving speciation by using an integrative approach based on genomic and morphometric data. We found large intraspecific divergence within P. taurica and resolved geographically coherent western and eastern genetic groups, which likewise differed morphologically. A morphometric survey of type material showed that Plagiolepis from the western group were more similar to P. barbara pyrenaica Emery, 1921 than to P. taurica; we thus lift the former from synonymy and establish it as separate species, P. pyrenaica stat. rev. Explicit evolutionary model testing based on genomic data supported a peripatric speciation for the species pair, probably as a consequence of steppe contraction and isolation during the mid-Pleistocene. We speculate that this scenario could be exemplary for many stenotopic steppe species, given the emphasized dynamics of Eurasian steppes.

Fungi Associated with Messor Ants on the Balkan Peninsula: First Biogeographical Data

Ant nests’ relatively stable and long-lasting microhabitats present ideal living conditions for many uni- and multicellular organisms, whose relationships range from mutualistic to parasitic. Messor harvester ants inhabit arid and semi-arid open areas where their colonies consist of large numbers of individuals. Due to the high number of other organisms associated with harvester ants, their nests can be defined as islands for unique biota. Despite significant progress in research on ant-associated fungi in Europe, little is still known about the recently described ectoparasitic fungus Rickia lenoirii Santamaria, 2015 (Laboulbeniales), found on two species of ants of the genus Messor. Here we report for the first time the occurrence of the ectoparasitic ant-associated fungus R. lenoirii from three countries (Albania, Bulgaria, and continental Greece) and multiple localities in the Balkans. The fungus was detected on four ant host species—Messor structor (Latreille, 1798), M. wasmanni Krausse, 1910, M. hellenius Agosti & Collingwood, 1987, and M. mcarthuri Steiner et al., 2018 with the latter two representing new host records. Furthermore, spores of the widespread endoparasitic fungus of ants, Myrmicinosporidium durum Hölldobler, 1933 (Blastocladiomycota), were reported for the first time in Messor structor (Bulgaria). Images of the ant-associated Rickia lenoirii taken with a scanning electron microscope, a comparison with R. wasmannii, and a distribution map are also presented.

Characterization and Phylogenetic Implication of Complete Mitochondrial Genome of the Medicinal Ant Formica sinae (Hymenoptera: Formicidae): Genomic Comparisons in Formicidae

Ants (Hymenoptera: Formicidae) are among the largest and most widespread families of terrestrial insects and are valuable to medical and ecological investigations. The mitochondrial genome has been widely used as a reliable genetic marker for species identification and phylogenetic analyses. To further understand the mitogenome-level characteristics of the congeneric Formicidae species, the complete mitogenome of Formica sinae (Hymenoptera: Formicidae) was sequenced, annotated, and compared with other 48 Formicidae species. The results showed that gene composition, content, and codon usage were conserved. The complete mitochondrial genome of F. sinae was 17,432 bp, including 13 protein-coding genes (PCGs), 22 transfer RNA genes (tRNAs), two ribosomal RNA genes (rRNAs), and one control region located between rrnS and trnM, which was 1,256 bp long, the longest of all sequenced species. Gene rearrangement was not detected in Formica species (Hymenoptera: Formicidae). All PCGs of F. sinae were initiated with ATN codons and terminated with the TAA codon. The overall nucleotide composition of F. sinae was AT-biased (83.51%), being 80.58% in PCGs, 86.68% in tRNAs, 87.10% in rRNAs, and 88.70% in the control region. Phylogenetic analyses indicated that each subfamily formed a strongly monophyletic group. Furthermore, F. sinae clustered with Formica fusca (Hymenoptera: Formicidae) and Formica selysi (Hymenoptera: Formicidae). This work enhances the genetic data of Formicidae and contributes to our understanding of their phylogenic relationship, evolution, and utilization.

An updated checklist of ants (Hymenoptera, Formicidae) of Bulgaria, after 130 years of research

Background

The Bulgarian myrmecofauna is one of the richest in the Balkans. This is a result of both the physicogeographical and paleoecological features of the area, as well as relatively well-studied fauna. The earliest myrmecological paper on Bulgarian fauna, listing 54 species, was published 130 years ago. The publication was later followed by numerous new faunistic records and three comprehensive reviews that significantly widened knowledge on the ant diversity from this country. The most recent checklist was released 12 years ago and considered 163 ant species from 40 genera.

New information

This work provides an updated checklist of 195 ant species from 43 genera occurring in Bulgaria. Since the last Bulgarian catalogue of ants, 44 species have been added, while 24 species have been synonymised or excluded after critical analysis of the last taxonomic revisions. Additionally, we discuss the status and distribution of 12 species described from Bulgaria, 23 species considered endemic and subendemic for this country, 19 species with conservation status and four non-native species.

Characterization of the complete mitochondrial genome of a harvesting ant Messor structor (Hymenoptera: Formicidae: Myrmicinae)

Messor structor (Latreille, 1798) is a keystone ant species in the genus Messor (Formicidae: Myrmicinae). Here, we reported the complete mitochondrial genome of M. structor. The circular mitogenome of M. structor is 17628 bp including 13 protein-coding genes, two ribosomal RNA genes, 22 transfer RNA genes, and a control region. The base composition was AT-biased (84.07%). Phylogenetic analysis suggests that it is closely related to Aphaenogaster famelica. The mitochondrial genome of M. structor will be a good source for understanding molecular evolutionary studies of this species and related ant species.

New and little-known ant species (Hymenoptera, Formicidae) from Bulgaria

Background

Many faunistic studies on the myrmecofauna of Bulgaria have been carried out and about 180 ant species (Hymenoptera, Formicidae) from 43 genera and six subfamilies have been discovered as a result. Although the Bulgarian ant fauna is considered to be relatively well studied, the finding of unrecorded species continues, especially amongst the rare social parasites and the species with a more southern distribution in the Balkans.

New information

The current study presents data on 11 ant species recorded for the first time in Bulgaria (Messorhellenius Agosti & Collingwood, 1987, M.mcarthuri Steiner et al., 2018, Crematogasterionia Forel, 1911, Monomoriummonomorium Bolton, 1987, Temnothoraxaeolius (Forel, 1911), T.cf.exilis(formdarii Forel, 1911), T.finzii (Menozzi, 1925), T.rogeri Emery, 1869, Tetramoriumcf.punicum, Plagiolepisxene Stärcke, 1936 and Lasiusreginae Faber, 1967), as well as new locality data on 15 rarely found species. Some of the species, such as Hypoponeraeduardi (Forel, 1894), Strumigenysargiola (Emery, 1869), Temnothoraxgraecus (Forel, 1911), Tetramoriumdiomedeum Emery, 1908, Camponotusionius Emery, 1920 and C.tergestinus Müller, 1921, have been known so far only from a single locality in Bulgaria.The dataset of all records presented in this work was published separately through Global Biodiversity Information Facility (GBIF, https://doi.org/10.15468/mngbzp).

Is mimicry a diversification-driver in ants? Biogeography, ecology, ethology, genetics and morphology define a second West-Palaearctic Colobopsis species (Hymenoptera: Formicidae)

The West-Palaearctic Colobopsis ant populations have long been considered a single species (Colobopsis truncata). We studied the diversity of this species by employing a multidisciplinary approach and combining data from our surveys, museum and private collections, and citizen science platforms. As a result, we have revealed the existence of a second species, which we describe as Colobopsis imitans sp. nov., distributed allopatrically from Co. truncata and living in the Maghreb, Sicily and southern Iberia. While the pigmentation of Co. truncata is reminiscent of Dolichoderus quadripunctatus, that of Co. imitans is similar to Crematogaster scutellaris, with which Co. imitans lives in close spatial association, and whose foraging trails it habitually follows, similar to Camponotus lateralis and other ant-mimicking ants. The isolation between Co. imitans and Co. truncata seems to have occurred relatively recently because of significant, yet not extreme, morphometric differentiation, and to mtDNA polyphyly. Both Co. imitans and Co. truncata appear to employ mimicry of an unpalatable or aggressive ant species as an important defensive strategy; this ‘choice’ of a different model species is motivated by biogeographic reasons and appears to act as a critical evolutionary driver of their diversification.

Biogeography of Iberian Ants (Hymenoptera: Formicidae)

Ants are highly diverse in the Iberian Peninsula (IP), both in species richness (299 cited species) and in number of endemic species (72). The Iberian ant fauna is one of the richest in the broader Mediterranean region, it is similar to the Balkan Peninsula but lower than Greece or Israel, when species richness is controlled by the surface area. In this first general study on the biogeography of Iberian ants, we propose seven chorological categories for grouping thems. Moreover, we also propose eight biogeographic refugium areas, based on the criteria of “refugia-within-refugium” in the IP. We analysed species richness, occurrence and endemism in all these refugium areas, which we found to be significantly different as far as ant similarity was concerned. Finally, we collected published evidence of biological traits, molecular phylogenies, fossil deposits and geological processes to be able to infer the most probable centre of origin and dispersal routes followed for the most noteworthy ants in the IP. As a result, we have divided the Iberian myrmecofauna into four biogeographical groups: relict, Asian-IP disjunct, Baetic-Rifan and Alpine. To sum up, our results support biogeography as being a significant factor for determining the current structure of ant communities, especially in the very complex and heterogenous IP. Moreover, the taxonomic diversity and distribution patterns we describe in this study highlight the utility of Iberian ants for understanding the complex evolutionary history and biogeography of the Iberian Peninsula.

The Myrmecofauna (Hymenoptera: Formicidae) of Hungary: Survey of Ant Species with an Annotated Synonymic Inventory

Simple Summary

Abundance is a hallmark of ants (Hymenoptera: Formicidae). They are exceedingly common in both natural and artificial environments and they constitute a conspicuous part of the terrestrial ecosystem; every 3 to 4 out of 10 kg of insects are given by ants. Due to their key role in natural habitats, they are at the basis of any nature conservation and pest management policy. Thus, the first step in developing adequate management strategies is to build a precise faunistic inventory. More than 16,000 valid ant species are registered worldwide, of which 126 are known to occur in Hungary. Thanks to the last decade’s efforts in the Hungarian myrmecological research, and because of the constantly changing taxonomy of several problematic ant genera, a new checklist of the Hungarian ants is presented here. A comparison of the Hungarian myrmecofauna to other European countries’ ant fauna is also provided in this paper. The current dataset is a result of ongoing work on inventorying the Hungarian ant fauna, therefore it is expected to change over time and will be updated once the ongoing taxonomic projects are completed.

Abstract

Ants (Hymenoptera: Forimicidae) are exceedingly common in nature. They constitute a conspicuous part of the terrestrial animal biomass and are also considered common ecosystem engineers. Due to their key role in natural habitats, they are at the basis of any nature conservation policy. Thus, the first step in developing adequate conservation and management policies is to build a precise faunistic inventory. More than 16,000 valid ant species are registered worldwide, of which 126 are known to occur in Hungary. Thanks to the last decade’s efforts in the Hungarian myrmecological research, and because of the constantly changing taxonomy of several problematic ant genera, a new checklist of the Hungarian ants is presented here. The state of the Hungarian myrmecofauna is also discussed in the context of other European countries’ ant fauna. Six species (Formica lemani, Lasius nitidigaster, Tetramorium immigrans, T. staerckei, T. indocile and Temnothorax turcicus) have been reported for the first time in the Hungarian literature, nine taxon names were changed after systematic replacements, nomenclatorial act, or as a result of splitting formerly considered continuous populations into more taxa. Two species formerly believed to occur in Hungary are now excluded from the updated list. All names are nomenclaturally assessed, and complete synonymies applied in the Hungarian literature for a certain taxon are provided. Wherever it is not self-evident, comments are added, especially to explain replacements of taxon names. Finally, we present a brief descriptive comparison of the Hungarian myrmecofauna with the ant fauna of the surrounding countries. The current dataset is a result of ongoing work on inventorying the Hungarian ant fauna, therefore it is expected to change over time and will be updated once the ongoing taxonomic projects are completed.

Cuticular hydrocarbons as potential mediators of cryptic species divergence in a mutualistic ant association

Upon advances in sequencing techniques, more and more morphologically identical organisms are identified as cryptic species. Often, mutualistic interactions are proposed as drivers of diversification. Species of the neotropical parabiotic ant association between Crematogaster levior and Camponotus femoratus are known for highly diverse cuticular hydrocarbon (CHC) profiles, which in insects serve as desiccation barrier but also as communication cues. In the present study, we investigated the association of the ants' CHC profiles with genotypes and morphological traits, and discovered cryptic species pairs in both genera. To assess putative niche differentiation between the cryptic species, we conducted an environmental association study that included various climate variables, canopy cover, and mutualistic plant species. Although mostly sympatric, the two Camponotus species seem to prefer different climate niches. However in the two Crematogaster species, we could not detect any differences in niche preference. The strong differentiation in the CHC profiles may thus suggest a possible role during speciation itself either by inducing assortative mating or by reinforcing sexual selection after the speciation event. We did not detect any further niche differences in the environmental parameters tested. Thus, it remains open how the cryptic species avoid competitive exclusion, with scope for further investigations.