Search for: All records

Abstract The evolutionary history of fungus-farming ants has been the subject of multiple morphological, molecular phylogenetic, and phylogenomic studies. Due to its rarity, however, the phylogenetic position, natural history, and fungal associations of the monotypic genus Paramycetophylax Kusnezov have remained enigmatic. Here we report the first excavations of colonies of Paramycetophylax bruchi (Santschi) and describe its nest architecture and natural history. Utilizing specimens from these collections, we generated ultraconserved-element (UCE) data to determine the evolutionary position of Paramycetophylax within the fungus-farming ants and ribosomal ‘fungal barcoding’ ITS sequence data to identify the fungal cultivar. A maximum-likelihood phylogenomic analysis indicates that the genus Paramycetophylax is the sister group of the yeast-cultivating Cyphomyrmex rimosus group, an unexpected result that renders the genus Cyphomyrmex Mayr paraphyletic. A Bayesian divergence-dating analysis indicates that Paramycetophylax diverged from its sister group around 36 mya (30–42 mya, HPD) in the late Eocene-early Oligocene, a period of global cooling, expansion of grasslands, and large-scale extinction of tropical organisms. Bayesian analysis of the fungal cultivar ITS gene fragment indicates that P. bruchi practices lower agriculture and that the cultivar grown by P. bruchi belongs to the Clade 1 group of lower-attine fungi, a clade that, interestingly, also includes the C. rimosus-group yeast cultivars. Based on these results, we conclude that a better understanding of P. bruchi and its fungal cultivar, including whole-genome data, is critical for reconstructing the origin of yeast agriculture, a major transition in the evolution of fungus-farming ants. 

Fungi shape the diversity of life. Characterizing the evolution of fungi is critical to understanding symbiotic associations across kingdoms. In this study, we investigate the genomic and metabolomic diversity of the genus Escovopsis , a specialized parasite of fungus-growing ant gardens. Based on 25 high-quality draft genomes, we show that Escovopsis forms a monophyletic group arising from a mycoparasitic fungal ancestor 61.82 million years ago (Mya). Across the evolutionary history of fungus-growing ants, the dates of origin of most clades of Escovopsis correspond to the dates of origin of the fungus-growing ants whose gardens they parasitize. We reveal that genome reduction, determined by both genomic sequencing and flow cytometry, is a consistent feature across the genus Escovopsis, largely occurring in coding regions, specifically in the form of gene loss and reductions in copy numbers of genes. All functional gene categories have reduced copy numbers, but resistance and virulence genes maintain functional diversity. Biosynthetic gene clusters (BGCs) contribute to phylogenetic differences among Escovopsis spp., and sister taxa in the Hypocreaceae. The phylogenetic patterns of co-diversification among BGCs are similarly exhibited across mass spectrometry analyses of the metabolomes of Escovopsis and their sister taxa. Taken together, our results indicate that Escovopsis spp. evolved unique genomic repertoires to specialize on the fungus-growing ant-microbe symbiosis. 

Abstract The ant genus Nylanderia Emery has a cosmopolitan distribution and includes 150 extant described species and subspecies, with potentially hundreds more undescribed. Global taxonomic revision has long been stalled by strong intra- and interspecific morphological variation, limited numbers of diagnostic characters, and dependence on infrequently collected male specimens for species description and identification. Taxonomy is further complicated by Nylanderia being one of the most frequently intercepted ant genera at ports of entry worldwide, and at least 15 globetrotting species have widespread and expanding ranges, making species-level diagnoses difficult. Three species complexes (‘bourbonica complex’, ‘fulva complex’, and ‘guatemalensis complex’) include globetrotting species. To elucidate the phylogenetic positions of these three complexes and delimit species boundaries within each, we used target enrichment of ultraconserved elements (UCEs) from 165 specimens representing 98 Nylanderia morphospecies worldwide. We also phased the UCEs, effectively doubling sample size and increasing population-level sampling. After recovering strong support for the monophyly of each complex, we extracted COI barcodes and SNPs from the UCE data and tested within-complex morphospecies hypotheses using three molecular delimitation methods (SODA, bPTP, and STACEY). This comparison revealed that most methods tended to over-split taxa, but results from STACEY were most consistent with our morphospecies hypotheses. Using these results, we recommend species boundaries that are conservative and most congruent across all methods. This work emphasizes the importance of integrative taxonomy for invasive species management, as globetrotting occurs independently across at least nine different lineages across Nylanderia. 

The fungus-growing ant Mycetomoellerius (previously Trachymyrmex ) zeteki (Weber 1940) has been the focus of a wide range of studies examining symbiotic partners, garden pathogens, mating frequencies, and genomics. This is in part due to the ease of collecting colonies from creek embankments and its high abundance in the Panama Canal region. The original description was based on samples collected on Barro Colorado Island (BCI), Panama. However, most subsequent studies have sampled populations on the mainland 15 km southeast of BCI. Herein we show that two sibling ant species live in sympatry on the mainland: Mycetomoellerius mikromelanos Cardenas, Schultz, & Adams and M . zeteki . This distinction was originally based on behavioral differences of workers in the field and on queen morphology ( M . mikromelanos workers and queens are smaller and black while those of M. zeteki are larger and red). Authors frequently refer to either species as “ M . cf. zeteki ,” indicating uncertainty about identity. We used an integrative taxonomic approach to resolve this, examining worker behavior, chemical profiles of worker volatiles, molecular markers, and morphology of all castes. For the latter, we used conventional taxonomic indicators from nine measurements, six extrapolated indices, and morphological characters. We document a new observation of a Diapriinae (Hymenoptera: Diapriidae) parasitoid wasp parasitizing M . zeteki . Finally, we discuss the importance of vouchering in dependable, accessible museum collections and provide a table of previously published papers to clarify the usage of the name T . zeteki . We found that most reports of M . zeteki or M . cf. zeteki —including a genome—actually refer to the new species M . mikromelanos . 

Abstract Although calcareous anatomical structures have evolved in diverse animal groups, such structures have been unknown in insects. Here, we report the discovery of high-magnesium calcite [CaMg(CO 3 ) 2 ] armor overlaying the exoskeletons of major workers of the leaf-cutter ant Acromyrmex echinatior . Live-rearing and in vitro synthesis experiments indicate that the biomineral layer accumulates rapidly as ant workers mature, that the layer is continuously distributed, covering nearly the entire integument, and that the ant epicuticle catalyzes biomineral nucleation and growth. In situ nanoindentation demonstrates that the biomineral layer significantly hardens the exoskeleton. Increased survival of ant workers with biomineralized exoskeletons during aggressive encounters with other ants and reduced infection by entomopathogenic fungi demonstrate the protective role of the biomineral layer. The discovery of biogenic high-magnesium calcite in the relatively well-studied leaf-cutting ants suggests that calcareous biominerals enriched in magnesium may be more common in metazoans than previously recognized. 

The standard latitudinal diversity gradient (LDG), in which species richness decreases from equator to pole, is a pervasive pattern observed in most organisms. Some lineages, however, exhibit inverse LDGs. Seemingly problematic, documenting and studying contrarian groups can advance understanding of LDGs generally. Here, we identify one such contrarian clade and use a historical approach to evaluate alternative hypotheses that might explain the group's atypical diversity pattern. We focus on the biogeographical conservatism hypothesis (BCH) and the diversification rate hypothesis (DRH).

Global.

Ants (Hymenoptera: Formicidae: Stenammini).

We examined the shape of the LDG in Stenammini by plotting latitudinal midpoints for all extant, described species. We inferred a robust genome‐scale phylogeny using UCE data. We estimated divergence dates using beast2 and tested several biogeographical models inBioGeoBEARS. To examine diversification rates and test for a correlation between rate and latitude, we used the programs BAMM and STRAPP, respectively.

Stenammini has a skewed inverse LDG with a richness peak in the northern temperate zone. Phylogenomic analyses revealed five major clades and several instances of non‐monophyly among genera (Goniomma,Aphaenogaster). Stenammini and all its major lineages arose in the northern temperate zone. The tribe originated ~51 Ma during a climatic optimum and then diversified and dispersed southward as global climate cooled. Stenammini invaded the tropics at least seven times, but these events occurred more recently and were not linked with increased diversification. There is evidence for a diversification rate increase in HolarcticAphaenogaster + Messor, but we found no significant correlation between latitude and diversification rate generally.

Our results largely support the BCH as an explanation for the inverse latitudinal gradient in Stenammini. The clade originated in the Holarctic and likely became more diverse there due to center‐of‐origin, time‐for‐speciation and niche conservatism effects, rather than latitudinal differences in diversification rate.