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Fungus-growing attine ants rely on an obligatory nutritional mutualism with fungi. Most attine ant genera cultivate fungi in the basidiomycete tribe Leucocoprineae (Agaricales: Agaricaceae). Although fungal partners show high genetic diversity, only two fungal species cultivated by leaf-cutting ants were formerly described. This is partly due to the lack of sexual structures (basidiomata) which are rarely formed in ant colonies. Moreover, basidiomata from leucocoprinaceous fungi grown by lower attines have not been observed in field colonies, but only when induced in artificial media in the absence of the ants. Here, we obtained basidiomata growing on oatmeal agar from fungal cultivars of Mycocepurus goeldii and Mycetophylax morschi, two lower attine ant species found in different biomes in Brazil. Morphological and phylogenetic analyses allowed us to describe two new species, Leucocoprinus attinorum from M. goeldii and Lc. dunensis from M. morschi. The new descriptions are the first to set formal names for Leucocoprineae fungi cultivated by lower attines and highlight the importance of in vitro cultures as a tool to assess the largely hidden taxonomic diversity of mushroom species grown by these attines. [ABSTRACT FROM AUTHOR]

Leaf‐cutting ants and their fungal crops are a textbook example of a long‐term obligatory mutualism. Many microbes continuously enter their nest containing the fungal cultivars, destabilizing the symbiosis and, in some cases, outcompeting the mutualistic partners. Preferably, the ant workers should distinguish between different microorganisms to respond according to their threat level and recurrence in the colony. To address these assumptions, we investigated how workers of Atta sexdens sanitize their fungal crop toward five different fungi commonly isolated from the fungus gardens: Escovopsis sp., Fusarium oxysporum, Metarhizium anisopliae, Trichoderma spirale, and Syncephalastrum sp. Also, to investigate the plasticity of these responses toward recurrences of these fungi, we exposed the colonies with each fungus three times fourteen days apart. As expected, intensities in sanitization differed according to the fungal species. Ants significantly groom their fungal crop more toward F. oxysporum, M. anisopliae, and Syncephalastrum sp. than toward Escovopsis sp. and T. spirale. Weeding, self‐, and allogrooming were observed in less frequency than fungus grooming in all cases. Moreover, we detected a significant increase in the overall responses after repeated exposures for each fungus, except for Escovopsis sp. Our results indicate that A. sexdens workers are able to distinguish between different fungi and apply distinct responses to remove these from the fungus gardens. Our findings also suggest that successive exposures to the same antagonist increase hygiene, indicating plasticity of ant colonies' defenses to previously encountered pathogens. [ABSTRACT FROM AUTHOR]

Maintaining symbiosis homeostasis is essential for mutualistic partners. Leaf-cutting ants evolved a long-term symbiotic mutualism with fungal cultivars for nourishment while using vertical asexual transmission across generations. Despite the ants’ efforts to suppress fungal sexual reproduction, scattered occurrences of cultivar basidiomes have been reported. Here, we review the literature for basidiome occurrences and associated climate data. We hypothesized that more basidiome events could be expected in scenarios with an increase in temperature and precipitation. Our field observations and climate data analyses indeed suggest that Acromyrmex coronatus colonies are prone to basidiome occurrences in warmer and wetter seasons. Even though our study partly depended on historical records, occurrences have increased, correlating with climate change. A nest architecture with low (or even the lack of) insulation might be the cause of this phenomenon. The nature of basidiome occurrences in the A. coronatus–fungus mutualism can be useful to elucidate how resilient mutualistic symbioses are in light of climate change scenarios. [ABSTRACT FROM AUTHOR]

Plant and animal community composition changes at higher elevations on mountains. Plant and animal species richness generally declines with elevation, but the shape of the relationship differs between taxa. There are several proposed mechanisms, including the productivity hypotheses; that declines in available plant biomass confers fewer resources to consumers, thus supporting fewer species. We investigated resource availability as we ascended three aspects of Helvellyn mountain, UK, measuring several plant nutritive metrics, plant species richness and biomass. We observed a linear decline in plant species richness as we ascended the mountain but there was a unimodal relationship between plant biomass and elevation. Generally, the highest biomass values at mid-elevations were associated with the lowest nutritive values, except mineral contents which declined with elevation. Intra-specific and inter-specific increases in nutritive values nearer the top and bottom of the mountain indicated that physiological, phenological and compositional mechanisms may have played a role. The shape of the relationship between resource availability and elevation was different depending on the metric. Many consumers actively select or avoid plants based on their nutritive values and the abundances of consumer taxa vary in their relationships with elevation. Consideration of multiple nutritive metrics and of the nutritional requirements of the consumer may provide a greater understanding of changes to plant and animal communities at higher elevations. We propose a novel hypothesis for explaining elevational diversity gradients, which warrants further study; the 'nutritional complexity hypothesis', where consumer species coexist due to greater variation in the nutritional chemistry of plants. [ABSTRACT FROM AUTHOR]

Each day, as the amount of genomic data and bioinformatics resources grows, researchers are increasingly challenged with selecting the most appropriate approach to analyze their data. In addition, the opportunity to undertake comparative genomic analyses is growing rapidly. This is especially true for fungi due to their small genome sizes (i.e. mean 1C = 44.2 Mb). Given these opportunities and aiming to gain novel insights into the evolution of mutualisms, we focus on comparing the quality of whole genome assemblies for fungus-growing ants cultivars (Hymenoptera: Formicidae: Attini) and a free-living relative. Our analyses reveal that currently available methodologies and pipelines for analyzing whole-genome sequence data need refining. By using different genome assemblers, we show that the genome assembly size depends on what software is used. This, in turn, impacts gene number predictions, with higher gene numbers correlating positively with genome assembly size. Furthermore, the majority of fungal genome size data currently available are based on estimates derived from whole-genome assemblies generated from short-read genome data, rather than from the more accurate technique of flow cytometry. Here, we estimated the haploid genome sizes of three ant fungal symbionts by flow cytometry using the fungus Pleurotus ostreatus (Jacq.) P. Kumm. (1871) as a calibration standard. We found that published genome sizes based on genome assemblies are 2.5- to 3-fold larger than our estimates based on flow cytometry. We, therefore, recommend that flow cytometry is used to precalibrate genome assembly pipelines, to avoid incorrect estimates of genome sizes and ensure robust assemblies. [ABSTRACT FROM AUTHOR]

In this study, we document and describe the new Cortinarius section Austroamericani. Our results reveal high species diversity within this clade, with a total of 12 recognized species. Of these, only C. rufus was previously documented. Seven species are described as new based on basidiomata collections. The four remaining species are only known from environmental sequences. All examined species form ectomycorrhizal associations with species of Nothofagaceae and are currently only known from Argentinean and Chilean Patagonia. The phylogenetic analysis based on the nuc rDNA internal transcriber spacer (ITS1-5.8S-ITS2 = ITS) and partial 28S gene (28S) sequences shows that this section is related to other taxa from the Southern Hemisphere. Species in this group do not belong to subg. Telamonia, where C. rufus was initially placed. Cortinarius rufus and the newly described C. subrufus form a basal clade within sect. Austroamericani that has a weakly supported relationship with the core clade. Because the two species are morphologically similar to species from the core clade and share their distribution and Nothofagaceae associations, we include them here as part of sect. Austroamericani sensu lato (s.l.) until more material is available to refine the delimitation. [ABSTRACT FROM AUTHOR]

Attine ants evolved farming 55-60 My before humans. Although evolutionarily derived leafcutter ants achieved industrial-scale farming, extant species from basal attine genera continue to farm loosely domesticated fungal cultivars capable of pursuing independent reproductive interests. We used feeding experiments with the basal attine Mycocepurus smithii to test whether reproductive allocation conflicts between farmers and cultivars constrain crop yield, possibly explaining why their mutualism has remained limited in scale and productivity. Stoichiometric and geometric framework approaches showed that carbohydrate-rich substrates maximize growth of both edible hyphae and inedible mushrooms, but that modest protein provisioning can suppress mushroom formation. Worker foraging was consistent with maximizing long-term cultivar performance: ant farmers could neither increase carbohydrate provisioning without cultivars allocating the excess toward mushroom production, nor increase protein provisioning without compromising somatic cultivar growth. Our results confirm that phylogenetically basal attine farming has been very successful over evolutionary time, but that unresolved host-symbiont conflict may have precluded these wildtype symbioses from rising to ecological dominance. That status was achieved by the evolutionarily derived leafcutter ants following full domestication of a coevolving cultivar 30-35 Mya after the first attine ants committed to farming. [ABSTRACT FROM AUTHOR]

Background: Xyloglucan is an important component in plant cell walls that herbivores cannot digest without microbial symbionts. Leaf-cutting ants are major insect herbivores in the Neo-Tropics that rely on fungus-garden enzymes for degrading plant cell walls. However, many of these ants discard much of their harvested plant material after partial degradation, which has led to the hypothesis that the fungal symbionts are primarily producing cell wall degrading enzymes to gain access to intracellular nutrients rather than for obtaining sugars from recalcitrant cell wall polymers, such as (hemi-)cellulose. Results: The fungal symbiont provides a single xyloglucanase (Xeg1) to its ant farmers by upregulating the expression of this protein in the inflated hyphal tips (gongylidia) that the ants ingest. Similar to other enzymes ingested this way, also Xeg1 is not digested but vectored to the fresh leaf-fragment pulp at the top of fungus gardens via ant fecal fluid. Xeg1 is 4-5 times more active in fecal fluid when ants ingest their normal fungal food, compared to a sucrose control diet, as expected when they cannot produce Xeg1 themselves. We confirm substrate specificity of fungal Xeg1 towards xyloglucan by heterologous expression in yeast and show that xyloglucanase activity is higher in the oldest, bottom layers of fungus gardens and in discarded debris material than in the upper and middle layers of fungus gardens. Conclusion: Our results are consistent with Xeg1 playing a role in the initial breakdown of plant cell wall hemicellulose to provide sugars for aggressive hyphal growth before intracellular proteins become available. Xeg1 does not play a major decomposition role in the middle layer of fungus gardens where it is produced by the gongylidia. Overall high xyloglucanase activity in old mycelium that is (about to be) discarded is striking and quite possibly serves defensive purposes by precluding that competing microorganisms can grow. Our results support the hypothesis that the ant-fungus symbiosis prioritizes access to the protein-rich contents of live plant cells and that carbohydrates are not a limiting resource. [ABSTRACT FROM AUTHOR]

The mutualism between leaf-cutting ants and their fungal symbionts revolves around processing and inoculation of fresh leaf pulp in underground fungus gardens, mediated by ant fecal fluid deposited on the newly added plant substrate. As herbivorous feeding often implies that growth is nitrogen limited, we cloned and sequenced six fungal proteases found in the fecal fluid of the leaf-cutting ant Acromyrmex echinatior and identified them as two metalloendoproteases, two serine proteases and two aspartic proteases. The metalloendoproteases and serine proteases showed significant activity in fecal fluid at pH values of 5-7, but the aspartic proteases were inactive across a pH range of 3-10. Protease activity disappeared when the ants were kept on a sugar water diet without fungus. Relative to normal mycelium, both metalloendoproteases, both serine proteases and one aspartic protease were upregulated in the gongylidia, specialized hyphal tips whose only known function is to provide food to the ants. These combined results indicate that the enzymes are derived from the ingested fungal tissues. We infer that the five proteases are likely to accelerate protein extraction from plant cells in the leaf pulp that the ants add to the fungus garden, but regulatory functions such as activation of proenzymes are also possible, particularly for the aspartic proteases that were present but without showing activity. The proteases had high sequence similarities to proteolytic enzymes of phytopathogenic fungi, consistent with previous indications of convergent evolution of decomposition enzymes in attine ant fungal symbionts and phytopathogenic fungi. [ABSTRACT FROM AUTHOR]

The genera Atta and Acromyrmex are often grouped as leaf-cutting ants for pest management assessments and ecological surveys, although their mature colony sizes and foraging niches may differ substantially. Few studies have addressed such interspecific differences at the same site, which prompted us to conduct a comparative study across six sympatric leaf-cutting ant species in Central Panama. We show that foraging rates during the transition between dry and wet season differ about 60 fold between genera, but are relatively constant across species within genera. These differences appear to match overall differences in colony size, especially when Atta workers that return to their nests without leaves are assumed to carry liquid food. We confirm that Panamanian Atta specialize primarily on tree-leaves whereas Acromyrmex focus on collecting flowers and herbal leaves and that species within genera are similar in these overall foraging strategies. Species within genera tended to be spaced out over the three habitat categories that we distinguished (forest, forest edge, open grassland), but each of these habitats normally had only a single predominant Atta and Acromyrmex species. We measured activities of twelve fungus garden decomposition enzymes, belonging to the amylases, cellulases, hemicellulases, pectinases and proteinases, and show that average enzyme activity per unit of fungal mass in Atta gardens is lower than in Acromyrmex gardens. Expression profiles of fungal enzymes in Atta also appeared to be more specialized than in Acromyrmex, possibly reflecting variation in forage material. Our results suggest that species- and genus-level identities of leaf-cutting ants and habitat-specific foraging profiles may give predictable differences in the expression of fungal genes coding for decomposition enzymes. [ABSTRACT FROM AUTHOR]

Leaf-cutting ants are often considered agricultural pests, but they can also benefit local people and serve important roles in ecosystems. Throughout their distribution, winged reproductive queens of leaf-cutting ants in the genus Atta Fabricius, 1804 are consumed as a protein-rich food source and sometimes used for medical purposes. Little is known, however, about the species identity of collected ants and the accuracy of identification when ants are sold, ambiguities that may impact the conservation status of Atta species as well as the nutritional value that they provide to consumers. Here, 21 samples of fried ants bought in San Gil, Colombia, were identified to species level using Cytochrome Oxidase I (COI) barcoding sequences. DNA was extracted from these fried samples using standard Chelex extraction methods, followed by phylogenetic analyses with an additional 52 new sequences from wild ant colonies collected in Panama and 251 publicly available sequences. Most analysed samples corresponded to Atta laevigata (Smith, 1858), even though one sample was identified as Atta colombica Guérin-Méneville, 1844 and another one formed a distinct branch on its own, more closely related to Atta texana (Buckley, 1860) and Atta mexicana (Smith, 1858). Analyses further confirm paraphyly within Atta sexdens (Linnaeus, 1758) and A. laevigata clades. Further research is needed to assess the nutritional value of the different species. [ABSTRACT FROM AUTHOR]