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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]

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]

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]