Search for: All records

Very high tropical alpine ice cores provide a distinct paleoclimate record for climate changes in the middle and upper troposphere. However, the climatic interpretation of a key proxy, the stable water oxygen isotopic ratio in ice cores (δ¹⁸O_ice), remains an outstanding problem. Here, combining proxy records with climate models, modern satellite measurements, and radiative-convective equilibrium theory, we show that the tropical δ¹⁸O_iceis an indicator of the temperature of the middle and upper troposphere, with a glacial cooling of −7.35° ± 1.1°C (66% CI). Moreover, it severs as a “Goldilocks-type” indicator of global mean surface temperature change, providing the first estimate of glacial stage cooling that is independent of marine proxies as −5.9° ± 1.2°C. Combined with all estimations available gives the maximum likelihood estimate of glacial cooling as −5.85° ± 0.51°C.

 

Abstract Fungi have evolved over millions of years and their species diversity is predicted to be the second largest on the earth. Fungi have cross-kingdom interactions with many organisms that have mutually shaped their evolutionary trajectories. Zygomycete fungi hold a pivotal position in the fungal tree of life and provide important perspectives on the early evolution of fungi from aquatic to terrestrial environments. Phylogenomic analyses have found that zygomycete fungi diversified into two separate clades, the Mucoromycota which are frequently associated with plants and Zoopagomycota that are commonly animal-associated fungi. Genetic elements that contributed to the fitness and divergence of these lineages may have been shaped by the varied interactions these fungi have had with plants, animals, bacteria, and other microbes. To investigate this, we performed comparative genomic analyses of the two clades of zygomycetes in the context of Kingdom Fungi, benefiting from our generation of a new collection of zygomycete genomes, including nine produced for this study. We identified lineage-specific genomic content that may contribute to the disparate biology observed in these zygomycetes. Our findings include the discovery of undescribed diversity in CotH, a Mucormycosis pathogenicity factor, which was found in a broad set of zygomycetes. Reconciliation analysis identified multiple duplication events and an expansion of CotH copies throughout the Mucoromycotina, Mortierellomycotina, Neocallimastigomycota, and Basidiobolus lineages. A kingdom-level phylogenomic analysis also identified new evolutionary relationships within the subphyla of Mucoromycota and Zoopagomycota, including supporting the sister-clade relationship between Glomeromycotina and Mortierellomycotina and the placement of Basidiobolus as sister to other Zoopagomycota lineages. 

Anaerobic fungi and methanogenic archaea are two classes of microorganisms found in the rumen microbiome that metabolically interact during lignocellulose breakdown. Here, stable synthetic co-cultures of the anaerobic fungusCaecomyces churrovisand the methanogenMethanobacterium bryantii(not native to the rumen) were formed, demonstrating that microbes from different environments can be paired based on metabolic ties. Transcriptional and metabolic changes induced by methanogen co-culture were evaluated inC. churrovisacross a variety of substrates to identify mechanisms that impact biomass breakdown and sugar uptake. A high-quality genome ofC. churroviswas obtained and annotated, which is the first sequenced genome of a non-rhizoid-forming anaerobic fungus.C. churrovispossess an abundance of CAZymes and carbohydrate binding modules and, in agreement with previous studies of early-diverging fungal lineages, N6-methyldeoxyadenine (6mA) was associated with transcriptionally active genes. Co-culture with the methanogen increased overall transcription of CAZymes, carbohydrate binding modules, and dockerin domains in co-cultures grown on both lignocellulose and cellulose and caused upregulation of genes coding associated enzymatic machinery including carbohydrate binding modules in family 18 and dockerin domains across multiple growth substrates relative toC. churrovismonoculture. Two other fungal strains grown on a reed canary grass substrate in co-culture with the same methanogen also exhibited high log2-fold change values for upregulation of genes encoding carbohydrate binding modules in families 1 and 18. Transcriptional upregulation indicated that co-culture of theC. churrovisstrain with a methanogen may enhance pyruvate formate lyase (PFL) function for growth on xylan and fructose and production of bottleneck enzymes in sugar utilization pathways, further supporting the hypothesis that co-culture with a methanogen may enhance certain fungal metabolic functions. Upregulation of CBM18 may play a role in fungal–methanogen physical associations and fungal cell wall development and remodeling.

 

Insolation changes play an important role in driving monsoon changes at orbital time scales. One key issue that has remained outstanding is whether the Asian monsoon is driven by local insolation from the Northern Hemisphere (NH) or remote insolation from the Southern Hemisphere (SH) at orbital band. Here, we perform a set of sensitivity experiments to quantify the impacts of local and remote insolation changes on the Afro‐Asian summer monsoon at 11 ka BP relative to the present. We show that the Afro‐Asian summer monsoon is overwhelmingly driven by the precession induced local insolation change in the tropical‐subtropical NH. The insolation from NH high latitudes also affects the Afro‐Asian summer monsoon. In contrast, the insolation from SH plays a negligible role. Our model experiments support the idea that the Afro‐Asian summer monsoon are driven predominantly by the direct forcing of NH low latitudes summer insolation for the Holocene.