Fernandez-Marin, H. | bioRxiv Science

bioRxiv2026

Atta Leafcutter Ants are Fine-Scale Bioindicators of Geographic and Seasonal Climate Changes Across the Americas

AimWe develop Atta leafcutter-ants as bioindicators that respond at fine scales to geographic and seasonal climate changes in the Americas, thereby addressing the paucity of versatile insect bioindicator systems capable of monitoring climate in both Southern and Northern Hemispheres. LocationAmerican tropics and sub-tropics from latitudes S33.6{degrees} to N33.2{degrees}, with case studies from Colombia, Mexico, and southern USA. Time Period2012-2024. Taxon StudiedAtta leafcutter-ants. MethodsWe elucidate biogeographic patterns of mating-flight phenology of Atta leafcutter-ants across the entire Atta range from Uruguay/Argentina to the USA, using 2335 records of Atta reproductives from the community database iNaturalist, then ground-truth these patterns by comparison with (i) mating-flight records (n=806) from the Atta literature; and (ii) mating-flight observations (n=836) accumulated by a consortium of experts who have researched Atta for a combined 1000+ work-years. Onset of mating flights can be timed with great precision in Atta populations because mass-mating flights are synchronized and triggered by the first major rainfall of a rainy season. ResultsBiogeographic patterns in climate-dependent mating-flight phenologies recorded at iNaturalist are corroborated by observations accumulated in the literature and by Atta experts. Analyses reveal so-far unknown gradients in mating-flight phenology (e.g., Colombia to USA) that are correlated to geographic climate gradients, and season switches of mating flights from early to late in the year between proximate Atta populations (e.g., 200 kilometers apart), for example in the climatically complex Andean regions of Colombia. Regional differences in Atta mating-flight phenology correspond to temporal differences in rainfall between ecoregions of Colombia. Main ConclusionsAtta ants are tractable insect bioindicators to monitor climate impacts with detailed spatial and temporal resolution across a 9200-kilometer trans-equatorial transect in the Americas. We outline future research directions to explore climate-dependent biology using the continuously growing, and now ground-truthed, information at iNaturalist on Atta mating behavior.

ecology↗

bioRxiv2025

Comparative genomics of Sympodiorosea identifies genome evolution mediated through selective pressure on the metabolic gene repertoire

Biological interactions involving host-associated fungi are manifestations of chemistry shaped over evolutionary time. For antagonistic fungi, specialization to host fungi is often facilitated through the acquisition of genes encoding novel secretions, including proteins and specialized metabolites that shape interactions with host defenses, as well the acquisition of nutrients. Alternatively, novel function may arise from diversifying selection eliciting evolutionary innovation in inert secretions. Through specialization, fungal metabolic capacity can serve as an imprint of the selective forces imposed on the antagonist and provide insights into its natural history and occupied niche. Here, we conduct a phylogenomic investigation of antagonistic ascomycetes in the genus Sympodiorosea, which are commonly found in basal fungus-growing ant gardens. Sympodiorosea and closely related genera of Escovopsis, Luteomyces, and Escovopsioides are canonically referenced as virulent mycoparasites, however, recent work has illuminated the possibility for diverse, non-virulent species to emerge within these attine-associated fungi. We explored genomic variation in Sympodiorosea to gain insight into the genomic potential for alternative lifestyles, focusing on diversity and evolution of metabolic genes. Our study revealed a constrained selective landscape across the Sympodiorosea genome. However, outcomes of in vitro interactions with host fungi are diverse and predictable based on the antagonists ant-species-of-origin, suggesting functional diversification. Phylogenomics reveals that gain/loss events of genes involved in secretions (secretome) are potential drivers of diversification. Additionally, we demonstrate that purifying selection acts more intensely on secretome-related genes relative to other genes. In contrast, few genes from the secretome experience diversifying selection, suggesting a mechanistic role for driving both functional differences between strains and host-specialization. Comparative genomics including other fungi within the family Hypocreales reveals that Sympodiorosea has experienced expansions and contractions in proteases genes that are discordant from expectations under a strictly mycoparasitic lifestyle, indicating either the potential for an alternative lifestyle within ant gardens, or that Sympodiorosea recently evolved from other niches. These results provide novel insight into genomic evolution of these fungi and inform future experimental studies of the ecology and chemistry of interactions within the complex fungus-growing ant symbiosis.

evolutionary biology↗