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1. Enforced specificity of an entrenched symbiosis

   https://doi.org/10.1016/j.cub.2025.10.066  

   Wagner, Julian M; Wong, Jason H; Millar, Jocelyn G; Haxhimali, Enes; Brückner, Adrian; Naragon, Thomas H; Boedicker, James Q; Parker, Joseph (December 2025, Current Biology)

   The Metazoa encompasses inordinate lineages of symbionts and ecological specialists that obligately depend on particular hosts. The maintenance and fidelity of these lifestyles are often posited to hinge on sensory tuning to host-derived cues, a paradigm supported by studies of neural function in host-specific models. We experimentally reconstituted a socially complex relationship between an obligately symbiotic rove beetle and its single, natural host ant species, permitting us to probe its sensory basis. We show that cuticular hydrocarbons—the ant’s nestmate recognition pheromones—elicit host recognition by the beetle and the execution of ant grooming behavior, enabling the beetle to chemically mimic its host and infiltrate the nest as a parasitic impostor. The beetle also follows host trail pheromones, permitting inter-colony dispersal. Yet the beetle also performs these symbiotic behaviors with non-host ants separated by up to ∼95 million years, is able to socially assimilate into their colonies, and shows minimal sensory preference for its natural host over non-host species. Agent-based modeling reveals that the specificity of the beetle emerges not from sensory tuning but from physiological limits on dispersal and negative fitness interactions with alternative hosts, constraining the otherwise promiscuous beetle to its natural host. Recreating the in silico model with living insects empirically demonstrates specificity arising from these enforcing barriers. Our findings show how entrenched symbioses can obviate selection for taxonomically precise host recognition, with specificity emerging from forces external to the symbiont. Chance realization of latent compatibilities with alternative hosts may facilitate host switching, explaining the diversification and deep-time success of such taxa. 

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2. Symbiotic entrenchment through ecological Catch-22

   https://doi.org/10.1016/j.cell.2025.12.041  

   Naragon, Thomas H; Viliunas, Joani W; Yousefelahiyeh, Mina; Brückner, Adrian; Wagner, Julian M; Okamoto, K Esther; Ryon, Hannah M; Collinson, Danny; Kitchen, Sheila A; Wijker, Reto S; et al (February 2026, Cell)

   Why symbiotic organisms evolve irreversible dependencies on hosts is an outstanding question. We report a biological stealth device in a beetle that permits infiltration of ant societies. Via transcriptional silencing, the beetle switches off biosynthesis of cuticular hydrocarbons (CHCs)—body surface pheromones that function pleiotropically as a waxy desiccation barrier. Silencing transforms the beetle into a chemical blank slate onto which ant CHCs are transferred via grooming behavior, leading to perfect chemical mimicry and acceptance into the colony. Silencing is irreversible, however, forcing the beetle into a chronic dependence on ants to both maintain mimicry and prevent desiccation. We show that evolutionary reversion of the silencing mechanism would render the beetle detectable to ants; conversely, reversion of the beetle’s attraction to ants would render it desiccation prone. Symbiotic entrenchment can thus arise from epistasis between symbiotic traits, locking lineages into a Catch-22 that obstructs reversion to living freely. 

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3. Bacterial communities of fungus-growing ant queens are species-specific and suggest vertical transmission

   https://doi.org/10.1371/journal.pone.0306011  

   Sadowski, Victoria A; Sapountzis, Panagiotis; Kooij, Pepijn W; Boomsma, Jacobus J; Adams, Rachelle_M M (October 2025, PLOS One)

   Chaline, Nicolas (Ed.)

   Multipartite symbioses are inherently complex, involving dynamic ecological interactions between organisms with intertwined yet distinct evolutionary histories. The fungus-growing (attine) ants facilitate maintenance of a symbiotic species network through maternal vertical transmission of a fungal symbiont. While the gut microbiomes of fungus-growing ant species are remarkably simple, their fungus gardens support diverse microbial communities. Here, we focus on the garden pellet stored in the nest-founding queen’s infrabuccal pocket—a food filter in the head that allows ants to expel large particles. The pellet is an inoculate of the new fungal garden but also contains other microbes. We used 16S rRNA gene amplicon sequencing to reconstruct the extent of vertical transmission of bacteria to new gardens via queen pellets in four sympatric fungus-growing ant species from Central Panama (Atta sexdens,Atta cephalotes,Acromyrmex echinatior,andMycetomoellerius mikromelanos). We also characterized the bacterial communities associated with queen eggs and tissues (mesosomas, guts and ovaries) to assess whether queens are likely to transmit symbiotic bacteria, such as cuticular Actinomycetota and endosymbionts (Wolbachia,Mesoplasma, andSpiroplasma). We made within and between species comparisons, focusing on three hypotheses: (H1) Queens vertically transmit garden-associated bacteria in the garden pellet. (H2) Fungus-growing ant-associated bacteria are maintained through vertical transmission by queens. (H3) Vertically transmitted bacterial communities have host ant species-specificity. While we found mixed evidence for vertical transmission of garden bacteria, our results support maternal transmission as an important route for ant-associated symbionts. The ant species-specificity we see in queen bacterial microbiota mirrors patterns of known symbiont presence in workers from previous studies. Overall, our results suggest that vertical transmission of bacterial associates is mediated by the ant hosts, however the mechanism behind bacterial acquisition before a mating flight and dispersal is not yet understood. 

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4. Non-reciprocal coevolution in a fungus-gardening ant

   https://doi.org/10.1016/j.ympev.2026.108608  

   Beigel, Katherine; Bringhurst, Blake; Greenwold, Matthew; Kellner, Katrin; Seal, Jon N (July 2026, Molecular Phylogenetics and Evolution)

   Symbioses are often characterized by nonrandom associations between hosts and symbionts. Hosts may obtain symbionts horizontally from the environment or vertically from a parent or sometimes use both methods. Macroevolutionary examinations of fungus-gardening ants and their fungi have shown either a 1:1 coevolution model or a ‘diffuse’ model between ant host and fungal symbionts. However, some of these conclusions may have been based on using relatively conservative molecular markers, which could obscure cryptic variation. The use of whole genome approaches potentially offer more power in elucidating coevolutionary history. In this study, we examined patterns of coevolution in a single species (Trachymyrmex septentrionalis) using genomic and experimental approaches. We tested whether ant-fungal specificity patterns reflected either 1:1 or diffuse models of coevolution. While we report significant co-phylogenetic signal among intraspecific ant host and fungal symbiont lineages, we found evidence of 1:1 coevolution in some lineages and diffuse in others. These conclusions were supported by the results of experiments where newly mated T. septentrionalis queens were forced to grow novel fungi that suggested that not all fungi are equivalent symbionts and would require specialized hosts. Thus, within a single ant species, there is a mixed support for both models. 

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5. Genomic insights into the evolution of secondary metabolism of Escovopsis and its allies, specialized fungal symbionts of fungus-farming ants

   https://doi.org/10.1128/msystems.00576-24  

   Berasategui, Aileen; Salem, Hassan; Moller, Abraham G; Christopher, Yuliana; Vidaurre_Montoya, Quimi; Conn, Caitlin; Read, Timothy D; Rodrigues, Andre; Ziemert, Nadine; Gerardo, Nicole (July 2024, mSystems)

   The metabolic intimacy of symbiosis often demands the work of specialists. Natural products and defensive secondary metabolites can drive specificity by ensuring infection and propagation across host generations. But in contrast to bacteria, little is known about the diversity and distribution of natural product biosynthetic pathways among fungi and how they evolve to facilitate symbiosis and adaptation to their host environment. In this study, we define the secondary metabolism of Escovopsis and closely related genera, symbionts in the gardens of fungus-farming ants. We ask how the gain and loss of various biosynthetic pathways correspond to divergent lifestyles. Long-read sequencing allowed us to define the chromosomal features of representative Escovopsis strains, revealing highly reduced genomes composed of seven to eight chromosomes. The genomes are highly syntenic with macrosynteny decreasing with increasing phylogenetic distance, while maintaining a high degree of mesosynteny. An ancestral state reconstruction analysis of biosynthetic pathways revealed that, while many secondary metabolites are shared with non-ant-associated Sordariomycetes, 56 pathways are unique to the symbiotic genera. Reflecting adaptation to diverging ant agricultural systems, we observe that the stepwise acquisition of these pathways mirrors the ecological radiations of attine ants and the dynamic recruitment and replacement of their fungal cultivars. As different clades encode characteristic combinations of biosynthetic gene clusters, these delineating profiles provide important insights into the possible mechanisms underlying specificity between these symbionts and their fungal hosts. Collectively, our findings shed light on the evolutionary dynamic nature of secondary metabolism in Escovopsis and its allies, reflecting adaptation of the symbionts to an ancient agricultural system.Microbial symbionts interact with their hosts and competitors through a remarkable array of secondary metabolites and natural products. Here, we highlight the highly streamlined genomic features of attine-associated fungal symbionts. The genomes of Escovopsis species, as well as species from other symbiont genera, many of which are common with the gardens of fungus-growing ants, are defined by seven chromosomes. Despite a high degree of metabolic conservation, we observe some variation in the symbionts’ potential to produce secondary metabolites. As the phylogenetic distribution of the encoding biosynthetic gene clusters coincides with attine transitions in agricultural systems, we highlight the likely role of these metabolites in mediating adaptation by a group of highly specialized symbionts. 

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