The Architecture of Species Interactions

Symbioses span the tree of life and impact human health in myriad ways—both beneficial and harmful. Understanding how these interactions originate during evolution is invaluable to how we approach them biomedically. Yet, knowledge of how symbiotic lifestyles evolve at the molecular and cellular levels is scarce. Our work has harnessed a virtuoso group of organisms to break open basic questions on the origin and evolution of interspecies relationships. Rove beetles (Staphylinidae) are a species-rich clade in which numerous of lineages have evolved from free-living organisms into highly specialized symbionts that obligately depend on ant colonies. The high frequency of transitions from free living to symbiotic creates a unique and powerful system to retrace key evolutionary steps leading to a complex but stereotyped form of symbiosis. The symbiotic transition involves dramatic changes in chemical biosynthesis and behavior that assimilate the beetle into the ant society. Through comparisons between model free-living and symbiotic species, this proposal will uncover how changes in these beetle's genomes, biosynthetic pathways, cell types and nervous systems can transform a free-living organism into an obligate symbiont that is entrenched within its host's biology. Our research falls into four connected areas: 1) the evolution of cellular and biochemical innovations that have enabled rove beetles to interact chemically with ants—defensively in free living species, and though chemical manipulation of ant behavior in symbiotic species; 2) the cellular basis for the symbiotic integration of rove beetles inside host colonies through evolutionary changes in mechanisms of pheromonal biosynthesis, and via chemosensory mechanisms of host finding and recognition; 3) the genetic basis for the irreversibility of symbiotic evolution via epistatic interactions between symbiotic traits that entrench the symbiosis; 4) reconstituting symbiotic evolution via genetically engineering the free-living rove beetle phenotype, to test how critical changes unlock the ant colony niche and facilitate the transition to host dependence. This proposal will be foundational for understanding the evolutionary trajectory of symbiotic lineages, from the conditions that predispose them to form nascent interactions with other species, to the evolutionary path of specialization leading to obligate host dependence. Project Number: 1R35GM164058-01 | Fiscal Year: 2026 | NIH Institute/Center: National Institute of General Medical Sciences (NIGMS) | Principal Investigator: JOSEPH PARKER | Institution: CALIFORNIA INSTITUTE OF TECHNOLOGY, PASADENA, CA | Award Amount: $467,500 | Activity Code: R35 | Study Section: Special Emphasis Panel[ZRG1 MGG-D (55)] View on NIH RePORTER: https://reporter.nih.gov/project-details/11331709