title: Interaction between workers during a short time window is required for bacterial symbiont transmission in Acromyrmex leaf-cutting ants.
abstract: Stable associations between partners over time are critical for the evolution of mutualism. Hosts employ a variety of mechanisms to maintain specificity with bacterial associates. Acromyrmex leaf-cutting ants farm a fungal cultivar as their primary nutrient source. These ants also carry a Pseudonocardia Actinobacteria exosymbiont on their bodies that produces antifungal compounds that help inhibit specialized parasites of the ants' fungal garden. Major workers emerge from their pupal cases (eclose) symbiont-free, but exhibit visible Actinobacterial coverage within 14 days post-eclosion. Using subcolony experiments, we investigate exosymbiont transmission within Acromyrmex colonies. We found successful transmission to newly eclosed major workers fostered by major workers with visible Actinobacteria in all cases (100% acquiring, n = 19). In contrast, newly eclosed major workers reared without exosymbiont-carrying major workers did not acquire visible Actinobacteria (0% acquiring, n = 73). We further show that the majority of ants exposed to major workers with exosymbionts within 2 hours of eclosion acquired bacteria (60.7% acquiring, n = 28), while normal acquisition did not occur when exposure occurred later than 2 hours post-eclosion (0% acquiring, n = 18). Our findings show that transmission of exosymbionts to newly eclosed major workers occurs through interactions with exosymbiont-covered workers within a narrow time window after eclosion. This mode of transmission likely helps ensure the defensive function within colonies, as well as specificity and partner fidelity in the ant-bacterium association.
authors: Department of Bacteriology, University of Wisconsin, Madison, Wisconsin, United States of America.
authors: Sarah E
authors: SE
authors: Marsh
authors: Department of Bacteriology, University of Wisconsin, Madison, Wisconsin, United States of America.
authors: Michael
authors: M
authors: Poulsen
authors: Departamento de Bioquímica, Facultad de Medicina, Universidad de Costa Rica, San Pedro de Montes de Oca, San José, Costa Rica; Centro de Investigación en Estructuras Microscópicas, Universidad de Costa Rica, San Pedro de Montes de Oca, San José, Costa Rica.
authors: Adrián
authors: A
authors: Pinto-Tomás
authors: Department of Bacteriology, University of Wisconsin, Madison, Wisconsin, United States of America; U.S. Department of Energy Great Lakes Bioenergy Research Center, University of Wisconsin, Madison, Wisconsin, United States of America.
authors: Cameron R
authors: CR
authors: Currie
mesh_terms: D039903:Actinobacteria / Q000145:classification / Q000235:genetics; D000192:Actinomycetales / Q000145:classification / Q000235:genetics / Q000502:physiology*; D000819:Animal Communication; D000818:Animals; D001000:Ants / Q000382:microbiology* / Q000502:physiology*; D058507:Host Specificity / Q000235:genetics; D010802:Phylogeny; D018515:Plant Leaves; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D017422:Sequence Analysis, DNA; D013045:Species Specificity; D013559:Symbiosis / Q000235:genetics; D013997:Time Factors
chemical_list: D012336:RNA, Ribosomal, 16S