title: By their own devices: invasive Argentine ants have shifted diet without clear aid from symbiotic microbes.
abstract: The functions and compositions of symbiotic bacterial communities often correlate with host ecology. Yet cause-effect relationships and the order of symbiont vs. host change remain unclear in the face of ancient symbioses and conserved host ecology. Several groups of ants exemplify this challenge, as their low-nitrogen diets and specialized symbioses appear conserved and ancient. To address whether nitrogen-provisioning symbionts might be important in the early stages of ant trophic shifts, we studied bacteria from the Argentine ant, Linepithema humile - an invasive species that has transitioned towards greater consumption of sugar-rich, nitrogen-poor foods in parts of its introduced range. Bacteria were present at low densities in most L. humile workers, and among those yielding quality 16S rRNA amplicon sequencing data, we found just three symbionts to be common and dominant. Two, a Lactobacillus and an Acetobacteraceae species, were shared between native and introduced populations. The other, a Rickettsia, was found only in two introduced supercolonies. Across an eight-year period of trophic reduction in one introduced population, we found no change in symbionts, arguing against a relationship between natural dietary change and microbiome composition. Overall, our findings thus argue against major changes in symbiotic bacteria in association with the invasion and trophic shift of L. humile. In addition, genome content from close relatives of the identified symbionts suggests that just one can synthesize most essential amino acids; this bacterium was only modestly abundant in introduced populations, providing little support for a major role of nitrogen-provisioning symbioses in Argentine ant's dietary shift.
authors.affiliation: Department of Biology, Drexel University, Philadelphia, PA, 19104, USA.
authors.forename: Yi
authors.identifier: http://orcid.org/0000-0002-1086-2072
authors.initials: Y
authors.lastname: Hu
authors.affiliation: Division of Biological Sciences, University of California-San Diego, La Jolla, CA, 92093, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Holway
authors.affiliation: Department of Biology, Drexel University, Philadelphia, PA, 19104, USA.
authors.forename: Piotr
authors.initials: P
authors.lastname: Łukasik
authors.affiliation: Department of Biology, Drexel University, Philadelphia, PA, 19104, USA.
authors.forename: Linh
authors.initials: L
authors.lastname: Chau
authors.affiliation: Department of Biology, University of St. Thomas, St. Paul, MN, 55105, USA.
authors.forename: Adam D
authors.initials: AD
authors.lastname: Kay
authors.affiliation: Department of Integrative Biology, The University of Texas at Austin, Austin, TX, 78703, USA.
authors.forename: Edward G
authors.initials: EG
authors.lastname: LeBrun
authors.affiliation: Department of Biology, University of St. Thomas, St. Paul, MN, 55105, USA.
authors.forename: Katie A
authors.initials: KA
authors.lastname: Miller
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, 02138, USA.
authors.forename: Jon G
authors.initials: JG
authors.lastname: Sanders
authors.affiliation: Department of Animal Biology, University of Illinois Urbana-Champaign, Urbana, IL, 61801, USA.
authors.forename: Andrew V
authors.initials: AV
authors.lastname: Suarez
authors.affiliation: Department of Biology, Drexel University, Philadelphia, PA, 19104, USA.
authors.forename: Jacob A
authors.initials: JA
authors.lastname: Russell
mesh_terms: D000818:Animals; D001000:Ants / Q000382:microbiology* / Q000502:physiology; D001118:Argentina; D001419:Bacteria / Q000145:classification*; D004032:Diet; D005247:Feeding Behavior; D058865:Introduced Species; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D013559:Symbiosis
chemical_list: D012336:RNA, Ribosomal, 16S
keywords: insects; microbial biology; next-generation sequencing; symbiosis