title: Patterns, causes and consequences of defensive microbiome dynamics across multiple scales.
abstract: The microbiome can significantly impact host phenotypes and serve as an additional source of heritable genetic variation. While patterns across eukaryotes are consistent with a role for symbiotic microbes in host macroevolution, few studies have examined symbiont-driven host evolution or the ecological implications of a dynamic microbiome across temporal, spatial or ecological scales. The pea aphid, Acyrthosiphon pisum, and its eight heritable bacterial endosymbionts have served as a model for studies on symbiosis and its potential contributions to host ecology and evolution. But we know little about the natural dynamics or ecological impacts of the heritable microbiome of this cosmopolitan insect pest. Here we report seasonal shifts in the frequencies of heritable defensive bacteria from natural pea aphid populations across two host races and geographic regions. Microbiome dynamics were consistent with symbiont responses to host-level selection and findings from one population suggested symbiont-driven adaptation to seasonally changing parasitoid pressures. Conversely, symbiont levels were negatively correlated with enemy-driven mortality when measured across host races, suggesting important ecological impacts of host race microbiome divergence. Rapid drops in symbiont frequencies following seasonal peaks suggest microbiome instability in several populations, with potentially large costs of 'superinfection' under certain environmental conditions. In summary, the realization of several laboratory-derived, a priori expectations suggests important natural impacts of defensive symbionts in host-enemy eco-evolutionary feedbacks. Yet negative findings and unanticipated correlations suggest complexities within this system may limit or obscure symbiont-driven contemporary evolution, a finding of broad significance given the widespread nature of defensive microbes across plants and animals.
authors: Department of Biology, Drexel University, Philadelphia, PA, 19104, USA.
authors: Andrew H
authors: AH
authors: Smith
authors: Piotr
authors: P
authors: Łukasik
authors: Michael P
authors: MP
authors: O'Connor
authors: Amanda
authors: A
authors: Lee
authors: Garrett
authors: G
authors: Mayo
authors: Milton T
authors: MT
authors: Drott
authors: Steven
authors: S
authors: Doll
authors: Robert
authors: R
authors: Tuttle
authors: Rachael A
authors: RA
authors: Disciullo
authors: Andrea
authors: A
authors: Messina
authors: Kerry M
authors: KM
authors: Oliver
authors: Jacob A
authors: JA
authors: Russell
mesh_terms: D000220:Adaptation, Biological / Q000235:genetics*; D000818:Animals; D001042:Aphids / Q000382:microbiology*; D004755:Enterobacteriaceae / Q000145:classification* / Q000235:genetics; D064307:Microbiota; D018895:Microsatellite Repeats; D008969:Molecular Sequence Data; D009511:New England; D012621:Seasons; D017422:Sequence Analysis, DNA; D013559:Symbiosis; D013696:Temperature
keywords: Acyrthosiphon pisum; Aphidius ervi; Pandora neoaphidis; contemporary evolution; selection; symbiosis