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ViewAttendees 4

Student 10-Minute Paper

Systematics, Evolution, and Biodiversity

Student Competition

Student

Grad Competition SysEB: Genetics

(2nd Place) Insects, bacteria, and the Red Queen: How is defensive symbiont diversity maintained?

Monday, November 6, 2023
11:18 AM – 11:30 AM ET
Location: Gaylord National Resort & Convention Center, Chesapeake 7-9
In-Person Student Competition
Many insect species harbor heritable bacterial symbionts protecting them against pathogens or parasites. Referred to as defensive symbionts, these bacteria are often comprised of multiple strains even within a single insect population. This leads us to ask, how is this variation maintained over time? Balancing selection provides a potential explanation for continued variation. Balancing selection offers a potential explanation, with symbionts engaging in red queen dynamics with natural enemies, driving variation and oscillation of strains over time. We tested this idea using the pea aphid (Acyrthosiphon pisum) model symbiont system. In our focal populations the most common symbiont is Hamiltonella defensa, a maternally-inherited multi-strain endosymbiont that defends against the parasitoid wasp Aphidius ervi. This defense varies among strain with the differing strains of an encoded prophage, APSE, a required element for anti-parasitoid defense. Using 10 year longitudinal data from two pea aphid populations we have found significant variation in Hamiltonella/APSE strain prevalence over time. In southeastern Pennsylvannia we found predominant strains fluctuated with a 3 year periodicity. To test whether these fluctuations resulted from antagonistic coevolution with parasitoids, we challenged five sub-lines of a single aphid clone with multiple isofemale lines of A. ervi. We found a rock-paper-scissors pattern, with flip-flopping virulence hierarchies against aphid sub-lines with two different APSE strains encoded by the same strain of Hamiltonella. Genetic diversity in parasitoids and heritable symbionts can, thus, facilitate Red Queen dynamics. While other ecological services should be considered, such dynamics may explain the sustained maintenance of symbiont diversity.