Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 113, Issue 46, Pages 13114-13119Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1610749113
Keywords
coevolution; maternal transmission; cytonuclear interactions; Acyrthosiphon pisum; Buchnera aphidicola
Categories
Funding
- Agriculture and Food Research Initiative Competitive Grant from the US Department of Agriculture National Institute of Food and Agriculture [2016-67012-24676]
- National Science Foundation [IOS1347116]
- University of Texas at Austin
- NIFA [2016-67012-24676, 810686] Funding Source: Federal RePORTER
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Symbiotic relationships promote biological diversification by unlocking new ecological niches. Over evolutionary time, hosts and symbionts often enter intimate and permanent relationships, which must be maintained and regulated for both lineages to persist. Many insect species harbor obligate, heritable symbiotic bacteria that provision essential nutrients and enable hosts to exploit niches that would otherwise be unavailable. Hosts must regulate symbiont population sizes, but optimal regulation may be affected by the need to respond to the ongoing evolution of symbionts, which experience high levels of genetic drift and potential selection for selfish traits. We address the extent of intraspecific variation in the regulation of a mutually obligate symbiosis, between the pea aphid (Acyrthosiphon pisum) and its maternally transmitted symbiont, Buchnera aphidicola. Using experimental crosses to identify effects of host genotypes, we measured symbiont titer, as the ratio of genomic copy numbers of symbiont and host, as well as developmental time and fecundity of hosts. We find a large (> 10-fold) range in symbiont titer among genetically distinct aphid lines harboring the same Buchnera haplotype. Aphid clones also vary in fitness, measured as developmental time and fecundity, and genetically based variation in titer is correlated with host fitness, with higher titers corresponding to lower reproductive rates of hosts. Our work shows that obligate symbiosis is not static but instead is subject to short-term evolutionary dynamics, potentially reflecting coevolutionary interactions between host and symbiont.
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