A Veritable Menagerie of Heritable Bacteria from Ants, Butterflies, and Beyond: Broad Molecular Surveys and a Systematic Review

and Beyond: Broad Molecular Surveys and a Systematic Review. PLoS ONE 7(12): e51027. doi:10.1371/journal.pone.0051027 A Veritable Menagerie of Heritable Bacteria from Ants, Butterflies, and Beyond: Broad Molecular Surveys and a Systematic Review Jacob A. Russell 0 1 Colin F. Funaro 0 1 Ysabel M. Giraldo 0 1 Benjamin Goldman-Huertas 0 1 David Suh 0 1 Daniel J. C. Kronauer 0 1 Corrie S. Moreau 0 1 Naomi E. Pierce 0 1 John McCutcheon, University Of Montana - Missoula, United States of America 0 a Current address: Department of Entomology, North Carolina State University , Raleigh , North Carolina, United States of America b Current address: Department of Biology, Boston University , Boston , Massachusetts, United States of America c Current address: Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona, United States of America d Current address: New York University College of Dentistry, New York, New York, United States of America e Current address: Laboratory of Insect Social Evolution, The Rockefeller University , New York, New York , United States of America 1 1 Department of Biology, Drexel University, Philadelphia, Pennsylvania, United States of America, 2 Department of Organismic and Evolutionary Biology, Harvard University , Cambridge, Massachusetts , United States of America , 3 Field Museum of Natural History , Department of Zoology , Chicago, Illinois , United States of America Maternally transmitted bacteria have been important players in the evolution of insects and other arthropods, affecting their nutrition, defense, development, and reproduction. Wolbachia are the best studied among these and typically the most prevalent. While several other bacteria have independently evolved a heritable lifestyle, less is known about their host ranges. Moreover, most groups of insects have not had their heritable microflora systematically surveyed across a broad range of their taxonomic diversity. To help remedy these shortcomings we used diagnostic PCR to screen for five groups of heritable symbionts-Arsenophonus spp., Cardinium hertigii, Hamiltonella defensa, Spiroplasma spp., and Wolbachia spp.across the ants and lepidopterans (focusing, in the latter case, on two butterfly families-the Lycaenidae and Nymphalidae). We did not detect Cardinium or Hamiltonella in any host. Wolbachia were the most widespread, while Spiroplasma (ants and lepidopterans) and Arsenophonus (ants only) were present at low levels. Co-infections with different Wolbachia strains appeared especially common in ants and less so in lepidopterans. While no additional facultative heritable symbionts were found among ants using universal bacterial primers, microbes related to heritable enteric bacteria were detected in several hosts. In summary, our findings show that Wolbachia are the dominant heritable symbionts of ants and at least some lepidopterans. However, a systematic review of symbiont frequencies across host taxa revealed that this is not always the case across other arthropods. Furthermore, comparisons of symbiont frequencies revealed that the prevalence of Wolbachia and other heritable symbionts varies substantially across lower-level arthropod taxa. We discuss the correlates, potential causes, and implications of these patterns, providing hypotheses on host attributes that may shape the distributions of these influential bacteria. - Funding: This research was supported by National Science Foundation (NSF) grants 0400889 and 1050360 to JAR and NSF grant 1050243 to CSM (www.nsf.gov). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Insects colonize nearly every terrestrial habitat on the planet, having diversified into millions of extant species. Their roles as pollinators, herbivores, predators, parasites, and mutualists make them integral parts of terrestrial ecosystems, and their biomass within these habitats is largely unrivaled by other animals. Across these invertebrates, the evolutionary innovations enabling adaptation, niche shifts, and diversification have primarily been driven by mutations in their endogenous genomes. Yet, exogenous agents have also played roles in these processes, as many insects harbor maternally transmitted bacteria that provide an additional source of genetic variation with adaptive potential [1]. The variety of these heritable symbionts is impressive, with bacteria from multiple families, orders, and phyla having evolved this highly specialized lifestyle [1]. Several have also independently evolved similar strategies to spread within host populations, making their living through manipulation of host reproduction, or through benefits to host nutrition, defense, or environmental tolerance [27]. These effects have enabled heritable symbionts to shape the ecology and evolution of their hosts, and occasional instances of horizontal transfer between species [812] have allowed their impacts to be disseminated across the insects and beyond. Wolbachia are by far the best known of the maternally transmitted symbionts. These intracellular members of the Alphaproteobacteria infect a majority of the worlds insect species, and they are also found in isopods, arachnids, and nematodes [13 16]. Other heritable bacteria are typically less prevalent across the arthropods, with lower frequencies and seemingly patchier distributions across many host groups [1721]. Since their overall prevalence can vary among host taxa, it is likely that some possess host range restrictions or that some insect groups are either especially accommodating or especially inhospitable. Patchy distributions are also apparent, to some extent, for Wolbachia. Although few host groups appear to be off-limits to these microbes, several are rarely infected, just as some host taxa show impressively high rates of Wolbachia infection [2224]. In addition, some Wolbachia lineages are primarily confined to a limited range of related arthropods [25,26], suggesting recently derived host range restrictions. Despite our expanding knowledge of symbiont distributions, outside of the genus Drosophila [27] most insects have not been screened with great depth or breadth at lower taxonomic levels. When we consider that Wolbachia frequencies can differ widely across related host families, and even related genera [28], it becomes apparent that this lack of information has hindered our understanding of the factors that shape symbiont distributions. Given the known effects of heritable bacteria, surveys for such microbes are likely to identify bacterial species with profound impacts on the nutritional ecology, defensive interactions, reproduction, development, and genome evolution of their host arthropods [2,29]. To further elucidate their distributions, we utilized a series of molecular approaches to study five heritable symbio (...truncated)