Nicole M Gerardo

• Professor (Associate) at Emory University

Symbiotic interactions, central to most life on Earth, are interwoven associations that vary in intimacy and duration. Some of the most well-known examples of symbioses occur between animals and gut bacteria. These associations lead to physiological integration of host and symbionts. The diversity of microbes within animal hosts can make studying t...

Diet profoundly influences the composition of an animal’s microbiome, especially in holometabolous insects, offering a valuable model to explore the impact of diet on gut microbiome dynamics throughout metamorphosis. Here, we use monarch butterflies (Danaus plexippus), specialist herbivores that feed as larvae on many species of chemically well-def...

Fungus-farming ants cultivate multiple lineages of fungi for food, but, because fungal cultivar relationships are largely unresolved, the history of fungus-ant coevolution remains poorly known. We designed probes targeting >2000 gene regions to generate a dated evolutionary tree for 475 fungi and combined it with a similarly generated tree for 276...

Specialized host-microbe symbioses are ecological communities, whose composition is shaped by various processes. Microbial community assembly in these symbioses is determined in part by interactions between taxa that colonize ecological niches available within habitat patches. The outcomes of these interactions, and by extension the trajectory of c...

The metabolic intimacy of symbiosis often demands the work of specialists. Natural products and defensive secondary metabolites can drive specificity by ensuring infection and propagation across host generations. But in contrast to bacteria, little is known about the diversity and distribution of natural product biosynthetic pathways among fungi an...

Many insects selectively associate with specific microbes in long-term, symbiotic relationships. Maintaining these associations can be vital for the insect hosts’ development, but insects must also contend with potential coinfections from other microbes in the environment. Fending off microbial threats while maintaining mutualistic microbes has res...

Microbial community assembly is determined in part by interactions between taxa that colonize ecological niches available within habitat patches. The outcomes of these interactions, and by extension the trajectory of community assembly, can display priority effects - dependency on the order in which taxa first occupy these niches. The underlying me...

Specialized host–microbe symbioses canonically show greater diversity than expected from simple models, both at the population level and within individual hosts. To understand how this heterogeneity arises, we utilize the squash bug, Anasa tristis, and its bacterial symbionts in the genus Caballeronia. We modulate symbiont bottleneck size and inocu...

The metabolic intimacy of symbiosis often demands the work of specialists. Natural products and defensive secondary metabolites can drive specificity by ensuring infection and propagation across host generations. But in contrast to bacteria, little is known about the diversity and distribution of natural product biosynthetic pathways among fungi an...

The impacts of host-associated microbes for their hosts varies along a continuum of antagonistic, neutral, and beneficial interactions. Transmission mode is predicted to contribute to transitions along the continuum by altering opportunities for the alignment of host and microbe fitness interests. Under vertical transmission, microbial evolution is...

Course-based undergraduate research experiences (CUREs) rapidly have become more common in biology laboratory courses. The effort to implement CUREs has stimulated attempts to differentiate CUREs from other types of laboratory teaching. The Laboratory Course Assessment Survey (LCAS) was developed to measure students’ perceptions of how frequently t...

Fungi shape the diversity of life. Characterizing the evolution of fungi is critical to understanding symbiotic associations across kingdoms. In this study, we investigate the genomic and metabolomic diversity of the genus Escovopsis, a specialized parasite of fungus-growing ant gardens. Based on 25 high-quality draft genomes, we show that Escovops...

Many interspecific interactions are shaped by coevolution. Transmission mode is thought to influence opportunities for coevolution within symbiotic interactions. Vertical transmission maintains partner fidelity, increasing opportunities for coevolution, but horizontal transmission may disrupt partner fidelity, potentially reducing opportunities for...

Reciprocal adaptation between hosts and symbionts can drive the maintenance of symbioses, resulting in coevolution and beneficial genotypic interactions. Consequently, hosts may experience decreased fitness when paired with non‐sympatric partners compared to sympatric symbionts. However, coevolution does not preclude conflict—host and symbiont can...

Contributors explore common elements in the evolutionary histories of both human and insect agriculture resulting from convergent evolution. During the past 12,000 years, agriculture originated in humans as many as twenty-three times, and during the past 65 million years, agriculture also originated in nonhuman animals at least twenty times and in...

We are at a historic point in which scientists and Tibetan monastics are working together to investigate ancient questions of mind and matter, and to serve the best interests of humanity. To facilitate this collaboration, His Holiness the Dalai Lama supported the development of the Emory University-Tibet Science Initiative (ETSI), which reflects th...

Many insects harbor microbial symbiotic partners that offer protection against pathogens, parasitoids, and other natural enemies. Mounting evidence suggests that these symbiotic microbes can play key roles in determining infection outcomes in insect vectors, making them important players in the quest to develop novel vector control strategies. Usin...

Mutualism depends on the alignment of host and symbiont fitness. Horizontal transmission can readily decouple fitness interests, yet horizontally transmitted mutualisms are common in nature. We hypothesized that pairwise coevolution and specialization in host-symbiont interactions underlies the maintenance of cooperation in a horizontally transmitt...

Fungi in the genus Escovopsis (Ascomycota: Hypocreales) are prevalent associates of the complex symbiosis between fungus-growing ants (Tribe Attini), the ants’ cultivated basidiomycete fungi and a consortium of both beneficial and harmful microbes found within the ants’ garden communities. Some Escovopsis spp. have been shown to attack the ants’ cu...

Most insects maintain associations with microbes that shape their ecology and evolution. Such symbioses have important applied implications when the associated insects are pests or vectors of disease. The squash bug, Anasa tristis (Coreoidea: Coreidae), is a significant pest of human agriculture in its own right and also causes damage to crops due...

Most insects maintain associations with microbes that shape their ecology and evolution. Such symbioses have important applied implications when the associated insects are pests or vectors of disease. The squash bug, Anasa tristis (Coreoidea: Coreidae), is a significant pest of human agriculture in its own right and also causes damage to crops due...

Humoral and cellular immune responses provide animals with major defenses against harmful pathogens. While it is often assumed that immune genes undergo rapid diversifying selection, this assumption has not been tested in many species. Moreover, it is likely that different classes of immune genes experience different levels of evolutionary constrai...

A pervasive pest of stored leguminous products, the bean beetle (Coleoptera: Chrysomelidae: Callosobruchus maculatus ) associates with a simple bacterial community during adulthood. Despite its economic importance, little is known about the compositional stability, heritability, localization, and metabolic potential of the bacterial symbionts of C....

Protective symbionts can allow hosts to occupy otherwise uninhabitable niches. Despite the importance of symbionts in host evolution, we know little about how these associations arise. Encountering a microbe that can improve host fitness in a stressful environment may favor persistent interactions with that microbe, potentially facilitating a long‐...

In formal learning spaces, students must navigate making meaning of both new knowledge and potentially new worldviews. In this qualitative grounded theory study, we examined how adult Buddhist monastic students learned about and described the origin of biodiversity in an introductory biology course. The study was conducted at a Tibetan settlement i...

Despite the ubiquity and importance of mutualistic interactions, we know little about the evolutionary genetics underlying their long‐term persistence. As in antagonistic interactions, mutualistic symbioses are characterized by substantial levels of phenotypic and genetic diversity. In contrast to antagonistic interactions, however, we, by and larg...

Immune system processes serve as the backbone of animal defences against pathogens and thus have evolved under strong selection and coevolutionary dynamics. Most microorganisms that animals encounter, however, are not harmful, and many are actually beneficial. Selection should act on hosts to maintain these associations while preventing exploitatio...

Numerous adaptations are gained in light of a symbiotic lifestyle. Here, we investigated the obligate partnership between tortoise leaf beetles (Chrysomelidae: Cassidinae) and their pectinolytic Stammera symbionts to detail how changes to the bacterium’s streamlined metabolic range can shape the digestive physiology and ecological opportunity of it...

Vector-borne pathogens pose significant threats to agricultural productivity. Methods that exploit associations between insects and their symbiotic microbes, dubbed symbiont-mediated vector control, are emerging as viable alternatives to insecticides for the control of vector-borne agricultural plant pathogens. The development of methods for effect...

Abiotic and biotic factors can affect host resistance to parasites. Host diet and host gut microbiomes are two increasingly recognized factors influencing disease resistance. In particular, recent studies demonstrate that (1) particular diets can reduce parasitism; (2) diets can alter the gut microbiome; and (3) the gut microbiome can decrease para...

Herbivorous insects have evolved many mechanisms to overcome plant chemical defences, including detoxification and sequestration. Herbivores may also use toxic plants to reduce parasite infection. Plant toxins could directly interfere with parasites or could enhance endogenous immunity. Alternatively, plant toxins could favour down-regulation of en...

Many species interactions are dependent on environmental context, yet the benefits of obligate, mutualistic microbial symbioses to their hosts are typically assumed to be universal across environments. We directly tested this assumption, focusing on the symbiosis between the sap-feeding insect Megacopta cribraria and its primary bacterial symbiont...

Immune genes presumably rapidly evolve as pathogens exert strong selection pressures on host defense, but the evolution of immune genes is also constrained by trade-offs with other biological functions and shaped by the environmental context. Thus, immune genes may exhibit complex evolutionary patterns, particularly when organisms disperse to or li...

Herbivorous insects have evolved many mechanisms to overcome plant chemical defenses, including detoxification and sequestration. Herbivores may also use toxic plants to reduce parasite infection. Plant toxins could directly interfere with parasites or could enhance endogenous immunity. Alternatively, plant toxins could favor down-regulation of end...

Microbes can provide their hosts with protection from biotic and abiotic factors. While many studies have examined how certain bacteria can increase host lifespan, fewer studies have examined how host reproduction can be altered. The nematode Caenorhabditis elegans has been a particularly useful model system to examine how bacteria affect the fitne...

The geographic and phylogenetic scale of ecologically relevant microbial diversity is still poorly understood. Using a model mutualism, fungus-growing ants and their defensive bacterial associate Pseudonocardia , we analyzed genetic diversity and biosynthetic potential in 46 strains isolated from ant colonies in a 20km transect near Barro Colorado...

Environmental stressors can be key drivers of phenotypes, including reproductive strategies and morphological traits. The response to stress may be altered by the presence of microbial associates. For example, in aphids, facultative (secondary) bacterial symbionts can provide protection against natural enemies and stress induced by elevated tempera...

Aphids, like most animals, mount a diverse set of defenses against pathogens. For aphids, two of the best studied defenses are symbiont-conferred protection and transgenerational wing induction. Aphids can harbor bacterial symbionts that provide protection against pathogens, parasitoids and predators, as well as against other environmental stressor...

Animal-associated microbial communities have important effects on host phenotypes. Individuals within and among species differ in the strains and species of microbes that they harbour, but how natural selection shapes the distribution and abundance of symbionts in natural populations is not well understood. Symbionts can be beneficial in certain en...

Determining the factors governing investment in immunity is critical to understanding host–pathogen ecological and evolutionary dynamics. Studies often consider disease resistance in the context of life‐history theory, with the expectation that investment in immunity will be optimized in anticipation of disease risk. Immunity, however, is constrain...

Parasites evolve within complex abiotic and biotic environments. Because of this, it is often challenging to ascertain how evolutionary and ecological processes together affect parasite specialization. Here, we use the fungus-growing ant system, which consists of ancient, likely coevolved, complex communities, to explore the ecological and evolutio...

Significance Many organisms are specialists living within a narrow range of conditions. Pathogens are often adapted to efficiently exploit only a few hosts species, or sometimes, only some genotypes within a species. The genomes of such parasites are predicted to maintain genes critical for host utilization and to lose genes no longer necessary out...

Endosymbionts can fundamentally alter host physiology. Whether such changes are beneficial or detrimental to one or both partners may depend on the dynamics of the symbiotic relationship. Here we investigate the relationship between facultative symbionts and host immune responses. The pea aphid, Acyrthosiphon pisum, maintains an obligate primary sy...

Across animals and plants, numerous metabolic and defensive adaptations are a direct consequence of symbiotic associations with beneficial microbes. Explaining how these partnerships are maintained through evolutionary time remains one of the central challenges within the field of symbiosis research. While genome erosion and co-cladogenesis with th...

The interdependence of some microbes and their hosts is profound. Coevolution has led to hosts whose survival and reproduction is dependent upon the presence of a specific microbial partner, and to microbes that have adapted to life within hosts. Such obligate microbial symbioses are present across the tree of life, and study of associations betwee...

Many organisms harbor microbial associates that have profound impacts on host traits. The phenotypic effect of symbionts on their hosts may include changes in development, reproduction, longevity, and defense against natural enemies. Determining the consequences of associating with a microbial symbiont requires experimental comparison of hosts with...

Microbial associations are integral to all eukaryotes. Mutualism, the interaction of two species for the benefit of both, is an important aspect of microbial associations, with evidence that multicellular organisms in particular benefit from microbes. However, the microbe's perspective has largely been ignored, and it is unknown whether most microb...

Background/Question/Methods Hosts have evolved a range of mechanisms to protect themselves against parasites that are a large threat to their fitness. In addition to canonical immune responses, hosts can utilize biotic factors, or living species, in their environment for additional protection. Monarch butterfly (Danaus plexippus) larvae actively...

Individuals vary in their ability to defend against pathogens. Determining how natural selection maintains this variation is often difficult, in part because there are multiple ways that organisms defend themselves against pathogens. One important distinction is between mechanisms of resistance that fight off infection, and mechanisms of tolerance...

Non-essential facultative endosymbionts can provide their hosts with protection from parasites, pathogens, and predators. For example, two facultative bacterial symbionts of the pea aphid (Acyrthosiphon pisum), Serratia symbiotica and Hamiltonella defensa, protect their hosts from parasitism by two species of parasitoid wasp. Previous studies have...

Immune responses are costly, causing trade-offs between defense and other host life history traits. Aphids present a special system to explore the costs associated with immune activation since they are missing several humoral and cellular mechanisms thought important for microbial resistance, and it is unknown whether they have alternative, novel i...

Figure S1. Survival curves from live bacterial virulence trials. Figure S2. Proportion of aphids reproducing over time after challenge with heat killed pathogens or sterile stab. Figure S3. Proportion of aphids reproducing over time after challenge with heat killed pathogens or sterile stab.

Many organisms have intimate associations with beneficial microbes acquired from the environment. These host-symbiont associations can be specific and stable, but they are prone to lower partner specificity and more partner switching than vertically transmitted mutualisms. To investigate partner specificity in an environmentally acquired insect sym...

While many endosymbionts have beneficial effects on hosts under specific ecological conditions, there can also be associated costs. In order to maximize their own fitness, hosts must facilitate symbiont persistence while preventing symbiont exploitation of resources, which may require tight regulation of symbiont populations. As a host ages, the ab...

Pea aphids have an obligate nutritional symbiosis with the bacteria Buchneraaphidicola and frequently also harbor one or more facultative symbionts. Aphids are also susceptible to bacterial pathogen infections, and it has been suggested that aphids have a limited immune response towards such pathogen infections compared to other, more well-studied...

Background/Question/Methods Following parasitic infection, immune mechanisms are energetically costly to activate and maintain in an invertebrate host. The tradeoff between immunological investment and host fecundity has been proposed as a mechanism for host life history traits in nature. For example, certain morphs of pea aphids (Acyrthosiphon p...

Studying the association between mealybugs and two bacterial symbionts, Husnik et al. (2013) demonstrated that both integration of metabolic pathways across the partners' genomes and horizontal gene transfer from diverse bacteria into the insect host genome are integral to symbiosis.

Plants represent a large reservoir of organic carbon comprised primarily of recalcitrant polymers that most metazoans are unable to deconstruct. Many herbivores gain access to nutrients in this material indirectly by associating with microbial symbionts, and leaf-cutter ants are a paradigmatic example. These ants use fresh foliar biomass as manure...

Here we show that a bacterial endosymbiont, Regiella insecticola, protects pea aphids (Acrythosiphon pisum) from the aphid-specific fungal entomopathogen Zoophthora occidentalis, but not from the generalist insect fungal pathogen Beauveria bassiana. This finding highlights the complex influence of fungi on the dynamics of this economically importan...

Human bodies house trillions of symbiotic microorganisms. The genes in this human microbiome outnumber human genes by 100 to 1, and their study is providing profound insights into human health. But humans are not the only animals with microbiomes, and microbiomes do not just impact health. Recent research is revealing surprising roles for microbiom...

In their Letter “Competencies: A cure for pre-med curriculum” (11 November 2011, p. [760][1]), W. A. Anderson and colleagues endorse a proposed shift in pre-medical education toward core competencies. We believe that the specific competencies proposed by the Association of American Medical

An official journal of the Genetics Society, Heredity publishes high-quality articles describing original research and theoretical insights in all areas of genetics. Research papers are complimented by News & Commentary articles and reviews, keeping researchers and students abreast of hot topics in the field.

Carotenoids are organic pigments commonly synthesized by plants, algae and some micro-organisms. Through absorption of light energy, carotenoids facilitate photosynthesis and provide protection against photo-oxidation. While it was presumed that all carotenoids in animals were sequestered from their diets, aphids were recently shown to harbour geno...

Species interactions are fundamental to ecology. Classic studies of competition, predation, parasitism and mutualism between macroscopic organisms have provided a foundation for the discipline, but many of the most important and intimate ecological interactions are microscopic in scale. These microscopic interactions include those occurring between...

To better understand the molecular basis underlying aphid immune tolerance to beneficial bacteria and immune defense to pathogenic bacteria, we characterized how the pea aphid Acyrthosiphon pisum responds to Escherichia coli K-12 infections. E. coli bacteria, usually cleared in the hemolymph of other insect species, were capable of growing exponent...

Parasites and hosts live in communities consisting of many interacting species, but few studies have examined how communities affect parasite virulence and transmission. We studied a food web consisting of two species of milkweed, two milkweed herbivores (monarch butterfly and oleander aphid) and a monarch butterfly-specific parasite. We found that...

After parasite infection, invertebrates activate immune system-based defenses such as encapsulation and the signaling pathways of the innate immune system. However, hosts are often able to defend against parasites without using these mechanisms. The non-immunological defenses, such as behaviors that prevent or combat infection, symbiont-mediated de...

The innate immune system of insects provides effective defence against a range of parasites and pathogens. The pea aphid, Acyrthosiphon pisum, is a novel study system for investigating host-parasite interactions due to its complex associations with both well-characterised bacterial symbionts and a diversity of pathogens and parasites, including sev...

Leaf-cutter ants are one of the most important herbivorous insects in the Neotropics, harvesting vast quantities of fresh leaf material. The ants use leaves to cultivate a fungus that serves as the colony's primary food source. This obligate ant-fungus mutualism is one of the few occurrences of farming by non-humans and likely facilitated the forma...

Fungus-growing ants (tribe Attini) engage in a mutualism with a fungus that serves as the ants' primary food source, but successful fungus cultivation is threatened by microfungal parasites (genus Escovopsis). Actinobacteria (genus Pseudonocardia) associate with most of the phylogenetic diversity of fungus-growing ants; are typically maintained on...

Aphids are striking in their prodigious reproductive capacity and reliance on microbial endosymbionts, which provision their hosts with necessary amino acids and provide protection against parasites and heat stress. Perhaps as a result of this bacterial dependence, aphids have limited immune function that may leave them vulnerable to bacterial path...

Host–parasite associations are potentially shaped by evolutionary reciprocal selection dynamics, in which parasites evolve to overcome host defences and hosts are selected to counteract these through the evolution of new defences. This is expected to result in variation in parasite-defence interactions, and the evolution of resistant parasites caus...

Symbiosis, the intimate association between two or more organisms, is a fundamental component of biological systems. Our ability to understand the processes involved in the establishment and function of Symbiosis has critical consequences for the health of humans and the world we live in. For example, a deeper understanding of how legumes and insec...

Aphids are important agricultural pests and also biological models for studies of insect-plant interactions, symbiosis, virus vectoring, and the developmental causes of extreme phenotypic plasticity. Here we present the 464 Mb draft genome assembly of the pea aphid Acyrthosiphon pisum. This first published whole genome sequence of a basal hemimetab...

Aphids are important agricultural pests and also biological models for studies of insect-plant interactions, symbiosis, virus vectoring, and the developmental causes of extreme phenotypic plasticity. Here we present the 464 Mb draft genome assembly of the pea aphid Acyrthosiphon pisum. This first published whole genome sequence of a basal hemimetab...

Aphids are important agricultural pests and also biological models for studies of insect-plant interactions, symbiosis, virus vectoring, and the developmental causes of extreme phenotypic plasticity. Here we present the 464 Mb draft genome assembly of the pea aphid Acyrthosiphon pisum. This first published whole genome sequence of a basal hemimetab...

Aphids are important agricultural pests and also biological models for studies of insect-plant interactions, symbiosis, virus vectoring, and the developmental causes of extreme phenotypic plasticity. Here we present the 464 Mb draft genome assembly of the pea aphid Acyrthosiphon pisum. This first published whole genome sequence of a basal hemimetab...

Aphids are important agricultural pests and also biological models for studies of insect-plant interactions, symbiosis, virus vectoring, and the developmental causes of extreme phenotypic plasticity. Here we present the 464 Mb draft genome assembly of the pea aphid Acyrthosiphon pisum. This first published whole genome sequence of a basal hemimetab...

Table S1: pea aphid immune and stress gene list. Table S2: samples for quantitative PCR expression study. Table S3: primers for quantitative PCR expression study. Table S4: relative expression of recognition and signaling genes. Table S5: relative expression of response genes. Table S6: gut EST library statistics. Table S7: list of selected ESTs fr...

Recent genomic analyses of arthropod defense mechanisms suggest conservation of key elements underlying responses to pathogens, parasites and stresses. At the center of pathogen-induced immune responses are signaling pathways triggered by the recognition of fungal, bacterial and viral signatures. These pathways result in the production of response...

Following publication of the first aphid genome in February 2010, aphid biology is entering a new era focused on deciphering many of the specialized biological adaptations underlying the role of aphids as plant pests. Meeting this challenge will be facilitated by the accessibility of NextGen Sequencing strategies, functional genome annotation and c...

The distribution of genetic and phenotypic variation in both hosts and parasites over their geographic ranges shapes coevolutionary dynamics. Specifically, concordant host and parasite distributions facilitate localized adaptation and further specialization of parasite genotypes on particular host genotypes. We here compare genetic population struc...

Switching by parasites to novel hosts has profound effects on ecological and evolutionary disease dynamics. Switching requires that parasites are able to establish contact with novel hosts and to overcome host defenses. For most host–parasite associations, it is unclear as to what specific mechanisms prevent infection of novel hosts. Here, we show...

No-Choice Bioassay II, Interaction and Genetic Matrices Results of no-choice bioassay II (top) were used to generate four interaction matrices (middle). We then used Mantel tests to test for a correlation between interaction matrices and genetic-distance matrices (bottom). Details of the methods can be found in the text. (1.2 MB EPS)

The fungus-growing ant-microbe symbiosis consists of coevolving microbial mutualists and pathogens. The diverse fungal lineages that these ants cultivate are attacked by parasitic microfungi of the genus Escovopsis. Previous molecular analyses have demonstrated strong phylogenetic congruence between the ants, the ants-cultivated fungi and the garde...

Agriculture has evolved independently in three insect orders: once in ants, once in termites, and seven times in ambrosia beetles. Although these insect farmers are in some ways quite different from each other, in many more ways they are remarkably similar, suggesting convergent evolution. All propagate their cultivars as clonal monocultures within...

Several insect groups have obligate, vertically transmitted bacterial symbionts that provision hosts with nutrients that are limiting in the diet. Some of these bacteria have been shown to descend from ancient infections. Here we show that the large group of related insects including cicadas, leafhoppers, treehoppers, spittlebugs, and planthoppers...

Fungus-growing ants, their cultivated fungi and the cultivar-attacking parasite Escovopsis coevolve as a complex community. Higher-level phylogenetic congruence of the symbionts suggests specialized long-term associations of host-parasite clades but reveals little about parasite specificity at finer scales of species-species and genotype-genotype i...