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STRI SCIENCE SYMPOSIUM TROPICAL MICROBIAL ECOLOGY & EVOLUTION OCTOBER 26-27, 2016 EARL S. TUPPER AUDITORIUM STRI SCIENCE SYMPOSIUM SCHEDULE | OCTOBER 26 AND 27, 2016 AGENDA WEDNESDAY, OCTOBER 26 THURSDAY, OCTOBER 27 8:15 |EARLY MORNING 8:15 |EARLY MORNING INTRODUCTIONS: ALLEN HERRE Overview of terrestrial and microbial assets at STRI (Intellectual and logistical resources with some examples of how they can be used) Speakers: JOSEPH WRIGHT; LUIS MEJIA; KRISTIN SALTONSTALL; KIMBERLY MIGHELL 11:00 |LATE MORNING INTRODUCTIONS: ALLEN HERRE Soil microbial relationships and their influence on ecosystem ecology Speakers: JIM DALLING; ELLEN SIMMS; JEFFERSON HALL; TRUMAN YOUNG 11:00 |LATE MORNING Influence of microbiomes in insects and amphibians The interactions among leaf chemistry, leaf microbial communities, and herbivore gut floras Speakers: BILL WCISLO; CHRIS KOZAK; JORDAN KUENEMAN Speakers: BRIAN SEDIO; ERIC GRIFFIN; TOBIN HAMMER 12:30 - 2:00 LUNCH BREAK 12:30 - 2:00 LUNCH BREAK 2:00 | EARLY AFTERNOON 2:00 |EARLY AFTERNOON Symbiont and Microbial effects on ecosystem function Speakers: MATTHIEU LERAY; JANE LUCAS; ANDREW NOTTINGHAM Microbial effects on host plant abundances and distributions within plots, across the isthmus Speakers: SCOTT MANGAN; ERIN SPEAR; CAMILO ZALAMEA 4:00 |LATE AFTERNOON Disease transmission ecology in tropical mammals, with implications for humans Speakers: HELEN ESSER; STEFAN BRÄNDEL; MARCO MARKLEWITZ; CRISTINA PILAR 4:00 |LATE AFTERNOON Factors affecting microbial community assembly, composition, and functional effects on hosts Speakers: KRISTA MCGUIRE; JOHN SCHOEDER; MERLIN SHELDRAKE; NATALIE CHRISTIAN POST-TALK RECEPTION AND POSTER SESSION: COROTU PLAZA POST-TALK RECEPTION AND DISCUSSION WEDNESDAY MORNING SESSIONS JOE WRIGHT Academic Affiliation: Smithsonian Tropical Research Institute E-mail: [email protected] Integrating decades of data on survival and growth of seeds, seedlings, trees, plant traits, and nutrient addition plots with microbial surveys ABSTRACT One of the distinguishing characteristics of the Smithsonian Tropical Research Institute in Panama is the commitment to and continued support of long term (decades) collection of a variety of types of data that relate to tropical forest species composition, function, and dynamics. In addition to a 50 hectare plot on BCI where all individual woody plants above 1 Cm dbh have been tagged, located and repeatedly censused, we have access to similar information for seed rain, seedling establishment and long-term survival. We have established plots where plant nutrients of known fundamental importance (e.g., N, P, K) have been experimentally manipulated, and the effects of those manipulations can be assessed on plant functions. We possess in depth knowledge of the relative abundances, geographical distributions, and traits of the flora (life histories, physiological properties such as photosynthesis and water relationships, defense syndromes, and, increasingly, secondary chemistry). We are now in a position to add detailed knowledge of the microbial communities in soils, leaves, roots and begin to unveil how tropical plants relate with the tropical microbial community. I will give a few examples from my own collaborations, and the many speakers at this symposium will provide more. TALKS 1 WEDNESDAY | EARLY MORNING LUIS MEJÍA Academic Affiliation: INDICASAT (Instituto de Investigaciones Científicas y Servicios de Alta Tecnología), Smithsonian Tropical Research Institute E-mail: [email protected] 2 WEDNESDAY | EARLY MORNING Opportunities provided by the application of Microbial and Genomic tools available at STRI and INDICASAT KRISTIN SALTONSTALL Academic Affiliation: Smithsonian Tropical Research Institute E-mail: [email protected] Changes in soil microbial diversity across land use types in wet and dry tropical forests of Panama ABSTRACT ABSTRACT I will discuss some of the microbial and molecular resources currently available at STRI, with the objective of outlining how they can be used to understand the ecological and functional (physiological and genetic) basis of interactions of pathogenic and mutualistic microbes (mostly fungi) with tropical host plants. Extensive surveys of fungal and bacterial communities associated with different tropical host plants indicate that there is considerable overlap in what foliar endophytic fungi (FEF) occur in different host species. However, common garden experiments show that the microbiota of any given host plant is typically dominated by a few recurring species that often do not overlap with other host plant species. That is, within general overlap there are clear preferential host associations. At STRI we have pioneered experimental manipulations of FEF. Combined with physiology, stable isotopes, and genomic tools we have developed for both host plants (e.g., Theobroma cacao) and endophytic and pathogenic fungi (e.g., Colletotrichum spp.) we have shown that asymptomatic fungal endophytes: 1) reduce pathogen damage; 2) reduce herbivore damage; 3) increase lignin and cellulose deposition; 4) reduce photosynthetic competence; 5) shift stable isotope composition of Carbon and Nitrogen in the host; 6) dramatically affect host genetic expression (e.g., up-regulation of defense pathways such as receptor kinases and PR genes) in ways that explain increased resistance and shifted metabolism. Comparing the reactions of different host species (or different races within a host) to given pathogens or symbionts can help explain ecological patterns of host plant success. Similarly, microbial genetic expression in planta presents an opportunity to understand the genetic basis of why a given microbe is a pathogen in one host or a mutualist in another. Forest recovery following abandonment of agricultural lands in the tropics depends on a variety of factors, including the surrounding vegetation communities, levels of soil degradation, and natural disturbance processes. Belowground microbial communities may also play an important role in the recovery of aboveground forest communities, as microbes may either enhance or postpone forest recovery. Soil samples were collected from three land-use types (pasture, young secondary and old secondary forests, n=12 in each) in the Agua Salud landscape near Colon, Panama (wet forest) and the Azuero Peninsula near Pedasi (dry forest). We investigated changes in soil bacterial and fungal communities across these land use types by sequencing 16s and ITS metagenomic libraries on an Illumina MiSeq. Nutrients and pH of each soil sample, as well as aboveground vegetation cover at each site were also analyzed. We have found that at the community level, the bacteria and fungi of pasture soils are distinct from old secondary forest soils, with young secondary forest plots having communities representative of both pastures and older forest. These sites are ideal for looking at the effect of land use and vegetation cover on soil microbial communities as they contain a mosaic of landscapes across an area with relatively homogeneous soils and other edaphic factors. Detailed analysis of soil properties and vegetation cover will enhance our understanding of the role that soil microbial communities may play in successional processes of tropical forests. 3 WEDNESDAY | EARLY MORNING KIMBERLY MIGHELL (co-authors: Kristin Saltonstall & Sunshine Van Bael) Academic Affiliation: Dept. of Ecology and Evolutionary Biology, Tulane University, STRI WEDNESDAY | LATE MORNING Plasticity in endophytic communities of Jatropha curcas BILL WCISLO Academic Affiliation: Smithsonian Tropical Research Institute E-mail: [email protected] Opening the doors to the microbial ecology of tropical ants and bees E-mail: [email protected] 4 ABSTRACT ABSTRACT Soil is a major source of bacterial symbionts in plants. Select bacteria colonize the rhizosphere and subsequently the endosphere, where they reside as endophytes. The composition of the bacterial endosymbiont community is influenced by soil chemistry, edaphic factors, biogeography and host biology. Jatropha curcas (Euphorbiaceae) is a drought-tolerant biodiesel crop plant that is native to dry areas of Central America. We investigated how soil factors, biogeography, and local environmental conditions contribute to the endophytic bacterial community assembly in J. curcas seedlings in a field and greenhouse setting. Plants assembled unique endophytic communities at different sites in the field, but greenhouse-grown plants using soil from these localities showed a convergence in endophyte communities. One interpretation is that lack of water stress in the greenhouse resulted in plants hosting a convergent bacterial community. This suggests that the bacterial microbiome of J. curcas is plastic and that endosymbiont effects on their hosts may vary by the host’s location and stress level. I will discuss the implications for behavior, adaptive radiation, co-evolution, agriculture and public health of a few of the groundbreaking studies of the composition and function of the microbiota associated with leaf cutter ants and Megalopta bees that have been conducted at STRI. 5 WEDNESDAY | LATE MORNING KRZYSZTOF “CHRIS” KOZAK Academic Affiliation: Biodiversity Genomics Fellow, Smithsonian Tropical Research Institute, Gamboa, Panama E-mail: [email protected] 6 WEDNESDAY | LATE MORNING Varied prevalence of endosymbionts across an admixing butterfly radiation JORDAN G. KUENEMAN Academic Affiliation: Department of Ecology and Evolutionary Biology | University of Colorado at Boulder E-mail: [email protected] Ecology of the amphibian skin- associated microbiome and its role in pathogen defense ABSTRACT ABSTRACT The role of adaptive introgression in the speciation of Heliconius butterflies has been demonstrated extensively with genomic datasets. The existing data can be leveraged further to interrogate many aspects of evolution and ecology in this complex radiation. I present a survey of microbial diversity in total DNA libraries from across the Neotropics, revealing a surprisingly small variety of endosymbionts in Heliconius. Spiroplasma is the only common endosymbiont, with diverse strains infecting several species, especially in Amazonia. However, there is no evidence for the role of introgression in the transfer of bacteria. Host-associated microbial communities perform many beneficial functions including resisting pathogens and training the immune system. Here, I show amphibian microbial communities are highly species specific, but are also structured by abiotic factors. I explore the process of amphibian development and the co-development of their microbial associations. Through exploration of bacterial and micro-eukaryotic skin communities across amphibian development, I find support that the primary function of larval microbial associations is to inhibit fungal colonization of the amphibian host. I will discuss the consequences of captivity on amphibian skin associations, the implications for release efforts and outcomes for defense against environmental pathogens. Lastly, I show that protection from Batrachochytrium dendrobatidis can be accomplished through probiotic additions and that new metagenomic tools can greatly assist in amphibian conservation efforts. 7 WEDNESDAY AFTERNOON SESSIONS MATTHIEU LERAY Academic Affiliation: Postdoctoral fellow, STRI, NAOS E-mail: [email protected] JANE LUCAS The role of mutualist assemblages on coral performance MATTHIEU LERAY ABSTRACT Coral reefs are the most diverse marine systems, yet our understanding of the processes that maintain such extraordinary diversity remains limited. Mutualisms are common on coral reefs, particularly with scleractinian corals, the foundation species of the coral reef ecosystem. The best-known relationship involves corals and endosymbiotic algae (zooxanthellae), a mutualism considered fundamental for the persistence of coral reefs in oligotrophic waters. Exosymbiotic crustaceans have recently received more attention because of their potential importance for the growth, reproduction, and survival of corals. I will present results of field surveys and experiments showing that mutualist diversity and abundance affect the services provided to host corals. Our data suggest that species and species interactions are not functionally equivalent. The distribution of exosymbionts may affect the likelihood of coral populations to survive stressful environmental conditions with potential large-scale effects on reef dynamics. 8 WEDNESDAY | EARLY AFTERNOON Academic Affiliation: University of Oklahoma, Biology E-mail: [email protected] The role of antibiosis in tropical forests ABSTRACT Antibiotics were discovered from soil microbes >100 years ago, yet the ecology of antibiotics remains virtually unexplored. Our study investigated the effects of antibiotic compounds on microbial and invertebrate communities, as well as decomposition rates in tropical forests. We used molecular (DNA barcoding) and field techniques to assess the effects of antifungal and antibacterial compounds in both field and mesocosm experiments. At Barro Colorado Island in Panama and Yasuni Research Site in Ecuador, we found that antibiotic compounds decreased rates of decomposition through the depression of key fungal and bacterial decomposers. In both field and mesocosm studies, we found that antibiotics decreased abundance and diversity of soil invertebrates. Furthermore, we address the hypothesis that this deleterious effect may have encouraged soil invertebrates to develop an ability to sense and avoid antibiotic compounds. Our study suggests that antibiotic compounds can have widespread impacts on communities and play a role in creating the patchy nature of forest floor communities. 9 WEDNESDAY | EARLY AFTERNOON ANDREW NOTTINGHAM Academic Affiliation: School of GeoSciences, University of Edinburgh; STRI E-mail: [email protected] 10 Tropical forest soil microbes and climate warming: An Andean-Amazon gradient and ‘SWELTR’ BCI WEDNESDAY | LATE AFTERNOON HELEN ESSER Academic Affiliation: Wageningen University & Research, Department of Environmental Sciences, STRI E-mail: [email protected] Community ecology of wildlife, ticks and tick-borne pathogens in Panama ABSTRACT ABSTRACT Climate warming predicted for the tropics in the coming century will result in average temperatures under which no closed canopy forest exists today. There is, therefore, great uncertainty associated with the direction and magnitude of feedbacks between tropical forests and our future climate – especially relating to the response of soil microbes and the third of global soil carbon contained in tropical forests. While warming experiments are yet to be performed in tropical forests, natural temperature gradients are powerful tools to investigate temperature effects on soil microbes. Here I draw on studies from a 3.5 km elevation gradient - and 20oC mean annual temperature gradient - in Peruvian tropical forest, to investigate how temperature affects the structure of microbial communities, microbial metabolism, enzymatic activity and soil organic matter cycling. Finally, I describe SWELTR (Soil Warming Experiment in Lowland Tropical Rainforest), a new soil warming experiment being undertaken on Barro Colorado Island, designed to improve our understanding of biogeochemical feedbacks to climate warming. Given that ticks (Acari: Ixodida) are among the most important vectors of disease to both animals and humans, we have been studying the factors that influence their patterns of host association, species diversity and distribution. Analyses of molecular data and a comparative dataset of feeding associations between 45 tick species and 171 host species, including mammals, birds, reptiles and amphibians, from Panama reveal: 1) high host specificity of adult ticks for phylogenetically closely related host species; 2) relatively low host affinities of the immature stages (larvae and nymphs); 3) larger-bodied vertebrates have a higher diversity of adult ticks, often from different lineages, than smaller host species that are usually more numerous in a given locale; 4) low parasitism rates of birds, predominately by immature tick stages, with migratory species less likely to carry ticks than residents. At a habitat level, tick parasitism rates did not vary with rainfall or temperature. However, analyses of camera trap surveys and tick drag sampling data revealed that tick diversity declines rapidly as host diversity declines following habitat fragmentation, with less diverse communities being dominated by generalist ticks. These observations may have important implications for disease transmission as generalist tick species tend to feed more from disease reservoir hosts (small mammals) in impoverished communities, thereby potentially facilitating interspecies transmission of pathogens (e.g., the causal agents of Lyme Disease or Rocky Mountain Spotted Fever). 11 WEDNESDAY | LATE AFTERNOON STEFAN BRÄNDEL AND MARCO MARKLEWITZ Academic Affiliation: University of Ulm, Institute of Evolutionary Ecology and Conservation, Genomics, Ulm, Germany | University of Bonn Medical Center, Institute of Virology, Bonn, Germany E-mail: [email protected] [email protected] WEDNESDAY | LATE AFTERNOON Impact of habitat fragmentation on the diversity of animal hosts and viruses in the Canal Zone: part I. “mammalian hosts” and part II. “arthropod hosts and vectors” ABSTRACT Disturbance of tropical ecosystems may alter virus abundance and prevalence patterns via changes in host species assemblages. Diverse host communities are hypothesized to dilute the prevalence of specific pathogens, whereas biodiversity loss can increase infection rates in target species. Experimental studies as yet mainly focused on the effects of epidemic human and livestock pathogens using single-host and single-pathogen systems. Here we study the effects of habitat fragmentation on virus abundance and diversity patterns in specimens collected in a fragmented landscape using a multiplepathogen and multiple-species approach. Habitats include different degrees of isolation: continuous forest, forest fragments surrounded by agriculture used land and forested islands. 12 CHRISTINA PILAR VARIAN (co-authors: Azael Saldana, Luis Fernando Chaves, Jose Calzada, Franklin Samudio, Susan Tanner, Karen Wu, Caitlin Mertzlufft, Jessica Dyer, Kadir Gonzalez, Anamaria Santamaria, Vanessa Pineda, Chystrie Rigg, Milixa Perea, Julie Velasquez-Runk, Nicole L. Gottdenker) Academic Affiliation: University of Georgia, Instituto Conmemorativo Gorgas de Estudios de la Salud, STRI E-mail: [email protected] A multidisciplinary approach to understanding the ecology of Chagas disease and American Cutaneous Leishmaniasis in Anthropogenic Landscapes of Central Panama ABSTRACT Combining social and ecological theoretical frameworks, our research objective is to understand how ecological processes related to deforestation and historical, socioeconomic, and cultural factors interact to influence human disease risk of two of the most significant neglected tropical diseases of the Neotropics: Chagas disease and American Cutaneous leishmaniasis (ACL). These pathogens are excellent models to examine the larger question of connections between deforestation and the persistence and rise of vector-borne diseases because they are 1) shaped by land use history and 2) endemically maintained in human systems by links between ecological and social conditions. To date, our research has shown that deforestation and forest fragmentation are associated with increased vector abundance and infection with the Chagas disease agent Trypanosoma cruzi. In deforested landscapes, the change in host mammal community structure favors the abundance of smaller, “r-selected” hosts. Blood meals from these smaller hosts drives increased infection rates of vector populations with T. cruzi. Ongoing research explores how anthropogenic land use, microclimate, and food web structure influences vector populations in their Attalea palm tree habitats. Studies of leishmania infection show that anthropogenically disturbed habitats lead to changes in sandfly vector community structure to favor a predominance of anthropophilic sandflies that are highly competent leishmania vectors. Interview data suggests that dynamic processes, namely time since deforestation, impact leishmania transmission to humans. In addition to ecological factors, we also aim to pinpoint historical and contemporary socioeconomic and cultural factors driving Chagas and leishmania risk at household and community levels-information that can be applied to the prevention of vector-borne disease transmission in Panama. 13 THURSDAY MORNING SESSIONS JIM DALLING Academic Affiliation: Department of Plant Biology, University of Illinois, Urbana-Champaign ELLEN L. SIMMS Monodominance, mycorrhizas and montane forests E-mail: [email protected] 14 THURSDAY | EARLY MORNING (co-author: Kimberly J. La Pierre) Academic Affiliation: Department of Biology, University of California, Berkeley Mutualisms and biodiversityecosystem function E-mail: [email protected] ABSTRACT ABSTRACT Mid-elevational forests in Central America lie at the ecotone between diverse lowland tree communities that associate with arbuscular mycorrhizal (AM) fungi, and montane communities that are often dominated by ectomycorrhizal (EM) species of oaks and walnuts. At Fortuna in western Panama we find strong interacting effects of these community types with soil fertility resulting in dramatic compositional differences at fine (<1 km) spatial scales. These conditions provide opportunities to explore the mechanisms that could facilitate EM dominance. We find that the EM tree Oreomunnea mexicana (Juglandaceae) achieves local monodominance at Fortuna by reducing the availability of inorganic nitrogen to competing species. Reduced N availability, in turn is reflected in the isotopic composition of the EM fungal community, consistent with an increase in N sequestration by EM fungi as EM host abundance increases. Finally, a long-term N addition experiment in EM dominated forest has shown a strong growth response in AM tree species while EM tree species show no response. We are using legumes as a model system for identifying direct mechanisms by which microbial mutualisms influence biodiversityecosystem function (BEF) relationships. Mutualism theory identifies key resource-exchange traits that co-evolve between legumes and N-fixing rhizobia. These traits drive BEF patterns via their effects on niche differentiation (ND) and relative fitness differences (RFD) among legumes as well as between legumes and non-legumes. Mutualism theory also predicts how these traits will respond to global changes in the availability of resources exchanged between legumes and rhizobia. I will describe some of the results of our recent research on these topics. 15 THURSDAY | EARLY MORNING THURSDAY | EARLY MORNING JEFFERSON HALL Academic Affiliation: STRI E-mail: [email protected] TRUMAN YOUNG Paterns of Nitrogen fixation across 300 years of forest succession (co-authors:co-authors: Kelly Gravuer, Grace Charles, Corinna Riginos and Kari Veblen) Academic Affiliation: University of California at Davis E-mail: [email protected] 16 Microbes and Megaherbivores: initial patterns from the Kenya Long-term Exclosure Experiment (KLEE) ABSTRACT ABSTRACT Forests contribute a significant portion of the land carbon sink, but their ability to sequester CO2 may be constrained by nitrogen, a major plant-limiting nutrient. Many tropical forests possess tree species capable of fixing atmospheric nitrogen (N2), but it is unclear whether this functional group can supply the nitrogen needed as forests recover from disturbance or previous land use, or expand in response to rising CO2. Here we identify a powerful feedback mechanism in which N2 fixation can overcome ecosystemscale deficiencies in nitrogen that emerge during periods of rapid biomass accumulation in tropical forests. Over a 300-year chronosequence in Panama, N2-fixing tree species accumulated carbon up to nine times faster per individual than their non-fixing neighbors (greatest difference in youngest forests), and showed species-specific differences in the amount and timing of fixation. As a result of fast growth and high fixation, fixers provided a large fraction of the nitrogen needed to support net forest growth (50,000 kg carbon per hectare) in the first 12 years. A key element of ecosystem functional diversity was ensured by the presence of different N2-fixing tree species across the entire forest age sequence. These findings show that symbiotic N2 fixation can have a central role in nitrogen cycling during tropical forest stand development, with potentially important implications for the ability of tropical forests to sequester CO2. For over twenty years, we have been excluding different combinations of cattle, wildlife, and mega-herbivores (e.g., elephants and giraffes) from replicated plots in an African savanna, exploring various cascades associated with these keystone herbivore guilds. We have recently demonstrated multiple microbial responses, and infer others. These include microbial symbionts (mycorrhizae, gut bacteria, termite fungi), disease pathogens, and soil microbial communities. The later may contribute to documented differences in soil respiration associated with herbivore treatments. One of the more striking results is that soil microbial diversity is positively correlated with the number of herbivore guilds present and with tree density (itself modified by elephant exclusion). We are only beginning to unravel the mechanistic causes and ecosystem consequences of these patterns. 17 THURSDAY | LATE MORNING BRIAN SEDIO Academic Affiliation: Smithsonian Tropical Research Institute and Center for Biodiversity and Drug Discovery, Instituto de Investigaciones Científicas y Servicios de Alta Tecnología E-mail: [email protected] 18 THURSDAY | LATE MORNING Molecular networks reveal the interaction between foliar secondary chemistry and fungal endophytes in Psychotria and Theobroma cacao ERIC GRIFFIN Academic Affiliation: INDICASAT, Smithsonian Tropical Research Institute E-mail: [email protected] Foliar bacteria and soil fertility mediate seedling performance: a new and cryptic dimension of niche differentiation ABSTRACT ABSTRACT Thousands of secondary metabolites influence interactions between plants and microbes. Chemical differences among plant species can affect the microbes with which they interact. In turn, microbes alter the secondary chemistry metabolome of leaf tissue they inhabit. However, the overwhelming diversity of plant secondary chemistry and the phylogenetic rarity of any particular compound has long stymied efforts to understand the role that chemical defenses play in plant ecology and evolution. I take advantage of recent advances in tandem mass spectrometry informatics that enable the comparison of the structures of unknown molecules to each other and to libraries of known compounds. Mass spectrometry molecular networks reveal the chemical traits that determine the host ranges of fungal endophytes of co-occurring species of Psychotria, and also identify the effect on foliar chemistry of Theobroma cacao of inoculation with asymptomatic and pathogenic species of the endophyte Colletotrichum. The phyllosphere is one of the world’s largest microbial habitats and is host to an abundant and diverse array of bacteria. Nonetheless, the degree to which bacterial communities are benign, harmful, or beneficial to trees in situ is unknown. We tested the hypothesis that the net effect of antibiotics would vary substantially among host species (from harmful to beneficial) and this would be strongly mediated by soil resource availability. To test this, we monitored co-occurring tree seedling growth responses to commercial antibiotics among replicated resource supply treatments (N, P, K) in a tropical forest in Panama. Overall, the effect of antibiotics on performance was highly host specific. Perhaps more importantly, the degree to which foliar bacteria were harmful or not varied with soil resource supply. Our results demonstrate that foliar bacterial manipulations can have very strong positive and negative effects on seedling performance, and moreover these effects were clearly mediated by soil resource availability. Though speculative, we suggest that foliar bacteria may interact with soil fertility to comprise an important, yet cryptic dimension of niche differentiation, which can have important implications for species coexistence. 19 THURSDAY AFTERNOON SESSIONS THURSDAY | LATE MORNING TOBIN HAMMER Academic Affiliation: Dept. of Ecology and Evolutionary Biology, University of Colorado at Boulder E-mail: A minor role for microbial symbionts in caterpillar herbivory [email protected] 20 SCOTT MANGAN Academic Affiliation: Washington University, Saint Louis, Missouri E-mail: [email protected] Negative plant–soil feedback predicts (more than just) relative abundance of tree species in a tropical forest ABSTRACT ABSTRACT Over fifty years of research have uncovered numerous instances of microbial involvement in insect physiology and ecological interactions with plants. For example, in some herbivorous insect groups, microbes have critical roles in their hosts’ ability to digest, detoxify, or acquire sufficient nutrients from plant material. These studies have led to a conceptualization of all insects (and other animals) as “holobionts” whose biology is universally dependent on, and tightly integrated with, beneficial microorganisms. However, this work has largely ignored certain insect taxa that are otherwise well-studied, and which are highly diverse, abundant, and ecologically important. One such group is the Lepidoptera, the butterflies and moths and their leaf-feeding caterpillar larvae. Using 16S rDNA sequencing and quantitative PCR, I surveyed gut microbial communities from 150 species of wild caterpillar in Costa Rica and the United States. I found that caterpillars generally hosted low numbers of gut microbes, many of which may be latent pathogens and/or transients derived from foliage. A subsequent experiment on the model caterpillar Manduca sexta found that reducing the (already low) number of gut bacteria, using antibiotics, had no detectable effect on insect fitness. Together, these findings indicate that microbial symbionts may not be important to larval feeding and development for a major insect order, the Lepidoptera. Further, they suggest that animals are not universally and equally dependent on microbiomes, as is now commonly discussed. Quantitative observational methods and experimental manipulations will be useful in testing which insect-plant interactions are, or are not, mediated by beneficial microbes. Our previous experiments have shown that the net effects of soilborne microbes on plants exhibit a high functional level of species specificity, sufficient for the maintenance of local plant diversity. Further, the degree to which plants suffer from their own enemies differs across species. On BCI, less common tree species exhibit stronger negative interactions with their own soil-borne enemies (i.e. negative plant-soil feedbacks) than do more common tree species. Ongoing work by my group in both tropical forests of Panama and temperate prairies couples field and greenhouse experiments, plant pathology, and metagenomics to answer: What are the principle soil-borne enemies that drive negative plant-soil feedbacks? Do less abundant species always (or usually) exhibit stronger negative interactions with their enemies than those that are common? What are the underlying abiotic, physiological, genetic mechanisms that determine why some plant species suffer more from their own enemies at any given site? Do the effects of soil-borne microbes trump other processes such as direct competitive interactions as driving forces to the maintenance of diversity? Collectively, answers to these questions are required to more fully understand the degree to which plant-enemy interactions (relative to other mechanisms) are the driving force in determining plant-community assembly. 21 THURSDAY | EARLY AFTERNOON ERIN R. SPEAR Academic Affiliation: Department of Biology, Regis University, Denver, CO E-mail: [email protected] 22 THURSDAY | EARLY AFTERNOON Multi-host pathogens and the maintenance of forest diversity in Panama CAMILO ZALAMEA Academic Affiliation: Smithsonian Tropical Research Institute - University of Illinois E-mail: [email protected] Seed-fungal interactions in the soil: Impacts of fungal diversity on seed fate in tropical pioneer trees. ABSTRACT ABSTRACT Host-specific pathogens of plants are frequently credited with regulating the relative abundances of plant species and maintaining plant diversity under the Janzen-Connell hypothesis. Yet, in diverse forests, selection should favor phytopathogens with broad host ranges given the relative rarity of tree species and the passive dispersal of plant pathogens. Despite the ubiquity and postulated importance of phytopathogens in natural systems, we know relatively little about their identities, host ranges, and spatial distributions. Based on common garden experiments, culturebased surveys of fungi associated with symptomatic seedlings, and shadehouse-based inoculation experiments, we found that, in the diverse forests of Panama, fungal pathogens of seedlings are generally multi-host, attacking tree species in multiple families. Concordant with broad host ranges, operational taxonomic units of fungal pathogens were shared between forests (~45 km apart) with almost no overlap in the tree species present. Multi-host phytopathogens could influence forest community composition via interspecific differences in sensitivity to disease among tree species. We found that some tree species were seemingly resistant to all fungal isolates tested and others were susceptible to multiple isolates. Furthermore, the outcome of infection by a shared pathogen varied among tree species (e.g., tissue damage vs. death). Thus, multi-host phytopathogens may influence forest community composition via host-specific impacts rather than the host specificity originally envisioned under the Janzen-Connell hypothesis. In tropical forests, our knowledge regarding interactions between tropical seeds and their associated fungi is very limited. Using a seed burial and retrieval experiment established on BCI to simulate the soil seed bank, I examined seed fate at various temporal and spatial scales. Filamentous fungi recovered from seeds were isolated to pure culture. Total genomic DNA was extracted from cultures to assess potential associations among seeds and cultivable fungi. I have found that the composition of fungal OTUs that infect seeds is most strongly determined by host identity. Importantly, I found that fungi that tend to be associated with live seeds in one host were more likely associated with dead seeds of another host. Although plant host identity is the best predictor of the seed-associated fungal communities, associations between the best-sampled plant species and the most common OTU do not reveal narrow host-specificity. These results highlight the fact that not every fungal isolate is able to colonize seeds of every host species, even when seeds of potential host plants are in close proximity, but at the same time, a single fungus can colonize several hosts. I found differential effects of the same fungal isolates on germination and seed viability of different plant species. Together, these results highlight the importance of the various roles that microbial communities play in seed survival and plant recruitment, and therefore the relevance of soil microbiota in promoting and maintaining exceptional tropical plant diversity. 23 THURSDAY | LATE AFTERNOON THURSDAY | LATE AFTERNOON KRISTA McGUIRE Academic Affiliation: Department of Biology, Barnard College, and Department of Ecology, Evolution and Environmental Biology,Columbia University E-mail: [email protected] JOHN SCHROEDER Predicting soil microbial composition from tree identities and plant traits ABSTRACT Explicitly integrating aboveground-belowground interactions into testable theories of plant dynamics and ecosystem ecology requires a predictive understanding of the biotic and abiotic factors that structure microbial composition and function. Plant identity has been frequently cited as a key determinant of microbial composition, due to interspecific differences in chemical microsites that individual tree species create with root and litter inputs. On the 50-hectare plot at Barro Colorado Island we found that soil microbial composition was correlated with the taxonomic and phylogenetic structure of the aboveground plant community. Aboveground plant traits were more predictive of microbial composition than belowground root identities sequenced from the same soil core. In a similar study from the Luquillo plot in Puerto Rico, we found that individual tree species had unique microbial signatures in both soil and litter surrounding the tree bases, and that aboveground plant trait distance was correlated with distance in fungal composition. Together, these studies show how localscale variation in microbial composition can be predicted from aboveground tree composition, which has implications for scaling up aboveground-belowground relationships to the landscape. 24 Academic Affiliation: Department of Biology, Stanford University E-mail: [email protected] Host tree abundance affects specificity in a diverse community of Neotropical rootassociated fungi ABSTRACT Interactions between plants and root-associated fungi (RAF) affect ecosystem-level characteristics and processes including plant community assembly, nutrient cycling and diversity maintenance. Host-symbiont compatibility is a prerequisite for these processes, but information on critical patterns of host-association, such as how host-specificity varies with host abundance, is lacking. We analyzed the patterns of association between RAF and their tree hosts in a tropical rainforest, specifically addressing the hypothesis that a greater proportion of host specialists associate with common tree species than rare tree species. Using DNA metabarcoding, we measured host-specificity and characterized RAF communities associated with six species, including three common and three rare con-familial tropical trees. Three salient patterns emerged. First, we uncovered a remarkably diverse RAF community, comprised of 2,051 molecularly defined taxa. Second, family-level host-specificity was common across fungal functional groups (including arbuscular mycorrhizae, saprotrophs, plant pathogens, and others), and species-level host-specificity was also found for some functional groups. Third, a greater proportion of host-specialists associated with common tree species than with rare species, especially in the case of arbuscular mycorrhizae, confirming our hypothesis. These results suggest that host abundance influences the ecology and evolution of host-specificity and warrant further corroboration in other tropical and non-tropical systems. 25 THURSDAY | LATE AFTERNOON MERLIN SHELDRAKE Academic Affiliation: Department of Plant Sciences, University of Cambridge E-mail: [email protected] THURSDAY | LATE AFTERNOON A phosphorus threshold for the functioning of arbuscular mycorrhizal fungal symbioses in tropical forest ABSTRACT The functioning of plant associations with arbuscular mycorrhizal (AM) fungi — a major group of beneficial plant symbionts — is poorly understood in natural systems. AM fungi typically facilitate the uptake of limiting mineral nutrients by plants in exchange for plant carbon, but hundreds of non-photosynthetic plants — known as mycoheterotrophs — depend entirely on AM fungi for carbon as well as mineral nutrition. Here, we show that individual AM fungal taxa undergo distinct functional ‘phase changes’ in response to phosphorus in lowland tropical forests, affecting the success of their plant partners in a species-dependent manner. Mycoheterotrophs were entirely absent when soil exchangeable phosphate levels exceeded 2 mg P kg-1, both across a strong phosphorus gradient spanning the isthmus of Panama, and also in a long-term nutrient addition experiment. Experimental phosphorus addition did not eliminate the fungi required by the mycoheterotrophic plants, indicating that the absence of mycoheterotrophs was driven by a functional shift in the relationships between plants and their AM fungal symbionts that rendered the AM fungi inhospitable to mycoheterotrophs, rather than the absence of required fungal partners. The soil phosphorus concentration of 2 mg P kg-1 corresponds to a marked shift in tree community composition, indicating that our findings have broad ecological significance. The response of mycoheterotrophs helps to define a critical threshold for the functioning of plant–AM fungal symbioses in relation to phosphorus, a primary limiting nutrient, providing a key insight into the regulation of the symbiosis in a highly diverse ecosystem. 26 NATALIE CHRISTIAN Academic Affiliation: Department of Biology, Indiana University Bloomington E-mail: [email protected] Community assembly of endophytic fungi and their functional effects in Theobroma cacao ABSTRACT We need to better understand the basic ecological and evolutionary processes that govern host-associated microbiomes. Foliar endophytic fungi (FEF) are environmentally acquired symbionts, whose diverse communities reside cryptically within healthy photosynthetic tissue of all plant species. Here we show that manipulating local spore sources and vertical stratification within the forest canopy affects community assembly in the fungal microbiome of Theobroma cacao, which subsequently has pronounced consequences for plant health. Specifically, seedlings treated with T. cacao litter collected from healthy conspecific adults were the most resistant to pathogen infection. We also examined if plants can preferentially allocate nutrients to FEF. We inoculated leaves of T. cacao with combinations of beneficial, neutral, and harmful FEF and then traced allocation of nutrients to leaves using isotope-ratio mass spectrometry. We found that inoculation by a beneficial FEF increased plant nitrogen uptake compared to uninoculated controls, and that plants can preferentially allocate nutrients to FEF, the degree to which was dependent on FEF identity. Complementary in vitro tests suggested that FEF directly competed with one another. Finally, we found that when infected by a pathogen, plants increase allocation of N to infected leaves in the presence of beneficial FEF. In the absence of FEF, the host reduces N supply to pathogen-infected leaves. Taken together, this work elucidates how the fungal microbiome of plants assembles and is maintained, and informs what functional implications FEF have for plant host health. 27 AGENDA | stri.si.edu SmithsonianPanama Stri_panama