Download stri science symposium - Smithsonian Tropical Research Institute

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 |
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