NSF Dimensions Booklet Abstract

Project #1542639:

Dimensions: Collaborative Research: Biodiversity Gradients in Obligate Symbiotic Organisms: A Case Study in Lichens in a Global Diversity Hotspot

University of Colorado Participants:
Erin Tripp

Nolan Kane

Christy McCain

New York Botanical Garden Participant:
James Lendemer

400-450 Word Project Summary:

Obligate symbioses are relationships between two or more species that depend entirely on each other for growth and survival. Such symbioses characterize some of the most common and ecologically important relationships on Earth, ranging from human gut bacteria to diseases to corals to specialized plant-pollinator relationships. Many of these obligate symbioses are imperiled by unprecedented rates of environmental change and permanent biodiversity losses. Compared to single branches on the tree of life such as birds, flowering plants, or mammals, much less is known about factors that facilitate or limit the geographical distributions of obligate symbioses that abound in nature. Moreover, research on biodiversity distributions has focused largely on abiotic factors (e.g., temperature, precipitation, elevation) rather than on biotic factors (i.e., other organisms) that influence geographical distributions. This project aims to transform understanding of factors that impact diversity and distributions of obligate symbiotic biodiversity through investigation of lichens as a model system in a unique natural laboratory and global lichen diversity hotspot: the southern Appalachian Mountains.

Proposed mechanisms for factors that generate and maintain biodiversity remain contentious despite decades of research. Biotic factors have long been proposed as drivers but are rarely studied due to the difficulty of assessing the multitude of possible interactions. Because of the inherent biotic interaction that exists between obligate symbionts, this project will explore both biotic and abiotic drivers of biodiversity across multiple dimensions. Through field and genomic inventories of lichens in a biodiversity hotspot, this project will generate and investigate data from symbiotic biodiversity initiated from a single information source: a unique museum voucher. Across local, regional, and landscape scales, inventories will yield site-specific metrics for phylogenetic (including taxonomic) and functional diversity together with site-specific metrics for a mostly unexplored genetic dimension—potential of diversity—that quantifies the availability of compatible symbiont propagules in the environment. Analyses of these metrics in light of biotic and abiotic variables will enable assessment of factors that impact overall dimensions of biodiversity. These analyses will also permit understanding of interactions among dimensions, for example, whether phylogenetic, functional, and genetic dimensions are positively correlated and predicted by the same sets of variables, or in what contexts other types of correlations exist. This project will yield two major conceptual advances in ecology and evolutionary biology. First, information gained will likely reveal new, emergent properties of biodiversity gradients in symbiotic organisms. Second, deconstructing constraints on individual partners of the symbiosis and quantifying feedbacks between/among them will make possible full analysis (i.e., including biotic constraints) of the factors that impact diversity and distribution of the symbiotic organism as a whole.

Broader impacts of this research will improve scientific literacy, expand awareness of symbiotic biodiversity, build capacity in U.S. lichenology, broaden collaborations between scientists and land managers, and establish new ‘big data’ resources for a diverse audience of researchers and educators. Finally, this project will advance conservation of an ecologically important group of understudied organisms in a premier biodiversity hotspot.

25-40 Word Synopsis: Diversity and distributions of obligate symbiotic organisms: lichens as a model system for deconstructing biotic and abiotic factors that drive major patterns in macroecology and macroevolution.

3-8 Print Resolution Photographs (300 dpi minimum JPEG format only):

This slideshow requires JavaScript.

Lichen Photos:

            Anaptychia palmulata: A foliose lichen of the southern Appalachian Mountains (Voucher   Specimen: James Lendemer 33129 [NY Herbarium]; Photo Credit: Erin Tripp)           

Lobaria pulmonaria: An ecologically important foliose lichen indicative of high quality habitats in   eastern North America (Voucher Specimen: Erin Tripp 4994 [NY Herbarium]; Photo Credit: James Lendemer)

Early Stages of Lichen Development: One of the most important biotic interactions for obligate   symbiotic organisms is the earliest stages of development in which suitable partners must successfully encounter one another in nature. Shown here is a germinating spore of a lichen mycobiont (Rhizocarpon disporum) encountering and enveloping a potentially suitable photobiont with its fungal hyphae (Photo Credit: Vanessa Díaz)

People Photos:

Lichen Reproduction 6: Masters student Vanessa Díaz (background) and undergraduate student researcher Heather Stone (foreground) install forest experiment to trap lichen propagules, to document early stages of lichen colonization. Field supplies: cheese cloth, lab tape, and microscope slides soaked in various media to cultivate mycobiont and photobiont (Photo Credit: Erin Tripp)

James Lendemer: Working in laboratory to identify field collections at the Southern Appalachian Highlands Learning Center (aka ‘Purchase Knob’), Great Smoky Mountains National Park (Photo Credit: Erin Tripp)

Landscape Photos:

GSMNP: Great Smoky Mountains National Park contains more species of lichens than any other national park in the United States and is an important reservoirs of lichen biodiversity within the greater southern Appalachian Mountains. GSMNP is also the most visited national park in the United States and as such, park staff face a delicate balancing act between facilitating tourism and needing to protect the park’s natural heritage by minimizing human impacts.

Purchase Knob: The Appalachian Highlands Science Learning Center at Purchase Knob is a high altitude educational facility located in the heart of the southern Appalachian Mountains. Each year, staff members Paul Super, Susan Sachs, and associated personnel host upwards of 5,000   visiting students, teachers, scientists, and volunteers with the common goal of expanding       knowledge, awareness, and scholarship of the rich biodiversity of the southern Appalachians (Photograph taken from front porch of Purchase Knob; Photo Credit: Molly Stevens)

Recent publications or news items related to the project

• PIs Lendemer and Tripp publish a new species of lichen endemic to high elevation, nutrient-rich rocks of the Southern Appalachians (Lendemer & Tripp [2015], The Bryologist 118: 1-10: Lecanora anakeestiicola (Lecanorales): an unusual new fruticose species from Great Smoky Mountains National Park in eastern North America

• Co-PI Kane is currently training undergraduate and graduate students to assemble lichen mycobiont and photobiont genomes during his Genomics course at the University of Colorado

• PIs Tripp and Lendemer are currently in the process of recruiting PhD students to advance aspects of the Dimensions research;

• Co-PI McCain is spearheading the development of the field inventory sampling strategy; fieldwork will begin in early 2016.

• PIs Lendemer and Tripp are collaborating with the Center for Biological Diversity to assess the federal conservation status of ~30 rare and mostly endemic southern Appalachian lichens

This slideshow requires JavaScript.

Between 2-4 October 2015, students enrolled in Plant Systematics (EBIO 4520/5520) traveled to Black Canyon of the Gunnison National Park for a botany camping trip. Participatory were: Reese Beeler, Ryan Byrne, Keric Lamb, Mandy Malone, Kelsey McCoy, Matt Schreiber, and Sydney Sharek along with Erin Tripp (course instructor) and Matt Sharples (teaching assistant). A botany fieldtrip anywhere in October in Colorado is risky, given we hit the end of the growing season a month ago. We needed a site that was sheltered from early frosts and cold weather, and speculated that the depths of a deep canyon might provide such refuge for a few lingering plants in flower or fruit.

We were right! On Friday afternoon, we punched it down to Black Canyon of the Gunnison, arriving late but not too late for homemade tostadas. We stayed at the North Rim Campground, which is a very small, funky, climbers’ favorite. The Black Canyon is without doubt one of the most dramatic landscapes in Colorado and indeed much of the west. It derives its name from the darkness created by the sheer walls, narrow width, and tremendous depth, which limit sunlight illumination of some portions of the canyon bottom to less than 30 minutes on any given day. Over the last 2 million years of Earth’s history, the canyon was carved out by the massive and in some parts very remote Gunnison River. Other canyons of the West are longer, and some are deeper, but none combine the length, depth, and sheerness of Black Canyon.

We awoke Saturday morning to start our long descent down quite the extreme slope – only 1.75 miles in length but 2,000 ft. vertical descent – a Class 3 scramble affectionately known as the “S.O.B route”. This is one of the only routes in the entire area that can be used to reach the bottom of the canyon without advanced, technical climbing. Conveniently, it leaves directly from the campground. We took our time descending, learning the dominant plant community along the way: Artemesia tridentata (Sagebrush), Juniperus osteosperma (Utah Juniper), Quercus gambelii (Gambel Oak), Amelanchier alnifolia (serviceberry), Cercocarpus ledifolius (Mountain Mahogany), and Pinus edulis (Pinyon Pine – one of many sources of pine nuts, which are actually not nuts but rather seeds). The bottom of the canyon was lush and thrilling – we learned several additional species as a group before setting out on our own in various directions. Many of us took a welcomed dip into the Gunnison – a perfect 58˚F.

We reached camp around 5 pm. The weather was balmy – mid 60s and so delightful. We spent the next 2 hours sitting at the picnic table keying various plants we saw at the bottom of the gorge. Among them was Petrophytum caespitosum (Rock Spiraea), which grows “on precipitous and often inaccessible canyon walls” (in Dr. Bill Weber’s words) and Polanisia dodecandra (Clammyweed) – a curious member of the caper family (Capparaceae) and one that represents a new plant record for Montrose County! Dinner was a botanical medley (squash and zucchini [Cucurbitaceae], shallots & garlic [Alliaceae], carrots [Apiaceae], potatoes [Solanaceae]), lightly tossed with olive oil [Oleaceae], salt, black pepper [Piperaceae], and chipotle powder [Solanaceae again…sigh], wrapped in foil then cooked on hot embers in the fire for a perfect 25 minutes. We all had a solid night’s rest before heading home the next morning.

The journey home: complete with blazing aspens and a flat tire with no easy means for a fix.  But we managed with a tire plug and the compressor of a kind stranger. That’s life as a biologist: never a dull moment.

[The below write-up is based on a manuscript in press: Rabinowitz, O. and E. Tripp. 2015. A note on the observable bark Colorado of Populus tremuloides. Western North American Naturalist]

The Mystery of Aspen Powder

I was born in Israel, raised in New Jersey, and graduated with a B.A. in Ecology and Evolutionary Biology at The University of Colorado-Boulder in 2014. In the late fall of 2013, I joined the Tripp Lab to pursue a research question that Erin and I had discussed when I was a student in her Plant Systematics class. I wanted to find out what the powder found on aspen tree bark was made of. I asked Erin, who suggested the question was to her knowledge an unanswered one. I immediately signed up for independent study, and together we designed a study aimed at elucidating why aspen tree bark was powdery, and what the possible functions of this powder are.

We began our investigation with a literature review in November of 2013 followed immediately by fieldwork. Most people who have put their palms to an aspen tree are familiar with this curious powder in question. It tends to stick to your fingers and feels like a dusty chalk. Observations made by scientists who studied the aspen tree in the 1900’s recorded many helpful observations about the presence and color of the powder. Some non-scholarly sources claimed (and still claim) that the powder is actually a wild yeast that can be used for homestyle fermentation, or as a natural sunblocks. The most recently recorded observation was made by Univ. of Colorado Emeritus Professor (and Botany Curator) Dr. William Weber in his Colorado Flora: Eastern Slope, published in 2012. In that work, Dr. Weber speculated that the powder might be the developing thallus of a lichen.

Erin and I devised a working hypothesis that the white powder that characterizes aspen bark was actually aspen bark cells and that beta-carotene was the pigment responsible for the orange coloration of the powder. Beta-carotene is a carotenoid important to plant photosynthesis: not as an active contributor to the process but rather a molecule that helps transmit energy to chlorophyll while also playing a protective role for chlorophyll via its antioxidant properties. Starting in December of 2014, we collected samples from 11 aspen populations in Boulder County. Small squares of bark were cut, tagged, returned to the lab, then refrigerated. Once dry, thin, hand cross-sections of samples were prepared via thin hand and then photographed under magnification for further study. Subsamples were then pulverized and extracts of bark pigment were made with acetone. These extracts were spotted onto Thin Layer Chromatography (TLC) plates to determine presence or absence of photosynthetic pigments and accessory pigments present in the bark powder.

Microscopy and cross-section analyses revealed that the bark layer of the aspen tree is divided into three layers (from inner to outer): the cork cambium, a layer of orange cells, and finally a layer of white cells. The cork cambium is immediately subtended by green, photosynthetic chlorenchyma, and our TLC trials confirmed that this tissue layer contains all photosynthetic pigments you would normally find in the leaves (e.g., beta-carotene, pheophytin, chlorophyll-a, chlorophyll-b, and xanthophyll). In contrast, the outer two layers (orange, white) contained no photosynthetic compounds. As such, the orange pigmentation present in powdery aspen bark is not beta-carotene and remains unidentified. The orange layer is composed of heavily conglutinated cells that, as they age, become white and lose cohesion.

Our study demonstrated that aspen trees exhibit a unique method of bark cell shedding. The accumulated layer of bark cells on the surface of aspen trees do not stick together and do not form a solid mass of protective tissue. Rather, the aspen sheds mature bark cells in a powder so that sunlight can continue to penetrate the cork and cambium to reach the chlorenchyma-rich later. When powder is removed from aspen trees, the orange cambium is visible above the verdant chlorenchyma directly beneath. Younger cork cells tend to be orange in color whereas older cork cells are white and give aspens their ghostly appearance.

Many questions remain regarding the physiology of aspens and aspen bark. What is the orange pigment responsible for the orange hue? Is sunlight the primary factor that bleaches the orange bark cells? Does weathering and physical removal of white cork cells make aspen bark more prone to sun-scald? How do aspens prevent secondary infection by organisms without a thick bark layer? Oren thinks these questions can be answered by the next undergraduate to join the Tripp Lab!

Our manuscript is currently in press in the journal Western North American Naturalist. We thank Barbara Denmig-Adams and William Adams for early conversations on the research topic.

 

 

***

 

This slideshow requires JavaScript.

I am a Boulder native and a recent graduate of CU-Boulder. In the Tripp Lab, I began my work on a project in collaboration with the COLO Herbarium (co-advised by Collections Manager Dina Clark) regarding variation in a perennial shrub known as Amorpha nana, or colloquially, Dwarf Indigo. This plant has been treated as a single species in western North America, but some populations of Dwarf Indigo in southeastern Colorado, specifically in the Purgatory River Watershed, an extensive area of remote canyons and tablelands that stretches south of the Arkansas River Valley to the New Mexico State Line, are rather different in appearance than populations of Dwarf Indigo elsewhere in the West. Could Purgatory populations represent a different species? In order to find out, I started comparing the DNA of Amorpha nana from the Purgatory to the DNA of Amorpha nana from other locations in the West.

My project eventually evolved to include the study of other species found statewide that are also different in appearance in the Purgatory.  Our working hypothesis is that, because this unique and remote area is at an intersection of vastly different ecological areas (north of the Chihuahuan Desert and east of the Rockies) and consists of miles of isolated canyons, the Purgatory Watershed might represent a region of neoendemism in western North America. Neoendemism refers to the recent evolution of new species that haven’t yet had time to disperse to different geographic areas—in other words, newly evolved species that are endemic (restricted to) a very small geographic area of Earth. Thus far, I have found evidence that Dwarf Indigo harbors a molecular signature of neoendemism in southeastern Colorado, with unique DNA mutations specific to plants of this area and not occurring in any other populations of this species. I am now branching out to test this hypothesis of neoendemism in other plants of this area including cacti and aquatic species.

This summer, I made a field trip to the Purgatory with Dina, Dr. Tripp, and graduate student Vanessa Diaz. Although field and lab work are very time consuming, I’ve enjoyed doing research in Dr. Tripp’s lab and with Dina and Dr. Tripp in the University of Colorado Herbarium because all results (perhaps even results that do not support the hypothesis) yield new insights into ecology and evolutionary biology, which I find to be very exciting. I hope that the work I am doing will inspire others to pursue research on the rich and unexpected diversity and rich evolutionary histories that can be found in southeastern Colorado!