Lisa McDonald
Many species of plants show variable host plant chemistry; however, few studies have closely examined the ecological and evolutionary consequences of this variation on the specialist herbivores found on highly variable host plants. Although cardenolide chemistry has been long studied in the Asclepiadaceae (milkweed family), very little effort has been put into understanding this mode of defense in the related Apocynaceae (dogbane family). Members of the genus Apocynum are highly variable morphologically and are known to form fertile hybrids. This propensity to hybridize, combined with extreme morphological variation may be the primary reason that diagnosis of species in this genus has proven difficult. In 1930, Woodson described nearly 90 species in this genus, today there are thought to be 3-4 highly variable members of Apocynum in North America (Johnson et al. 1998): A. cannabinum, A. androsaemifolium, and their putative hybrid, A. x floribundum (=medium). Given the potentially high cost of coping with particularly noxious toxins like cardenolides, the ecological and evolutionary consequences of extreme host plant variation on members of the specialist arthropod community could be wide ranging. My research will concentrate on some of these possible consequences. In general, differences in the arthropod community composition might be expected, as might differences in the chemical defense strategy of herbivores that sequester cardenolides from their host plants. Additionally, local adaptation might lead to differences in population level preferences for a high and low cardenolide diet. Accordingly, performance differences may be expected between locally adapted populations feeding on noxious host plants. Finally, heritable differences in the sequestration ability of specialist herbivores might be an evolutionary consequence of particularly variable host plant chemistry. Less obvious outcomes of local adaptation between herbivores and their host plants might also lead to differences in both chemical induction and the magnitude or direction of indirect interactions between specialist herbivores feeding on these plants.
Jason Robinson
I am broadly interested in stream ecology, particularly in the factors that influence the distribution of organisms at different spatial scales. My M.S. research (NC State University, 2003) documented new records of several stream fishes in a small watershed in western NC, the upper Savannah (Toxaway and Horsepasture Rivers), that has a fish fauna distinct from all other rivers in NC. In this system, geological features (the uplift of the Brevard Fault) form barriers that have limited the upstream invasion of some fishes. Headwater streams in the project area had fish assemblages identical to those in the Little Tennessee and French Broad watersheds, suggesting that stream capture and headwater piracy have structured the composition of these fish faunas, as opposed to invasion from downstream.
During this project I became interested in benthic macroinvertebrates and spent the next several years working on biodiversity surveys in the Pisgah and Nantahala national forests, as well as devising a monitoring protocol suitable for use by non-professional volunteers. In 2005 I began working in Nate Sanders' lab (at UT), and with Chuck Parker (a USGS biologist stationed in the Great Smoky Mountains National Park) as a technician on an ambitious biodiversity survey of aquatic insects in 17 national parks in the Appalachian uplift, Piedmont, Highland Rim and Cumberland Plateau ecoregions. We are wrapping up the collections portion of this project and slugging through the sorting and identifications of our collections. To date, we have 34,256 specimens in our database and hope to add at least that many again before the completion of the project. This effort has resulted in the discovery of many new distributional records and the discovery of more than 8 undescribed species of caddisflies and stoneflies. A collaboration with the Bar Code Institute of Guelph University, and many others, has generated mitochondrial sequence data for over 1300 specimens of over 230 species of trichoptera collected from these national parks. These data will be used to test phylogenetic and biogeographic hypotheses that relate to the main question asked by the 17 park survey: How much of regional aquatic diversity is conserved by existing national parks?
Romina Dimarco
rdimarco@utk.edu
I am broadly interested in the ecological and evolutionary implications of plant/animal interactions, and address questions relevant to this by studying chemical ecology, insect ecology, behavior and genetics. More specifically, my current research interest is focused on understanding plant-insect interactions and how these interactions can affect species distribution, species coexistence and local adaptation. My focal study organisms are two genera of swallowtail butterflies in the tribe Troidini (Parides and Battus). Both are specialists on plants of the genus Aristolochia (Aristolochiaceae) that contain toxic alkaloids (nitrophenanthrene carboxylic acids) called aristolochic acids. These toxins are sequestered by Parides and Battus as larvae, rendering both larvae and adults chemically defended against most predators. Also, the relationships between these genera of butterflies and their host plant are very specific. The butterflies are highly adapted to their local species of Aristolochia and a change in the host plant produces notable changes in chemical sequestration and other aspects of the butterflies’ biology. This distinctive system is ideal for answering a variety of exciting questions. As part of my doctoral dissertation, I plan to assess: 1) whether co-occurring Troidini species show variation in usage of locally available Aristolochia species, which might indicate the partitioning of host plant resources, and 2) whether performance variation exists among butterfly species reared on different host plants.
Studying these butterflies in a range of habitats in both South and North America, and their relationships with their host plants, will allow us to have a deep understanding of the ecological and evolutionary processes at work in this highly specific plant-insect interaction.