2022 REU Projects

Bencosme, Gerardo (University of Puerto Rico - Río Piedras), Mentor: Corlett Wood (University of Pennsylvania).
Host-Microbe Interactions in a Warming World: Can warm-adapted microbes increase host fitness?
 Climate change alters abiotic factors such as precipitation patterns, surface temperatures and soil temperatures. These changes may impact ecological relationships such as host-microbe mutualisms. In turn, microbial presence can increase host survival rates under stressful conditions, such as increasing temperatures. Could microbial mutualists further aid in a plant population’s adaptation to climate change? In this study, we ask if warm-adapted microbes can increase host performance in warming environmental conditions. To address this question, we ran two experiments. First, we inoculated the legume Medicago lupulina with either warm-adapted or cold-adapted strains of rhizobia and grew plants under experimentally warmed conditions and ambient conditions. To evaluate host performance, we determined the number of leaves and estimated stem length per plant. Also, we ran a second experiment to test for rhizobia thermal adaptation. We cultured rhizobia strains from high and low elevations in cold, room and warm temperatures. For our first experiment, we hypothesized that the effect of growth temperature on plant performance would depend on the rhizobia a plant was inoculated with. For our second experiment, we hypothesized that rhizobia performance under the different temperature assays would depend on rhizobia origin. Analysis of variance (ANOVA) results indicated that rhizobia source elevation and treatment temperature had no significant effect on plant performance. However, data from our second experiment shows that rhizobia strains from high elevations were thermally adapted to cold conditions.

Brueshaber, Matthew S. (Nash Community College), Mentor: David Beamer (Nash Community College).
The effects of competition on populations of the Northern Gray-Cheeked Salamander (Plethodon montanus)
Abstract: Past research has shown that geographically sympatric species within the salamander genus Plethodon are often allopatric in elevational distribution (Grobman 1944, Hairston 1949).  Plethodon montanus is a species of large Plethodon, which is often allopatric with other large species of Plethodon, as it often lives alone on mountaintops (Hairston 1949, Highton & Peabody 2000).  There have been many hypotheses and a variety of research into what causes this allopatry, however there has not yet been conclusive evidence.  One leading hypothesis is that interspecific competition or interference is preventing these species from living sympatrically.  To test this hypothesis we compared population density and home range size in populations of P. montanus which were in the presence of varying levels of competition.  We used eight 5 meter x 5 meter plots to perform a capture, mark, and release study at Mountain Lake Biological Station and Whitetop Mountain in Virginia, USA.  Within each plot we also measured a variety of environmental metrics to increase our confidence in the results of our analyses.  We found no significant correlations between home range size and competition, nor between home range size and any of our environmental metrics.  However, we found highly significant correlations between population density and competition, and between population density and each of our environmental metrics.  Due to insufficient sample size we were unable to confidently determine the nature of the correlation between population density and competition.  However, a lack of a strong negative correlation could indicate that competition is not the primary cause of the allopatry displayed by large Plethodon.

Feist, Victoria (University of Virginia), Mentor: Corlett Wood (University of Pennsylvania).
The Symbiont Battleground: Untangling the role of parasites in microbial community variation
Abstract: Parasites can harm hosts in a variety of ways, one of them potentially being through a direct interaction with the host’s microbiome. This interaction has the capacity to compositionally change these microbial communities. However, much of what is known about this phenomenon does not reflect functional changes in the microbiome, nor whether the effect of parasites is significant enough to contribute to natural microbial community variation. In this study, we aimed to characterize functional variation among rhizosphere microbiomes of Medicago lupulina across numerous populations and address whether the parasitic root-knot nematode, Meloidogyne hapla, could contribute to this functional variation. We addressed these questions by comparing microbiome function between nematode-infected and uninfected wild plants across multiple field sites and via experimentally manipulating nematode infection in the  greenhouse. Microbial communities of Medicago lupulina significantly differed between field sites. Within sites, the microbiomes of uninfected and infected plants significantly differed in function, providing evidence of natural variation within plant populations based on infection status. However, parasites did not induce functional differences in the greenhouse two weeks post-infection. Taken together, our results suggest that the differences we detected between infected and uninfected plants in the field may have preceded the infection and potentially resulted in variation in host susceptibility to Meloidogyne hapla.

Halbert, Ella (Oberlin College), Mentors: Chloé Lahondère and Joanna Reinhold (Virginia Tech).
Feces, fungus, and blood… Understanding how mosquitoes target and transmit pathogens to their frog hosts
Abstract: Culex territans is a mosquito species that feeds almost exclusively on ectothermic hosts and has the potential to transmit pathogens. There is a lot of research on warm-blooded feeding mosquitoes, how they locate their hosts (eg. thermal and chemical cues), and what pathogens they transmit. However, little is known about how this species locates and interacts with its hosts. With amphibian populations in decline worldwide, it is pertinent to understand any potential threats, such as vector-borne diseases. In this study, I focused on three main objectives: 1) determine if Cx. territans is attracted to anuran feces, 2) discover if Cx. territans can carry  Batrachochytrium dendrobatidis (Bd) at Mountain Lake Biological Station (MLBS) as well as the prevalence of Bd among frog populations, and 3) ascertain if Cx. territans is transmitting blood pathogens (ranaviruses and trypanosomes) at MLBS. To address these questions, olfactometer assays, transmission assays, and PCR techniques were performed. I found that Cx. territans 1) is not attracted to anuran feces, 2) can transmit Bd in a lab experimental setting, and 3) can uptake ranaviruses and trypanosomes. This project will provide insight into mosquito-host interactions and the evolution of blood-feeding, as well as amphibian conservation.  

Macpherson, Esme (University of Toronto), Mentor: David Beamer (Nash Community College).
Puzzling Plethodontids: Looking for traces of an introduced Dusky salamander (Desmognathus, Plethodontidae) using DNA barcoding and morphometric analyses
Abstract: Defining species and species boundaries is difficult in many taxonomic groups and of importance to many fields of biology.  Lungless salamanders (Plethodontidae) often pose a challenge to taxonomists because of their high diversity, variable morphology, and frequent hybridization. One group once the Desmognathus ochrophaeus complex, has recently been divided into several sets of sister taxa, and provides an excellent study system for investigating species relationships. One part of this complex, Desmognathus orestes, is the allopatric sister species to Desmognathus ochrophaeus but may have been anthropogenically introduced within its range at a field station in southwest Virginia. We used DNA barcoding to examine the presumed populations of D. ochrophaeus salamanders at the Mountain Lake Biological Station, and discovered that most carry D. orestes mtDNA. The origin of the naturalized D. orestes appears to be Whitetop Mountain, the type locality and historic origin of another salamander introduction in the late 1930s. We further employed linear analyses on morphological data to identify if the two species have unique physical traits, and found several significantly variable body dimensions. The two populations surveyed also appear to have significantly varying morphological characteristics, possibly suggestive of local adaptation or founder’s effect. These results emphasize the importance of employing genetic tools in understanding community-level species composition, especially with cryptic species. Future work should consider nuclear DNA data to clarify how the naturalized D. orestes appears to have integrated into the community, and whether the native D. ochrophaeus remains present at the station.

Pattisall, Keely (University of Virginia), Mentor: Sarah McPeek (University of Virginia).
Species interactions vary locally on small spatial and temporal scales
Abstract: Variation in species interactions across populations and through time have been studied to better understand how and why this variation occurs. However, very small scale spatial and temporal variation could explain variation in interactions within a population. In plant-pollinator interactions, this small-scale variation could shed light into how nectar influences pollinator visitation to plants. In this study, I measured how per flower mean nectar variation between patches within the plant population influences pollinator visitation to individual plants. I also analyzed how variation in temperature within the flowering season affects the per flower nectar expression of individual plants. We found that both individual per flower mean nectar volume and patch level per flower mean nectar volume significantly contribute to differences in pollinator visitation. We also found that temperate variation affects nectar expression of flowers, meaning the same plant could express its nectar trait differently throughout the flowering season. This study provides insight into how plants and pollinators interact within a population and a single flower seasoning. These results could explain why extreme nectar variation is maintained at the population level.

Tassell, Darby (Indiana University), Mentor: Sarah McPeek (University of Virginia).
Behavioral studies on the invertebrate community of Amianthium muscaetoxicum
Abstract: Many plant species have diverse invertebrate communities that live and feed on their plant hosts. In a highly toxic plant, such as our study species Amianthium muscaetoxicum (Melianthiaceae) or “fly poison”, it is curious when insects are able to safely feed on the plant’s tissue and nectar. It is especially interesting that the plant’s pollinators, beetles Strangalepta abbreviata (Cerambycidae) and Trichiotinus affinis, (Scarabaeidae) are attracted to this toxic nectar and seemingly feed on it almost exclusively. This study aims to investigate the adaptations and reasons behind these behaviors, first through a study of biodiversity, and then through a study of pollinator foraging behavior. A biodiversity survey of A. muscaetoxicum plants revealed invertebrates of eleven orders and over thirty families, providing us with a multitude of further research directions. A choice assay revealed a trend of S. abbreviata and T. affinis preferring toxic nectar concentrations over non-toxic sucrose solution. Both of these experiments require further data collection, but we were able to learn more about the A. muscaetoxicum invertebrate community and their interactions with the plant.