2010 REU Projects

Barco, Brenden (Duke University).  Mentors:  Peter Fields and Andrea Berardi (University of Virginia).
Investigations of male fertility in Silene vulgaris (Caryophyllaceae).
Abstract: Silene vulgaris (Caryophyllaceae) has long been a model system for studying population genetics and the effects of genomic conflicts, specifically an epistatic interaction between cytoplasmic male sterility genes and nuclear male fertility restorers. I investigated the extent to which male fertility is affected by this genomic conflict, and most notably whether females are truly male-sterile. Numerous traits of interest such as sex ratio, calyx pigmentation, number of flowers, number of fruits, calyx dimension, fruit dimension, pollen viability, and pollen dimension, and level of inbreeding were measured and assessed in terms of site and sex-specific effects.  Individuals from six populations in Giles County, VA were sampled (n=67). Sex ratio varied greatly among populations. There was no relationship between calyx pigmentation and male fertility in S. vulgaris. Flower and fruit number were impacted by site effects to a great extent, and calyx and fruit width to a lesser extent. This is likely due to the presence of disturbance regimes such as mowing. As expected, hermaphrodites were also found to have on average a greater percentage of viable pollen, but with a few exceptions. I found that some females had viable pollen, though anther dehiscence was still unlikely to occur. I also controlled our fitness measurements with an estimate of heterozygosity. I found a significant interaction between sex and genomic heterozygosity affecting two fecundity measures, pollen viability and flower number, which I hypothesize to be a result of increased heterozygosity being correlated with an increased likelihood of exposure to nuclear restorer alleles.

Fetters, Tamara (Virginia Tech.).  Mentor:  Kristal Cain (Indiana University).
Examining the role of preen oil in nest predation. 
Abstract: Ground nesting birds are under selective pressure by olfactory-oriented mammalian predators to minimize nest odor in order to limit nest predation. The odor of the nest may be attributable to the volatile compounds in preen oil, which are transferred to the nest during incubation, making these preen oil volatiles a potential target for selection. We compared nest predation rates on artificial nests that are treated with the scent of the Dark-eyed Junco (Junco hyemalis) a common ground nesting species, and the scent of the House Finch (Carpodacus mexicanus), a novel tree nesting species, in order to determine if preen oil plays a role in rates of nest predation. We then compared nest predation rates on artificial nests treated with the scent of female or male Dark-eyed Juncos in order to determine if nests of the incubating sex were preferentially predated. We found that nests treated with no scent or the scent of the common ground nesting species were predated faster than those treated with the scent of the novel tree nesting species, though the probability of a nest being predated throughout the trial did not differ across treatments. We also found a trend towards nests treated with the scent of the incubating sex being predated more quickly than nests treated with the scent of the non-incubating sex. These results indicate that mammalian predators can differentiate between preen oil odors from different bird species and from different sexes, and that preen oil may serve as an olfactory cue that indicates whether or not an item is a food source.

Forrester, Nikki (College of William and Mary).  Mentors:  Henry Wilbur and Becky Wilbur (University of Virginia). 
The spatial distribution of Eastern Hemlock and Yellow Birch.
Abstract: Two species co-dominant forests are ideal communities for studying maintenance of species diversity. Tsuga canadensis and Betula alleghaniensis seem to be paired in certain forest communities, yet the precise relationship between these species remains undiscerned. The aims of this study are to determine (1) what factors influence growth and development of T. canadensis and B. alleghaniensis trees, (2) whether canopy layer T. canadensis and B. alleghaniensis trees are positively associated or randomly distributed, and (3) whether canopy layer T. canadensis and B. alleghaniensis trees occupy different niches. Based on field observations, there seems to be a positive association between herb layer individuals of one species and canopy individuals of the other species. If this observation holds true, the processes that generate such a pattern are sufficient to maintain a stable, mixed stand. Herb layer dynamics were inferred by surveying plots along each transect. Canopy layer spatial distributions were estimated by measuring distance to nearest neighbors. Canopy cover and substrate are important factors for B. alleghaniensis and T. canadensis growth and survival. There was positive association between seedlings, however, this pattern was not observed in any other size classes. Instead, B. alleghaniensis and T. canadensis appear to occupy different microhabitats within the forest community. Understanding the dynamics in simple co-dominant forests is a crucial step in determining the mechanisms that permit species co-existence and promote diversity. Knowledge of these dynamics can then be applied to more complex communities.

Hawkins, Shalantae (Hampton University).  Mentor:  Barbara Abraham (Hampton University). 
The resources utilized by native bees during late spring/early summer in Giles County.
Abstract: [missing] 

Johnson, Andrew (University of Virginia).  Mentors:  Henry Wilbur and Becky Wilbur (University of Virginia). 
The effect of American Chestnut density on the occurrence of chestnut blight.
Abstract: Cryphonectria parasitica is a highly virulent pathogen abundant and endemic throughout the entire range of one of its target hosts in North America, Castanea dentata. The emergence of C. parasitica in North America as an invasive species in the 20th century almost entirely destroyed old growth chestnut and chestnut-oak forests across much of Eastern North America.  At present, C. dentata endures as an understory species with sprouts from the root collar unable to grow into the canopy before becoming infected with C. parasiticaand dying. In order for C. dentata to one day return as a dominant canopy tree, resistant strains and new forestry techniques must be employed to maximize the chance of hybrid C. dentata survival not just as a seedling, but as a canopy tree. In order to accomplish this re-introduction, information on the epidemiology of C. parasitica must be assembled to make informed decisions regarding where and in what conditions to reintroduce the species. The effect of C. dentata density on the occurrence of C. parasitica in a region will be vital in determining the area in which to introduce hybrids based on level of their resistance. 

 Stem density and percent disease occurrence within random, circular sample plots were taken from stands in areas of varying C. dentata density to estimate the correlation between the density of C. dentata and its infection with C. parasitica. Linear and quadratic regression analysis was performed with the collected data and indicated no effect of density at any level on the occurrence of C. parasitica. Several reasons may account for this lack of density dependence in C. parasitica infection, for example the unknown spore dispersal distance of C. parasitica, the spatial distribution of C. dentata in modernforests, alternative hosts, and fauna specifically attracted to C. dentata.

Lane, Gabriel (Middlebury College).  Mentors:  Eric Nagy and Laura Galloway (University of Virginia).  
Limiting resources and herbivory tolerance in an understory herb.
Abstract: The ability to tolerate herbivory is tightly linked to the availability of resources, though this interaction depends greatly on the type of damage sustained and the biotic and abiotic conditions at time of damage and during recovery. In this study, I investigated factors involved in herbivory tolerance with Campanulastrum americanum, a palatable forest edge herb which has been shown to be less tolerant to deer herbivory in light gaps than in the understory. Specifically, I addressed the following questions: (1) Are plants in light gaps browsed more heavily than those in the understory? (2) Are there differences between the architecture of plants in gaps and in the understory? (3) Does the timing of damage matter for tolerance? (4) Are the plants limited by water in their tolerance of damage? (5) Is the loss of fitness observed in these plants due to loss of growth or photosynthetic potential? The first two questions were investigated by observing natural growth and herbivory patterns. The remaining questions were approached through a manipulative field experiment involving only simulated herbivory. Plants in light gaps were browsed more heavily than those in the understory. Plants in gaps had a greater number of meristems but understory plants had a greater proportion of meristems in the upper portion of the plants. The role of timing in tolerance was ambiguous; total length of branches was significantly greater in early damaged plants but there was no difference in flower number between early and late damaged plants. Water did not have a significant effect on herbivory tolerance. The loss of tolerance in damaged plants was clearly due to lost growth potential, not lost photosynthetic potential. Of the factors I identified as possible mechanisms for the differential tolerance based on light environment, only growth response based on timing was significant, though data on fruit number is pending. These results suggest that there is likely another mechanism responsible for the pattern.

Mitchell, Zenovia (Hampton University).  Mentor:  Barbara Abraham (Hampton University). 
A comparison of bee communities by roadside survey along route 613 using bee bowls.
Abstract: Developing an understanding of the native bee community is important for getting to know, and to appreciate the plant/pollinator relationships that support natural ecosystems and the pollination of crops. There is an estimated 25,000-30,000 species of obligate flower visiting bees, many of which play an important role on an evolutionary scale. The activities of pollinators makes them agents of selection and gene flow, causing plant speciation and molding flower phenotype (Kearns et al., 1998). Most bee species are solitary in terms of interaction with their own kind; they have individual nests in which the females lay eggs that they solely care for in cells (Stubbs and Coverstone, 2009). Accordingly, this study focused on determining whether or not there were differences among native bee communities at sites along Route 613 in Giles County, Virginia. Community ecology is important for understanding distribution, abundance and interactions between coexisting populations. This study will use a measure of species diversity to describe native bee communities. The community will be sampled using three colors of bee bowls to maximize catch. Studies have documented results of trials that compared numbers of bees captured across a wide variety of ultraviolet and non UV colors. The results showed that yellow, blue, and white bowls were effective at capturing bees, and their UV counterparts were perhaps more effective (Droege, 2010).

Pandit, Meelyn (Indiana University).  Mentor:  Elizabeth Carlton (Indiana University). 
Is song performance an honest indicator of immunological state in Dark-eyed Juncos?
Abstract: Between organisms, signals are any type of trait that conveys some form of information.  A signal becomes honest when the signal correlates with some form of quality and when the signaler cannot lie about its quality through its signal.  Bird songs are a broadly studied signal, and a characteristic of songs that may signal quality is song performance.  Song performance is a way of measuring how physiologically demanding it is to sing a song by measuring the trade-off between trill rate and frequency bandwidth.  Song performance may be an honest signal because only high quality individuals can sing near their physiological limit.  Thus, we hypothesized that song performance may be used by birds to signal the current immunological state or body condition of an individual.  This study examined if song performance and song rate were honest signals of immunological state and body condition in the Dark-eyed Junco.  Using a high performance song playback, a male Dark-eyed Junco’s song output was recorded and analyzed for trill rate, frequency bandwidth, and song rate.  After recording, the individual was captured to obtain a blood sample for leukocyte concentration analysis and morphological measurements to assess body condition.  We calculated song performance scores and song rates for each individual and related them to leukocyte concentrations and body condition.  Our analyses showed that individuals with high leukocyte concentrations and who were in poorer body condition had high performance songs, while individuals in better body condition had high song rates. Based on these results, we conclude that there is not strong evidence for song performance as an honest signal of immunological state or body condition, however song rate may be an honest signal of body condition. 

Park, Timothy (University of Virginia).  Mentors:  Henry Wilbur and Becky Wilbur (University of Virginia). 
Host-parasite interactions between Conopholis americana and Quercus spp.
Abstract: Parasitic plants are often studied because of their impact on important crop species. However, host-parasite interactions in natural communities can have important implications on community structure and biodiversity. The parasitic angiosperm, Conopholis americana, is a useful study organism because it is specific to Quercus rubra, a common dominant canopy tree in eastern North American deciduous forests. This study addresses the following questions: (1) Does C. americana have a significant impact on Q. rubra growth? (2) Does Q. rubra have any mechanism to combat parasitism? (3) Is there a relationship between host age and parasite load? C. americana had no demonstrable impact on oak growth as measured by radial growth of stems, however preliminary data suggest that oaks may be able to combat parasitism, most likely through passive transport of tannins. In addition, there is no strong correlation between host age and parasite load. Further studies on host-parasite interactions are necessary to understand the role of parasites in natural communities.

Ruiz, Jean (University of Puerto Rico).  Mentor:  Courtney Thomason (Texas Tech University). 
Getting deep in the gut: novel explorations of parasites gut communities.
Abstract: In the last decades, parasite biology was conducted using a one host-one parasite framework, but evidence recently suggests that a more complex approach is needed. In natural systems, individuals are often co-infected by many species of parasites. At Mountain Lake Biological Station (MLBS), evidence suggests that wild Peromyscus populations can carry up to 10 different species of parasite, and most individuals are co-infected with 2 or more parasites. It has been theorized that endo-parasite communities may function in a similar manner as typical ecological communities. However, consequences of alterations to the parasite network are unknown in many cases. To test this idea, classic ecological concepts were applied to a natural host-parasite system consisting of two host species (Peromyscus maniculatus and Peromyscus leucopus) by disturbing the parasite communities through nematode removal. No statistically significant differences in the parasite communities were detected pre- and post-treatment. However, interesting trends were reported  in Ivermectin  treated mice that  were infected with nematodes that were limited  to just one site of the digestive tract, while the control group had a random distribution of worms throughout the gut. The remaining community may seem affected post-treatment showing a decrease in intestinal parasite burden and species richness of ecto-parasites, possibly because of a strong immune response that stimulated changes in the normal intestinal architecture. We may need longer trapping sessions and more than one grid, to have a good sample size in order to get more conclusive results and evidence the consequences of the alteration of the parasite network community.

Smith, Rhonda (University of Virginia).  Mentors:  Henry Wilbur and Becky Wilbur (University of Virginia). 
Patterns of sex expression in Striped Maple (Acer pensylvanicum) at the individual and modular level.
Abstract: In the last decades, parasite biology was conducted using a one host-one parasite framework, but evidence recently suggests that a more complex approach is needed. In natural systems, individuals are often co-infected by many species of parasites. At Mountain Lake Biological Station (MLBS), evidence suggests that wild Peromyscus populations can carry up to 10 different species of parasite, and most individuals are co-infected with 2 or more parasites. It has been theorized that endo-parasite communities may function in a similar manner as typical ecological communities. However, consequences of alterations to the parasite network are unknown in many cases. To test this idea, classic ecological concepts were applied to a natural host-parasite system consisting of two host species (Peromyscus maniculatus and Peromyscus leucopus) by disturbing the parasite communities through nematode removal. No statistically significant differences in the parasite communities were detected pre- and post-treatment. However, interesting trends were reported  in Ivermectin  treated mice that  were infected with nematodes that were limited  to just one site of the digestive tract, while the control group had a random distribution of worms throughout the gut. The remaining community may seem affected post-treatment showing a decrease in intestinal parasite burden and species richness of ecto-parasites, possibly because of a strong immune response that stimulated changes in the normal intestinal architecture. We may need longer trapping sessions and more than one grid, to have a good sample size in order to get more conclusive results and evidence the consequences of the alteration of the parasite network community.

Troth, Ashley (Indiana University).  Mentor:  Vince Formica (University of Virginia). 
Incorporating social networks into sexual selection analysis.
Abstract: An individual’s position in its social network has been predicted to have important effects on fitness. While causes of social network position have been investigated in great depth, little work has been done to unlock relationships between individual traits, social network position, and fitness. Social network analysis could help elucidate some of these relationships, provided that social network position presents a clearer picture than individual attributes alone. Observational, social, and phenotypic data was collected from four artificial populations of Bolitotherus cornutus totaling 120 beetles over twenty-two days. A candidate model approach and the Akaike information criterion were used to compare six possible models, most of which included network metrics as mediators between phenotypic traits and fitness, and one that did not. This was done to test whether inclusion of these network metrics provides a clearer picture of the relationship between phenotypic traits and fitness. Analysis showed that the candidate model containing no network metrics was the most efficient descriptor of the data, and that elytra length and activity level both correlated significantly to fitness. However the majority of the models were within an acceptable range of candidate model A, suggesting that inclusion of network metrics did not significantly increase the explanatory power of the sexual selection model.

Vanderbilt, Carla (Stetson University).  Mentor:  Dustin Reichard (Indiana University).   
Understanding the function of short-range song in the dark-eyed junco (Junco hyemalis).
Abstract: Long-range song (LRS) is a high amplitude acoustic signal used by many vertebrate and invertebrate taxa that typically functions in territoriality and mate attraction.  Short-range song (SRS), in contrast, is a low amplitude signal that has received little attention in the literature, and its overarching function remains unknown.  I studied the relationship between structure and function of SRS in the dark-eyed junco (Junco hyemalis) during the breeding season while each focal male’s mate was incubating eggs and not fertile. Males received three playbacks: LRS, slow tempo SRS, and fast tempo SRS.  These songs were played within the target male’s territory with 45 minutes between each trial.  During the playbacks, I recorded the number of flights, vocalizations, time spent near the speaker, closest approach, latency to song, and latencies to within 1 m and 5 m of the speaker.  Males responded significantly more strongly to fast SRS than LRS during the playback and response to slow SRS trended towards a stronger response over LRS.  However, there was no significant difference in response toward slow SRS and fast SRS. Males responded to fast SRS with closer approaches, more time spent within 5 m of the speaker, less songs, and a higher latency to begin singing in comparison to LRS.  When they received the slow SRS treatment, males only spent more time within 5m of the speaker in comparison to LRS.  Also, males retained a strong response toward fast SRS in comparison to LRS throughout the post-playback, whereas they did not for slow SRS.  These results suggest that slow SRS and fast SRS may serve similar functions, yet are potentially different in intensity and/or function from LRS. 

Yule, Kelsey (Rice University).  Mentor:  Ashley Wilkinson (University of Virginia). 
Response to TTX presence by adult Red Spotted Newts (Notophthalmus viridescens).
Abstract: Organisms use chemical signals between individuals to elicit behavioral responses in a variety of ecologically important situations from predation to reproduction.  Toxins are one important group of potential chemical signals.  Adult eastern red-spotted newts (Notophthalmus viridescens) use olfactory cues to seek out other newts with which to mate, but the chemicals responsible remain unknown.  Larval newts of a closely related species have the ability to respond to tetrodotoxin (TTX) contained and released by North American newts through specialized cells in the olfactory epithelium.  Assuming adults can also sense freely diffusing TTX in the water, this toxin, which is found throughout the body of adult newts and within eggs, may serve as the mechanism by which mates and eggs are located, serving as a co-option of an anti-predator trait.  In this study, a T-maze experiment was used to determine if adult N. viridescens individuals preferably swam towards or away from freely diffusing TTX.  Although more studies are necessary to rule out phenological effects and to determine if an adequate concentrations of toxin were used, no significant evidence was found to support TTX as a chemical attractant or repellent in this species.