2012 REU Projects

Alford, Kaitlin (University of Virginia).  Mentor:  Sam Slowinski (Indiana University). 
The effect of olfactory cues on male courtship behavior in Dark-eyed Juncos (J. hyemalis).  
Abstract:  Olfactory cues have been shown to be important in behaviors across many taxa and most recently in birds. For example, previous studies of the dark-eyed junco (Junco hyemalis) have indicated that the composition of preen oil volatiles varies among individuals, sexes, and populations as well as that individuals can discern between preen oil odors of birds of differing sexes and body sizes. These variations in preen oil volatiles could function as a signal for mate selection. Juncos are a mildly dimorphic species with few visual differences between the sexes. Olfactory cues may be important to distinguish male from female and to reduce time spent fruitlessly courting the wrong sex. In this study, males were presented with a female lure in an airtight cage with two sets of scent treatments. Each male was given either 1) a male and a control treatment or 2) a female and a control treatment. Audio recordings were used to score 20-minute trials for male courtship behaviors. Treatment orders were randomized to control for order effects. There was no significant effect of odor, lure, or odor x lure interaction on male courtship behavior. No evidence was found that olfactory cues affect male courtship behavior and that visual cues could potentially outweigh the importance of olfactory.

Dinneen,Linda (San Francisco State University).  Mentor:  Janet Steven (Sweet Briar College). 
Effects of nitrogen on White-Tailed Deer herbivory in sun and shade environments.
Abstract:  Deer are economic and ecological pests in the eastern US because of their overwhelming numbers and selective browse-feeding behaviors. Deer are able to select plants for browsing that have excess nitrogen in their tissues. In some cases, nutrient levels may also mediate plant responses to herbivory. We tested the hypothesis that nitrogen increases a plant’s ability to recover from herbivory while focusing on the herbaceous species Campanulastrum americanum (Campanulaceae). We fertilized a sample of plants in the understory and clipped them to simulate herbivory. We then analyzed the percent tissue nitrogen of the clipped plants and quantified the response of all the plants by measuring size characteristics and maternal fitness characteristics. We did not see an increase in nitrogen in the fertilizer treatment nor did the fertilized plants experience any significant difference in response from the unfertilized plants, indicating a possible ineffectiveness of the fertilizer. Clipped plants did not show a difference in size characteristics from unclipped plants. However, the clipped plants did have significantly fewer fruits and flowers, indicating a decline in maternal fitness of the clipped plants. There is no evidence that increased soil nitrogen affects the response of C. americanum to herbivory. However, we can conclude that herbivory may have an overall detrimental effect on the fitness of C. americanum

Hess, Daniel Ray (Swarthmore College).  Mentor:  Vince Formica (University of Virginia). 
Social and physiological influences on aggression in Bolitotherus cornutus.
Abstract:  Aggression is a complex social behavior, which can be caused by competition for mates, and can be under sexual selection. There are many factors that influence aggression, including hormones, behavior, and morphology. In the sexually dimorphic social forked fungus beetle, Bolitotherus cornutus, horns are under strong sexual selection. In other words, large horned males copulate more often. It is presumed that male-male combat is the behavioral mechanism through which larger horns provide an advantage and is possibly driven by aggression, however this aggressive behaviors and the mechanisms that control them have yet to be examined in this species. We examined the impacts of hormones, behavior, and body size on aggression in forked fungus beetles. Juvenile hormone, a known inducer of aggression in female insects, was demonstrated to have a marginally significant depressive effect on male aggression in forked fungus beetles. It was also discovered that in pairings of male beetles, there is often a more aggressive beetle that is responsible for instigating on average 92% of attacks. This instigation is not explained by body size, with both smaller and larger members of pairings acting as aggressors. This suggests that there is a large degree of variation in aggressive behavior between individuals which could lead to dominance. It is clear that there are a variety of complex factors influencing aggressive behavior which in turn exerts selective pressures on the fitness of individuals and species, such as the forked fungus beetle. 

Kimmitt,Abby (University of Mary Washington).  Mentor: Dustin Reichard (Indiana University). 
Predictors of extra-pair courtship effort in male Dark-eyed Juncos.
Abstract:  Sexual selection via female preference and male-male competition has promoted the development of elaborate male courtship displays across all animal taxa.  In many taxa, females are known to prefer males that court more vigorously, but despite this preference for higher courtship intensity, courtship effort often varies among males. In this study, I investigated whether various aspects of male phenotype and mate status were correlated with male courtship effort in a songbird, the Dark-eyed Junco (Junco hyemalis). I conducted simulated sexual intrusions (SSI), by placing a live female junco on the territory of both mated and unmated male juncos and stimulated the male to court the female by broadcasting a female precopulatory trill playback. I then recorded each male’s courtship behaviors (e.g., song, ptiloerection, and tail-spread), and immediately following the trial, captured the male to take measurements. While it was found that phenotypic predictors did not significantly correlate with the behavior of the males, the courtship effort of mated and unmated males was significantly different. Mated males were found to approach more closely, be more active, sing less long-range song, and display at maximum levels of ptiloerection more frequently than unmated males. These results may suggest that courtship effort of males trying to establish pair bonds (unmated males) may be fundamentally different than courtship of males attempting to acquire an extra-pair mate (mated males). Phenotype may not correlate with courtship effort because many morphological characteristics are determined many months prior to breeding season (e.g. feathers) and may not be indicative of the current nutritional state of the male. Collectively, our results suggest that mate status of the male is the only predictor that we evaluated that affected courtship effort. 

Kone,Dominique (Colby College).  Mentor:  Courtney Thomason (Texas Tech University). 
The efficacy of Ivermectin in parasite removal and effects on community structure.
Abstract:  The interactions of co-infecting parasite species are primarily responsible for shaping various parasite communities. A single parasite species has the potential to infect multiple hosts, and hosts have the potential to be infected by multiple parasite species. In this study, I have examined the infection of multiple gastrointestinal parasites on two species of wild mouse; Peromyscus leucopus and P. maniculatus. Past research has shown that the interactions between the three types of parasites (nematodes, coccidia, and cestodes) are responsible for structuring this parasitic community. Furthermore, the introduction of Ivermectin played a key role in disrupting interactions between these parasites and ultimately altered the community. We have furthered this study by manipulating the parasitic community with the introduction of Ivermectin, analyzed the differences in prevalence, number of eggs, and number of species within fecal samples at different time periods. To examine the effects of the manipulations, we trapped several mice using a single-mark recapture protocol, administered the Ivermectin treatment, and used a Generalized Linear Mixed Model to analyze the results. There were no significant differences in any of the variables except for eggs per gram, which showed significant differences at all time periods. Therefore, this study could only suggest and not conclude that competition was taking place between the different parasite species group, but it could conclude that the composition of the parasite community had changed after the introduction of Ivermectin to the Peromyscus population.

McCauley,Michelle (University of Virginia).  Mentor:  Brian Sanderson (University of Virginia). 
Contribution of inbreeding to extraordinary sex ratios in Silene vulgaris.
Abstract:  This study investigated sexual dimorphism in a gynodioecious system (individuals are hermaphroditic or female), Silene vulgaris. Because gynodioecious species lack sex chromosomes, sex is determined by allelic variation. Factors affecting allelic variation, therefore, were expected to affect sexual dimorphism as well. The goal was the study was (1) to determine the extent of sexual dimorphism in populations of Silene vulgaris and (2) to determine the effect population on sexual dimorphism­– specifically, the sex ratio of the populations. Flowers were collected from five populations, and the sex of the individual was recorded. Six floral traits were measured on each flower: calyx width and length, petal width and length, ovary width, and style number. Univariate tests were run for each individual trait, demonstrating a significant difference between sexes. Overall, hermaphrodites had larger calyx width and length and larger petal width and length than females, as well as smaller ovaries than females. Style number had very little variation. Two MANOVAs were run to evaluate the effects of population and sex ratio on sex. In both models, sex was found to be a significant effect, suggesting the presence of sexual dimorphism. Furthermore, there was a significant effect of the interaction of sex and population, suggesting that levels of sexual dimorphism vary among populations. Overall, we found that hermaphrodites generally have larger flowers than females, and that sexual dimorphism varies across populations. 

Mitchell, Michael (Hampton Univeristy).  Mentor:  Barbara Abraham (Hampton University). 
Effects of selected environmental factors on flower visitation rates by bumblebees.

Nelson, Meredith (University of Virginia).  Mentors:  Henry Wilbur and Becky Wilbur (University of Virginia). 
The effect of damage on sexual expression in Acer pensylvanicum.
Abstract:  Some members of the plant genus Acer exhibit labile sex determination in which they change sex in response to their environment.  This experimental study investigates the association between sexual expression and damage in Acer pensylvanicum, or striped maple.  We predicted an increase in the likelihood of reproductive expression as well as an increase in the probability of female expression in response to damage.  In October 2010, trees in a natural population were randomly assigned into either a control group (N=589) or a treatment group (N=472) that received a simulated deer scrape to damage the stem of the tree.  The mortality and sex expression of the trees were observed from Fall 2010 to Summer 2012.  The treatment did significantly increase the mortality rate of the study population in 2010-2011, but not in 2011-2012.  For smaller sized trees, the treatment also significantly increased the probability of reproductive expression.  The likelihood of reproductive expression increased with the size of the tree for the control group.  A slight increase was observed in the probability of femaleness for trees of smaller sizes in the treatment group, although the probability of female expression was still quite low.  The treatment did not have any significant effect on the proportion of reproductive modules on an individual tree.  We observed that male expression increased linearly with size of the tree.  Our results show that damage does have an effect on the sexual expression of A. pensylvanicum, affirming evidence for striped maple as a sexually labile species.  A. pensylvanicum most likely responds to serious damage by devoting more resources to sex expression in order to ensure reproductive success. 

Peterson,Nancy (University of Virginia).  Mentors:  Henry Wilbur and Becky Wilbur (University of Virginia). 
The effects of fire on the herb layer at Mountain Lake Biological Station.
Abstract:  During the summer of 2012 we sampled 80 random plots stratified among six zones of Mountain Lake Biological Station in Giles County, Virginia. We sampled vascular plant species presence in the herb, shrub, and tree layers in addition to environmental factors (canopy cover, slope, aspect, soil pH, surface rock types, herbivory).  We ordinated our 80 plots using nonmetric multidimensional scaling, implemented in PC-Ord. We then added environmental vectors that best correlated to the vegetative difference to help explain the vegetative differences.  Our study showed high variance in the herb layer across our plots. The environmental and tree factors that most correlated to variance were: Rosehill surface rock presence; slope; number of live Quercus rubra stems; live Quercus rubra basal area; number of live Quercus alba stems; number of dead Pinus rigida stems, and heat load.  We recorded 92 species, with an average of 17.8 herb species per plot and a Simpson’s diversity index of 0.713. The average plot slope was 4.4°, heat load was .195, canopy closure was 97.1%, and percent H+ ion concentration was 0.0001.  We will use these data and further studies of aerial photographs, tree rings, and soil analysis to correlate land use history with current community structure. Our project is part of a larger project to map the flora of MLBS, which will be available to future researchers. In addition, our local flora will contribute to a better understanding of North American flora.

Styer,Alexander (Georgetown University).  Mentor:  Janet Steven (Sweet Briar College). 
The effects of a heterogeneous light environment on pollen movement.
Abstract:  Campanulastrum americanum (Campanulaceae) is a bumblebee pollinated herb found throughout the eastern United States that grows both under the patchy light of a forest canopy and within light gaps. To test the hypothesis that heterogeneous light environments potentially provide barriers to gene flow, we assessed the movement of pollen throughout a population of C. americanum through the mark and recapture of bumblebees, by observing bees’ preference to forage in the light rather than the shade, and by calculating neighborhood areas for plants in both the light and shade. We found that bees are faithful to both light environment and patch, though faithfulness of light environment may simply be a consequence of patch fidelity. Additionally, bees preferentially forage in the sun, though this fact may be superseded by the importance of plant population density: the majority of observed bee activity occurred in the more densely populated light gaps. However, given the same plant in both light and shade conditions, bees visit the plant in the light with significantly more frequency than they do when it is in the shade, clearly indicating a behavioral change in response to light environment. Our calculations of neighborhood area suggest that the light gaps in this population are reproductively isolated, but shade patches appear to share gene flow. These data combined suggest that genetic sub-structuring may be occurring in this population of C. americanum, specifically along shade-light boundaries. 

Wice,Eric (University of Virginia).  Mentor:  Corlett Wood (University of Virginia). 
Oviposition decisions and larval competition in Forked Fungus Beetles.
Abstract:  In many species, parental care and investment are important determinants of an individual’s fitness.  For ovipositing species, the decision of where and how to lay eggs constitutes a large investment in care that a parent makes to ensure offspring survival and success.  Oviposition site selection can affect how well offspring survive based on many environmental factors present at a site. This bodes true for our species of study, the forked fungus beetle (Bolitotherus cornutus).  Female B. cornutus oviposit their eggs on the surface of wood-decaying fungal brackets where after hatching, the larvae burrow in and consume the fungal tissue.  We studied how oviposition in the wild was affected by environmental variables such as resource availability, quality, and host species.  For this study, data was gathered over the course of a summer looking at egg accumulation on multiple logs infected with three species of B. cornutus and their host fungi.  We found that oviposition is occurring in response to multiple environmental variables, while other factors that we expected to be affecting oviposition behavior did not have any effects.  The results that we found suggest that female B. cornutus are indeed ovipositing in response to environmental resource cues, which could be maximizing offspring survival and success and their own inclusive fitness. 

Willingham,Brittany (University of Michigan).  Mentor:  Barbara Abraham (Hampton University). 
Factors affecting flower choices of Tradescantia ohiensis visitors.
Abstract:  Bees are among the world’s most valuable plant pollinators.   Individuals within a species, as well as between species, have specific traits that they prefer when selecting flowers.  In this study, I observed visitors of the herbaceous plant Tradescantia ohiensis.  Flowers in my study sites were naturally exposed to varying light environments and a flower’s location in the sun or shade was assessed as a factor contributing to bee preference.  There is also a large variety of flower color among T. ohiensis.  I assessed whether there is also variation in the amount of ultraviolet reflectance from flowers of different colors and if this has any effect on types of visitors.  Lastly, I analyzed pollen found on T. ohiensis visitors to assess how they use the flowers, if they were also visiting other types of flowers nearby, and whether they were potential pollinators of T. ohiensis.  Flower color and light environment both significantly affected the flower choices of T. ohiensis visitors.  Flowers of different colors did not reflect different amounts of ultraviolet light; however, different types of bees were attracted to different amounts of ultraviolet reflectance.  T. ohiensis visitors used a variety of other plant species as pollen sources and Apis melliferaBombus spp. and halictids could all be potential T. ohiensis pollinators.  These results indicate that foraging behavior of different types of bees varies and gives insight into the specific preferences of different groups of bees.  They also show that bees other than A. mellifera and Bombus spp. can play an important role as pollinators.