2016 REU Projects

Anderson, Abby (University of California, Berkeley). Mentors: Butch Brodie and Robin Costello (University of Virginia).
Maternal effects as drivers of egg color variation in the false Colorado potato beetle (Leptinotarsa juncta)
Abrstact: Maternal effects occur when the mother’s genotype or environment influences offspring phenotype beyond direct genetic effects. Since adaptive maternal effects respond to cues from the environment, they promote the distribution of phenotypes across microenvironments into areas where they are most fit. Maternal effects may be responsible for egg color variation in the false Colorado potato beetle (Leptinotarsa juncta), whose eggs vary from yellow to red. Color in this species confers a fitness advantage, as redder eggs experience a higher hatching success than yellower eggs. In this study, I tested whether oviposition microenvironment affects L. juncta egg color. To investigate if oviposition microenvironment influences egg color, I measured the temperature, UV radiation, and egg color of clutches I found in the field. UV radiation significantly affected the red chroma of eggs. In addition, when comparing two fields, the field that had significantly higher UV radiation also had significantly higher red chroma, indicating that this relationship exists across multiple scales. Maternal manipulation of egg color in response to UV radiation at oviposition sites provides a potential explanation for the significant effect of oviposition microenvironment on egg color. If true, these maternal effects may increase offspring fitness by allowing for rapid adaptation in continually changing light environments.

Debray, Reena (Duke University). Mentor: Butch Brodie (University of Virginia).
Are behavioral traits consistent or plastic in forked fungus beetles?
Abrstact: Social network analyses are often used to capture structural patterns in populations in which individuals interact to varying degrees with conspecifics. However, it is not well known why individuals hold particular network positions, and a potential criticism of social network theory is that networks may only capture individual behaviors, such as activity. If this were true, network-level analyses would not provide novel insights in the study of social behavior. This study measured three types of activity behaviors in forked fungus beetles (Bolitotherus cornutus) to understand the relationship between behavior and network position. We tested a captive population of beetles (n=91) three times to examine repeatability of activity behaviors. We also tested a population of beetles (n=64) from a field population on which social network interactions were observed three times per day for seven weeks. The three behaviors were all significantly repeatable (latency to movement: R=0.451, p=6.01x10-11; distance moved: R=0.474, p=2.19x10-9; top speed: R=0.567, p=6.2x10-13). None of the behaviors were significantly correlated with any of three social network metrics (strength, betweenness, and clustering coefficient). Although these results are preliminary, they suggest that network position may capture information above and beyond individual behavior or activity. This study is an important first step in understanding the factors that influence social network position. Studying whether these factors are consistent and able to respond to selection will provide insight into how social systems evolve.

Earl, Samantha (State University of New York, College of Environmental Science and Forestry). Mentor: Alex Novarro (University of Maryland).
Competition strategies in the eastern red-backed salamander (Plethodon cinereus)
Abrstact: Social network analyses are often used to capture structural patterns in populations in which individuals interact to varying degrees with conspecifics. However, it is not well known why individuals hold particular network positions, and a potential criticism of social network theory is that networks may only capture individual behaviors, such as activity. If this were true, network-level analyses would not provide novel insights in the study of social behavior. This study measured three types of activity behaviors in forked fungus beetles (Bolitotherus cornutus) to understand the relationship between behavior and network position. We tested a captive population of beetles (n=91) three times to examine repeatability of activity behaviors. We also tested a population of beetles (n=64) from a field population on which social network interactions were observed three times per day for seven weeks. The three behaviors were all significantly repeatable (latency to movement: R=0.451, p=6.01x10-11; distance moved: R=0.474, p=2.19x10-9; top speed: R=0.567, p=6.2x10-13). None of the behaviors were significantly correlated with any of three social network metrics (strength, betweenness, and clustering coefficient). Although these results are preliminary, they suggest that network position may capture information above and beyond individual behavior or activity. This study is an important first step in understanding the factors that influence social network position. Studying whether these factors are consistent and able to respond to selection will provide insight into how social systems evolve.

Kisare, Samantha (Duke University). Mentor: Chloe Lash (University of Tennessee).
Does an elaiosome diet affect the colony health of Aphaenogaster ants infected with Beauvaria?
Abrstact: Myrmecochory (ant seed dispersal) is a widespread mutualism that has independently evolved multiple times. The benefits of myrmecochory to the myrmecochore (plant counterpart) are well known, yet the benefits to the ant are not fully understood. Ants and plants are not isolated in this relationship, however, as they both extensively interact with microbes in their environments. Several species of ants secrete antimicrobial compounds via the metapleural gland to defend against microbial pathogens. Similarly, some plants contain antimicrobial compounds in their tissues. These antimicrobial defenses could influence one partner’s relationships with their mutualism counterparts. Here, we investigate the potential antimicrobial benefits myrmecochores provide to ants within the myrmecochory mutualism by studying the interactions among Aphaenogaster ants, Sanguinaria canadensis, and Beauveria bassiana. We infected A. rudis and A. picea ant colonies with Beauveria at one of three dosages: high, low, or none and presented these colonies with one of three diets: S. canadensis seeds, standard insect protein food, or standard insect protein food with sanguinarine. We measured the number of dead ants, the degree of infection, and the egg production of each colony.  We found that ants fed a sanguinarine diet had a significantly higher survival rate and a trend of lower infection levels than those that were fed an elaiosome or standard insect protein diet. There was no significant difference in egg counts across the different diets. These results suggest that sanguinarine as an antimicrobial may improve survival from an entomopathogen although it may not provide a reproductive benefit. This also suggests that a fungal third party might be complicating what is normally assumed to be a simple pairwise mutualism.

Leibman, Lia (Whitman College). Mentors: Laura Galloway and Matt Koski (University of Virginia).
Reproductive assurance among populations of Campanula americana
Abrstact: Although self-fertilization causes fitness reductions in progeny in many cases, floral traits that promote selfing have evolved numerous times in angiosperm lineages. This is because, with limited outcrossing opportunities, it can be beneficial to self-fertilize. Reproductive assurance, or the ability of a plant to self when no or limited outcrossing is available, is a mechanism many plants utilize to ensure fertilization. Changes over time in herkogamy and dichogamy, the separation of male and female functions of a flower spatially and temporally, respectively, are important mechanisms of reproductive assurance. Campanula americana (Campanulaceae) displays both herkogamy and dichogamy, and a wide variation in autogamy rates throughout its range. It is not known if reproductive assurance causes this variation in autogamy, and how floral traits may factor into this variation. This study aims to uncover the mechanisms behind autogamy variation in C. americana, and determine if reproductive assurance is present in this species. Four high and four medium autogamy populations underwent both high and low pollination treatments. Arrays were placed in the sun for high pollination treatments, while low pollination treatments were placed in the shade. Measurements of pollen removal, dichogamy, and herkogamy were taken for flowersin the arrays, and pollinator observations were made across sites and arrays. Pollen removal was more rapid in the sun, despite the fact that overall visitation was higher in the shade. Bumblebees may have been responsible for the high pollen removal in sun, given that they visited far more flowers per foraging bout in the sun compared to all other visitor groups. Dichogamy was determined by pollination environment, with flowers in the shade remaining male for, on average, one day less than flowers in the sun. A shorter male phase in the sun may be due to the faster pollen removal in those sites. Herkogamy, in terms of the distance from the stigma to the style (where pollen is presented), was smaller in high autogamy populations compared to medium autogamy populations, and did not depend on sun versus shade environment. These results provide insight into how herkogamy and dichogamy vary in different pollination environments and geographically, providing a potential link between high autogamy and small herkogamy in certain C. americana populations. Selfing rate will be determined for offspring to see if these traits/differences are associated with selfing.

Medina-Báez, Osmary (University of Puerto Rico, Mayagüez). Mentor: Alex Novarro (University of Maryland).
Which species is better equipped for climate change? Thermal limits in two widely distributed salamanders
Abrstact:
 With rising temperatures due to climate change, we expect shifts in the geographic range of many species. Among the species most affected by these dramatic changes in temperatures are the lungless salamanders (family Plethodontidae). Because plethodontids are ectotherms, have permeable skin, are lungless and therefore need cold and wet temperatures to receive oxygen, we expect rising temperatures to cause a reduction in suitable habitat. To determine whether lungless salamanders’ geographic range coincide with their thermal range, we measured critical thermal limits (CT limits) in two species with expansive, but varying geographic ranges: the eastern red-backed salamander (Plethodon cinereus), and the northern slimy salamander (Plethodon glutinosus). We measured CT limits for both species at high and low elevations and found that P. glutinosus has a broader thermal breadth than P. cinereus.

Noffsinger, Isaac (Bridgewater College). Mentor: Courtney Thomason (Virginia Tech).
Tapeworm and nematode competition in Peromyscus leucopus
Abrstact: It is widely accepted that free-living organisms interact with each other in food webs, and similarly parasites interact with their host and other parasites in within-host communities. Within-host parasite community interactions can be direct, indirect, antagonistic, or synergistic. At Mountain Lake Biological Station, Peromyscus within-host communities are well-defined, but comparatively little is known about cestodes in these communities. As a result, we determined whether cestodes interact with other members of the parasite community and impact host tolerance to infection. To address these questions in Peromyscus mice, a mark recapture study was conducted at MLBS  from May to July 2016. We found that nematodes and cestodes appear to be interacting with each other and that when population density is high healthier individuals had a higher cestode burden. However,  when population density is low, healthier individuals had a lower cestode burden. This has major implications for monitoring host health when hosts are co-infected.

Sullivan, Cierra (Christopher Newport University). Mentors: Laura Galloway and Matt Koski (University of Virginia).
An examination of abiotic and biotic factors underlying floral color variation in Campanula americana
Abrstact: Color variation in the American bellflower Campanula americana is seen within the petals and pollen. Studies on the maintenance of floral color variation appear biased towards biotic selection, especially pollinator preference. However, it is important to consider the alternative adaptive mechanics of abiotic selective agents, as well as non-adaptive mechanisms. This study tests for relationships between the abiotic factors of temperature and UV-B radiation with observed petal and pollen color variation. Pollen germination and average pollen tube length were used as viability measures of light and dark pollen colors under a low, medium (control), and high temperature regime. The same pollen viability measures were scored for light and dark pollen exposed to, or shielded from, UV-B radiation. Biotic selection pressure of pollinator preference was tested using observations of arrays of the different pollen colors with either a light petal or dark petal background to determine if the amount of color contrast produced by pollen-petal combinations had an effect on pollinator visitation. Our findings showed significant pollen color-treatment reactions, in which dark pollen had higher germination than light pollen at medium and high temperatures and in the presence of UV. Syrphid flies significantly over-visited dark pollen, while hymenoptera appeared to favor light pollen with marginal significance. There is strong evidence that climatic variables are maintaining the distribution of pollen color variation in the range of C.americana; however, to complete the picture, further pollinator experiments that look at the distribution of known pollinators and their preferences in the actual population sites need to be conducted to observe possible biotic selection.

Toumpas, Anastasia (Wells College). Mentor: Courtney Thomason (Virginia Tech).
Individual variation in parasite tolerance and its effect on super-spreading
Abrstact: The idea that individuals do not all carry and transmit infections in the same way is a fundamental aspect of epidemiology. It is estimated that only about 20% of infected individuals in a given population carry the majority of the total pathogen burden and therefore are responsible for a large proportion of disease transmission. Such individuals are often referred to as super-spreaders. The factors that determine whether or not an individual is a super-spreader are largely unknown, however it can be evaluated using either an individual-based or event-based approach. The goal of this study was to identify what factors might determine if an individual becomes a super-spreader using a wild population of Peromyscus mice infected with an intestinal microparasite, coccidia. We used a mark-recapture approach to evaluate host characteristics and parasite burden. We identified potential super-spreaders using home range overlap between individuals as an indicator of parasite transmission and correlated super-spreader status with host characteristics, disease tolerance and population density. No super-spreaders were identified within the 2016 (low density) population, but were found in the 2011 (high density) population. Only population density showed a relationship with super-spreading, with proportion of super-spreaders decreasing as density increased. Because all of the individual-level host factors examined in this study showed no relationship with super-spreading individuals, we concluded that the dynamics of super-spreading favor the event-based model over the individual-based. Determining how super-spreading fits into these models can change approaches to disease control and potentially improve its success and efficiency.