2015 REU Projects

Aguirre, Luis (University of Illinois-Chicago). Mentor: Jessamyn Manson (University of Alberta).
Effects of herbivory on floral traits and floral rewards in Asclepias spp.
 Herbivory and pollination both incur energetic costs for plants, as plants must invest in defenses while simultaneously investing in rewards and attractants. The presence and intensity of herbivory may affect how much energy and resources a plant may spend on reproduction. In this experimental study, we aimed to test different modes and durations of herbivory in Asclepias syriaca to assess whether the investment of energy in herbivore defense affects the reproductive potential of these plants. To measure whether herbivory has a detrimental effect on reproduction we looked at differences in reproductive traits in groups with various herbivory simulations. We measured floral traits, floral rewards and rates of pollinia removal and deposition as a proxy for pollination to assess the effects of herbivory. The results obtained showed hood size and ovule size were significantly affected by herbivory, with a trend towards smaller hoods and ovules, while nectar traits had non-significant trends towards a general reduction in nectar quantity and quality. These responses varied by duration but not by mode of herbivory. However, we did not see any reduction in pollination when plants were treated with several simulated modes and durations of herbivory. Our results suggest that although herbivory has a direct effect on reproduction related traits, other factors, such as weather, may be driving pollination responses in this system. We have come to the conclusion that purely mechanical simulations of herbivory and may not affect the pollination efficiency in Asclepias syriaca.

Blackman, Augie (Oberlin College). Mentor: Alex Navarro (University of Maryland).
How does coexistence affect intraspecific variation? Assessing the impact of an introduced salamander on the abundance and morphology of a native species 
​Abrstact: In order for species to coexist in a community, competitive interactions over food, space, and other resources must be diminished. Character displacement, or the evolution of differences that reduce competition, provides one mechanism through which coexistence can occur. The introduction of a nonnative species can disrupt this capacity for coexistence through the imposition of novel stressors upon the native community. We explored the ecological impact of the introduction of a nonnative species of salamander, Plethodon montanus on a very similar native salamander, P. cinereus within a novel system at Mountain Lake Biological Station. Specifically, we determined whether the introduction of P. montanus has impacted the abundance and morphology of P. cinereus. We found abundance estimates for the three population treatments (i.e., P. montanus absent, P. montanus introduced, and P. montanus native) using N-mixture models. We also contrasted cranial morphology of P. cinereus among these three population treatments using geomorph in R. We found significant differences in abundances estimates of P. cinereus between population treatments. We found significant differences in cranial morphology of P. cinereus between population treatments, however standard error was large.

Enriquez, Anita (University of New Mexico). Mentor: Brian Sanderson (University of Virginia).
Pollinator efficiency of diurnal and nocturnal pollinators of Silene vulgaris 
 Pollinators vary broadly in both the traits that attract them to flowers and the rewards that they seek. These preferences lead to differences in visitation frequency and pollen deposition efficiency of pollinators. Silene vulgaris is a gynodioecious perennial visited by both diurnal and nocturnal pollinators, as its flowers are open continuously for multiple days. Previous studies have suggested that there are differences in visitation and efficiency in temporally distinct pollinators of other Silene species. This study investigated differences between diurnal and nocturnal pollinators of S. vulgaris by excluding pollinators temporally from separate branches and comparing the treatments to positive and negative controls. The data show that there are temporal differences in pollination with night-pollinated treatments setting significantly higher fruit. It was also found that female plants set more fruit than hermaphrodite plants. These results prompt future pollinator studies to determine the mechanism responsible for temporal differences in fruit set.

Mady, Rachael (Towson University). Mentor: Jessica Graham (North Dakota State University).
Nest Identity Crisis: The relationship between predator abundance and nest site selection in the dark-eyed junco
 All organisms live in dynamic, changing environments. To survive and avoid extinction, individuals must be able to asses and react to these changes, whether they are abiotic or biotic. Because some of these changes are not directional and instead fluctuate over short periods of time, it is beneficial for certain phenotypic traits to be plastic. One such trait that may be affected by fluctuating environmental factors is nest site. For the dark-eyed junco (Junco hyemalis), nest site may be a plastic phenotypic trait influenced by varying levels of predation pressure. From year to year, the abundance of the primary nest predator, the eastern chipmunk (Tamias striatus), fluctuates in response to varying levels of acorn mast production. This should favor the ability of juncos to assess and adjust their nest site to the optimal location from year to year to maximize fitness. Varying proportions of elevated nests have been seen in previous years, but it has yet to be understood as to what factors are driving the dark-eyed junco off-ground. To see if predation pressure as well as another factor, weather, are related to nest site selection, data collected from previous studies was analyzed using various statistical models. Significant predictive relationships were found between rodent abundance and elevated nests while weather, in terms of temperature and precipitation did not seem to have a significant relationship. Looking at the fitness benefits of the plasticity of the trait, success of off-ground versus on-ground nests did not differ, even in years of high rodent abundance.

Mestas, Angie (New Mexico State University). Mentor: Charles Kwit (University of Tennessee).
Investigating antimicrobial benefits of the Sanguinaria Canadensis - Aphaenogaster picea seed dispersal mutualism
 The exemplary mutualism of myrmecochory (seed dispersal by ants) has numerous studies that back up the benefits to both partners.  While studies addressing some “macroscopic” metrics, such as ant colony performance and seed deposition, have resulted in questioning of the universality of the mutualism, short-term “microscopic” benefits, such as antimicrobial benefits each partner may convey to the other, have been notably neglected. The purpose of this study was to investigate antimicrobial benefits of the Sanguinaria canadensis - Aphaenogaster picea seed dispersal mutualism.  The proposed study  experimentally addressed whether (1) Sanguinaria canadensis diaspores (seeds + elaiosomes) have antimicrobial properties, which may ultimately benefit brood performance, and (2) Aphaenogaster picea treat Sanguinaria canadensis seeds in an antimicrobial fashion in the nest such that upon redispersal they are protected from microbes. This was  accomplished by measuring zones of inhibition from Sanguinaria canadensis, Aphaenogaster picea and A. picea-handled Sanguinaria canadensis seed combinant washes on plates inoculated with Fusarium oxysporum and Bacillus cereus. These measurements were used to assess the antimicrobial activity of each partner in this putative mutualism. The Sanguinaria canadensis antimicrobial compound, sanguinarine, was found to be too low to inhibit microbial growth.   While no inhibition of microbes was measured from Aphaenogaster picea secretions, it would be premature to discredit antimicrobial activity, as the identification of the active compounds remain unknown and the appropriate extraction method is speculative.  However, comparative studies of cultures from pre- and post- ant handled seeds have shown different microbial communities on the seed coat, indicating possible antibiotic and probiotic influences of seed handling. 

Nash, Jake (Oberlin College). Mentor: Charles Kwit (University of Tennessee).
Out of the Nest: Re-evaluating the predator escape hypothesis under the context of redispersal
 Seed dispersal is one of the most well studied mutualisms between animals and plants. Myrmecochory, or seed dispersal by ants, is documented in over 11,000 plants and has been shown to confer numerous fitness advantages to plants. However, a recent study showed that for a keystone genus of seed-dispersing ants in eastern North America, Aphaenogaster, redispersal of the seeds nearby but outside of the ant nest is the dominant mode of dispersal. This calls into question some of the putative benefits of myrmecochory, namely the role of myrmecochory as an escape from seed predation. I evaluate the hypothesis that myrmecochory in eastern forests does provide an escape from predation through two modes of action: 1) elaiosome removal and 2) short-distance redispersal. I conducted a field experiment that simulated myrmecochory to evaluate whether ant-mediated escape from conspecifics and ant handling provide an escape from seed predation for the spring ephemerals Jeffersonia diphylla and Asarum canadense. I present evidence that myrmecochory provides different advantages to different plants: for J. diphylla seeds, elaiosome removal reduced seed predation, whereas for A. canadense, relocation away from conspecifics reduced seed predation.

Quarles, Brandie (University of Virginia). Mentor: Brittany Sutherland (University of Virginia).
Understanding self-Incompatibility in a polyploid complex
 Polyploidy and self-incompatibility (SI) are two common and important mechanisms in flowering plants. However, the relationship between the two and other factors that may affect them are not well understood. It is hypothesized that polyploidy breaks down gametophytic self-incompatibility, but this hypothesis has not been widely confirmed. In this study we aimed to test this hypothesis using controlled geitonogamous and outcrosses within the polyploid complex Campanula rotundifolia. We also hoped to gain a better understanding of self-incompatibility in a polyploid complex by looking at its relationship with ploidy, migration patterns, and floral age. Our results confirm that Campanula rotundifolia polyploids are capable of self-fertilization. In addition, our results suggest that migration patterns have no effect on the proportion fruit set, mean seed set, or SI of these plants. Our results do not tell us much about how age affects SI in C. rotundifolia, but they do tell us that older flowers are less successful at making seeds than younger flowers. We also tested actual self-fertilization rates by marking flowering stems and evaluating fruit and seed set of those untouched stems. We found that a base level of selfing is occurring in all populations of C. rotundifolia.

Scher, Catherine Lane (University of Virginia). Mentor: Mikus Abolins-Abols (Indiana University).
The effect of increased competition on courting songs
 When courting a female, males of many species perform intricate and vibrant routines. These routines are important to a male’s fitness because he must attract a mate. On the other hand, other individuals, such as predators and conspecific competition, may notice these displays as well. This experiment focused on the courting tradeoff between attracting a mate and attracting the attention of a conspecific competitor, by looking specifically at the courting songs of Dark-eyed Juncos in conditions of low and high perceived competition. Simulated courtship interactions (SCI) were conducted on two groups of males: the control group, in which each male experienced a typical level of competition, and the high competition group, in which each male was treated with up to 7 simulated territorial intrusions on the day before the SCI trial. Each male’s behavior was observed while his songs were recorded, and this data was examined in collaboration with data regarding each male’s physical attractiveness. While most results were not significant, high competition males seem to sing less loud LRS and more soft LRS. An interaction between competition level and body size was also noticed, although not significant. It seems that in low competition, males of all sizes sing about the same amount and same complexity of SRS, while in high competition, smaller males sing more and more complex SRS than larger males.

Starkey, Jesse (Cornell University). Mentor: Jessamyn Manson (University of Alberta).
Does variation in nectar traits determine pollinator preference in sexually dimorphic plants?
 Plants that depend on insect pollination implement many different ways to attract pollinators to their flowers. Nectar rewards are obtained when visiting a flower, and different pollinators prefer different nectar characteristics. Nectar traits such as volume, sugar concentration, and sugar composition can vary across plant species and can also vary within morphs of a species, which may affect the attractiveness of different morphs. In Silene vulgaris (Caryophyllaceae, (Moench) Garcke), a gynodioecious plant with hermaphrodite and female morphs, hermaphrodites produce larger flowers and more concentrated nectar than the female morph, although females produce more flowers. Pollinators, however, do not appear to discriminate between the two morphs. We hypothesized that this is due to the variation in nectar traits. We manipulate nectar traits such as sugar concentration composition, mainly the presence of sucrose in both gender morphs. We split nectar manipulations into 3 treatments which the gender morph’s natural nectar traits was supplemented with additional nectar, both gender morph’s nectar was diluted with the same nectar, and each gender morph was supplemented with the other’s nectar. Pollinator preference was observed by releasing various Bombus spp. into an enclosure containing both manipulated morphs of S. vulgaris. We exposed bees to different treatment groups and then test preferences on those groups to see if nectar variation drives preference. We found no significant different in treatments for average visitation length or average visit number. However, we did find that average visit number was significant between genders independent of treatment. Looking at the plant data shows that hermaphrodites had larger petal sizes, which suggest they were more attractive. This implies that the pollinators used in this experiment were focusing more on the visual cues of the plant rather than nectar rewards to discriminate flower preference.

Wadleigh, Rachel (Earlham College). Mentor: Mikus Abolins-Abols (Indiana University).
The effect of competition on courtship of dark-eyed juncos (Junco hyemalis)
 Birds exhibit a diverse array of visual and vocal courtship behaviors that vary between taxa and individuals.  Uncovering the factors that drive the diversity of these behaviors is essential to understanding their evolution and ecology.  This study explores the effect of perceived competition on a variety of courtship behaviors exhibited by Dark-eyed Juncos (Junco hyemalis) and the impact of individual attractiveness on their responses to these different environments.  Dark-eyed juncos are a well-suited model organism to study these interactions.  As socially monogamous territorial birds who engage in extra-pair fertilizations, their courtship behaviors may be impacted by the competition of other birds in their environment.  Furthermore, female preference for larger males with more tail white may cause individuals to respond to these levels of competition differently.  Differences in apparent competition were induced by simulating territorial intrusions, male conspecific song playback.  Juncos experiencing high and low competition levels were then exposed to a live female conspecific to measure their courtship behavior. Competition did not have an impact on their visual displays but individuals exposed to high competition approached the female more closely.  Larger males spread their tails more than smaller males in high competition while in low competition size and tail spread were not related.  These findings indicate the importance of approach distance in courtship in respect to competition.  They also suggest that attractive individuals invest their energy differently in alternate social environments, which can help us to better understand what affects courtship interactions in birds and across all taxa.