2014 REU Projects

Breit, Ana (University of Wisconsin Stevens Point). Mentor: Jessamyn Manson (University of Alberta).
Post-herbivory nectar constituents in Asclepias syriaca and A. exaltata and their effects on pollinator behavior.  
 Pollinators place plants under selective pressures, changing variables associated with attraction such as nectar. However, herbivory may have consequences for floral traits, which could then affect pollination services. Flowers offer nectar to pollinators as a reward for visiting the plant. Nectar is under selective pressures by those pollinators. Those differences in nectar variables can impact pollinator behaviors and overall reproductive success of the plant. In this study, we examined whether simulated herbivory altered nectar traits and pollen movement in two milkweeds, Asclepias exaltata and Asclepias syriaca. Several nectar traits, such as volume produced and overall sugar concentration, were measured and we compared across species and treatments. This study found that A. syriaca had significantly more insertions than A. exaltata. Significantly more nectar was produced in plants that had been herbivorized, and the volume of nectar produced per flower differed significantly by species and by date. There were no significant differences in nectar sugar concentration. These results show little change in nectar traits and pollen movement under stressful conditions, which is contrary to what we predicted. Understanding how variation in nectar affects pollinator behavior is critical to understanding pollination, a key ecosystem process.

Brumbaugh, Amelia (Maryville College). Mentor: Brian Sanderson (University of Virginia). 
Influence of nectar production and floral traits on pollinator context in Silene vulgaris.
 Flowering plants rely on pollinator visitation for successful reproduction. To persist in a competitive environment, different species specialize phenotypic traits to attract certain pollinator types. Because fitness of these plant species depends on successful pollination, the traits through which plants attract pollinators are under strong selection. Different sexes of the same species can also diverge phenotypically in order to attract different pollinator groups, causing pollinator-mediated sexual selection, and leading to the evolution of sexual dimorphism. We used Silene vulgaris, a gynodioecious species, to assess pollinator preferences in regard to differences in nectar content and floral traits between hermaphrodite and female individuals. The nectar produced by female flowers had a significantly higher sugar concentration than hermaphrodites, which may play a role in attracting pollinators. However, day and night pollinator observations indicated that pollinators did not have a significant preference for floral or nectar traits, but they were more likely to visit hermaphrodites than females regardless of the time of day. Our analysis of these phenotypic differences allowed us to better understand sexual dimorphic traits in Silene vulgaris. Overall, this study has broadened our understanding of sexual dimorphism and the role of pollinator-mediated sexual selection in flowering plant evolution.

Cruz, Virnaliz (University of Puerto Rico). Mentor: Sam Slowinski (Indiana University).
Transfer of preen oil from Junco hyemalis to nestlings during brooding.
 Chemical communication is a very common mode of communication in organisms across all phyla. It is important both in inter and intra-specific communication. It relies on the detection and recognition of chemical odor cues perceived through the sense of smell and taste. These cues are often attributed to volatile compounds found in sebaceous glands. It is hypothesized that the production of volatile compounds in birds is associated with odor producing microbes that can be found in the preen gland; a holocrine sebaceous gland of the avian integument. In an unpublished work by Whittaker and Theis it was demonstrated that the nestlings’ preen gland microbial composition showed a stronger resemblance to the mother than to the father and it is also hypothesized that the transfer of odor-producing microbes could be a non-genetic mechanism of odor inheritance. We tested the hypothesis that dark-eyed juncos transfer preen oil, and by extension odor-producing microbes that make the volatile compounds found in their preen gland, to their offspring in the nest. Also, since the mother is the one that tends to do all the incubating and brooding; we further tested whether this could mean that females are more likely to transfer preen oil to the nestlings in comparison to the males. In order to test these predictions, we caught the parents at nests and we treated them by applying a small volume of Glo Germ (used  as a proxy to simulate the transfer of preen oil) on their preen gland. There were three treatments. In the female treatment, Glo Germ was applied to the preen gland of a brooding female, in the male treatment, Glo Germ was applied to the preen gland of the male, and in the control group neither the females nor males were treated. Four to six hours later the nestlings were examined under a UV light to see if there are traces of Glo Germ on them. We found no significant effect of treatment on the number of spots per nestling.

Dietz, Samantha (North Carolina State University). Mentor: Abby Kimmit (Indiana University).
Relationship between extra pair courtship effort and feeding frequency of nestlings in mated male Dark-eyed juncos. 
Abstract: TBAOrganisms utilize a variety of mating systems in order to increase fitness via reproductive success.  Monogamy is a type of mating system in which one male and one female mate exclusively for a breeding season or over multiple breeding seasons.  It was once thought that monogamy was very common, but developments in genetic testing have allowed us to do paternity tests and prove that true genetic monogamy is rare (Barelli et al., 2013)and social monogamy is much more prevalent.  In social monogamy, a male and a female form a pair bond and share a territory, resources and parental care of offspring (Sánchez-macouzet et al., 2014).  Unlike monogamy however, one or both members of the pair may seek out extra-pair copulations.  Males have limited energy and resources, and therefore face a trade-off between expending more energy on mate guarding and parental investment, or seeking out extra-pair copulations.  Both strategies have genetic advantages and costs associated with them and are likely to be under selection.  Junco hyemalis is a socially monogamous sparrow that has an extra-pair paternity rate of 28% (Ketterson et al., 1992).  This study investigated the relationship between parental investment and extra-pair courtship effort of male juncos.  In order to assess extra-pair courtship effort simulated courtship intrusions (SCIs) were conducted by placing a female lure on a male's territory and playing precopulatory trills to signal to the male the lure  was willing to copulate.  His courtship behaviors were recorded and scored.  In order to assess parental investment, a video camera was set up on the males nest when the nestlings were 6 days old in order to record activity.  When observing the video, the male was identified via the colored band combinations on his legs and the number of times the male fed the nestlings was counted.  There was no significant relationship between the courtship intensity of the male and the number of times he fed his nestlings.  

Escoto, Kathleen (Swarthmore College). Mentor: Malcolm Augat (University of Virginia). 
Relevant scale of social interaction in Silene vulgaris.
 Most organisms live among other organisms and these interactions within a population have been shown to have effects on the fitness of individuals in the population (Formica 2011). The behaviors of an organism determine what interactions, or social partners, an organism has. However, in sessile organisms the spatial distribution around the organism may better describe the relevant social partners for that organism. Sometimes, heterospecific organisms can interact with sessile organisms and create patterns of social interactions that might extend farther than just proximity through their behaviors. For example, angiosperms interact with other angiosperms mostly through pollinators, so it is important to look at pollinator behavior to understand these complex mechanisms of angiosperm phenotypes affecting the fitness of a plant. For this reason, we used Silene vulgaris to look at the effect of pollen availability at different spatial scales on fitness of an individual plant and also at pollinator behavior by analyzing pollinator travel distance. We found that for female plants, pollen availability on the population scale and at 2.7-3.6 m did had an effect on the fitness of the focal plant, if the plant was female. However, pollinator visitation was mostly found within less than 0.9 m meters from the plant. This suggests that the social partners of sessile organisms are not necessarily its immediate neighbors, and that the population pollen availability is a strong indicator of female plant fitness.

Fogliano, Rose (Gettysburg College). Mentor: Mikus Abolins-Abols (Indiana University).
Behavioral plasticity of territorial aggression in Dark-eyed juncos (Junco hyemalis): Predictors and fitness effects.
 To effectively maximize fitness, organisms need to invest in both survival and reproduction. Territorial defense is an important aspect of reproduction across a variety of taxa because individuals rely on territories for resources and mating opportunities. However, territoriality can be costly. Because territorial displays can decrease survival by increasing visibility to predators, individuals may benefit from being plastic in their territorial aggression under environmental conditions where predation is a major threat. However, studies have shown that individuals vary immensely in their tendency to be plastic. This study aims to understand why individual variation in territorial plasticity exists. Simulated territorial intrusions (STIs) were conducted on 26 male dark-eyed juncos. Each individual experienced one control STI (using a novel object) and one “owl” STI (using a taxidermy eastern screech owl). Junco long range song (LRS) was played for five minutes during each trial and a caged male lure was used as a visual. Aggressive behaviors including song, flights, fly-overs, and distance from the lure were scored during each trial. Plasticity was calculated by taking the difference in these behaviors between treatments for each individual. Overall, the presence of the owl had a significant effect on territorial aggression. Mean distance and latency to closest approach were most significantly affected by treatment. Reaction norms showed immense variation among individuals for plasticity of all aggressive behaviors. Life history traits including age, condition, mass to tarsus ratio, wing length, and tail white were examined as potential predictors of plasticity. A multivariate linear model revealed that age might explain some variation in plasticity. Older males tended to be more plastic, potentially because of selective pressure on plasticity at a younger age. Condition also explained some variation in PC3, a measure of aggression characterized mostly by mean and closest distance. Males in better condition tended to be less plastic in terms of distance from an invader. Possibly, stronger males perceive less risk in the presence of a predator due to an increased ability to fly away, so these individuals can afford to be less plastic.Other life history factors such as mate status and breeding condition may account for more of the variation in plasticity. Additionally, understanding whether plasticity is under selective pressure could shed light on this individual variation and help to explain whyplasticity in the population increases with age.

Lee, Joanna (University of Virginia). Mentor: Corlett Wood (University of Virginia).
The role of the gut microbial community in chitin digestion in Bolitotherus cornutus.
 All organisms experience symbiotic interactions with their associated bacteria. Because microorganisms play a basic role in the functioning of their host, these interactions must be considered to better understand any organism. The endosymbiotic gut microbiota in insects is an excellent example of this interaction, where insects are often consuming difficult to digest, nutrient-poor, or highly variable diets. The forked fungus beetle (Bolitotherus cornutus) was used to examine this crucial interaction in a mycophagous system.  The importance of the gut microbial community in larval growth was determined across three different diet types.  The larvae were split into diet and antibiotic treatments, and their growth was measured over the course of three weeks. Diet treatment, antibiotic treatment and the interaction between the two all had a significant effect on larval growth rate, demonstrating that not only are the environment and the associated microorganisms important for determining larval fitness, but that the effect of antibiotic treatment also varies across different diets. This investigation demonstrates that the significance of associated microorganisms can be context-dependent.

Pabon Figueroa, Diana (University of Puerto Rico Rio Piedras). Mentor: Corlett Wood (University of Virginia).
The effect of egg casings on the growth of the forked fungus beetle, Bolitotherus cornutus.
 Maternal effects are environmental effects resulting from the mother’s phenotype or environment that influence offspring growth, development, and fitness. The amount of protection and provisioning a mother applies to her eggs are significant maternal effects that can heavily influence her offspring’s survival. Many organisms cover their eggs in a casing or capsule, which perform numerous functions, including mechanical protection, protection from desiccation, and protection from predation and parasitism. In some cases, they can also provide a source of nutrition for the newly hatched offspring, but the effect that these casings have on the growth of these hatchlings is often unclear. The purpose of this study was to determine the effect of egg casings and of the maternal diet (fungus species) on the growth of the larvae of the forked fungus beetle. To achieve this objective, I collected eggs from forked fungus beetles maintained on three different fungus species and removed the egg casings from half the eggs. The eggs were then reared in the three different fungi. The time to hatching and hatching success of the eggs was measured, as well as the growth rate of the larvae. I found that there was no effect of the parental diet on hatching or larval growth. However, the absence of an egg casing caused larvae raised in one fungus to grow significantly faster than larvae in the other fungi. These results suggest that the presence of a casing may inhibit growth in some larvae, and may trade off with other functions that were not tested.

Rosenbauer, Annie (University of Vermont). Mentors: Henry Wilbur and Becky Wilbur (University of Virginia).
The effects of White-tailed deer on the herbaceous layer.
Abstract:  White-tailed deer (Odocoileus virginianus) have been impacting forests surrounding Mountain Lake Biological Station since their population boomed in the last half of the 20th century. Numerous long-term studies have documented the effects of deer on tree regeneration and forest ecosystem dynamics, however not many have considered the effects of herbivory on the herbaceous layer. This study was designed 1) to determine the effects of deer on herbaceous species abundance and diversity 2) to measure the response of herbaceous community structure over 8 years when deer are excluded, and 3) to determine which species are most sensitive to deer herbivory and which are able to persist despite long term, repeated loss of reproductive structures. This experiment tested the hypothesis that deer affect the structure of the herbaceous layer by measuring species responses to fencing. We found that deer browsing has differential impacts on herbaceous layer species. There was a significant difference in cover of functional groups between fenced and control plots in every year except 2006, when the fences were first erected.  There was a significant difference in cover and prevalence of species between fenced and control plots in 2014. Many herbaceous species we observed are able to persist in a vegetative state despite long-term loss of reproductive structures.  Results from this study can be used to inform future forest management practices.

Shimel, Philip (University of Alabama). Mentor: Jessamyn Manson (University of Alberta). 
Effects of herbivory on Asclepias syriaca and A. exaltata pollinator behavior.
Abstract:  Pollination and herbivory pose a conflicting challenge to flowering plants, which must simultaneously repel and attract similar organisms. If a plant’s adaptations to herbivory and pollination conflict, then an evolutionary trade-off must be balanced. Here we examined whether herbivore damage to milkweeds changes pollinator visitation or pollination success. To test this, we manipulated several populations of two milkweed species, Asclepias syriaca and A. exaltata, with a folivory simulation, and compared this group to a control group. I measured pollinator behavior by observing flower visits (number and duration), and I measured milkweed pollination success by counting pollinaria insertions and removals. I detected no reduction in pollinator visits or pollination success due to leaf damage in A. syriaca or A. exaltata. This result could be an artifact of a small sample size or biases due to weather. This lack of effect could be attributed to a lack of change in pollination related traits in the milkweeds, a lack of discrimination among pollinators, or an inadequate herbivory simulation. If pollinators are actually unaffected by damage to the leaves of the plants they pollinate, it perhaps indicates that plants have evolved specificity in their defenses against herbivores so as not to also harm their pollinators.