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2018-2019

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  • Thumbnail for  Flower Color, Anthocyanin and UV Damage in Ipomopsis aggregata
    Flower Color, Anthocyanin and UV Damage in Ipomopsis aggregata by Godtfredsen, Elsa Bea

    Plants require access to photosynthetically active radiation (PAR), which also exposes them to potentially damaging ultraviolet wavelengths. Anthocyanin is a secondary compound which provides red coloration for flowers and has been shown to absorb light in the UV spectrum. Ipomopsis aggregata displays flower color varying from pink to scarlet red, correlated with anthocyanin content. In this study, we compared the UV protective qualities of I. aggregata individuals with scarlet flowers (dark-colored) to plants with pink flowers (light-colored) using a combination of field observations (Manitou Experimental Forest) and in situ experimental manipulations. The field methodology included measurements on photosynthetic efficiency, stomatal conductance, anthocyanin content, chlorophyll content and leaf temperature to attempt to understand if there were differences among the light and dark colored morphs. Germination rate and seed mass were also quantified. The dark morphologies had greater anthocyanin content which could allow them greater UV protection. Dark morphologies also had higher photosystem efficiency, chlorophyll content, stomatal conductance, seed mass and germination rate. However, light morphologies may have a greater diversity of pollinators. This could indicate a reproductive and survivorship trade-off, connected directly to flavonoid content, between pollinator attraction and protection from UV damage in a mid-elevation plant population.

  • Thumbnail for Assessing Fitness Costs Associated with Selection for Insecticide Resistance in Aedes aegypti Mosquitoes
    Assessing Fitness Costs Associated with Selection for Insecticide Resistance in Aedes aegypti Mosquitoes by Amer, Keenan

    Worldwide Aedes aegypti is the principal urban vector of several major human pathogens, including dengue, Zika, chikungunya and yellow fever viruses. In Mexico, control of this mosquito strongly relies on the use of pyrethroids against adults and larvae. In consequence, many Ae. aegypti field populations have become resistant to insecticides. Pyrethroids kill mosquitoes by binding to the voltage gated sodium channel (VGSC) and preventing its proper functioning. Resistance to pyrethroids arises through nonsynonymous mutations in the VGSC gene that reduce pyrethroid binding, known as knockdown resistance (kdr). The insecticide resistance mutations have been shown to have a large fitness benefit in the presence of insecticide treatment. However, in the absence of insecticide, there is frequently reported reduced frequency of the mutant allele which suggests the mutation has a fitness cost. We evaluated the fitness cost of some kdr mutations on several life-history parameters as well as common abiotic stresses faced in the field. Specifically, we compared 2 populations differing in the frequency of the kdr mutations but otherwise of identical genetic background and we found a significant difference between the resistant and susceptible strains in adult dry mass upon emergence, adult water reserves, adult lipid reserves, and larval thermal tolerance. In contrast, both strains responded similarly to larval salinity stress and adult desiccation stress. Our results suggest that these Ae. aegypti kdr mutations indeed have some fitness cost, whether directly or indirectly associated with them. This is critical to determining the extent to which insecticide resistance interacts with life history traits and should provide key information for vector control in the future.

  • Thumbnail for Evolution of Life History in Three High Elevation Puya (Bromeliaceae)
    Evolution of Life History in Three High Elevation Puya (Bromeliaceae) by Veldhuisen, Leah

    The Andes are known as a hotspot for biodiversity and high species endemism for both plants and animals. Two important tropical, high-elevation ecosystems in the Andes are the puna in Peru, Bolivia and Chile between 7° and 27° South, and the páramo in Colombia, Venezuela and Ecuador between 11° North and 8° South; both are found at elevations above 3500 meters. The genus Puya (Bromeliaceae) is found throughout the puna and the páramo, and is relatively under-studied. Life history of most Puya species is largely unknown, with the notable exception of entirely semelparous Puya raimondii, which flowers once right before dying and does not reproduce clonally. Other species in the genus do reproduce clonally to varying degrees; their life history strategies have not been defined. Decreased cloning ability in Puya may be evolving convergently as in other plant groups endemic to high-elevation, tropical ecosystems. We studied three species of Puya (P. raimondii, P. cryptantha and P. goudotiana) across the two ecosystems in Bolivia and Colombia, and collected data on threshold size at flowering and clonal reproduction. Data were also analyzed in conjunction with life history theory to hypothesize each species’ life history strategy. All three species were found to have a consistent and predictable minimum size at flowering, while P. cryptantha was found to also have a minimum size for clonal reproduction. No such evidence was found for P. goudotiana. Our data supported that P. raimondii is fully semelparous, and indicated that P. goudotiana and P. cryptantha may be semi-semelparous.

  • Thumbnail for Evolution of Pollination Mechanisms in Pleurothallis
    Evolution of Pollination Mechanisms in Pleurothallis by Zhao, Kehan

    The orchid genus Pleurothallis is believed to be predominantly fly-pollinated based on limited field studies. I hypothesized that both reward and deceit pollination syndromes occur in the genus and deceit pollination, more specifically, pseudocopulation has evolved more than once. Flowers were sampled from several infrageneric groups within Pleurothallis and examined by scanning electron microscopy. Morphological features of the labellum of the flower, such as the presence or absence of a glenion or other secretory tissue, or cavities possibly involved in pseudocopulation, were used to infer possible pollination mechanisms. Additionally, new nuclear ITS and plastid 3’ ycf1 sequences were added onto the phylogenies generated by previous students in Wilson Laboratory. Pollination mechanisms inferred from floral morphology was mapped onto the phylogenies. Preliminary data suggest that pseudocopulation may have evolved more than once in Pleurothallis.

  • Thumbnail for Spatial structure of treeline on Pikes Peak
    Spatial structure of treeline on Pikes Peak by Su, Chenyang

    Spatial structure of alpine treeline plays a key role in its response to climate change, yet the processes that are responsible for creating that structure are poorly understood. Here, we describe a treeline on the west side of Pikes Peak with different tools to gain insight of the structure at a local scale and to investigate the potential endogenous mechanisms that appear to influence it. We hypothesized that the trees will be clustered in the system through positive intraspecific interactions and that the treeline is a potential phase transition system with classical criticality. With the classical description of treeline structure, we divided the zone into different sections of increasing elevation range with the assumption that the mechanisms driving the structure of each are the same, and ran Ripley’s K function for cluster analyses. Ripley’s K function showed significant tree clustering through the sections in the study area, especially between the elevation of 3600m and 3680m. Clustering among large-sized trees were significant across the entire treeline. To examine the potential of the treeline as phase transitions, which allows us to treat the system as continuous rather than in sections, we analyzed presence of fractal structure in the treeline. Analysis of the spatial structure reveals significant fractal geometry in size classes, as well as on the edges of big tree clusters which has the potential to evolve into a percolation cluster. The analyses show evidences that the system could more likely be in robust criticality rather than phase transition. This study provides insights into describing the treeline on a local scale and could contribute to the current study of treeline dynamics and treeline as a complex system.

  • Thumbnail for The Rodent Eats the Raptor: Impacts of Red Squirrels (Tamiasciurus hudsonicus) on Flammulated Owl (Psiloscops flammeolus) Nest Success and Habitat Selection
    The Rodent Eats the Raptor: Impacts of Red Squirrels (Tamiasciurus hudsonicus) on Flammulated Owl (Psiloscops flammeolus) Nest Success and Habitat Selection by Ellison, Jordan

    Previous research has demonstrated the importance of nest predation as a major force affecting the reproductive success of birds. The evolution of different life histories, reproductive strategies, and habitat selection in response to predation has been well- documented across avian taxa. However, no studies have focused on a cavity-nesting species with a low reproductive rate. I investigated how the Flammulated Owl (Psiloscops flammeolus), a small secondary cavity-nesting raptor, has adapted in response to predation by the North American Red Squirrel (Tamiasciurus hudsonicus) on the Manitou Experimental Forest in Central Colorado. I evaluated several mechanisms of predator avoidance that Flammulated Owls may have evolved as part of their nest habitat selection, including selecting locations with lower squirrel density or lower squirrel activity, and selecting nesting locations that limit attacks by squirrels. I estimated squirrel density from detections along line transects, mapped locations of squirrels that were detected, and mapped the location of squirrel middens within and outside owl territories. Habitat variables were quantified at owl nest trees and adjacent forests and compared to available but unused sites. I found that squirrel density per hectare was greater in owl territories (3.1 ± 0.4) than random territories (0.3 ± 0.1; t=6.1, df=2, p<0.05), but I found no correlation between squirrel abundance and midden characteristics. Cavity height was on average higher at owl nests (7.7 ± 0.2m) than available but unused cavities (6.0 ± 0.3m; t=2.7, df=369, p<0.01), and successful nests (8.9 ± 0.4m) were higher than depredated nests (6.6 ± 0.3m; t=4.1, df=69, p<0.001). A similar pattern was found with nest tree height, and a positive correlation was found between the two habitat characteristics (p<0.001, R2=0.26). Although squirrel density was higher in owl territories, it is possible that underlying habitat differences exist across the study area, and that common characteristics are associated with high-quality habitat for both owls and squirrels. Selection for higher nesting cavities by Flammulated Owls may be an adaptive response to perceived predation risk or decreased nesting success in lower cavities, as has been corroborated by other studies of cavity-nesting birds.

  • Thumbnail for The Status of Green Crabs (Carcinus maenas) in the Damariscotta River: Population Dynamics and Competition Influenced Niche Partitioning
    The Status of Green Crabs (Carcinus maenas) in the Damariscotta River: Population Dynamics and Competition Influenced Niche Partitioning by Wray, Anita Elliott

    Invasive species have the potential to drastically shift the community composition of habitats through increased competitive interactions. In economically important ecosystems, this can cause populations to decline and economies to collapse. The European Green Crab (Carcinus maenas) is an omnivorous and prolific crab which has invaded much of both North American coasts, causing damage to some major bivalve fisheries. My study sought to identify the population trends of the green crab along a river estuary system in the Gulf of Maine. In addition, my study investigated the potential for interspecific competition between rock crabs (Cancer irroratus) and green crabs. Subtidal traps were placed biweekly along the shoreline of the Damariscotta River for the 2013, 2014, 2015, and 2018 summer seasons. Carapace width, total weight, sex, ovigerous status, and number of intact legs per individual were quantified for each individual of both species (N=1,208). A caged in-lab experiment was used to observe potential competition for food between rock crabs and green crabs of the same size. My study was unable to find a significant difference between 2015 and 2018 green crab catch rates, suggesting there was no population growth present. In addition, rock crabs were identified as the dominant species in my lab trials. This study suggests that competitive dominance in the native crab species could have the potential to shift the habitat of the invasive green crab to a higher position in the water column, which could limit any further population growth. As green crabs significantly contributed to the collapse of many bivalve fisheries (e.g. the soft-shelled clam), this result could help to inform more effective fisheries and aquaculture management.