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Developmental and Genetic Mechanisms of Ovariole Number Evolution in Drosophila
Get PDFThe goal of the "Quantitative Trait Gene" (QTG) program is to identify genes and mutations that underlie natural phenotypic variation. My goal with this work was to contribute an additional model to the program: ovariole number evolution in Drosophila. In this thesis I describe the progress I have made towards identifying a specific genetic change that contributed to the divergence of ovariole number between two Drosophila lineages. I identify specific developmental mechanisms relevant to establishing ovariole number in different Drosophila lineages by detailing ovarian cell-type specific specification, proliferation, and differentiation. I test specific candidates of genetic regulators of these developmental mechanisms with mutational analysis in D. melanogaster. I show that independent evolution of ovariole number has resulted from changes in distinct developmental mechanisms, each of which may have a different underlying genetic basis in Drosophila. I use the interspecies comparison of D. melanogaster versus D. sechellia to test for functional differences in insulin/insulin-like growth factor (IIS) signaling between the two species. I show that IIS activity levels and sensitivity have diverged between species, leading to both species-specific ovariole number and species-specific nutritional plasticity in ovariole number. Moreover, plastic range of ovariole number correlates with ecological niche, suggesting that the degree of nutritional plasticity may be an adaptive trait. My work and quantitative genetic analyses strongly support the hypothesis that evolution of the Drosophila insulin-like receptor (InR) gene, specifically, is at least partially responsible for the divergence in ovariole number and nutritional plasticity of ovariole number between D. melanogaster and D. sechellia. I detail ongoing experiments to test this hypothesis explicitly via cross-species transgenesis
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Eco-Evolutionary Ramifications of Herbicide-Driven Plant Modifications on Plant-Herbivore Interactions in Modern Agricultural Landscapes
No full textNatural populations evolve in response to biotic and abiotic changes in their environment, which lead to wide variation in defense traits that can shape species interactions. Often, variation in defense is a result of complementary or conflicting strategies for dealing with external stressors. Agricultural systems can introduce novel stressors via herbicide exposure to non-crop plant systems surrounding fields. Of the various plant defense strategies, trichomes, or hair-like appendages on the outermost boundary, are known to play a critical role in how these sessile organisms interact with their environment. While herbicide drift is known to produce a variety of toxic effects in plants, little is known about its impact on plant-herbivore interactions and the evolution of plant defense strategies. Thus, my dissertation addresses the overarching question: Does herbicide drift impact plant-herbivore interactions and the evolution of plant trichomes?
Using the annual invasive velvetleaf (Abutlion theophrasti) as the focal species, I conducted various field, greenhouse, and growth room experiments to explore the potential effects of herbicide drift. In the first data chapter (Chapter 2) of this dissertation, I investigate the impact of dicamba, a novel herbicide known to travel particularly far distances, on plant-herbivore interactions. The findings from this multi-year study revealed a significant increase in the phloem feeding silverleaf whitefly (Bermisia tabaci) abundance on plants exposed to herbicide. Here, I identified a significant phenotypic tradeoff between whitefly resistance and herbicide resistance. I also found evidence that dicamba drift significantly increased leaf chlorophyll content (mg/cm2) which positively affected whitefly abundance.
In the second (Chapter 3) and third (Chapter 4) data chapters of this dissertation, I assessed whether glyphosate, a traditional herbicide found in “Roundup”, acts as an agent of selection on induced trichome traits (polymorphs and density) and whether variation observed in trichome traits represents dual or conflicting roles against herbicide and herbivory damage. I identified positive correlations between induced total trichome production and herbicide resistance as well as induced branched trichomes and herbicide resistance. The selection analysis revealed positive linear selection acting on induced trichome production and correlative selection favoring high induced trichome production and intermediate plant growth. In the third data chapter, I found that having a high proportion of branched trichomes not only had a positive effect on herbicide resistance, but it also had a positive effect on chewing herbivory resistance.
In brief, my dissertation demonstrates that herbicide exposure can alter plant-herbivore interactions mediated by modified plant phenotypes. My thesis demonstrates that herbicide drift can create unintended reservoirs for agricultural pests like phloem feeding whiteflies that are attracted to chlorophyll content. It also provides novel evidence that herbicide is a selective agent on induced trichome production and demonstrates that branched trichomes can contribute synergistically to herbicide and chewing herbivory resistance, serving as a dual structural form of resistance reducing plant injury. While responses are expected to be species and herbicide dependent, collectively, this work reveals that herbicide exposure to non-target plant systems can significantly alter species interactions and community dynamics in habitats located at the agro-ecological interface.PhDEcology and Evolutionary BiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/177892/1/nmjo_1.pd
Bird Magnetoreception Across Scales: From Comparative Neuroanatomy to Macroecology
No full textMagnetoreception, the ability to detect and use Earth's magnetic fields for navigation and orientation, is a mysterious sensory system. Despite decades of research, scientists do not know the physiological mechanisms by which it functions in birds. Most magnetoreception research is done in carefully controlled experiments with captive model organisms. My dissertation focused on expanding the scales at which we research magnetoreception in birds to understudied parts of the avian tree of life and larger spatiotemporal contexts. This allows me to test hypotheses regarding the use of magnetoreception in more complex environments, as well as the evolution of magnetoreception relative to seasonal migration.
Accurate navigation is critical for successful seasonal migration. Migration has been gained and lost many times over evolutionary history, but it is unclear how many of the components of the migratory phenotype, including magnetoreception, are retained when migration re-evolves. Two of my chapters compared magnetoreception in three passerine bird families that evolved or re-evolved migration independently, thereby testing the relationship between magnetoreception and the evolution of migration.
In chapter 2, I tested for magnetic compass orientation behavior in Tyrannidae, Turdidae, and Vireonidae. Flycatchers (Tyrannidae) had never been tested for magnetic orientation and lack cryptochrome 4 (Cry4), a protein thought to be critical for magnetoreception through a visual pathway. None of my study species showed a consistent magnetic response, making our results challenging to interpret. However, I unexpectedly found that flycatchers and vireos (Vireonidae) seemed more liable to show phototactic behavior than thrushes (Turdidae), despite evidence for an opposite relationship with phototaxis when the same birds migrate in the wild.
In chapter 3, I compared brain stimulation patterns linked to magnetoreception in the same three families. Cluster N is a region in the visual wulst in the forebrain that is active at night in night-migratory songbirds. I exposed birds to a day/night and a magnetic stimulation treatment and measured Egr-1 expression, a protein indicative of neurostimulation, using immunohistochemistry. All three bird families showed cluster N activation patterns at night and little indication of a magnetic response. Cluster N activation in flycatchers is especially surprising because cluster N is thought to be linked to Cry4, which flycatchers lack. My results instead suggested that all major radiations in Passeriformes show cluster N activation. I argue that while cluster N is tightly linked to nocturnal migration, its link to magnetoreception requires further investigation, especially given its activation in flycatchers.
In chapter 4, I tested for effects of space weather-induced geomagnetic disturbances on nocturnal bird migration. Large impacts of magnetized energy from the Sun can destabilize Earth's magnetic field, presumably making it less reliable for navigation. I measured the intensity, direction, and altitude of nocturnal bird migration using weather radar data and compared it to a radar-specific custom magnetic disturbance index. Using two complementary statistical methods, I found decreases in migration intensity, or the number of birds migrating, in the spring and fall during large geomagnetic disturbances. In the fall, I also found that birds spent less energy flying against the wind when it was overcast during strong geomagnetic disturbances, suggesting that they might not be able to navigate as effectively without other navigation cues. This study allowed me to examine macroecological effects of magnetoreception in a complex environment at a larger spatial and ecological scale than previously possible.PhDEcology and Evolutionary BiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/194473/1/ergc_1.pd
Social Group Formation and Cooperation in Paper Wasps (P. Fuscatus)
No full textSocial group formation is theorized to play an important role in the evolution and maintenance of cooperation, as assortment of beneficial cooperators is critical for maintaining the benefits of cooperating. While there is growing appreciation for the profound variability in social phenotypes within populations, little work has examined how individual traits might shape the process and outcome of social group formation. Individual differences in social phenotypes are important because selection should act on individuals and traits within social groups, thus impacting how cooperation may evolve. Through a series of experiments conducted in a large naturalistic enclosure, I characterized and examine the social and fitness consequences of two different social phenotypes, personality and social intelligence, in the primitively eusocial paper wasps Polistes fuscatus (P. fuscatus).
My second chapter examines social and non-social personality traits in nest-founding queens. I find that social and non-social personality traits form behavioral syndromes which has important implications for how social traits may be selected across contexts. In my second and third chapter, I empirically test how personality (Chapter 3) and social cognition (Chapter 4) impact social group foundation in nest founding queens. By monitoring behavior of wasps throughout their lifespan, I find that individual traits have important implications for the process and outcome of social group formation. Further, individuals vary significantly in how they assess social partners, join groups, and behave within these groups. Excitingly, I find that individuals do not benefit equally within social groups and that individual traits have significant impacts on success within social groups.
In Chapter 2, I find that social group formation may be subjected to similar trade-offs present in mate selection. Personality mediates a trade-off between assessment of social partners
and formation of stable social bonds, with more exploratory and active individuals sampling more partners but joining groups later. Additionally, I find that this difference in sampling impacts the likelihood of achieving social dominance through “first-arriver effects”, suggesting that personality may impact reproductive opportunities in cooperative breeders through differences in group formation.
In Chapter 3, I demonstrate that social cognition has important impacts on how social groups form, cooperate, and reproduce. Excitingly, I find that social cognition is linked with both a fitness benefit and behaviors that promote group reproduction, suggesting that cognition is a socially selected trait. Individuals with better performance on a cognitive test engage in more cooperative behaviors, spend more days in stable groups, and build larger nests. Additionally, this fitness effect is observed when only comparing the cognitive abilities of individuals that should receive the majority or reproduction on nests, demonstrating that cognition may be socially selected at the level of the individual. In total, this work supports the predictions of the social intelligence hypothesis, finding that cognition is linked with both success and behavioral mechanisms to promote success in social groups.
This body of work advances the study of evolution through demonstrating that cooperation can evolve through selection on individuals within social groups and suggests that cognition may play a role in the evolution of cooperative behaviors. Furthermore, my work demonstrates that differences in social group formation may impact the reproductive opportunities of individuals within social groups. Collectively, this work advances understanding of how individual traits impact the process and outcome of social group formation.PhDEcology and Evolutionary BiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/177966/1/eclaub_1.pd
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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