The Graduate Program in Latin American Studies at the University of Texas at Austin

Latin American Studie

Morphogenesis along the animal-vegetal axis: fates of primary quartet micromere daughters in the gastropod Crepidula fornicata.

BackgroundThe Spiralia are a large, morphologically diverse group of protostomes (e.g. molluscs, annelids, nemerteans) that share a homologous mode of early development called spiral cleavage. One of the most highly-conserved features of spiralian development is the contribution of the primary quartet cells, 1a-1d, to the anterior region of the embryo (including the brain, eyes, and the anterior ciliary band, called the prototroch). Yet, very few studies have analyzed the ultimate fates of primary quartet sub-lineages, or examined the morphogenetic events that take place in the anterior region of the embryo.ResultsThis study focuses on the caenogastropod slipper snail, Crepidula fornicata, a model for molluscan developmental biology. Through direct lineage tracing of primary quartet daughter cells, and examination of these cells during gastrulation and organogenesis stages, we uncovered behaviors never described before in a spiralian. For the first time, we show that the 1a2-1d2 cells do not contribute to the prototroch (as they do in other species) and are ultimately lost before hatching. During gastrulation and anterior-posterior axial elongation stages, these cells cleavage-arrest and spread dramatically, contributing to a thin provisional epidermis on the dorsal side of the embryo. This spreading is coupled with the displacement of the animal pole, and other pretrochal cells, closer to the ventrally-positioned mouth, and the vegetal pole.ConclusionsThis is the first study to document the behavior and fate of primary quartet sub-lineages among molluscs. We speculate that the function of 1a2-1d2 cells (in addition to two cells derived from 1d12, and the 2b lineage) is to serve as a provisional epithelium that allows for anterior displacement of the other progeny of the primary quartet towards the anterior-ventral side of the embryo. These data support a new and novel mechanism for axial bending, distinct from canonical models in which axial bending is suggested to be driven primarily by differential proliferation of posterior dorsal cells. These data suggest also that examining sub-lineages in other spiralians will reveal greater variation than previously assumed

Weight Adjustment Methods and Their Impact on Sample-based Inference

Weighting samples is important to reflect not only sample design decisions made at the planning stage, but also practical issues that arise during data collection and cleaning that necessitate weighting adjustments. Adjustments to base weights are used to account for these planned and unplanned eventualities. Often these adjustments lead to variations in the survey weights from the original selection weights (i.e., the weights based solely on the sample units' probabilities of selection). Large variation in survey weights can cause inferential problems for data users. A few extremely large weights in a sample dataset can produce unreasonably large estimates of national- and domain-level estimates and their variances in particular samples, even when the estimators are unbiased over many samples. Design-based and model-based methods have been developed to adjust such extreme weights; both approaches aim to trim weights such that the overall mean square error (MSE) is lowered by decreasing the variance more than increasing the square of the bias. Design-based methods tend to be ad hoc, while Bayesian model-based methods account for population structure but can be computationally demanding. I present three research papers that expand the current weight trimming approaches under the goal of developing a broader framework that connects gaps and improves the existing alternatives. The first paper proposes more in-depth investigations of and extensions to a newly developed method called generalized design-based inference, where we condition on the realized sample and model the survey weight as a function of the response variables. This method has potential for reducing the MSE of a finite population total estimator in certain circumstances. However, there may be instances where the approach is inappropriate, so this paper includes an in-depth examination of the related theory. The second paper incorporates Bayesian prior assumptions into model-assisted penalized estimators to produce a more efficient yet robust calibration-type estimator. I also evaluate existing variance estimators for the proposed estimator. Comparisons to other estimators that are in the literature are also included. In the third paper, I develop summary- and unit-level diagnostic tools that measure the impact of variation of weights and of extreme individual weights on survey-based inference. I propose design effects to summarize the impact of variable weights produced under calibration weighting adjustments under single-stage and cluster sampling. A new diagnostic for identifying influential, individual points is also introduced in the third paper

Creepiness Creeps In: Uncanny Valley Feelings Are Acquired in Childhood

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/150519/1/cdev12999_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150519/2/cdev12999.pd

HEALTH DISPARITIES: THE GENETIC CONTRIBUTION IN THE AFRICAN AMERICAN COMMUNITY

poster abstractSince the completion of the Human Genome Project, it has been found that genes and their function play a role in 9 out of 10 of the leading causes of death in the U.S. Some of these causes such as heart disease, cancer, stroke and diabetes are significantly prevalent in the African American community. African Americans often experience the largest differences in health risks when compared to their White counterparts. This research project will examine how mutated genes and their function, contribute to health disparities in the African American community. The population for this research project will only include individuals of African ancestry born in the U.S. A brief survey will be conducted to inquire about participants’ knowledge of genetics and its influence on disease inheritance. The data collected will be interpreted as a representation of average African Americans’ knowledge of genetic influences on disease inheritance. Additionally, data will be obtained from facilities that offer genetic testing services. Specifically, I hope to obtain information on the racial populations who utilize these services, primarily, those with higher occurrences of genetic disorders. Coupled with the survey’s data, I will use the testing centers’ information to determine whether a correlation exists between the following variables: knowledge of genetics, use of genetic testing services and prevalence of inheritable diseases. I expect a strong correlation between afore mentioned variables. My hypothesis is that this correlation will prove undetected gene mutations when inherited, contribute to health disparities in the African American community

Infants' use of social partnerships to predict behavior

The experiences of social partners are important motivators of social action. Can infants use such experiences to make predictions about how social agents will behave? Sixteen‐month‐old infants were introduced to two social pairs. Initial events established within‐pair cooperation as well as between‐pair conflict involving an individual from each pair. Following these events, infants looked longer when between‐pair members who had never previously interacted now cooperated – instead of conflicted – with each other. Thus, infants tracked the third‐person allegiances and inferred that the conflict would generalize across social partnerships. These findings demonstrate a critical feature of early social cognition and promote needed, further research on the role of social allegiances in social cognition across development.The experiences of social partners are important motivators of social action. Can infants use such experiences to make predictions about how social agents will behave? In three studies, following initial instances of conflict between individual members of different social pairs, sixteen‐month‐old infants looked longer when those individuals' social partners–who had never previously interacted–cooperated rather than conflicted with one other. Thus, infants tracked the agents' third‐person allegiances and inferred that the conflict would generalize across social partnerships.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/115912/1/desc12267.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/115912/2/desc12267_am.pd

Variability of acute extracellular action potential measurements with multisite silicon probes

Device miniaturization technologies have led to significant advances in sensors for extracellular measurements of electrical activity in the brain. Multisite, silicon-based probes containing implantable electrode arrays afford greater coverage of neuronal activity than single electrodes and therefore potentially offer a more complete view of how neuronal ensembles encode information. However, scaling up the number of sites is not sufficient to ensure capture of multiple neurons, as action potential signals from extracellular electrodes may vary due to numerous factors. In order to understand the large-scale recording capabilities and potential limitations of multisite probes, it is important to quantify this variability, and to determine whether certain key device parameters influence the recordings. Here we investigate the effect of four parameters, namely, electrode surface, width of the structural support shafts, shaft number, and position of the recording site relative to the shaft tip. This study employs acutely implanted silicon probes containing up to 64 recording sites, whose performance is evaluated by the metrics of noise, spike amplitude, and spike detection probability. On average, we find no significant effect of device geometry on spike amplitude and detection probability but we find significant differences among individual experiments, with the likelihood of detecting spikes varying by a factor of approximately three across trials

Infants Use Statistical Sampling to Understand the Psychological World

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/133581/1/infa12131.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/133581/2/infa12131_am.pd