UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item A comparative analysis of sperm storage in six brachyuran superfamilies: mating behavior, ecological variation and phylogenetic patterns(2010) Rodgers, Paula Jane; Reaka, Marjorie L; Hines, Anson H; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)While life history traits are shaped by allometric, phylogenetic, environmental and behavioral factors, few comparative studies of brachyuran life history patterns have considered sperm storage traits as important components of reproductive strategies. To understand the evolutionary forces selecting for sperm storage and their interactions with other life history traits, I (1) used controlled laboratory experiments and field mating observations to examine variation in male sperm transfer patterns, (2) sampled variation in female reproductive output and sperm storage for two species across a latitudinal gradient, (3) conducted a survey of life history traits across a broad range of brachyuran taxa, and (4) used phylogenetic analyses to identify patterns in the evolution of life history traits in brachyurans. From mating experiments and observations on five species, I found that males transfer more sperm with longer than shorter copulation durations and that variation in copulation duration was shaped by differences in the species' ecologies. Latitudinal surveys of two species with contrasting mating systems identified seasonal and geographical variation in female reproductive output. While the variation in most reproductive traits could best be explained at smaller spatial scales, a sperm storing species, Callinectes sapidus became sperm limited at low latitudes. From a comparative survey of male and female life history traits across 61 species of brachyurans, I found that allometry, phylogeny and mating strategies explained much of the variation in life history traits. Using rigorous phylogenetic techniques, male life history traits showed more plasticity across the phylogeny than female traits suggesting male traits may be influenced more by behavioral and environmental factors. After correcting for phylogenetic signals, species with larger male sperm stores had larger amounts of sperm stored by the female. In summary this dissertation illustrates the importance of partitioning variation in mating behavior, phylogeny, environmental factors and allometry when examining the evolution of life history traits in brachyurans.Item Family Structure and Income Redistribution: Comparing Child Poverty Outcomes in Canada, the United Kingdom, and the United States(2007-06-14) Grutzmacher, Stephanie; Anderson, Elaine A.; Family Studies; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The United States has greater income inequality and higher child poverty than any other industrialized, wealthy nation, which greatly impacts opportunities for American children. Given that social and economic institutions are predicated on the breadwinner-homemaker family structure as the ideal family, family formation and living arrangements also appear to create disadvantages and high poverty risk for some children. Government income redistribution policies have varied success in reducing child poverty, especially among children living in vulnerable family structures. Cross-national comparisons may provide useful information for improving the effectiveness of antipoverty policies. This study used data from Wave V of the Luxembourg Income Study to comparatively analyze income redistribution and relative child poverty in various family structures in nationally representative samples from Canada, the United Kingdom, and the United States. Single mother, single father, two-parent, single grandmother, single grandfather, and two-parent grandparent families with children under the age of 18 were analyzed. Structural functional theory is used as a guiding conceptual framework. Results indicate that income from government programs is differentially redistributed across various family structures in all three countries, often with smaller child poverty reductions among more vulnerable family structures. Single mother families have the highest child poverty rates at each phase of income redistribution, while two-parent families have the lowest rates. Children living in grandparent-headed families experience the largest reductions in poverty through income redistribution. Children living in households with young children have higher poverty rates at each phase of income redistribution than children living in households with no young children, yet they experience smaller reductions in poverty across all three countries. The United States has the highest child poverty rates in all examined structures at each phase of income redistribution, while the United Kingdom reduces child poverty by the largest proportion. While income is redistributed differentially by family structure, the utilization of structural characteristics for policy development is questioned. Policy implications for improving child poverty reduction efforts in the United States through labor market regulation, caregiving relief, and caregiving support are discussed.