A combinatorial model for computing volumes of flow polytopes

We introduce new families of combinatorial objects whose enumeration computes volumes of flow polytopes. These objects provide an interpretation, based on parking functions, of Baldoni and Vergne's generalization of a volume formula originally due to Lidskii. We recover known flow polytope volume formulas and prove new volume formulas for flow polytopes that were seemingly unapproachable. A highlight of our model is an elegant formula for the flow polytope of a graph we call the caracol graph. As by-products of our work, we uncover a new triangle of numbers that interpolates between Catalan numbers and the number of parking functions, we prove the log-concavity of rows of this triangle along with other sequences derived from volume computations, and we introduce a new Ehrhart-like polynomial for flow polytope volume and conjecture product formulas for the polytopes we consider.Comment: 34 pages, 15 figures. v2: updated after referee reports; includes a proof of Proposition 8.7. Accepted into Transactions of the AM

Maternal Life Course Adversity: The Intersection of Psychosocial and Biobehavioral Adaptive Response in Pregnancy

The link between life course adversity and adverse health outcomes is well established, particularly early life adversity (ELA). There is also evidence that the physiologic adaptations associated with stress, depression and ELA can be transmitted intergenerationally via long-term set-point changes within the maternal hypothalamic-pituitary-adrenal axis (HPA). It is unknown how the type and timing of maternal stress and adversity influences HPA regulation during pregnancy and whether maternal coping attenuates this relationship. Manuscript 1 was an integrative review of studies examining the association between maternal ELA and HPA regulation during pregnancy. In manuscripts 2 and 3 the findings of the dissertation study are presented. The purpose of this dissertation was to further examine how the type and timing of maternal adversity is linked to physiologic HPA adaptations in pregnancy and whether psychosocial processes moderate the relationship between life adversity and HPA regulation. From a qualitative perspective, this study examined how situational factors in women’s lives influence their goals, motivations, and notions of health in pregnancy. The sample (N = 72) included women in the 2nd trimester of a singleton, uncomplicated pregnancy. The data collected included surveys, interviews, and salivary cortisol samples. Quantitative data were analyzed using correlation and general linear modeling. Lifetime stress was significantly correlated with higher cortisol during pregnancy. Childhood adversity accounted for cortisol elevations in the morning, while adult stress and depression accounted for elevated cortisol levels in the evening. Women’s willingness to seek social support significantly attenuated HPA reactivity. Neither stress nor cortisol were associated with birth outcomes. The qualitative study found that contextual and sociodemographic factors have a profound influence on the way that women prioritize life goals and health during pregnancy. Overall, women’s experience of adversity throughout the life course results in specific psychosocial and biobehavioral adaptive responses that shape the gestational environment and pregnancy experience

Stress exposure from in-utero to adolescence, the HPA-axis response to stress, and symptoms of depression and anxiety in adulthood

This doctoral thesis used a prospective design in a series of four studies to investigate links between common early-life stress exposures, from in-utero to age 17, alterations in the HPA-axis physiological response to a stressor at age 18, and depression and anxiety symptoms at age 20, with consideration of sex differences. Findings are important as they may help inform the timing of intervention and support strategies for reducing exposure to early-life stress

Telomere length is highly heritable and independent of growth rate manipulated by temperature in field crickets

Many organisms are capable of growing faster than they do. Restrained growth rate has functionally been explained by negative effects on lifespan of accelerated growth. However, the underlying mechanisms remain elusive. Telomere attrition has been proposed as a causal agent and has been mostly studied in endothermic vertebrates. We established that telomeres exist as chromosomal-ends in a model insect, the field cricket Gryllus campestris, using terminal restriction fragment and Bal 31 methods. Telomeres comprised TTAGGn repeats of 38 kb on average, more than four times longer than the telomeres of human infants. Bal 31 assays confirmed that telomeric repeats were located at the chromosome-ends. We tested whether rapid growth between day 1, day 65, day 85, and day 125 is achieved at the expense of telomere length by comparing nymphs reared at 23°C with their siblings reared at 28°C, which grew three times faster in the initial 65 days. Surprisingly, neither temperature treatment nor age affected average telomere length. Concomitantly, the broad sense heritability of telomere length was remarkably high at ~100%. Despite high heritability, the evolvability (a mean-standardized measure of genetic variance) was low relative to that of body mass. We discuss our findings in the context of telomere evolution. Some important features of vertebrate telomere biology are evident in an insect species dating back to the Triassic. The apparent lack of an effect of growth rate on telomere length is puzzling, suggesting strong telomere length maintenance during the growth phase. Whether such maintenance of telomere length is adaptive remains elusive and requires further study investigating the links with fitness in the wild.</p

Influence of Maternal Prior Life Adversity on the Psycho-Neuroendocrine-Immune Profile During Pregnancy

Pregnancy is accompanied by a multitude of physical and psychological changes. Adaptation to these changes through reduced anxiety and attenuated stress responsiveness is necessary across gestation and into the postpartum period for optimal maternal-infant health. In contrast, exposure to higher amounts of stressors during pregnancy can disrupt neuroendocrine-immune processes required for successful pregnancy outcomes. Evolving evidence demonstrates that exposure to adversity early in life has long-lasting effects on stress response systems that alter stress reactivity during adulthood. Given this evidence, it is posited that women who experience greater pre-pregnancy adversity during their childhood are at greater risk for negative maternal-infant health sequelae. Thus, the purpose of this study is to investigate the relationship between maternal childhood adversity and the psychological-neuroendocrine-immune profile during pregnancy. In addition, maternal risk and protective factors posited to moderate this profile were examined. Lastly, the relationship among maternal childhood adversity, maternal PNI profile during pregnancy, and neonatal outcomes were explored. The findings can contribute to improved approaches to identify and stratify risk for adverse maternal-infant health outcomes, as well as guide the development of early intervention programs and health policy for women who are pregnant or who plan to become pregnant. This is significant because the well-being of mothers and infants determines the health of the next generation. Improving maternal-infant well-being can markedly reduce public health challenges and ultimately reduce health care costs across the lifespan (U.S. Department of Health and Human Service, 2011)