Causal hypotheses accounting for correlations between decomposition rates of different mass fractions of leaf litter

Whole-leaf decomposition rates are the sum of the decomposition rates of each chemical fraction (water-soluble, cellulose, hemicellulose, lignin), but the decomposition rates of each fraction show complicated patterns of covariation. What explains these patterns of covariation? After measuring the k values of each fraction in 42 different mixtures of tree leaf litters from five species, we tested three alternative causal hypotheses that have been proposed in the literature concerning these mixture interactions using structura equations modeling. All three hypotheses were rejected by the data. We then proposed a new hypothesis, in which rapid decomposition of the labile (water-soluble) fraction stimulates the decomposition of lignin by white-rot fungi and the decomposition of hemicellulose by brown-rot fungi. A more rapid decomposition of hemicellulose then stimulates the decomposition of cellulose. This hypothesis is both consistent with known biology and with our data and is proposed as the most viable current hypothesis.

Associations of birth size, infancy, and childhood growth with intelligence quotient at 5 years of age: a Danish cohort study

BACKGROUND

The correlates of prenatal and postnatal growth on Intelligence Quotient (IQ) in childhood in term-born children living in high-income countries are not well known.

OBJECTIVES

We examined how birth size and growth in infancy and childhood were associated with IQ at age 5 y in term-born children using path analysis.

METHODS

The study sample comprised 1719 children from the Danish National Birth Cohort who participated in a substudy in which psychologists assessed IQ using the Wechsler Primary and Preschool Scales of Intelligence-Revised. Measured weight, length/height, and head circumference at birth, 5 mo, 12 mo, and 5 y were included in a path model to estimate their total, indirect, and direct effects on IQ. All growth measures were included in the model as sex- and age-standardized z-scores.

RESULTS

After adjusting for potential confounders, a positive association between birth weight and IQ was observed, and 88% of the association was direct. Weight gain in infancy was associated with IQ [per z-score increase from 5 to 12 mo, IQ increased by 1.53 (95% CI: 0.14; 2.92) points] whereas weight gain from 12 mo to 5 y was not associated with IQ. Height and head circumference growth in childhood was associated with IQ [per z-score increase from 12 mo to 5 y, IQ increased by 0.98 (95% CI: 0.17; 1.79) and 2.09 (95% CI: 0.78; 3.41) points, respectively].

CONCLUSIONS

In children born at term in an affluent country with free access to health care, higher IQ was seen with greater size at birth and greater weight gain in infancy. Also, greater growth in height and head circumference throughout the first 5 y of life was associated with higher childhood IQ whereas greater weight gain after the first year of life was not.

Sex differences in type of lifetime trauma and suicidal ideation mediated by post-traumatic stress and anxio-depressive disorders in older adults

OBJECTIVES

Examine the association between trauma and daily stressors, post-traumatic stress syndrome (PTSS), anxio-depressive disorders, and suicidal ideation in older adults.

DESIGN

A cross-sectional study.

SETTING AND PARTICIPANTS

This study included 1446 older adults recruited in primary care practices (2011-2013) and participating in Quebec's longitudinal study on health services in the elderly.

MEASUREMENTS

Lifetime trauma and PTSS was assessed using the validated PTSS scale for older adults based on scores from the Impact of Events Scale-Revised, number of lifetime traumatic events and interference with daily activities. The presence of an anxio-depressive disorder was based on physician diagnoses. Path analyses were conducted to determine the pathways between trauma, daily stressors, PTSS and anxio-depressive disorders and SI. Analyses were conducted on the overall sample and by sex.

RESULTS

Seven percent and 12% reported SI and PTSS. In males, traumas of sexual assault, violence/stalked, war/combat/imprisonment and daily hassles were directly associated with SI. In females, daily hassles were directly associated with SI. In males, a number of traumas were associated with SI through the mediating effect of PTSS and anxio-depressive disorders. In females, PTSS but not anxio-depressive disorders mediated the relationship between traumas and daily stressors, and suicidal ideation.

CONCLUSIONS

The effects of lifetime traumas persist well into older age. Traumas leading to SI differ between males and females as do the pathways and comorbidity with PTSS and anxio-depressive disorders. This highlights differences in etiologic patterns, which may be used in primary care practice to identify symptom profiles of older persons at risk of suicidal ideation.

A fruit diet rather than invertebrate diet maintains a robust innate immunity in an omnivorous tropical songbird

Diet alteration may lead to nutrient limitations even in the absence of food limitation, and this may affect physiological functions, including immunity. Nutrient limitations may also affect the maintenance of body mass and key life‐history events that may affect immune function. Yet, variation in immune function is largely attributed to energetic trade‐offs rather than specific nutrient constraints.

To test the effect of diet on life‐history traits, we tested how diet composition affects innate immune function, body mass and moult separately and in combination with each other, and then used path analyses to generate hypotheses about the mechanistic connections between immunity and body mass under different diet compositions.

We performed a balanced parallel and crossover design experiment with omnivorous common bulbuls Pycnonotus barbatus in out‐door aviaries in Nigeria. We fed 40 wild‐caught bulbuls ad libitum on fruits or invertebrates for 24 weeks, switching half of each group between treatments after 12 weeks. We assessed innate immune indices (haptoglobin, nitric oxide and ovotransferrin concentrations, and haemagglutination and haemolysis titres), body mass and primary moult, fortnightly. We simplified immune indices into three principal components (PCs), but we explored mechanistic connections between diet, body mass and each immune index separately.

Fruit‐fed bulbuls had higher body mass, earlier moult and showed higher values for two of the three immune PCs compared to invertebrate‐fed bulbuls. These effects were reversed when we switched bulbuls between treatments after 12 weeks. Exploring the correlations between immune function, body mass and moult, showed that an increase in immune function was associated with a decrease in body mass and delayed moult in invertebrate‐fed bulbuls, while fruit‐fed bulbuls maintained body mass despite variation in immune function. Path analyses indicated that diet composition was most likely to affect body mass and immune indices directly and independently from each other. Only haptoglobin concentration was indirectly linked to diet composition via body mass.

We demonstrated a causal effect of diet composition on innate immune function, body mass and moult: bulbuls were in a better condition when fed on fruits than invertebrates, confirming that innate immunity is nutrient specific. Our results are unique because they show a reversible effect of diet composition on wild adult birds whose immune systems are presumably fully developed and adapted to wild conditions—demonstrating a short‐term consequence of diet alteration on life‐history traits.

Towards the validation of a new, blended theoretical model of fear of cancer recurrence

OBJECTIVE

Fear of cancer recurrence (FCR) is defined as "fear, worry, or concern about cancer returning or progressing". To date, only the seminal model proposed by Lee-Jones and colleagues has been partially validated, so additional model testing is critical to inform intervention efforts. The purpose of this study is to examine the validity of a blended model of FCR that integrates Leventhal's Common Sense Model, Mishel's Uncertainty in Illness Theory, and cognitive theories of worry.

METHODS

Participants (n = 106) were women diagnosed with stage I to III breast or gynecological cancer who were enrolled in a Randomized Controlled Trial of a group cognitive-existential intervention for FCR. We report data from standardized questionnaires (Fear of Cancer Recurrence Inventory-Severity and Triggers subscales; Illness Uncertainty Scale; perceived risk of recurrence; Intolerance of Uncertainty Scale; Why do people Worry about Health questionnaire; Reassurance-seeking Behaviors subscale of the Health Anxiety Questionnaire, and the Reassurance Questionnaire) that participants completed before randomization. Path analyses were used to test the model.

RESULTS

Following the addition of four paths, the model showed an excellent fit (χ2 = 13.39, P = 0.20; comparative fit index = 0.99; root mean square error of approximation = 0.06). Triggers, perceived risk of recurrence, and illness uncertainty predicted FCR. FCR was associated with maladaptive coping. Positive beliefs about worrying and intolerance of uncertainty did not predict FCR but led to more maladaptive coping.

CONCLUSIONS

These results provide support for a blended FCR model.

Understanding Suicidal Ideation in Latino/a Adolescents Living in Puerto Rico

Puerto Rican adolescents, as well as other Latinos/as, have been identified at higher risk for suicidal ideation and attempts compared to other ethnic groups. However, research designed to better understand suicidality among Puerto Rican adolescents is rare.

OBJECTIVE

A socio-cognitive vulnerability model of suicidal ideation was tested in adolescents living in Puerto Rico.

METHOD

Multiple group path analyses were performed to assess the effect of self-reported socio-environmental and vulnerability factors on suicidal ideation, by sex, in 233 students from the metropolitan area of San Juan, Puerto Rico.

RESULTS

Overall, the model explained a large amount of the variance in suicidal ideation (r2 = .59 for females and r2 = .48 for males). Depressive symptoms had the strongest total effect on suicidal ideation for both sexes (r = .69 for females and r = .53 for males) and negative life events were the most salient socio-environmental factor. Hopelessness had a direct effect on suicidal ideation for males only. Externalizing behaviors had a direct effect on suicidal ideation for both males and females, but it was particularly strong for females.

CONCLUSION

Results support the mediating role of vulnerability factors and the differential importance of socio-environmental and vulnerability factors in understanding suicidal ideation among Puerto Rican adolescents. The relevance of exploring different developmental paths to suicidal ideation, separately by sex, is discussed.

Mediating pathways and gender differences between shift work and subjective cognitive function

OBJECTIVES

Increased injury risk among shift workers is often attributed to cognitive function deficits that come about as a result of sleep disruptions. However, little is known about the intermediate influences of other factors (eg, work stress, health) which may affect this relationship. In addition, gender differences in these the complex relationships have not been fully explored. The purpose of this study is to (1) identify the extent to which work and non-work factors mediate the relationship between shift work, sleep and subsequent subjective cognitive function; and (2) determine if the mediating pathways differ for men and women.

METHODS

Data from the 2010 National Population Health Survey was used to create a cross-sectional sample of 4255 employed Canadians. Using path modelling, we examined the direct and indirect relationships between shift work, sleep duration, sleep quality and subjective cognitive function. Multigroup analyses tested for significantly different pathways between men and women. Potential confounding effects of age and self-reported health and potential mediating effects of work stress were simultaneously examined.

RESULTS

Work stress and sleep quality significantly mediated the effects of shift work on cognition. Age and health confounded the relationship between sleep quality and subjective cognition. No differences were found between men and women.

CONCLUSIONS

Occupational health and safety programmes are needed to address stress and health factors, in addition to sleep hygiene, to effectively address cognitive function among shift workers.

Differentiating Burnout from Depression: Personality Matters!

Stress-related affective disorders have been identified as a core health problem of the twenty-first century. In the endeavor to identify vulnerability factors, personality has been discussed as a major factor explaining and predicting disorders like depression or burnout. An unsolved question is whether there are specific personality factors allowing differentiation of burnout from depression. The present study tested the relation between one of the most prominent, biological personality theories, Cloninger's Temperament and Character Inventory, and common measures of burnout (Maslach Burnout Inventory General) and depression (Beck Depression Inventory 2) in a sample of German employees (N = 944) and a sample of inpatients (N = 425). Although the same personality traits (harm avoidance and self-directedness) were predominantly associated with burnout and depression, there was a much stronger association to depression than to burnout in both samples. Besides, we observed specific associations between personality traits and subcomponents of burnout. Our results underline differences in the association of burnout vs. depression to personality, which may mirror differences in scope. While symptoms of depression affect all aspects of life, burnout is supposed to be specifically related to the workplace and its requirements. The much stronger association of personality to depression can be important to select appropriate therapy methods and to develop a more specified treatment for burnout in comparison to depression.