The isotope values of fossil snail shells can be important archives of climate. Here, we present the first carbon (δ13C) and oxygen (δ18O) isotope values of snail shells in interior Alaska to explore changes in vegetation and humidity through the late-glacial period. Snail shell δ13C values were relatively consistent through the late glacial. However, late-glacial shell δ13C values are 2.8‰ higher than those of modern shells. This offset is best explained by the Suess effect and changes in the δ13C values of snail diet. Snail shell δ18O values varied through the late glacial, which can be partially explained by changes in relative humidity (RH). RH during the snail growing period was modeled based on a published flux balance model. Results suggest a dry period toward the beginning of the Bølling–Allerød (~14 ka) followed by two distinct stages of the Younger Dryas, a wetter stage in the early Younger Dryas from 12.9 to 12.3 ka, and subsequent drier stage in the late Younger Dryas between 12.3 and 11.7 ka. The results show that land snail isotopes in high-latitude regions may be used as a supplementary paleoclimate proxy to help clarify complex climate histories, such as those of interior Alaska during the Younger Dryas.

Recently developed quantitative models of psychopathology (i.e., Hierarchical Taxonomy of Psychopathology) identify an Antagonistic Externalizing spectrum that captures the psychological disposition toward criminal and antisocial behavior. The purpose of the present study was to examine relations between Antagonistic psychopathology (and associated Five-Factor model Antagonism/Agreeableness) and neural functioning related to social-cognitive Theory of Mind using a large sample (N = 973) collected as part of the Human Connectome Project (Van Essen et al., 2013a). No meaningful relations between Antagonism/Antagonistic Externalizing and Theory of Mind-related neural activity or synchrony were observed (p < .005). We conclude by outlining methodological considerations (e.g., validity of social cognition task and low test–retest reliability of functional biomarkers) that may account for these null results, and present recommendations for future research.

Quantitative models of psychopathology (i.e., HiTOP) propose that personality and psychopathology are intertwined, such that the various processes that characterize personality traits may be useful in describing and predicting manifestations of psychopathology. In the current study, we used data from the Human Connectome Project (N = 1050) to investigate neural activation following receipt of a reward during an fMRI task as one shared mechanism that may be related to the personality trait Extraversion (specifically its sub-component Agentic Extraversion) and internalizing psychopathology. We also conducted exploratory analyses on the links between neural activation following reward receipt and the other Five-Factor Model personality traits, as well as separate analyses by gender. No significant relations (p < .005) were observed between any personality trait or index of psychopathology and neural activation following reward receipt, and most effect sizes were null to very small in nature (i.e., r < |.05|). We conclude by discussing the appropriate interpretation of these null findings, and provide suggestions for future research that spans psychological and neurobiological levels of analysis.

Understanding the properties of time averaging (age mixing) in a stratigraphic layer is essential for properly interpreting the paleofauna preserved in the geologic record. This work assesses the age and quantifies the scale and structure of time averaging of land snail-rich colluvial sediments from the Madeira Archipelago (Portugal) by dating individual shells using amino acid racemization calibrated with graphite-target and carbonate-target accelerator mass spectrometry radiocarbon methods. Gastropod shells of Actinella nitidiuscula were collected from seven sites on the volcanic islands of Bugio and Deserta Grande (Desertas Islands), where snail shells are abundant and well preserved in Quaternary colluvial deposits. Results show that the shells ranged in age from modern to ~48 cal ka BP (calibrated radiocarbon age), covering the last glacial and present interglacial periods. Snail shells retrieved from two of the colluvial sites exhibit multimillennial age mixing (>6 ka), which significantly exceeds the analytical error from dating methods and calibration. The observed multimillennial mixing of these assemblages should be taking into consideration in upcoming paleoenvironmental and paleoecological studies in the region. The extent of age mixing may also inform about the time span of colluvial deposition, which can be useful in future geomorphological studies. In addition, this study presents the first carbonate-target radiocarbon results for land snail shells and suggests that this novel, rapid, and more affordable dating method offers reliable age estimates for small land snail shells younger than ~20 cal ka BP.

Comparisons between modern death assemblages and their source communities have demonstrated fidelity to species diversity across a variety of environments and taxonomic groups. However, differential species preservation and collection (including body-size bias) in both modern and fossil death assemblages may still skew the representation of other important ecological characteristics. Here, we move beyond live-dead taxonomic fidelity and focus on the recovery of functional ecology (how species interact with their ecosystem) at the community level for a diverse non-volant mammal community (87 species; Amboseli, Kenya). We use published literature to characterize species, using four functional traits and their associated categorical attributes (i) dietary mode (11 attributes; e.g., browser, grazer), (ii) preferred feeding habitat (16 attributes; e.g., grassland, woodland), (iii) preferred sheltering habitat (17 attributes; e.g., grassland, underground cavity), and (iv) activity time (7 attributes; e.g., diurnal, nocturnal, nocturnally dominated crepuscular). For each functional ecological trait we compare the death assemblage's recovered richness and abundance structure of constituent functional attributes with those of the source community, using Jaccard similarity, Spearman's rho, and the Probability of Interspecific Encounter (evenness). We use Monte Carlo simulations to evaluate whether these empirical comparisons are significantly different from expectations calculated from randomized sampling of species from the source community. Results indicate that although the Amboseli death assemblage is significantly overrepresented by large-bodied species relative to the Amboseli source community, it captures many functional dimensions of the ecosystem within expectations of a randomized collection of species. Additional resampling simulations and logistic regressions further illustrate that the size bias inherent to the Amboseli death assemblage is not a major driver of deviations between the functional ecological properties of the death assemblage and its source community. Finally, the Amboseli death assemblage also enhances our understanding of the mammal community by adding nine species and two functional attributes previously unknown from the ecosystem.

This study investigated the relationship between insulin-resistance and constituent components of executive function in a sample of neurologically intact older adult subjects using the homeostasis model assessment (HOMA-IR) and latent factors of working memory, cognitive control and processing speed derived from confirmatory factor analysis. Low-density lipoprotein (LDL), mean arterial pressure (MAP), along with body mass index (BMI) and white matter hypointensity (WMH) were used to control for vascular risk factors, adiposity and cerebrovascular injury. The study included 119 elderly subjects recruited from the University of California, San Francisco Memory and Aging Center. Subjects underwent neuropsychological assessment, fasting blood draw and brain magnetic resonance imaging (MRI). Partial correlations and linear regression models were used to examine the HOMA-IR-executive function relationship. Pearson correlation adjusting for age showed a significant relationship between HOMA-IR and working memory (rp=−.18; p=.047), a trend with cognitive control (rp=−.17; p=.068), and no relationship with processing speed (rp=.013; p=.892). Linear regression models adjusting for demographic factors (age, education, and gender), LDL, MAP, BMI, and WMH indicated that HOMA-IR was negatively associated with cognitive control (r=−.256; p=.026) and working memory (r=−.234; p=.054). These results suggest a greater level of peripheral insulin-resistance is associated with decreased cognitive control and working memory. After controlling for demographic factors, vascular risk, adiposity and cerebrovascular injury, HOMA-IR remained significantly associated with cognitive control, with working memory showing a trend. These findings substantiate the insulin-resistance-executive function hypothesis and suggest a complex interaction, demonstrated by the differential impact of insulin-resistance on processing speed and specific aspects of executive function. (JINS, 2015, 21, 622–628)