Emergence of the Shackleton Range from beneath the Antarctic Ice Sheet due to glacial erosion

This paper explores the long-term evolution of a subglacial fjord landscape in the Shackleton Range, Antarctica. We propose that prolonged ice-sheet erosion across a passive continental margin caused troughs to deepen and lower the surrounding ice-sheet surface, leaving adjacent mountains exposed. Geomorphological evidence suggests a change in the direction of regional ice flow accompanied emergence. Simple calculations suggest that isostatic compensation caused by the deepening of bounding ice-stream troughs lowered the ice-sheet surface relative to the mountains by ~800m. Use of multiple cosmogenic isotopes on bedrock and erratics (26Al, 10Be, 21Ne) provides evidence that overriding of the massif and the deepening of the adjacent troughs occurred earlier than the Quaternary. Perhaps this occurred in the mid-Miocene, as elsewhere in East Antarctica in the McMurdo Dry Valleys and the Lambert basin. The implication is that glacial erosion instigates feedback that can change ice-sheet thickness, extent, and direction of flow. Indeed, as the subglacial troughs evolve over millions of years, they increase topographic relief; and this changes the dynamics of the ice sheet. © 2013 Elsevier B.V

Changes in undergraduates’ marijuana, heavy alcohol and cigarette use following legalization of recreational marijuana use in Oregon

Background and AimsRecreational marijuana legalization (RML) went into effect in Oregon in July 2015. RML is expected to influence marijuana use by adolescents and young adults in particular, and by those with a propensity for substance use. We sought to quantify changes in rates of marijuana use among college students in Oregon from pre‐ to post‐RML relative to college students in other states across the same time period.DesignRepeated cross‐sectional survey data from the 2012–16 administrations of the Healthy Minds Study.SettingSeven 4‐year universities in the United States.ParticipantsThere were 10 924 undergraduate participants. One large public Oregon university participated in 2014 and 2016 (n = 588 and 1115, respectively); six universities in US states where recreational marijuana use was illegal participated both in 2016 and at least once between 2012 and 2015.MeasurementsSelf‐reported marijuana use in the past 30 days (yes/no) was regressed on time (pre/post 2015), exposure to RML (i.e. Oregon students in 2016) and covariates using mixed‐effects logistic regression. Moderation of RML effects by recent heavy alcohol use was examined.FindingsRates of marijuana use increased from pre‐ to post‐2015 at six of the seven universities, a trend that was significant overall. Increases in rates of marijuana use were significantly greater in Oregon than in comparison institutions, but only among students reporting recent heavy alcohol use.ConclusionsRates of Oregon college students’ marijuana use increased (relative to that of students in other states) following recreational marijuana legislation in 2015, but only for those who reported recent heavy use of alcohol. Such alcohol misuse may be a proxy for vulnerabilities to substance use or lack of prohibitions (e.g. cultural) against it.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138912/1/add13906_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138912/2/add13906.pd

Early adulthood: A developmental perspective on suicide prevention and intervention

Early adulthood is a time of transition when large segments of the population embrace new roles and show decreases in behaviors and problems thought to underlie suicide risk. Still, other segments show emergent or worsening psychopathology per-haps exacerbated by age-related disconnection from prior relational and institutional supports. Suicide prevention efforts are developmentally informed with respect to the distinction between adolescence and adulthood, but much less so in relation to earlier versus later adulthood. Developmentally sensitive approaches to suicide prevention during early adulthood should enhance the tried-and-true approaches of screening, means restriction, and treatment, and improve universal prevention by attending to (1) unique or high-risk developmental transitions (e.g., college dropout), (2) key institu-tional contexts in which most young adults spend significant time (e.g., workplace), (3) how ongoing dependence with respect to the family of origin can be leveraged by pre-ventionists, and (4) the ways in which health care utilization patterns weaken the utility of key prevention pathways, such as via screening by general practitioners. Multilevel, multicomponent suicide prevention models will be needed to make use of the array of effective but often unintegrated strategies and to develop new ones. Finally, funda-mental methodological considerations are required to advance the science, practice, and impact of suicide prevention in early adulthood

Evolutionary History and Attenuation of Myxoma Virus on Two Continents

The attenuation of myxoma virus (MYXV) following its introduction as a biological control into the European rabbit populations of Australia and Europe is the canonical study of the evolution of virulence. However, the evolutionary genetics of this profound change in host-pathogen relationship is unknown. We describe the genome-scale evolution of MYXV covering a range of virulence grades sampled over 49 years from the parallel Australian and European epidemics, including the high-virulence progenitor strains released in the early 1950s. MYXV evolved rapidly over the sampling period, exhibiting one of the highest nucleotide substitution rates ever reported for a double-stranded DNA virus, and indicative of a relatively high mutation rate and/or a continually changing selective environment. Our comparative sequence data reveal that changes in virulence involved multiple genes, likely losses of gene function due to insertion-deletion events, and no mutations common to specific virulence grades. Hence, despite the similarity in selection pressures there are multiple genetic routes to attain either highly virulent or attenuated phenotypes in MYXV, resulting in convergence for phenotype but not genotype. © 2012 Kerr et al

Entropy and the variational principle for actions of sofic groups

Recently Lewis Bowen introduced a notion of entropy for measure-preserving actions of a countable sofic group on a standard probability space admitting a generating partition with finite entropy. By applying an operator algebra perspective we develop a more general approach to sofic entropy which produces both measure and topological dynamical invariants, and we establish the variational principle in this context. In the case of residually finite groups we use the variational principle to compute the topological entropy of principal algebraic actions whose defining group ring element is invertible in the full group C*-algebra.Comment: 44 pages; minor changes; to appear in Invent. Mat

Associations Between Relocation and Seasonal Depression

Seasonal Affective Disorder (SAD) is a mood disorder that is characterized by depressive symptoms that onset and remit at the same times each year. Whereas few people (about 1%) experience problems severe enough to be labeled SAD, many people (estimates range from 30%-90%) may experience mild to moderate changes in depressive symptoms in response to day length and other seasonal changes. Given that latitude affects the extent to which day length varies seasonally, this study explored the extent to which international college students’ relocation to a new latitude (44.57° N; Corvallis, Oregon) may affect their seasonal depressive symptoms. It was hypothesized that 1) the severity of students’ current depressive symptoms (assessed in winter) would be related to the extent of latitudinal change between their previous residence and Corvallis, and 2) that lifetime histories of seasonal depression would be more prevalent among students from latitudes that are further from the equator. A convenience sample of 50 international students (N = 50, men=33, women=16, unreported=1) age 18 or older with evidence of English proficiency were recruited from an international learning center. Participants were surveyed on acculturative stress, social support, current depressive symptoms, and lifetime seasonal depressive symptoms. Nearly all (98%) participants came from a more southern latitude (mean latitude of origin was 27° N); thus many participants were potentially experiencing a significant latitudinal change, as well as more dramatic changes in day length. Half (49%) of participants reported clinically significant depressive symptoms. Contrary to the hypotheses, latitude change was not associated with severity of current depressive symptoms (r = 0.12). Current depressive symptoms were more related to lower social support (r = -.35, p < .05) and higher acculturative stress (r = .63 p < 0.001). Furthermore, latitude of origin was not related to lifetime history of seasonal depression (r = -.01). Thus, no support was found for the notion that latitude (considered a proxy for the magnitude of seasonal changes in day length) or change in latitude are powerful influences on international students’ depressive symptoms

Changing with the seasons : does vitamin D affect mood?

Seasonality is defined as a change in mood and behavior with the seasons. Research shows there is a possible connection between vitamin D levels and mood (Murphy & Wagner, 2008; Lansdowne & Provost, 1998). Given that vitamin D is produced when skin is exposed to sunlight and varies with sun exposure (Bertone-Johnson, 2009), the present study examined the relationships among vitamin D levels, season, and seasonality. Vitamin D levels were expected to be relatively 1) higher, but decreasing in fall; 2) lower, but stable in winter; and 3) higher, but increasing in spring. Further, it was hypothesized that these patterns would be stronger among participants with self-reported seasonality. College women (n=187) ages 18-25 (26.7% White/Caucasian) were recruited either in fall (n=82), winter (n=34), or spring (n=62) term. Participants’ vitamin D levels were measured from their blood samples collected at baseline (T1) and again 5 weeks later (T5). Participants reported their seasonality symptoms across their lifespan using the Seasonal Pattern Assessment Questionnaire (SPAQ) at T5, and were grouped into two categories based on their SPAQ scores: at least moderate seasonality (n=88) and mild to no seasonality (n=94). Repeated measures ANOVA was used to examine mean level and change in vitamin D (from T1 to T5) for individuals in the two seasonality groups, and whether any differences depended on season of recruitment. Overall, vitamin D levels showed the expected patterns by season, but not by self-reported seasonality. That is, contrary to the hypothesis, individuals with at least moderate seasonality did not show significantly more pronounced seasonal changes in vitamin D in comparison to others. However, non-significant trends emerged, indicating the need to examine these relationships further. Future research will address study limitations by following a larger sample of participants throughout the entire year, assessing their vitamin D levels and current mood states at each season

Probing Evolutionary Patterns in Neotropical Birds through DNA Barcodes

Background: The Neotropical avifauna is more diverse than that of any other biogeographic region, but our understanding of patterns of regional divergence is limited. Critical examination of this issue is currently constrained by the limited genetic information available. This study begins to address this gap by assembling a library of mitochondrial COI sequences, or DNA barcodes, for Argentinian birds and comparing their patterns of genetic diversity to those of North American birds. Methodology and Principal Findings: Five hundred Argentinian species were examined, making this the first major examination of DNA barcodes for South American birds. Our results indicate that most southern Neotropical bird species show deep sequence divergence from their nearest-neighbour, corroborating that the high diversity of this fauna is not based on an elevated incidence of young species radiations. Although species ages appear similar in temperate North and South American avifaunas, patterns of regional divergence are more complex in the Neotropics, suggesting that the high diversity of the Neotropical avifauna has been fueled by greater opportunities for regional divergence. Deep genetic splits were observed in at least 21 species, though distribution patterns of these lineages were variable. The lack of shared polymorphisms in species, even in species with less than 0.5M years of reproductive isolation, further suggests that selective sweeps could regularly excise ancestral mitochondrial polymorphisms. Conclusions: These findings confirm the efficacy of species delimitation in birds via DNA barcodes, even when tested on a global scale. Further, they demonstrate how large libraries of a standardized gene region provide insight into evolutionary processes.Fil: Kerr, Kevin C. R.. University of Guelph; CanadáFil: Lijtmaer, Dario Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Barreira, Ana Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Hebert, Paul David Neil. University of Guelph; CanadáFil: Tubaro, Pablo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentin