Selection, Linkage, and Population Structure Interact To Shape Genetic Variation Among Threespine Stickleback Genomes.

The outcome of selection on genetic variation depends on the geographic organization of individuals and populations as well as the organization of loci within the genome. Spatially variable selection between marine and freshwater habitats has had a significant and heterogeneous impact on patterns of genetic variation across the genome of threespine stickleback fish. When marine stickleback invade freshwater habitats, more than a quarter of the genome can respond to divergent selection, even in as little as 50 years. This process largely uses standing genetic variation that can be found ubiquitously at low frequency in marine populations, can be millions of years old, and is likely maintained by significant bidirectional gene flow. Here, we combine population genomic data of marine and freshwater stickleback from Cook Inlet, Alaska, with genetic maps of stickleback fish derived from those same populations to examine how linkage to loci under selection affects genetic variation across the stickleback genome. Divergent selection has had opposing effects on linked genetic variation on chromosomes from marine and freshwater stickleback populations: near loci under selection, marine chromosomes are depauperate of variation, while these same regions among freshwater genomes are the most genetically diverse. Forward genetic simulations recapitulate this pattern when different selective environments also differ in population structure. Lastly, dense genetic maps demonstrate that the interaction between selection and population structure may impact large stretches of the stickleback genome. These findings advance our understanding of how the structuring of populations across geography influences the outcomes of selection, and how the recombination landscape broadens the genomic reach of selection.

Environmental and Evolutionary Drivers of the Modular Gene Regulatory Network Underlying Phenotypic Plasticity for Stress Resistance in the Nematode Caenorhabditis remanei.

Organisms can cope with stressful environments via a combination of phenotypic plasticity at the individual level and adaptation at the population level. Changes in gene expression can play an important role in both. Significant advances in our understanding of gene regulatory plasticity and evolution have come from comparative studies in the field and laboratory. Experimental evolution provides another powerful path by which to learn about how differential regulation of genes and pathways contributes to both acclimation and adaptation. Here we present results from one such study using the nematode Caenorhabditis remanei We selected one set of lines to withstand heat stress and another oxidative stress. We then compared transcriptional responses to acute heat stress of both and an unselected control to the ancestral population using a weighted gene coexpression network analysis, finding that the transcriptional response is primarily dominated by a plastic response that is shared in the ancestor and all evolved populations. In addition, we identified several modules that respond to artificial selection by (1) changing the baseline level of expression, (2) altering the magnitude of the plastic response, or (3) a combination of the two. Our findings therefore reveal that while patterns of transcriptional response can be perturbed with short bouts of intense selection, the overall ancestral structure of transcriptional plasticity is largely maintained over time.

Associations Between Unhealthy Weight-Loss Strategies and Depressive Symptoms.

INTRODUCTION: There appears to be a link between weight loss and improved mental health, but less is known about how using unhealthy weight-loss strategies impacts the odds of reporting depression. METHODS: This study includes respondents from the National Health and Nutrition Examination Survey from 2005 to 2014 who attempted to lose weight over the past year. Analysis occurred in 2017. Multivariable logistic regression was used to describe associations between all weight-loss strategies, including those grouped as unhealthy (smoking, vomiting, laxatives, skipping meals, and using diet pills), and the adjusted odds of depression (Patient Health Questionnaire-9 score ≥10). The model was then stratified by BMI, sex, race, and antidepressant use to compare the effect of using at least one unhealthy weight-loss strategy and depression within certain populations. RESULTS: The sample included 6,765 respondents (weighted n=59.2 million, 95% CI=55.5, 62.9 million). Of these respondents, 18.0% (n=1,270) reported using at least one unhealthy weight-loss strategy. In unadjusted analysis, unhealthy weight-loss strategies were generally associated with higher incidence and odds of reporting depression. In multivariable analysis, using at least one unhealthy weight-loss strategy was significantly associated with odds of reporting depression (AOR=1.47, 95% CI=1.14, 1.91, p<0.01). When the model was stratified, this effect was statistically significant among respondents with class I or II obsesity (AOR=2.20, 95% CI=1.56, 3.10, p<0.01); female respondents (AOR=1.46, 95% CI=1.06, 2.00, p=0.02); and respondents who did not use an antidepressant (AOR=1.57, 95% CI=1.14, 2.15, p=0.01). CONCLUSIONS: Unhealthy weight-loss strategies are associated with increased odds of depression. This may inform screening practices and public health messaging.

Thromboembolic and Major Bleeding Events With Rivaroxaban Versus Warfarin Use in a Real-World Setting.

BACKGROUND: Although randomized trials demonstrate the noninferiority of rivaroxaban compared with warfarin in the context of nonvalvular atrial fibrillation (AF), little is known about how these drugs compare in practice. OBJECTIVE: To assess the relative effectiveness and safety of rivaroxaban versus warfarin in a large health system and to evaluate this association by time in therapeutic range (TTR). METHODS: We conducted a retrospective cohort study with propensity matching in the Cleveland Clinic Health System. The study included patients initiated on warfarin or rivaroxaban for thromboembolic prevention in nonvalvular AF between January 2012 and July 2016. The main outcomes were thromboembolic events and major bleeds. Analyses were stratified by warfarin patients' TTR. RESULTS: The cohort consisted of 472 propensity-matched pairs. The mean age was 73.6 years (SD = 11.7), and the mean CHADS2 score was 1.8. The median TTR for warfarin patients was 64%. In the propensity-matched analysis, there was no significant difference in thromboembolic or major bleeding events between groups. Among warfarin patients with a TTR <64% and their matched rivaroxaban pairs, there was also no significant difference in thromboembolic or major bleeding events. CONCLUSIONS: Under real-world conditions, warfarin and rivaroxaban were associated with similar safety and effectiveness, even among those with suboptimal therapeutic control. Individualized decision making, taking into account the nontherapeutic tradeoffs associated with these medications (eg, monitoring, half-life, cost) is warranted.

The transgenerational effects of heat stress in the nematode Caenorhabditis remanei are negative and rapidly eliminated under direct selection for increased stress resistance in larvae.

Parents encountering stress environments can influence the phenotype of their offspring in a form of transgenerational phenotypic plasticity that has the potential to be adaptive if offspring are thereby better able to deal with future stressors. Here, we test for the existence of anticipatory parental effects in the heat stress response in the highly polymorphic nematode Caenorhabditis remanei. Rather providing an anticipatory response, parents subject to a prior heat stress actually produce offspring that are less able to survive a severe heat shock. Selection on heat shock resistance within the larvae via experimental evolution leads to a loss of sensitivity (robustness) to environmental variation during both the parental and larval periods. Whole genome transcriptional analysis of both ancestor and selected lines shows that there is weak correspondence between genetic pathways induced via temperature shifts during parental and larval periods. Parental effects can evolve very rapidly via selection acting directly on offspring.

Rapid evolution of phenotypic plasticity and shifting thresholds of genetic assimilation in the nematode Caenorhabditis remanei.

Many organisms can acclimate to new environments through phenotypic plasticity, a complex trait that can be heritable, subject to selection, and evolve. However, the rate and genetic basis of plasticity evolution remain largely unknown. We experimentally evolved outbred populations of the nematode Caenorhabditis remanei under an acute heat shock during early larval development. When raised in a nonstressful environment, ancestral populations were highly sensitive to a 36.8° heat shock and exhibited high mortality. However, initial exposure to a nonlethal high temperature environment resulted in significantly reduced mortality during heat shock (hormesis). Lines selected for heat shock resistance rapidly evolved the capacity to withstand heat shock in the native environment without any initial exposure to high temperatures, and early exposure to high temperatures did not lead to further increases in heat resistance. This loss of plasticity would appear to have resulted from the genetic assimilation of the heat induction response in the noninducing environment. However, analyses of transcriptional variation via RNA-sequencing from the selected populations revealed no global changes in gene regulation correlated with the observed changes in heat stress resistance. Instead, assays of the phenotypic response across a broader range of temperatures revealed that the induced plasticity was not fixed across environments, but rather the threshold for the response was shifted to higher temperatures over evolutionary time. These results demonstrate that apparent genetic assimilation can result from shifting thresholds of induction across environments and that analysis of the broader environmental context is critically important for understanding the evolution of phenotypic plasticity.