Adaptation to fluctuating environments in a selection experiment with Drosophila melanogaster

A fundamental question in life-history evolution is how organisms cope with fluctuating environments, including variation between stressful and benign conditions. For short-lived organisms, environments commonly vary between generations. Using a novel experimental design, we exposed wild-derived Drosophila melanogaster to three different selection regimes: one where generations alternated between starvation and benign conditions, and starvation was always preceded by early exposure to cold; another where starvation and benign conditions alternated in the same way, but cold shock sometimes preceded starvation and sometimes benign conditions; and a third where conditions were always benign. Using six replicate populations per selection regime, we found that selected flies increased their starvation resistance, most strongly for the regime where cold and starvation were reliably combined, and this occurred without decreased fecundity or extended developmental time. The selected flies became stress resistant, displayed a pronounced increase in early life food intake and resource storage. In contrast to previous experiments selecting for increased starvation resistance in D. melanogaster, we did not find increased storage of lipids as the main response, but instead that, in particular for females, storage of carbohydrates was more pronounced. We argue that faster mobilization of carbohydrates is advantageous in fluctuating environments and conclude that the phenotype that evolved in our experiment corresponds to a compromise between the requirements of stressful and benign environments

Selection for Increased Starvation Resistance Using Drosophila melanogaster: Investigating Physiological and Life History Trait Responses to Starvation and Dietary Supplementation in the Context of an Obese Phenotype

Artificial selection for starvation resistance provided insight into the relationships between evolved physiological and life history trait responses following exposure to biologically induced stress. Investigations of alterations to body composition, metabolic rate, movement, and life history traits including development time, female egg production, and longevity in response to brief periods of starvation were conducted on genetically based starvation-resistant and control lines of Drosophila melanogaster. Analysis of the starvation-resistant lines indicated increased energy storage with increased triglyceride deposition and conversion of carbohydrates to lipid, as identified by respiratory quotient values. Correlations between reductions in metabolic rates and movement in the starvation-resistant lines, suggested the presence of an evolved physiological response resulting in energy conservation. Investigations of life history traits in the starvation-resistant lines indicated no significant differences in development time or reproduction between the selected and control lines. Measurements of longevity, however, indicated a significant reduction in starvation-resistant D. melanogaster lifespan. These results suggested that elevated lipid concentrations, similar to that observed with obesity, were correlated with premature mortality. Exposure of the starvation-resistant and control lines to diets supplemented with glucose, palmitic acid, and a 2:1 mixture of casein to albumin were used to investigate alterations in body composition, movement, and life history traits. Results obtained from this study indicated that increased sugar in the diet led to increased carbohydrate, glycogen, total sugar, trehalose, and triglyceride concentrations, while increased fat and protein in the diet resulted in increased soluble protein, carbohydrate, glycogen, total sugar, and trehalose concentrations. Examination of life history trait responses indicated reduced fecundity in females exposed to increased glucose concentrations. Increased supplementations of palmitic acid was consistently correlated with an overall reduction in lifespan in both the starvation-resistant and control Drosophila lines, while measurements of movement indicated increased female activity levels in flies exposed to diets supplemented with fat and protein. Analyses of the physiological and life history trait responses to starvation and dietary supplementation on Drosophila melanogaster used in the present study has implications for investigating the mechanisms underlying the development and persistence of human obesity and associated metabolic disorders

Evolution of starvation resistance in \u3ci\u3eDrosophila melanogaster\u3c/i\u3e: Measurement of direct and correlated responses to artificial selection

Laboratory selection for resistance to starvation has been conducted under relatively controlled conditions to investigate direct and correlated responses to artificial selection. With regard to starvation resistance, there are three physiological routes by which the trait can evolve: resource accumulation, energy conservation and starvation tolerance. A majority of energetic compounds and macromolecules including triglycerides, trehalose and other sugars, and soluble protein increased in abundance as a result of selection. Movement was additionally investigated with selected males moving less than control males and selected females exhibiting a similar response to selection. Results obtained from this study supported two of the possible evolutionary mechanisms for adaptation to starvation: energy compound storage and conservation. If the response to selection is based on an evolutionarily conserved pattern of genetic correlations (elevated lipid, elevated sugars and reduced movement), then the response to selection is medically relevant and the genetic architecture should be investigated in depth

Bariatric Metabolic Surgery Reduced Liver Enzyme Levels in Patients with Non-Alcohol Fatty Liver Disease

Introduction. Approximately 93.3 million Americans are obese (BMI>30) and 51% have non-alcoholic fatty liver disease (NAFLD).  Progression of NAFLD can lead to Non-Alcoholic Steatohepatitis (NASH), the leading cause of liver transplant in the United States. This study analyzed liver enzymes following bariatric surgery in NAFLD patients up to one-year post-surgical intervention. Methods. A retrospective analysis of adults with NAFLD who underwent bariatric surgery from 2009 to 2016 was conducted. The primary outcome were transaminase levels following weight loss. Secondary outcomes included effects on blood glucose, lipids, and blood pressure. Results. A total of 130 participants consisting of 80% Caucasian females with an average BMI of 47.5 participated in the study. Reductions were noted in ALT (66.2 to 28.6 units/L) and AST (46.3 to 24.2 units/L) at 1 year post-surgical intervention.  Significant reductions were also noted in blood glucose (22.34%; p < .0001), HbA1c (17.11% p < .0001), LDL (19.75% p = .0046), total cholesterol (10.12% p = .0153), and triglycerides (37.21% p < .0001) with an increase in HDL (17.22% p = .0007). Significant correlations between alkaline phosphatase and ALT were noted at six months (p=.0101) and one year (p= .0547) and AST at six months (p=.0009). When separated by obesity class, participants with class II obesity experienced improved outcomes. Conclusions. Data obtained from this study indicated that bariatric surgery reduces liver enzyme levels in NAFLD. These findings suggest that bariatric surgery is a viable treatment option for participants with NAFLD