Evolutionary Physiology of Drosophila melanogaster

Over the past 30 years of experimental evolutionary research on Drosophila, strong functional associations have been established between organismal characters, life history, and behavior. Evolutionary physiologists use stress as a tool, either to measure an organism’s physical robustness, or to create differentiated populations with which to study adaptation. However, many questions are unanswered. For example, do short periods of strong selection generate similar levels of functional divergence to those generated by long-sustained selection? And if so, can we take the already advantageous Drosophila model system and use it to effectively study vertebrate diseases (i.e. cardiovascular disease and obesity-related disorders). Chapter 1 examines the relationship between evolutionary history and physiological differentiation. We observed classic physiological characters, specifically stress resistance and locomotion, as well as a character of recent interest, heart robustness. We found that short periods of strong selection applied to outbred Mendelian populations can readily generate high levels of functional differentiation. Chapter 2 revolves around the interrelationships among major physiological systems. By combining electrical pacing and flight exhaustion assays with manipulative conditioning, we started to unpack the interrelationships between cardiac function, flight endurance, and stress resistance. One major insight is the adverse impact of lipids on Drosophila heart robustness, a parallel result to many comparable studies in human cardiology. With human obesity growing to epidemic proportions in the United States, and excessive lipid accumulation being a risk factor for heart disease, we sought to observe the effects of lipid accumulation in Drosophila. Chapter 3 discusses the effects of intense selection for increased starvation resistance on ten outbred Drosophila populations. These populations displayed cardiac dysfunction, increased adult mortality, and elevated lipid levels, making them a useful model system for heart disease and obesity-related disorders. In Chapter 4, I emulated the effects of chronic consumption of the high-fat, high-caffeine fast-food diet by exposing flies to coconut oil and caffeine. Similarly, the findings here continue to support the general inference that high lipid levels present challenges for the Drosophila heart. Fruit flies could be an invaluable resource in understanding the molecular, genetic and other machinery underlying heart disease

The effects of adaptation to urea on feeding rates and growth in Drosophila larvae.

A collection of forty populations were used to study the phenotypic adaptation of Drosophila melanogaster larvae to urea-laced food. A long-term goal of this research is to map genes responsible for these phenotypes. This mapping requires large numbers of populations. Thus, we studied fifteen populations subjected to direct selection for urea tolerance and five controls. In addition, we studied another twenty populations which had not been exposed to urea but were subjected to stress or demographic selection. In this study, we describe the differentiation in these population for six phenotypes: (1) larval feeding rates, (2) larval viability in urea-laced food, (3) larval development time in urea-laced food, (4) adult starvation times, (5) adult desiccation times, and (6) larval growth rates. No significant differences were observed for desiccation resistance. The demographically/stress-selected populations had longer times to starvation than urea-selected populations. The urea-adapted populations showed elevated survival and reduced development time in urea-laced food relative to the control and nonadapted populations. The urea-adapted populations also showed reduced larval feeding rates relative to controls. We show that there is a strong linear relationship between feeding rates and growth rates at the same larval ages feeding rates were measured. This suggests that feeding rates are correlated with food intake and growth. This relationship between larval feeding rates, food consumption, and efficiency has been postulated to involve important trade-offs that govern larval evolution in stressful environments. Our results support the idea that energy allocation is a central organizing theme in adaptive evolution

The effects of adaptation to urea on feeding rates and growth in Drosophila larvae.

A collection of forty populations were used to study the phenotypic adaptation of Drosophila melanogaster larvae to urea-laced food. A long-term goal of this research is to map genes responsible for these phenotypes. This mapping requires large numbers of populations. Thus, we studied fifteen populations subjected to direct selection for urea tolerance and five controls. In addition, we studied another twenty populations which had not been exposed to urea but were subjected to stress or demographic selection. In this study, we describe the differentiation in these population for six phenotypes: (1) larval feeding rates, (2) larval viability in urea-laced food, (3) larval development time in urea-laced food, (4) adult starvation times, (5) adult desiccation times, and (6) larval growth rates. No significant differences were observed for desiccation resistance. The demographically/stress-selected populations had longer times to starvation than urea-selected populations. The urea-adapted populations showed elevated survival and reduced development time in urea-laced food relative to the control and nonadapted populations. The urea-adapted populations also showed reduced larval feeding rates relative to controls. We show that there is a strong linear relationship between feeding rates and growth rates at the same larval ages feeding rates were measured. This suggests that feeding rates are correlated with food intake and growth. This relationship between larval feeding rates, food consumption, and efficiency has been postulated to involve important trade-offs that govern larval evolution in stressful environments. Our results support the idea that energy allocation is a central organizing theme in adaptive evolution

Experimental Evolution and Heart Function in Drosophila.

Drosophila melanogaster is a good model species for the study of heart function. However, most previous work on D. melanogaster heart function has focused on the effects of large-effect genetic variants. We compare heart function among 18 D. melanogaster populations that have been selected for altered development time, aging, or stress resistance. We find that populations with faster development and faster aging have increased heart dysfunction, measured as percentage heart failure after electrical pacing. Experimental evolution of different triglyceride levels, by contrast, has little effect on heart function. Evolved differences in heart function correlate with allele frequency changes at many loci of small effect. Genomic analysis of these populations produces a list of candidate loci that might affect cardiac function at the intersection of development, aging, and metabolic control mechanisms

Four Steps Toward The Control Of Aging: Following The Example Of Infectious Disease

The biotechnological task of controlling human aging will evidently be complex, given the failure of all simple strategies for accomplishing this task to date. In view of this complexity, a multi-step approach will be necessary. One precedent for a multi-step biotechnological success is the burgeoning control of human infectious diseases from 1840 to 2000. Here we break down progress toward the control of infectious disease into four key steps, each of which have analogs for the control of aging. (1) Agreement about the fundamental nature of the medical problem. (2) Public health measures to mitigate some of the factors that exacerbate the medical problem. (3) Early biotechnological interventions that ward off the more tractable disease etiologies. (4) Deep understanding of the underlying biology of the diseases involved, leading in turn to comprehensive control of the medical problems that they pose. Achievement of all four of these steps has allowed most people who live in Western countries to live largely free of imminent death due to infectious disease. Accomplishing the equivalent feat for aging over this century should lead to a similar outcome for aging-associated disease. Neither infection nor aging will ever be entirely abolished, but they can both be rendered minor causes of death and disability

Experimental Evolution and Heart Function in Drosophila.

Drosophila melanogaster is a good model species for the study of heart function. However, most previous work on D. melanogaster heart function has focused on the effects of large-effect genetic variants. We compare heart function among 18 D. melanogaster populations that have been selected for altered development time, aging, or stress resistance. We find that populations with faster development and faster aging have increased heart dysfunction, measured as percentage heart failure after electrical pacing. Experimental evolution of different triglyceride levels, by contrast, has little effect on heart function. Evolved differences in heart function correlate with allele frequency changes at many loci of small effect. Genomic analysis of these populations produces a list of candidate loci that might affect cardiac function at the intersection of development, aging, and metabolic control mechanisms

Effects of evolutionary history on genome wide and phenotypic convergence in Drosophila populations

Abstract Background Studies combining experimental evolution and next-generation sequencing have found that adaptation in sexually reproducing populations is primarily fueled by standing genetic variation. Consequently, the response to selection is rapid and highly repeatable across replicate populations. Some studies suggest that the response to selection is highly repeatable at both the phenotypic and genomic levels, and that evolutionary history has little impact. Other studies suggest that even when the response to selection is repeatable phenotypically, evolutionary history can have significant impacts at the genomic level. Here we test two hypotheses that may explain this discrepancy. Hypothesis 1: Past intense selection reduces evolutionary repeatability at the genomic and phenotypic levels when conditions change. Hypothesis 2: Previous intense selection does not reduce evolutionary repeatability, but other evolutionary mechanisms may. We test these hypotheses using D. melanogaster populations that were subjected to 260 generations of intense selection for desiccation resistance and have since been under relaxed selection for the past 230 generations. Results We find that, with the exception of longevity and to a lesser extent fecundity, 230 generations of relaxed selection has erased the extreme phenotypic differentiation previously found. We also find no signs of genetic fixation, and only limited evidence of genetic differentiation between previously desiccation resistance selected populations and their controls. Conclusion Our findings suggest that evolution in our system is highly repeatable even when populations have been previously subjected to bouts of extreme selection. We therefore conclude that evolutionary repeatability can overcome past bouts of extreme selection in Drosophila experimental evolution, provided experiments are sufficiently long and populations are not inbred

Effects of evolutionary history on genome wide and phenotypic convergence in Drosophila populations.

BackgroundStudies combining experimental evolution and next-generation sequencing have found that adaptation in sexually reproducing populations is primarily fueled by standing genetic variation. Consequently, the response to selection is rapid and highly repeatable across replicate populations. Some studies suggest that the response to selection is highly repeatable at both the phenotypic and genomic levels, and that evolutionary history has little impact. Other studies suggest that even when the response to selection is repeatable phenotypically, evolutionary history can have significant impacts at the genomic level. Here we test two hypotheses that may explain this discrepancy. Hypothesis 1: Past intense selection reduces evolutionary repeatability at the genomic and phenotypic levels when conditions change. Hypothesis 2: Previous intense selection does not reduce evolutionary repeatability, but other evolutionary mechanisms may. We test these hypotheses using D. melanogaster populations that were subjected to 260 generations of intense selection for desiccation resistance and have since been under relaxed selection for the past 230 generations.ResultsWe find that, with the exception of longevity and to a lesser extent fecundity, 230 generations of relaxed selection has erased the extreme phenotypic differentiation previously found. We also find no signs of genetic fixation, and only limited evidence of genetic differentiation between previously desiccation resistance selected populations and their controls.ConclusionOur findings suggest that evolution in our system is highly repeatable even when populations have been previously subjected to bouts of extreme selection. We therefore conclude that evolutionary repeatability can overcome past bouts of extreme selection in Drosophila experimental evolution, provided experiments are sufficiently long and populations are not inbred