Metabolism Underlies Physiological Homeostasis in \u3ci\u3eDrosophila\u3c/i\u3e

Organismal physiology emerges from metabolic pathways and subcellular structures like the mitochondria that can vary across development and among individuals. Here, we tested whether genetic variation at one level of physiology can be buffered at higher levels of biological organization during development by the inherent capacity for homeostasis in physiological systems. We found that the fundamental scaling relationship between mass and metabolic rate, as well as the oxidative capacity per mitochondria, changed significantly across development in the fruit fly Drosophila. However, mitochondrial respiration rate was maintained at similar levels across development. Furthermore, larvae clustered into two types—those that switched to aerobic, mitochondrial ATP production before the second instar, and those that relied on anaerobic, glycolytic production of ATP through the second instar. Despite genetic variation for the timing of this metabolic shift, metabolic rate in second-instar larvae was more robust to genetic variation than was the metabolic rate of other instars. We found that larvae with a mitochondrial-nuclear incompatibility that disrupts mitochondrial function had increased aerobic capacity and relied more on anaerobic ATP production throughout development relative to larvae from wild-type strains. By taking advantage of both ways of making ATP, larvae with this mitochondrial–nuclear incompatibility maintained mitochondrial respiratory capacity, but also had higher levels of whole-body reactive oxygen species and decreased mitochondrial membrane potential, potentially as a physiological defense mechanism. Thus, genetic defects in core physiology can be buffered at the organismal level via physiological plasticity, and natural populations may harbor genetic variation for distinct metabolic strategies in development that generate similar organismal outcomes. Suppl data attached below (170MB

Energy demand and the context-dependent effects of genetic interactions underlying metabolism

Genetic effects are often context dependent, with the same genotype differentially affecting phenotypes across environments, life stages, and sexes.We used an environmental manipulation designed to increase energy demand during development to investigate energy demand as a general physiological explanation for context-dependent effects of mutations, particularly for those mutations that affect metabolism. We found that increasing the photoperiod during which Drosophila larvae are active during development phenocopies a temperature-dependent developmental delay in a mitochondrial-nuclear genotype with disrupted metabolism. This result indicates that the context-dependent fitness effects of this genotype are not specific to the effects of temperature and may generally result from variation in energy demand. The effects of this genotype also differ across life stages and between the sexes. The mitochondrial-nuclear genetic interaction disrupts metabolic rate in growing larvae, but not in adults, and compromises female, but not male, reproductive fitness. These patterns are consistent with a model where context-dependent genotype-phenotype relationships may generally arise from differences in energy demand experienced by individuals across environments, life stages, and sexes

Energetic Causes and Consequences of Reproductive Diapause and Migration in Monarch Butterflies (Danaus plexippus L.)

Monarch butterflies (Danaus plexippus L.) undergo an iconic annual, long-distance migration taking them up to 4,000 km from their summer breeding grounds in southern parts of Canada and northern parts of the United States to their overwintering grounds in the mountains of central Mexico. My research leverages the unique life history and physiology of the monarch butterfly to better understand the physiology, development, and energetics of reproductive diapause, which is necessary for monarch butterfly migration and overwintering. While monarchs in North American (NA) are famous for their migration, they have recently dispersed to many locations around the globe where they no longer migrate across most of its range, i.e. Costa Rica (CR). My research leverages this demographic history to better understand what plastic strategies are important for N. American migration. We quantified plasticity across generations in NA monarchs for wing morphology and metabolic traits that are related to long-distance migration and asked whether CR monarch butterflies have lost or decreased plasticity in these traits. We found that the non-migratory CR descendants of the migratory NA population retain some, but not all ancestral seasonal trait plasticity. We reared monarchs under a decreasing photoperiod to induce and understand the developmental and energetic consequences of reproductive diapause. Monarchs reared under a short-day photoperiod enter reproductive diapause and were seasonally plastic in larval metabolism, development time, and adult head mass. Finally, I tested for differences in flight muscle structure and mitochondrial density in these same monarchs to understand whether the structures of the flight muscle and its mitochondria are plastic in response to photoperiod. We find that monarchs reared under short-day do not change their flight muscle structures or number of mitochondria. In summary, seasonal plasticity is lost in a piecemeal fashion in the absence of environmental heterogeneity in monarchs. Additionally, monarchs may rely on changes in the amount of overall flight muscle rather than in mitochondrial physiology to support more efficient long-distance flight

Metabolism Underlies Physiological Homeostasis in \u3ci\u3eDrosophila\u3c/i\u3e

Organismal physiology emerges from metabolic pathways and subcellular structures like the mitochondria that can vary across development and among individuals. Here, we tested whether genetic variation at one level of physiology can be buffered at higher levels of biological organization during development by the inherent capacity for homeostasis in physiological systems. We found that the fundamental scaling relationship between mass and metabolic rate, as well as the oxidative capacity per mitochondria, changed significantly across development in the fruit fly Drosophila. However, mitochondrial respiration rate was maintained at similar levels across development. Furthermore, larvae clustered into two types—those that switched to aerobic, mitochondrial ATP production before the second instar, and those that relied on anaerobic, glycolytic production of ATP through the second instar. Despite genetic variation for the timing of this metabolic shift, metabolic rate in second-instar larvae was more robust to genetic variation than was the metabolic rate of other instars. We found that larvae with a mitochondrial-nuclear incompatibility that disrupts mitochondrial function had increased aerobic capacity and relied more on anaerobic ATP production throughout development relative to larvae from wild-type strains. By taking advantage of both ways of making ATP, larvae with this mitochondrial–nuclear incompatibility maintained mitochondrial respiratory capacity, but also had higher levels of whole-body reactive oxygen species and decreased mitochondrial membrane potential, potentially as a physiological defense mechanism. Thus, genetic defects in core physiology can be buffered at the organismal level via physiological plasticity, and natural populations may harbor genetic variation for distinct metabolic strategies in development that generate similar organismal outcomes. Suppl data attached below (170MB

development time data

File 1: devtime.xlsx 5 data sheets Eclose16_LD.txt Eclose16_LL.txt Eclose22_LL.txt Eclose22_LD.txt Eclose25_LD.txt Rows: each row represents a single adult that eclosed on a given date with a particular development time in days (“EcloseDay”) Columns: Date — date vial was scored for progeny; Mito — mtDNA genotype; Nuc — nuclear genotype; Temp — rearing temperature; Light — photoperiod; 12,12 (LD) or 24,0 (LL); Vial — unique identifier for each vial; EcloseDay — days until eclosion

Data from: Maternal loading of a small heat shock protein increases embryo thermal tolerance in Drosophila melanogaster

Maternal investment is likely to have direct effects on offspring survival. In oviparous animals whose embryos are exposed to the external environment, maternal provisioning of molecular factors like mRNAs and proteins may help embryos cope with sudden changes in the environment. Here we sought to modify the maternal mRNA contribution to offspring embryos and test for maternal effects on acute thermal tolerance in early embryos of Drosophila melanogaster. We drove in vivo overexpression of a small heat shock protein gene (Hsp23) in female ovaries and measured the effects of acute thermal stress on offspring embryonic survival and larval development. We report that overexpression of the Hsp23 gene in female ovaries produced offspring embryos with increased thermal tolerance. We also found that brief heat stress in the early embryonic stage (0 to 1 hour-old) caused decreased larval performance later in life (5 to 10 days-old), as indexed by pupation height. Maternal overexpression of Hsp23 protected embryos against this heat-induced defect in larval performance. Our data demonstrate that transient products of single genes have large and lasting effects on whole-organism environmental tolerance. Further, our results suggest that maternal effects have a profound impact on offspring survival in the context of thermal variability

Thermal phenotypic data and qPCR data

Data are organized into separate sheets in the .xlsx file. Use the tabs to access each subset of the data

metabolic rate data

File 2: metrate.xlsx 4 data sheets MRdat_Group1616.txt MRdat_Group2525.txt MRdat_Group1625.txt MRdat_Group2516.txt Rows: each row represents a measure of average VCO2 from a chamber containing 10 adult flies Columns date — date of measurement; run — unique run of the respirometry system; rep — each chamber was sampled twice during the run; line — (mtDNA);nuclear genotype; mtDNA — mtDNA genotype; nuclear — nuclear genotype; tdev - development rearing temperature in C; tmeasure - temperature in C at which metabolic rate was measured; sex; CO2 — average rate of CO2 production; CO2.se — standard error of this average; mass — mass of 10 flies in chamber; MassMeasured — the initial mass of 10 flies corrected for any flies lost during the experiment (total mass - mean mass * number of flies lost); Act1 — the median absolute difference of the squared activity signal; Act2 — the standard error of the squared activity signa

reproduction data

File 3: reproduction.xlsx datasheet: mitofert.txt Rows: each row represents a single male’s number of offspring sired across three females Columns mtDNA — mtDNA genotype; nuclear — nuclear genotype; genotype — mtDNA;nuclear genotype; male — replicate male ID; females — number of females who survived and produced offspring; total — the sum of offspring for each male across the three females; totalper — total divided by the number of females; exp — block A or B datasheet: mitofecund.txt Rows: each row represents the number of eggs laid by each female (original data are reported in Meiklejohn et al. (2013) PLoS Genet 9:e1003238) Columns mtDNA — mtDNA genotype; nuclear — nuclear genotype; genotype — mtDNA.nuclear genotype; female — female ID number; day1-day10 — egg counts each day; total — summed egg counts across all day

Data from: Energy demand and the context-dependent effects of genetic interactions underlying metabolism

Genetic effects are often context-dependent, with the same genotype differentially affecting phenotypes across environments, life stages, and sexes. We used an environmental manipulation designed to increase energy demand during development to investigate energy demand as a general physiological explanation for context-dependent effects of mutations, particularly for those mutations that affect metabolism. We found that increasing the period during which Drosophila larvae are active during development phenocopies a temperature-dependent developmental delay in a mitochondrial-nuclear genotype with disrupted metabolism. This result indicates that the context-dependent fitness effects of this genotype are not specific to the effects of temperature and may result generally from variation in energy demand. The effects of this genotype also differ across life stages and between the sexes. Metabolic rates are disrupted by this genetic interaction in growing larvae, but not in adults; and reproduction of females, but not males, is compromised by this genetic interaction. These patterns are consistent with a model where context-dependent genotype-phenotype relationships may generally arise from differences in energy demand experienced by individuals across environments, life stages, and sexes