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Method Article
In this paper, we provide a detailed protocol for exposing species in the genus Drosophila to pollutants with the goal of studying the impact of exposure on a range of phenotypic outputs at different developmental stages and for more than one generation.
Emergent properties and external factors (population-level and ecosystem-level interactions, in particular) play important roles in mediating ecologically-important endpoints, though they are rarely considered in toxicological studies. D. melanogaster is emerging as a toxicology model for the behavioral, neurological, and genetic impacts of toxicants, to name a few. More importantly, species in the genus Drosophila can be utilized as a model system for an integrative framework approach to incorporate emergent properties and answer ecologically-relevant questions in toxicology research. The aim of this paper is to provide a protocol for exposing species in the genus Drosophila to pollutants to be used as a model system for a range of phenotypic outputs and ecologically-relevant questions. More specifically, this protocol can be used to 1) link multiple biological levels of organization and understand the impact of toxicants on both individual- and population-level fitness; 2) test the impact of toxicants at different stages of developmental exposure; 3) test multigenerational and evolutionary implications of pollutants; and 4) test multiple contaminants and stressors simultaneously.
Every year, approximately 1,000 new chemicals are introduced by the chemical industry1,2; however, the environmental impacts of only a small percentage of these chemicals are tested before distribution2,3. Although large-scale catastrophes are uncommon, sublethal and chronic exposure to a large variety of pollutants are widespread in both humans and wildlife4,5. The historical focus of ecotoxicology and environmental toxicology was to test lethality, single chemical exposure, acute exposure, and the physiological effects of exposure, as a means of measuring the impact of pollutants on survival6,7,8,9,10. Although there is a shift towards ethical and non-invasive approaches to animal testing, current approaches are limiting because of the role that development, emergent properties, and external factors (such as population-level and ecosystem-level interactions) play in mediating ecologically-important endpoints8. Therefore, there is a need for methods that incorporate a more holistic approach without sacrificing wildlife and/or vertebrates in the laboratory.
Invertebrate model systems, such as Drosophila melanogaster, are an attractive alternative to address the need for a more holistic approach to toxicity testing. D. melanogaster, was originally developed as an invertebrate model system for human-related genetic research about a century ago11.D. melanogaster is now prominently used as a vertebrate model alternative for several reasons: 1) the conservation of genes and pathways between D. melanogaster and humans; 2) short generation time compared to vertebrate models; 3) inexpensive cost of maintenance; 4) ease in generating large sample sizes; and 5) plethora of phenotypic- and ecologically-relevant endpoints available for testing11,12,13,14,15,16,17.
Several laboratories11,15,16,17,18,19,20,21,22,23,24,25 are now using D. melanogaster as a vertebrate model alternative for toxicity testing to understand the impacts of pollution on humans. Local wild species of Drosophila can be utilized, as well, as toxicity models for wildlife (and humans) to answer ecologically-, behaviorally-, and evolutionarily-relevant questions at multiple biological levels of organization. Using species within the Drosophila genus as a model, several measurable endpoints are possible11,15,16,18,19,20,21,22,23,24,25. In addition, using the Drosophila model, toxicologists can: 1) ethically link effects at multiple biological levels of the organization; 2) incorporate the role of emergent factors and development; 3) study ecologically-important endpoints (in addition to medically-important endpoints); 4) test multiple stressors simultaneously; 5) and test long-term multigenerational (e.g. evolutionary and transgenerational) implications of stressors. Therefore, using Drosophila as a model system enables a multitude of approaches, not limited to studying mechanistic approaches with inbred strains of D. melanogaster in the laboratory.
In this paper, we present the methods for rearing and collecting Drosophila to answer various toxicological questions. More specifically, we describe the methodology for 1) rearing Drosophila in medium laced with one or more pollutants; 2) collecting Drosophila throughout development (e.g. wandering third-instar larvae, pupal cases, newly-eclosed adults, and mature adults); and 3) rearing Drosophila in the contaminated medium to test intergenerational and transgenerational transmission, as well as evolutionary implications of long-term toxicant exposure. Using this protocol, previous authors18,19,20,21,22,23,24,25 have reported different physiological, genetic, and behavioral effects of developmental lead (Pb2+) exposure. This protocol enables toxicologists to use a more holistic toxicological approach, which is essential to understanding how pollutants are risk factors for both humans and wildlife in an ever increasingly polluted environment.
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The following protocol is an experimental protocol used to rear species in the Drosophila genus on contaminated medium when oral ingestion of a toxin is appropriate; other forms of exposure are possible using the Drosophila model11,15,16,26. The methods described in this protocol have been previously described by Hirsch et al.19 and Peterson et al.23,24,25.
1. Set Up Stock Populations of Drosophila in the Research Laboratory
Figure 1: Pictorial representation of traps and bait used to collect wild populations of Drosophila in the field. (A) Fly traps set at a local field site in Colorado. (B) A closer view of the fly traps set at this field site. Please click here to view a larger version of this figure.
2. Rear Drosophila in the Contaminated Medium
NOTE: If testing Drosophila in the laboratory for the first time or with a new contaminant(s), identify the lethal dose (see Castaneda et al.37 and Massie et al.38 for methods) and the LD50 (see Castaneda et al.37 and Akins et al.39 for methods) first. Then, run a dose-response curve to identify biologically-relevant concentrations for the desired phenotypic output; see Hirsch et al.19 and Zhou et al.40 for methods.
3. Collect Experimental Subjects at Various Developmental Stages
NOTE: Experimental subjects can be collected at any developmental stage, placed in the blind coded 15-mL conical tubes, and tested for accumulation. Methods for testing the accumulation of contaminants will depend on the contaminant being studied. For example, accumulation of PbAc can be tested using Inductively-Coupled Plasma Mass Spectrometry (ICP-MS)42. In addition, experimental subjects can be collected at any developmental stage to be tested for a variety of phenotypic effects of contaminants. Figure 2 illustrates the Drosophila life cycle43. Figure 3 illustrates the experimental protocol for exposure and the different developmental stages for collection.
Figure 2: Conceptual overview of the life cycle of D. melanogaster (the most commonly used Drosophila model system). The stages of Drosophila life cycle are: 1) egg, 2) first-instar larva, 3) second-instar larva, 4) third-instar larva, 5) wandering third-instar larva, 6) white-eye pupa, 7) red-eye pupa, 8) newly-eclosed adult, and 9) mature adult. Please click here to view a larger version of this figure.
Figure 3: Conceptual overview of the methods for orally exposing Drosophila to contaminated medium in both the parental (F0) and subsequent generations (F1 and onward). (A) Methods for oral exposure during development in the exposed generation. (B) Methods to test the transfer of contaminants to offspring (F1 to the desired generation). This figure has been modified from Peterson et al.24 Please click here to view a larger version of this figure.
4. Rear Experimental Subjects to Test the Effects of Multigenerational or Transgenerational Exposure.
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By orally exposing Drosophila to a contaminant(s) throughout development, various toxicological questions can be tested by exposing Drosophila at different levels of biological organization. This section presents representative results obtained using this protocol in previously published papers23,24. In particular, this protocol was previously used to evaluate the accumulation, elimination and sequestration of le...
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Drosophila melanogaster has been established as a powerful model for a range of biological processes due to the extensive conservation of genes and pathways between D. melanogaster and humans13,14. For the same reasons that it's a powerful model for medical science, Drosophila has emerged as a suitable model system to study the impact of anthropogenic pollution on a range of toxicological endpoints. Several laboratories are successf...
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The authors have nothing to disclose.
This publication was supported by a grant from the Department of Education (PR Award #P031C160025-17, Project title: 84.031C) to the Colorado State University-Pueblo (CSU-Pueblo) Communities to Build Active STEM Engagement (C-BASE). We thank Current Zoology and Elsevier for providing the rights to use the representative results published in previous papers, as well as the editors of JoVE for providing us with the opportunity to publish this protocol. We would also like to thank the C-BASE Program, Dr. Brian Vanden Heuvel (C-BASE and Department of Biology, CSU-Pueblo), CSU-Pueblo Biology department, Thomas Graziano, Dr. Bernard Possidente (Department of Biology, Skidmore College), and Dr. Claire Varian Ramos (Department of Biology, Colorado State University-Pueblo) for their support and assistance.
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Name | Company | Catalog Number | Comments |
Carolina Biological Instant Drosophila Medium Formula 4-24 | Carolina Biological | 173204 | |
Drosophila vials, Narrow (PS), Polystyrene, Superbulk, 1000 vials/unit | Genessee Scientific | 32-116SB | Used to store flies |
Flugs Closures for vials and bottles, Narrow plastic vials | Genessee Scientific | 49-102 | Used to store flies |
Cardboard trays, trays only, narrow | Genessee Scientific | 32-124 | Used to organize populations of flies |
Cardboard trays, dividers only, narrow | Genessee Scientific | 32-126 | Used to organize populations of flies |
Thermo Scientific Nalgene Square Wide-Mouth HDPE Bottles with Closure | Fischer Scientific | 03-312D | Useful for storage of contaminants |
Thermo Scientific Nalgene Color-Coded LDPE Wash Bottles | Fischer Scientific | 03-409-17C | Useful for storage of contaminants |
Eppendorf Repeater M4 Manual Handheld Pipette Dispenser | Fischer Scientific | 14-287-150 | Used to prepare medium |
Combitips Advanced Pipetter Tips - Standard, Eppendorf Quality Tips | Fischer Scientific | 13-683-708 | Used to prepare medium |
Flypad, Standard Size (8.1 X 11.6cm) | Genessee Scientific | 59-114 | Used to anesthetize flies |
Flystuff foot valve | Genessee Scientific | 59-121 | Used to anesthetize flies |
Tubing, green (1 continguous foot/unit) | Genessee Scientific | 59-124G | Used to anesthetize flies |
Mineral Oil, Light, White, High Purity Grade, 500 mL HDPE Bottle | VWR | 97064-130 | Used to make a morgue |
Glass Erlenmeyer Flask Set - 3 Sizes - 50, 150 and 250ml, Karter Scientific 214U2 | Walmart | Not applicable | Used to make a morgue |
BGSET5 Glass Beaker Set Of 5 | Walmart | ||
Inbred or wildtype line of Drosophila | Bloomington Drosophila Stock Center at Indiana University | https://bdsc.indiana.edu | |
Wild popultions of Drosophila | UC San Diego Drosophila Stock Center | https://stockcenter.ucsd.edu/info/welcome.php |
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