Name: experimental manipulation of body size to estimate morphological scaling relationships in drosophila
Uploaded: 2011-10-01T14:00:00
Duration: 6 min
Description: Watch this Scientific Journal Video about Experimental Manipulation of Body Size to Estimate Morphological Scaling Relationships in Drosophila at JoVE.com

The research described in this study was supported by a National Science Foundation grant (DEB-0805818) to W.A.F., A.W.S and I.D. This study was also supported by grants IOS-0845847 to A.W.S., IOS-0919855 to A.W.S. and I.D. and IOS-0920720 to W.A.F.

1. Rearing and manipulation of diet to produce variation in body size and wing size
Rational and Overview. The expression of scaling relationships ultimately hinges on the developmental regulatory processes that produce variation in final organ and body size. These processes are best described from work on fully metamorphic (i.e., holometabolous) insects such as D. melanogaster, where organs grow as undifferentiated 'imaginal discs' within the grub-like larva11,15-17. In Drosophila, final organ and body size are regulated by growth during the larval stages; larvae grow through the first and second larval instar until they reach a minimal viable weight for eclosion (MVWE) towards the beginning of the third larval instar18. Starvation before attainment of MVWE prevents adult eclosion. However, larvae that are starved at MVWE generate viable adults, albeit at a very small size. This is because reduced nutrition during development reduces final body and organ size, not just in flies but in almost all animals19-21. By manipulating food availability after MVWE is attained, but before pupation occurs, it is possible to induce extreme phenotypic plasticity in body size that greatly outweighs other sources of variation (e.g., individual genetic variation).
<ol>
	<li>Eggs are collected from the population to be phenotyped, divided into lots of 50 and placed in vials containing 10ml of standard fly food. Because oviposition occurs continuously, eggs are collected every 24h for three days, producing three age cohorts.</li>
	<li>When the oldest cohort reaches the wandering stage or has just begun to pupate, the diet manipulation is applied. At this point, the oldest cohort is well beyond the MVWE, the youngest cohort is very close to the MVWE and the remaining cohort is somewhere in between these extremes. Thus, removal of food at this point will produce very large adults from the oldest cohort, very small adults from the youngest cohort and intermediate-sized adults from the remaining cohort. To remove the larvae from the vials, approximately 5ml of 40% sucrose solution is added to all vials. To free the larvae, the food is agitated for 15-20 minutes on a shaker table set to an intermediate speed.</li>
	<li>Floating larvae are removed from the sucrose solution with a fine (00) paintbrush, placed into vials containing a wet cotton plug and allowed to pupate. Alternatively, larvae could be placed on a non-digestible food additive such as methyl cellulose22.</li>
</ol>
2. Estimation of body size
Rational and Overview. Previous studies indicate that thorax length is a less than ideal proxy for overall body size22. Instead, we use pupal size as a measure of body size. Maximum body size is fixed at the cessation of feeding that precedes pupation. As a result, there is a tight correlation between pupal size and adult body size23.
<ol>
	<li>Pupae are arranged ventral side up on glass microscope slides and imaged using a digital camera attached to a dissecting microscope. Each image is captured, assigned a unique identifying code and transferred onto a computer via a live feed connecting the digital camera to the computer.</li>
	<li>Imaged pupae are moved to individual 2 ml epitubes containing 1ml of fly food, labeled with the unique code for that individual, and punctured with airholes to allow gas exchange.</li>
	<li>Pupal size is estimated as the number of pixels of the pupal silhouette. Other size metrics could also be used.</li>
</ol>
3. Trait (wing) size estimation
Rational and Overview. To image wings, we use a 'wing grabber'24, which pulls and holds the wing of a live, anesthetized fly perpendicular to its body. Pressed between two pieces of glass, this allows the wing to be imaged as a two dimensional object.
<ol>
	<li>Flies are anesthetized lightly with CO2 and placed in position in the wing grabber on a dissecting microscope fitted with a digital camera that is connected to a computer.</li>
	<li>The wing is imaged and saved under the unique code for that individual.</li>
	<li>Wing size can be estimated using the minimum convex polygon that circumscribes marginal fixed landmarks or as the pixel count of the wing silhouette.</li>
</ol>
4. Scaling relationship estimation
<ol>
	<li>Data are pooled across cohorts but separated by sex and log-transformed.</li>
	<li>Scaling relationships are fit to the size data using Type II (i.e., Reduced Major Axis) regression (see review in 12) and the parameters estimated for each group.</li>
</ol>
5. Representative Results:
Our diet manipulation will produce a broad range of body sizes (Figure 1) and trait sizes (Figure 2). Plotting the log transformed traits against each other reveals their pattern of covariation within a given biological group and permits fitting the scaling relationship to the group (Figure 3). Extraction of the scaling relationship parameters that describe how shape scales with body size allows comparison of how shape covaries with size across groups.
<img alt="Figure 1" src="/files/ftp_upload/3162/3162fig1.jpg" /> 
Figure 1. Pupa from extremes of the size distribution produced via diet manipulation after individuals achieve the MVWE. Actual pupal images are shown at left with their corresponding silhouettes for the measurement of pupal size at right. Scale bar is 1mm.
<img alt="Figure 2" src="/files/ftp_upload/3162/3162fig2.jpg" /> 
Figure 2. Wings taken from extremes of the body size distribution produced via diet manipulation after individuals achieve the MVWE. Actual wing images are shown on the left with their corresponding silhouettes for the measurement of wing size shown on the right. Scale bar is 1mm.
<img alt="Figure 3" src="/files/ftp_upload/3162/3162fig3.jpg" /> 
Figure 3. Wing-body size scaling for Drosophila melanogaster by sex. Log-transformed data for individuals of each sex that were fully-fed (dark circles), starved one (grey circles) or two days (open circles) as larvae. Type II regression line is shown for each sex. Between each age cohort, declines in average wing area of ~0.1mm (~7%) and ~0.2mm (~8%) occurs, increasing the total range of phenotypes observed. The regressions reveal that females are slightly hypoallometric for this scaling relationship (slope of 0.96) whereas males are slightly hyperallometric (slope 1.06).

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No conflicts of interest declared.

Morphological scaling has been the subject of intense study in evolutionary biology for nearly a century. More recently, the proximate basis of the regulation of growth and scaling has become increasingly important in development, physiology and genetics (e.g., see reviews in 12,15,23-25). Our methodology permits estimation of morphological scaling relationships across the entire range of trait and body sizes. This can be important, as trait size may not scale linearly with body size (e.g., 13,14). However, this may not be apparent if animals are reared only under ideal lab conditions.
Although our protocol was developed explicitly to allow estimation of the wing-body size scaling relationship in Drosophila, it can be used with trait-specific modification to estimate the scaling relationship for any morphological trait in flies. Similarly, the diet manipulation can likely be used to produce the full range of trait and body sizes in other fully metamorphic insects; such applications simply require knowing when the MVWE is achieved and applying the manipulation at that point in ontogeny.

experimental manipulation of body size to estimate morphological scaling relationships in drosophila

The scaling of body parts is a central feature of animal morphology1-7. Within species, morphological traits need to be correctly proportioned to the body for the organism to function; larger individuals typically have larger body parts and smaller individuals generally have smaller body parts, such that overall body shape is maintained across a range of adult body sizes. The requirement for correct proportions means that individuals within species usually exhibit low variation in relative trait size. In contrast, relative trait size can vary dramatically among species and is a primary mechanism by which morphological diversity is produced. Over a century of comparative work has established these intra- and interspecific patterns3,4.
Perhaps the most widely used approach to describe this variation is to calculate the scaling relationship between the size of two morphological traits using the allometric equation y=bx&alpha;, where x and y are the size of the two traits, such as organ and body size8,9. This equation describes the within-group (e.g., species, population) scaling relationship between two traits as both vary in size. Log-transformation of this equation produces a simple linear equation, log(y) = log(b) + &alpha;log(x) and log-log plots of the size of different traits among individuals of the same species typically reveal linear scaling with an intercept of log(b) and a slope of &alpha;, called the 'allometric coefficient'9,10. Morphological variation among groups is described by differences in scaling relationship intercepts or slopes for a given trait pair. Consequently, variation in the parameters of the allometric equation (b and &alpha;) elegantly describes the shape variation captured in the relationship between organ and body size within and among biological groups (see 11,12).
Not all traits scale linearly with each other or with body size (e.g., 13,14) Hence, morphological scaling relationships are most informative when the data are taken from the full range of trait sizes. Here we describe how simple experimental manipulation of diet can be used to produce the full range of body size in insects. This permits an estimation of the full scaling relationship for any given pair of traits, allowing a complete description of how shape covaries with size and a robust comparison of scaling relationship parameters among biological groups. Although we focus on Drosophila, our methodology should be applicable to nearly any fully metamorphic insect.

Watch this Scientific Journal Video about Experimental Manipulation of Body Size to Estimate Morphological Scaling Relationships in Drosophila at JoVE.com

Experimental Manipulation of Body Size to Estimate Morphological Scaling Relationships in Drosophila

Morphological scaling relationships capture and describe organismal shape. We present a method to measure morphological scaling relationships across the natural range of body sizes in fully metamorphic insects. Using a simple diet manipulation we increase the distribution of trait sizes, permitting the accurate description of how shape and size co-vary.

Experimental Manipulation of Body Size to Estimate Morphological Scaling Relationships in Drosophila

The scaling of body parts is a central feature of animal morphology1-7. Within species, morphological traits need to be correctly proportioned to the body ...

experimental-manipulation-body-size-to-estimate-morphological-scaling

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Emergent properties and external factors (population-level and ecosystem-level interactions, in particular) play important roles in mediating ...

Establishment and Genetic Manipulation of Murine Hepatocyte Organoids

The liver is the largest organ in mammals. It plays an important role in glucose storage, protein secretion, metabolism and detoxification. As the executor for most of the liver functions, primary hepatocytes have limited proliferating capacity. This requires the establishment of ex vivo hepatocyte expansion models for liver physiological and pathological research. Here, we isolated murine hepatocytes by two steps of collagenase perfusion and established a 3D organoid culture as the 'mini-liver' to recapitulate cell-cell interactions and physical functions. The organoids consist of heterogeneous cell populations including progenitors and mature hepatocytes. We introduce the process in detailed to isolate and culture the murine hepatocytes or fetal hepatocyte to form organoids within 2-3 weeks and show how to passage them by mechanically pipetting up and down. In addition, we will also introduce how to digest the organoids into single cells for lentivirus infection of shRNA/ectopic construction, siRNA transfection and CRISPR-Cas9 engineering. The organoids can be used for drug screens, disease modelling, and basic liver research by modeling liver biology and pathobiology.

A long-term ex vitro 3D organoid culture system was established from mouse hepatocytes. These organoids can be passaged and genetically manipulated by lentivirus infection of shRNA/ectopic construction, siRNA transfection and CRISPR-Cas9 engineering.

The liver is the largest organ in mammals. It plays an important role in glucose storage, protein secretion, metabolism and detoxification. As the ...

Dissecting, Fixing, and Visualizing the Drosophila Pupal Notum

The pupae of Drosophila melanogaster are immobile for several days during metamorphosis, during which they develop a new body with a thin transparent adult integument. Their immobility and transparency make them ideal for in vivo live imaging experiments. Many studies have focused on the dorsal epithelial monolayer of the pupal&#160;notum because of its accessibility and relatively large size. In addition to the studies of epithelial mechanics and development, the notum has been an ideal tissue to study wound healing. After an injury, the entire epithelial repair process can be captured by live imaging over 6-12 h. Despite the popularity of the notum for live imaging, very few published studies have utilized fixed notum samples. Fixation and staining are common approaches for nearly all other Drosophila tissues, taking advantage of the large repertoire of simple cellular stains and antibodies. However, the pupal notum is fragile and prone to curling and distortion after removal from the body, making it challenging to complement live imaging. This protocol offers a straightforward method for fixing and staining the pupal notum, both intact and after laser-wounding. With this technique, the ventral side of the pupa is glued down to a coverslip to immobilize the pupa, and the notum is carefully removed, fixed, and stained. The notum epithelium is mounted on a slide or between two coverslips to facilitate imaging from the tissue&#39;s dorsal or ventral side.

Dissecting, Fixing, and Visualizing the Drosophila Pupal Notum

The present protocol details the preparation and visualization of fixed tissue of the Drosophila pupal notum. It can be used for either intact or wounded tissue, and the original architecture of the tissue is preserved. The procedures for dissecting, fixing, and staining are all described in this article.

The pupae of Drosophila melanogaster are immobile for several days during metamorphosis, during which they develop a new body with a thin transparent ...

Analyzing Starvation-Induced Autophagy in the Drosophila melanogaster Larval Fat Body

Autophagy is a cellular self-digestion process. It delivers cargo to the lysosomes for degradation in response to various stresses, including starvation. The malfunction of autophagy is associated with aging and multiple human diseases. The autophagy machinery is highly conserved-from yeast to humans.&#160;The larval fat body of Drosophila melanogaster, an analog for vertebrate liver and adipose tissue, provides a unique model for monitoring autophagy in vivo. Autophagy can be easily induced by nutrient starvation in the larval fat body. Most autophagy-related genes are conserved in Drosophila. Many transgenic fly strains expressing tagged autophagy markers have been developed, which facilitates the monitoring of different steps in the autophagy process. The clonal analysis enables a close comparison of autophagy markers in cells with different genotypes in the same piece of tissue. The current protocol details procedures for (1) generating somatic clones in the larval fat body, (2) inducing autophagy via amino acid starvation, and (3) dissecting the larval fat body, aiming to create a model for analyzing differences in autophagy using an autophagosome marker (GFP-Atg8a) and clonal analysis.

Analyzing Starvation-Induced Autophagy in the Drosophila melanogaster Larval Fat Body

The present protocol describes the induction of autophagy in the Drosophila melanogaster larval fat body via nutrient depletion and analyzes changes in autophagy using transgenic fly strains.

Autophagy is a cellular self-digestion process. It delivers cargo to the lysosomes for degradation in response to various stresses, including starvation. ...