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2017 Issue 3: Science on a small scale

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Consider the fruit fly

Consider the fruit fly

A light micrograph of a fruit fly
Pic credit: Steve Gschmeissner/Science Photo Library

A light micrograph of a fruit fly. Drosophila melangoster (the fruit fly) is a model organism for study in many fields.

 

Of what possible use is a fruit fly? Besides, of course, letting you know that those bananas in your kitchen have gone off. The fruit fly, or Drosophila (“Dew-lover” in Greek), is attracted to the yeasts in rotting fruit and in wine. For many, it is seen as a harmless annoyance. But for more than a century, the fruit fly has been a central player in the study of genetics. With its large chromosomes, rapid life cycle, and ready supply, Drosophila melanogaster has made a perfect model organism for study by scientists. Drosophila was first studied for genetic purposes in the 1880s by entomologist Charles W. Woodworth. In the early 1900s, Thomas Hunt Morgan, a biologist and geneticist, demonstrated, through his work with fruit flies, that genes are carried on chromosomes and are the mechanical basis of heredity. By 2000, the Drosophila genome had been fully sequenced.

“The fruit fly nervous system is very sophisticated,” says neurobiologist Mel Robertson, “and its brain is accessible to study by some very detailed techniques. You can do things with flies that you can’t do with a more complex nervous system. With the fly, because of its very fast reproduction and accessible genome, it is easier to do genetic manipulations. The genetic techniques for targeting specific tissues, and even specific neurons in the brain, and manipulating them, it’s amazing. If you say, ‘I’d like to do such-and-such elaborate experiment,’ probably you can do it on a fly.”

[photo of Dr. Adam Chippindale and his students]
From left to right: M.K. Hickox, Mansuba Rana, Josh Alpern, Adam Chippindale, Anastasia Shavrova. Photo: Bernard Clark

Adam Chippindale and his students study evolution in real time. “We do experimental evolution,” says Dr. Chippindale. “We have an artificial phylogeny – a tree of life – that we’ve created from common ancestry, with some that have been selected to reproduce at late ages, some at young ages, and some at extremely early ages. We have pushed them right to the speed limit of development.” Dr. Chippindale developed his line of early-developing fruit flies as a grad student at UC Irvine, studying with Michael Rose (Artsci’75, MSc’76, PhD, Sussex), a noted evolutionary biologist. Dr. Chippindale’s strain of fast developers has now gone through more than 1150 generations of evolution.

M.K. Hickox, BSc student. Ms. Hickox is working in the Chippindale lab this summer through the NSERC undergraduate student research award program. “We know that speciation is a widely occurring phenomenon. We’re hoping through our experiment that we’ll get a better understanding of when exactly it occurs. We’re studying it through reproduction and selection.” [Speciation is the evolution of two or more distinct species from one lineage.]

Mansuba Rana, Bsc student. Ms. Rana is working in the lab this summer through the Queen’s Summer Work Experience Program. “I’m working on a new method of sperm count of the fast and slow-developing fruit flies, studying flies that have GFP in their semen.” [GFP – that’s Green Fluorescent Protein – is used by scientists to study, among other things, reproduction in living model organisms.]

Josh Alpern, PhD student. Mr. Alpern is looking at fine-scale aspects of gene expression through growth, i.e., what genes are being turned on at which stages during larval growth. “I’m interested in evolution as a repeatable process. I’m looking for patterns, using the system that we have, to see if they have evolved the same way. if they have evolved in the same way, then the process is repeatable. if the process is repeatable, it can potentially be predictable.”

Adam Chippindale, Professor of Evolutionary Genetics. “Nature rarely offers us the opportunity of statistical replication. in the lab,we can take one population and make it evolve to be reproductive at late ages, take another and make it competent to reproduce at early ages. We can take five or six of each type, and so we can have different origins from different populations in nature. Then we can ask, ‘How repeatable is the evolutionary process?’ Because we can independently employ the same conditions in different lines and ask, ‘Do they change in a parallel fashion? Do they converge together in the same kind of organism in the end?’”

Anastasia Shavrova, MSc student. “I’m putting our two fruit fly lines, the very fast and the slower developers, under extreme environments. As we would predict, the ones that develop faster will get out of that environment a lot faster. I’m also looking at what that causes at the adult stages: can they find a mate successfully? Can they lay as many eggs successfully after being in an
extreme, crowded environment?”

The power of the model organism

“In an ecologically simplified setting, we can strip away the complexity of seasonal change, of migration, and environments,” says Dr. Chippindale, ”… all of the fluctuating factors that cause populations, as we know now, to evolve incredibly rapidly, but back and forth all the time. If this year is dry, then drought-tolerant individuals will survive and get selection moving in that direction, but then if we have a couple of years when it is wet, those individuals may be at a selective disadvantage, and selection goes the other way. We know that organisms evolve all the time but they don’t always evolve in the same direction for a long time. But we can, in a lab, take away a lot of that complexity and observe selection in the same direction for a long time.”

Geneticist Virginia Walker explores stress genes and the molecular basis for resistance. She has used fruit flies to study everything from human birth defects to gut health. A few years ago, Dr. Walker learned, from a student, about a brand of washing machine that incorporated silver nanoparticles into its wash cycle. The nanoparticles dropped into the laundry water killed the bacteria in the dirty clothes, keeping clothes cleaner for longer.

Nanoparticles and gut health

[photo of Dr. Virginia Walker]
Virginia Walker in her office. On the wall behind Dr. Walker, besides her many teaching awards, is an insect-themed print created for her by Melissa Mazar, BFA’95. Photo: Bernard Clark

Dr. Walker wondered, “What happens to the laundry water when it was dumped out into the environment? What does it do to all the soil microorganisms? And what does it do to invertebrates?”

Dr. Walker and her colleagues studied the effect of the particles both on soil and on fruit flies. They found that in the soil, silver nanoparticles killed off specific beneficial bacteria. And it had a dramatic effect on the development of fruit flies, killing many off before adulthood. “The few surviving adults themselves were very pale, without their usual stripes. They didn’t have as much energy. They were reminiscent of the fruit flies I had grown axenically, without bacteria. So I thought, maybe the impact of the nanoparticles was on the fruit fly microbiome – their gut bacteria. I dissected the guts of fruit flies and extracted and sequenced their DNA. I saw that the distribution of the microbes in their guts had completely changed. It had gone from a very diverse community to one that was not so diverse.”

Dr. Walker, with (then undergraduate student) Eric Saulnier, Artsci’15, and post-doctoral fellow Pranab Das, followed up these observations by looking at the effect of silver nanoparticles on the human gut, with University of Guelph professor Emma Allen-Vercoe. They found that the addition of minute amounts of antibiotics to silver nanoparticles killed off susceptible bacteria. While this needs further study, Dr. Walker says, “This may be a way of reducing antibiotic resistance. What I think is happening is that the silver nanoparticles may essentially be disrupting the membrane of the microbes and allowing sub-clinical doses of the antibiotic to go in and kill them.”

Fruit flies and the nervous system

In his lab, Dr. Robertson and his graduate students study how nervous systems cope with environmental stress. “We’re interested in the response of the nervous system to various stressors,” he says. “High temperatures, low temperatures, low oxygen. For insects, these are environmental stressors that they have to cope with, but we can use these as models for human pathology. For high temperature, think ‘fever,’ for low oxygen and low glucose, think ‘stroke.’ At the level of single neurons and the molecular properties of neurons, there is a great deal of similarity between insect neurons and human neurons. They work pretty much the same way.”

[photo of Mel Robertson and his PhD students]
Parn Srithiphaphirom, Shuang Qiu, and Mel Robertson examine a vial of fruit flies. Photo: Bernard Clark

Dr. Robertson’s lab has been the site for a number of research projects on both locusts and fruit flies that have promising leads for treatment in humans for stroke, epilepsy, and migraines. Gary Armstrong, who completed his PhD in 2009, received a Governor General’s Academic Gold Medal for his PhD thesis on cellular signalling pathways of the locust. His research examined the consequences of oxygen deprivation and similar phenomena related to the events that occur in the brain after stoke. (Now a professor at the Montreal Neurological Institute at McGill University, Dr. Armstrong continues his study of brain diseases, focusing now on ALS.)

Shuang Qiu, who recently defended her PhD thesis, studied the locomotor performance of fruit flies. She examined various effects, from age to long-term environmental effects to hypoxia, on the performance of fruit flies. She is also excited about the possibilities of Drosophila research to lead to medical advances in stroke prevention and treatment.

Parn Srithiphaphirom, a first-year doctoral student, is studying chill coma and neural function in locusts. But she is also exploring her options and has picked up some pointers on working with fruit flies from Dr. Qiu before she leaves Kingston. Dr. Qiu, who recently welcomed her second child, has accepted a faculty position at Nanjing University of Science and Technology.

[cover graphic of Queen's Alumni Review, issue 3, 2017]