Insects navigate in much the same way that ancient humans did: using the sky. Their primary cue is the position of the sun, but insects can also detect properties of skylight (the blue light scattered by the upper atmosphere) that give them indirect information about the sun’s position. Skylight cues include gradients in brightness and colour across the sky and the way light is polarised by the atmosphere. Together, these sky “compass cues” allow many insect species to hold a stable course.
At night, as visual cues become harder to detect, this process becomes more challenging. Some can use the light of the moon but one insect, the nocturnal dung beetle Scarabaeus satyrus, uses light from the Milky Way to orient itself. To find out exactly how this process works, my colleagues and I constructed an artificial Milky Way, using LEDs, to test the beetles’ abilities. We found that they rely on the difference in brightness between different parts of the Milky Way to work out which way to go.
Scarabaeus satyrus holds its course with apparent ease every night. They take to the air at dusk in the African Savanna, in search of the fresh animal droppings on which they feed. But they are not alone and, to escape competition from other dung beetles, they construct a piece of dung into a ball and roll it a few meters away from the dung pile before burying and consuming it.
To avoid returning to their starting point, they maintain a straight path while rolling their ball. Scientists discovered that the beetles could do this even on moonless clear nights. So in 2009, a group of researchers took some beetles on a trip to the planetarium in Johannesburg, and watched them try to orient themselves under different star patterns.
They found the beetles could hold their course well when the planetarium displayed just the Milky Way, the streak of light across the night sky produced by the disc-shaped arrangement of the stars in our galaxy. But the beetles became disoriented when only the brightest stars in the sky were shown.
What was still unclear was exactly what kind of compass cue the beetles extracted from the Milky Way. We knew, for example, that night-migrating birds learn the constellations surrounding the sky’s northern centre of rotation, much as sailors did before the advent of modern navigation systems. These constellations remain in the northern part of the sky as the Earth rotates, and so are a reliable reference for north–south journeys.
The planetarium experiments had shown that the beetles don’t use constellations of bright stars, but perhaps they could learn patterns within the Milky Way instead. My colleagues and I then proposed that the beetles might perform a brightness comparison, identifying either the brightest point in the Milky Way or a brightness gradient across the sky that is influenced by the Milky Way.
Artificial Milky Way
We used our artificial night sky to test this theory, constructing a simplified Milky Way streak that simulated different patterns of stars and brightness gradients. We found that the beetles became lost when given a pattern of stars within the artificial Milky Way. The beetles only maintained their heading when the two sides of the steak differed in brightness.
This suggests nocturnal beetles do not use the intricate star patterns within the Milky Way as their compass cue, but instead identify a brightness difference across the night sky to set their heading. This is similar to what their day-active relatives do when the sun is not visible but instead orient themselves using the brightness gradient of the daytime sky.
This brightness-comparison strategy may be less sophisticated than the way birds and human sailors identify specific constellations, but it’s an efficient solution to interpreting the complex information present in the starry sky—given how small the beetles’ eyes and brains are. In this way, they overcome the limited bandwidth of their information processing systems and do more with less, just as humans have learnt to do with technology.
This straightforward brightness comparison strategy is particularly effective over short distances. So although Scarabaeus satyrus is the only species known to hold its course in this way, the technique may also be used by many other nocturnal animals that perform short journeys at night.
Myths about diseases spread like wildfire. Malaria is a case in point. The Conversation Africa’s Health and Medicine Editor Joy Wanja Muraya asked Tabitha Mwangi to help sort out fact from fiction.
Mosquitoes only bite at night.
Not entirely true.
There are two types of mosquitoes that bite mostly at night; the Anopheles mosquito that transmits malaria and it’s noisier cousin, the Culex mosquito which spreads lymphatic filariasis, – also known as elephantiasis – that presents as severe swelling in the arms, legs or genitals.
A year-long study in Western Kenya showed that 15% of the mosquitoes bite between 6pm to 9pm while the majority (85%) bite from 9pm till morning. Data from this study puts further emphasis on the value of sleeping under an insecticide treated bednet.
The fact that this mosquito is active during the day makes it harder to control the diseases it spreads because bed nets aren’t an option.
Eating garlic before I sleep will repel mosquitoes.
There’s no scientific evidence to support this.
Garlic does produce a sulphur compound known as allicin which has some anti-bacterial, anti-fungal and anti-parasitic activities. Researchers have looked at it’s impact on mice that have been infected with malaria. In mice, use of allicin leads to a reduction in the number of malaria parasites in the blood, the higher the dose of allicin, the longer the mice survived. But no research has been done on its effect on the human immune system.
Mosquitoes like to bite women and children more than men.
This isn’t true, though there’s some evidence that they’re partial to pregnant women.
In The Gambia researchers found that pregnant women are twice as attractive to mosquitoes than non pregnant women.
The research involved 36 pregnant women and 36 women who weren’t pregnant. The two groups slept in separate huts under bed nets. In the morning, researchers collected and counted the mosquitoes found in the separate huts.
Twice as many mosquitoes were found in the huts in which the pregnant women had slept. There were two possible explanations for this. The first is that mosquitoes are attracted to carbon dioxide which pregnant women produce more of. In advanced pregnancy, women exhale 21% greater volumes than non pregnant women.
The second possible explanation is that pregnant women’s tummies are 0.7°C warmer than non pregnant women which could attract mosquitoes.
But there was an additional factor that the researchers suggested could have affected the results. Pregnant women – particularly women in advanced pregnancy – had to leave their huts at night more often than non-pregnant women because they need to urinate frequently.
Mosquitoes die after feeding.
This is not true. Male mosquitoes feed on sugary things while female mosquitoes need blood for their eggs to develop.
After feeding on blood, a female mosquito will rest to digest the blood and wait for the eggs to be ready.
The female mosquito rests for about two to three days then lays her eggs in water. After laying between 50 to 200 eggs, she then searches for another blood meal in order to lay another batch of eggs.
During her lifetime the female tries to lay as many eggs as she can which requires several blood meals.
In a laboratory, female mosquitoes can live for up to one month. But in natural conditions, few survive beyond one to two weeks.
Once you get malaria, you will never get it again.
Researchers have spent years monitoring people in malaria endemic areas to learn the patterns of immunity.
My PhD research involved collecting data on malaria from about 1,000 people in Coastal Kenya for two years. Children under five years had, on average, one clinical attack of malaria every year.
Malaria cases declined steeply after that and it was rare for adults who lived in this malaria endemic areas to have clinical attacks.
Other studies have shown that when highly immune adults spent long periods of time in places where they weren’t being bitten by infected mosquitoes, they could lose some of thatimmunity.
Scientists know that solid immunity to malaria only occurs in people who are constantly challenged. But it’s still not clear how this happens. This is one of the reasons why developing a malaria vaccine that works well has proved so difficult.
Mosquitoes only like the blood of humans.
This is true for some mosquitoes, but because female mosquitoes need a blood meal, most will take it from wherever they can find it. For example, livestock kept outside the homestead can attract mosquitoes. There’s even been a suggestion that cattle should be treated with insecticide as a malaria control strategy.
Dengue is a virus spread via the Aedes aegypti mosquito that infects as many as 100 million people annually in more than 100 tropical countries worldwide. It causes fevers, extreme headaches, and muscle and joint pains. In a few extreme cases, leakage of blood plasma through the walls of small blood vessels into the body cavity occurs, resulting in bleeding. This is known as dengue hemorrhagic fever.
The number and severity of dengue infections has been escalating since the Second World War, culminating in a 30-fold increase between 1960 and 2010. It is now 20 times more common than the flu. Because of global warming, decreased heavy pesticide use due to environmental concerns, and the Aedes mosquito’s preference for urban environments, the insect – and the virus it carries – are rapidly spreading around the world.
There is no treatment for dengue fever. At best, doctors can give their patients supportive care, such as painkillers and liquids to keep them hydrated. Untreated dengue fever has a mortality rate of about 5%; fortunately, with treatment that number drops to zero and each year “only” 20,000 dengue deaths are recorded.
As a result of its prevalence all around the world, scientists are looking for new ways to control Aedes mosquitoes – and thus dengue transmission.
The dengue virus does not harm its mosquito host. When an infected female mosquito bites a person, the virus enters the blood stream with the mosquito’s saliva and anticoagulant.
Aedes aegypti are smaller and quieter than the mosquitoes typically found in the US. They thrive in urban environments and are more at home in the city than in the jungle. Controlling and limiting Aedes habitats is extremely difficult since they like to live indoors, residing in places such as dim closets and cupboards. They can lay eggs in a single drop of water. The stealthy bloodsuckers enjoy feeding around human beings’ ankles, biting as many as 20 people a day.
Somehow, the simple dengue viruses with RNA genetic material coding for just 10 proteins can change the production of 147 different proteins expressed by Aedes. It makes the mosquito hungrier for human blood, its saliva more hospitable to the viruses, and changes the protein mix in the antennae of the mosquitoes making them more sensitive to odors – thereby increasing the mosquito’s ability to find a victim.
Bombarding them with bacteria
An Australian group led by Scott O’Neill at Monash University has infected mosquitoes with bacteria that prevent the dengue viruses from taking up residence in the mosquito. It prevents the dengue’s carrier from hosting the virus.
The Wolbachia-infected mosquitoes are the result of an idea that O’Neill had 20 years ago. He knew that Wolbachia-infected fruit flies would not transmit any RNA virus. So he hoped Wolbachia-infected Aedes aegypi would act in the same way and not transmit dengue, an RNA virus. The trouble was, even though Wolbachia infections are common in many insects, including non-Aedes mosquitoes, he couldn’t infect sufficient numbers of Aedes with the bacteria. He says he persisted because, “I thought the idea was a good idea, and I don’t think you get too many ideas in your life, actually. At least I don’t. I’m not smart enough.”
It wasn’t easy, but by obsessively trying new and different ways to infect Aedes with a strain of the bacteria obtained from the fruit fly, his group managed to overcome the mosquitoes’ resistance to Wolbachia. Infecting young Aedes eggs worked best, particularly since all female eggs that were infected grew into adult Aedes mosquitoes that passed on the bacteria to all their offspring.
Field trials in Australia, China, Vietnam, Brazil and Thailand have been promising. In Australia, within 10 weeks of releasing the infected mosquitoes, the Wolbachia spread through 100% of the Aedes population of the two towns studied. The mosquitoes have remained infected ever since. O’Neill is now dreaming of world-wide dengue eradication by his Wolbachia-infected Aedes.
Transgenic population crashers
A British biotech company, Oxitec, regularly releases millions of genetically modified mosquitoes in trials in Brazil. Its chief scientific officer, Luke Alphey, found a gene that kills off all Aedes offspring in their larval stage. In a neat trick, he also found a way to suppress the deadly gene’s expression using the antibiotic tetracycline. So in the presence of tetracycline, the larvae develop normally, allowing researchers to grow large batches of adult transgenic Aedes. Then they’re released into the wild, where of course the mosquitoes have no contact with the antibiotic antidote. The genetically modified mosquitoes breed with their wild counterparts, yielding offspring that will die as larvae.
When enough males are released, their mating with wild females will collapse the population. It’s like a form of birth control for the mosquitoes, since no offspring make it past the larval stage. In all field tests no genetically modified females are released. This is critical because Oxitec has to prevent the genetically modified insects from breeding with each other in the wild and to ensure that transgenic mosquitoes do not bite any humans – remember, only female mosquitoes bite.
In July 2012 the Minister of Health of Brazil, Alexandre Padilha, opened a new facility to create enough mosquitoes to protect a town of approximately 50,000 inhabitants from Aedes aegypti. At maximum production, the facility will produce 4 million sterile mosquitoes a week. Key West, Florida is next on the list. The US Food and Drug Administration is currently reviewing an application to release the Oxitec mosquitoes there.
While the Oxitec and Wolbachia mosquitoes are already being released in fairly large field trials, a new player has just entered the arena. Using computational methods, researchers at Virginia Tech have found a gene they call Nix that’s responsible for the male sexual characteristics of Aedes aegypti. More than two thirds of the females produced when the Nix gene is added to female Aedes embryos have male genitals and testicles, making them infertile and perfect vehicles, like the Oxitec mosquitoes, to collapse a local Aedes population.
The researchers acknowledge they’re still years from doing field tests. For example, they haven’t tested whether their masculinized females can bite and transmit disease. But Zach Adelman, one of the paper’s authors, sees some advantages of using the Nix gene over sterilization-based techniques, such as those used by Oxitec: “They’re throwing away half of the mosquitoes that they rear because they’re females. If we have a strain that doesn’t even make females then you don’t have to spend all the labor costs associating with separating those out, and you don’t have to spend the money rearing them and then throwing them away,” Adelman says.
Ongoing search for innovation
As long as there are no cures or vaccines for dengue fever, the only way to control the world’s fastest growing infectious disease is to manage the Aedes population, either by killing them or by making them inhospitable to the dengue viruses. The current techniques of removing all sources of stagnant water and using limited and targeted insecticide applications are insufficient.
These solutions that require scientifically altered mosquito releases are controversial. The most common fears people have are that the genetic modifications could cross over into other species, result in super-mosquitoes, or that the disappearance of Aedes from the ecosystem will affect other organisms that depend on them for survival.
Despite all the concerns about using genetically modified or bacterially infected Aedes mosquitoes, it’s hard to imagine a way to beat dengue that doesn’t involve them. And there are some clear advantages to using Wolbachia infections or genetically modified self-destructing mosquitoes. They are both species-specific and will not affect any other mosquitoes, butterflies or bees – as indiscriminate insecticide applications would – and they can reach places that only male mosquitoes could find.
Who doesn’t love butterflies? While most people won’t think twice about destroying a wasp nest on the side of the house, spraying a swarm of ants in the driveway, or zapping pesky flies at an outdoor barbecue, few would intentionally kill a butterfly. Perhaps because of their beautiful colors and intricate patterns, or the grace of their flight, butterflies tend to get a lot more love than other types of insects.
As a caretaker of one of the world’s largest collections of preserved butterflies and moths, and as a very active field researcher, I spend a lot of time explaining why we still need to collect specimens. All these cases of dead butterflies contribute greatly to our understanding of their still-living brothers and sisters. Collections are vitally important – not only for documenting biodiversity, but also for conservation.
Documenting what’s out there
Museums are storehouses for information generated by everyone who studies the natural world. Natural history collections constitute the single largest source of information on Earth’s biological diversity. Most of what we know about what lives where and when is derived from museum collections, accumulated over the past two-and-a-half centuries.
Methods of field collecting have changed little since butterfly collecting became popular in Victorian times. The butterfly net remains the primary tool of the trade. Most butterflies are attracted to flowers, although bait traps – with fermenting fruit, putrid liquefied fish, mammal dung, or even carrion – are used to attract certain species.
Butterflies live pretty much everywhere that has native plants. Many species are highly seasonal in occurrence, some only on the wing for a couple of weeks each year. Since most butterflies stay close to their caterpillar foodplants, even as adults, the best way to find a particular butterfly is to search out an area where its favorite plant grows in abundance.
Upon arriving home, collected specimens are pinned, with a single pin through the body (thorax). We position the open wings on a flat board so they’ll remain in the spread position once the butterfly has dried. Then we stick a label to the pin, indicating exactly where the specimen was collected, when and by whom. Dried specimens are extremely fragile and need to be protected from pests, light and humidity; if this is done successfully, specimens may last indefinitely – the oldest known pinned butterfly specimen was collected in 1702!
It’s these collected specimens that enable detailed studies of anatomy. These studies in turn contribute to taxonomy, the science of classification, which provides a basis for communication about organisms across all disciplines. As genetic technologies continue to advance, museum collections are increasingly important resources for DNA-based studies on taxonomy, climate change and conservation genetics.
New finds – in the field and display case
Despite their status as most-favored insects, there are still many undiscovered, unnamed butterflies, all over the world. Every year, we discover new butterfly species. Just like flies, beetles and wasps, a significant percentage of butterfly species remains to be formally identified, named and classified. This is especially true in tropical areas around the world, where new butterfly species are discovered on a monthly or even weekly basis; eight new tropical butterfly species have already been named in 2015 in just one journal!
Discoveries aren’t exclusively made in exotic, hard-to-reach locations, though. New species are frequently found within existing museum collections. When specimens are closely examined (or reexamined) by experts, it’s not unusual to find multiple species among what was previously considered just one. Such discoveries are made through traditional anatomical studies, as well as through newer DNA-based technologies, which can detect multiple species among specimens that appear, to our eyes, to be identical.
New species’ names become officially available for use once the formal description is published in a journal. There are rules that researchers must follow for their names to be considered valid, dictated by the International Code of Zoological Nomenclature. Even so, debates over the rank of a particular name are common, and what is originally described as a new species might be considered to be merely a subspecies of an existing species by other scientists. In most cases, over time and through independent investigations, consensus on the appropriate rank for each name is usually established.
Even though dozens of books and guides to the butterflies of the United States have been written, surprising new discoveries continue to be made here. New species are even being discovered among our largest and showiest butterflies, the swallowtails.
Swelling the ranks of swallowtail species
In 2002, the Appalachian Tiger Swallowtail (Pterourus appalachiensis) was described as a new species, based mainly on differences observed in recently collected specimens. Subsequent ecological and molecular studies, resulting from the collection of specimens in all parts of its range (as well as throughout the ranges of related species), coupled with the study of museum specimens, have supported the species-level status of this large and conspicuous southern Appalachian butterfly, which appears to have evolved through hybridization between Canadian and Eastern tiger swallowtails.
Last year, another new species of swallowtail butterfly was described from the United States, the Western Giant Swallowtail (Heraclides rumiko). This butterfly was “split off” from the Eastern Giant Swallowtail (Heraclides cresphontes) based on subtle but consistent differences in wing markings and in the form of the male and female genitalia, as well as in the DNA barcodes, small snippets of DNA taken from the same gene and compared across many species. This cryptic diversity was revealed through the study of numerous museum specimens, as well as through recent collections in areas where the two species meet in Texas.
Late in 2013, the Intricate Satyr (Hermeuptychia intricata) was described from the southeastern United States. It was first detected when specimens from a faunal survey of a Texas state park were DNA barcoded, and two distinct barcode groups were identified in what had been called the Carolina Satyr (Hermeuptychia sosybius). Upon closer examination, consistent differences were also observed in the genitalia of the two groups. A subsequent review of specimens in museum collections showed that the Intricate Satyr ranges broadly across eight southeastern states, and that, most of the time, adults can usually (but not always) be identified based on wing markings.
These examples are striking reminders that new species remain to be discovered even among the best-studied faunas, and that ongoing collecting coupled with the study of museum collections continues to play an important role in revealing biodiversity. While specimens of all three of these new butterfly species existed in museum collections before they were formally recognized as new, all of them were initially revealed as unique through differences found in recently collected material.
Collecting for conservation
Genetic data are widely used in management plans for rare and endangered species, and butterflies are no exception. Due to their generally small size and the current limitations of technology, studies of butterfly population genetics almost always include the collection of specimens. DNA quality rapidly deteriorates in museum specimens, so for detailed genetic information, fresh specimens almost always need to be collected from the wild.
One of the rarest butterflies in eastern North America is an as yet undescribed species, widely known as the Crystal Skipper (Atrytonopsis sp.). This species is found only in a small part of coastal North Carolina, and is of considerable conservation concern. Genetic studies resulting from samples taken at all known sites where the butterfly lives have shown that three distinct genetic groups exist across its limited range. Thus, if we aim to preserve the genetic diversity of this species, multiple sites will need to be maintained as suitable habitat across its range, not just one or two adjacent areas.
A recent paper suggested that collecting for scientific studies can contribute to the extinction of species. However, scientists studying various animal and plant groups widely contested this notion.
Due to their population dynamics, with a single female often laying hundreds of eggs, collecting a few butterfly specimens, even in a small population, would be unlikely to have a detrimental effect. The only proven method for driving a butterfly to extinction is habitat destruction and fragmentation. Sadly, there are many examples of butterflies that have been exterminated in this manner – the most famous in the US being the Xerces Blue. Now, these extinct species can only be seen and studied in one place – a museum collection.
The east coast of Australia is currently experiencing one of its worst outbreaks of mosquito-borne disease in years. Mosquitoes have plagued the summer and now there’s a dramatic increase in disease caused by Ross River virus, spread by the bite of mosquitoes.
A recent article in the journal Lancet Infectious Diseases reviews the factors contributing to future increases in mosquito-borne disease risk in the United Kingdom. While the authors identify increased temperatures as potentially providing suitable conditions for mosquitoes that spread pathogens, climate change alone wasn’t enough.
The mosquitoes that can spread dengue and chikungunya viruses, particularly the Asian Tiger Mosquito (Aedes albopictus), need to get there in the first place and, most likely, that is with people and their belongings.
It isn’t only the UK that is at risk. Until recently, chikungunya virus was unknown from the Americas but within a year of it being introduced into the Caribbean, it had spread to both North America and South America and is suspected to have infected over 1.2 million people.
As the researchers highlight, even the way authorities respond to the threats of climatic change, such as the construction or rehabilitation of wetlands to create a buffer against increasingly frequent storms and sea level rise, may further increase risk. Mosquitoes that spread West Nile virus could move into these wetlands.
Hitching a ride to Australia
The Asian Tiger Mosquito poses a significant threat to Australia. It was discovered in the Torres Strait in 2005, having thought to have hitchhiked on fishing boats from Indonesia. Its a question of when, not if, this mosquito will make its way to mainland Australia.
The mosquito has already hitchhiked to Europe and North America with eggs attached to used tyres and lucky bamboo. Movement of people, not shifts in climate is the biggest risk.
Exotic mosquitoes and viruses are a concern but there are still plenty of ways a local mosquito bite can make you sick.
Ross River virus is the most commonly reported local mosquito-borne disease. Every year about 5,000 fall ill due to this virus. While not fatal, it can cause fever, rash, headache, joint pain and fatigue that may last a few weeks or many months. It can be seriously debilitating.
By the end of March, New South Wales and Queensland will have recorded over 4,700 cases of Ross River virus disease. Those figures already exceed the total number of cases reported in each of the previous three to five years. This may be the biggest outbreak of mosquito-borne disease along the east coast of Australia since the mid-1990s.
Could the current outbreak be linked to a changing climate?
Thanks to the warmest spring on record and substantial rainfall associated with tropical cyclones, conditions have been perfect for mosquitoes. If these climatic events become more common, there is little doubt we’ll continue to see outbreaks of Ross River virus disease and other mosquito-borne diseases.
The current outbreak, however, may provide a glimpse of what lays ahead. With warmer weather, we may see an extension of the “mosquito season” each year. Aside from the risks to public health extending well into autumn (or possibly arriving earlier in summer), there is the increased economic burden on local authorities needing to expand mosquito control and disease surveillance programs.
There are still gaps in our understanding of the relationship between climate, mosquitoes and disease. But the current outbreak of Ross River virus disease should serve as a reminder that in the future, more of our “home grown” mosquito-borne disease, and not necessarily the spread of “tropical” disease such as dengue and chikungunya, could be our primary concern.
The world around us is full of amazing creatures. My favorite is an animal the size of a pinhead, that can fly and land on the ceiling, that stages an elaborate (if not beautiful) courtship ritual, that can learn and remember… I am talking about the humble fruit fly, Drosophila melanogaster. By day, a tiny bug content to live on our food scraps. By night, the superhero that contributes to saving millions of human lives as one of the key model systems of modern biomedical research.
Fruit flies entered the laboratory almost through the back window a little more than 100 years ago. The excitement was still fresh after rediscovery of Gregor Mendel’s work on the genetics of peas in 1900. It was an outlandish notion at the time that Mendel’s simple laws of inheritance could apply even to animals. To test this revolutionary idea, scientists were looking for an animal they could keep easily in the lab and reproduce in large numbers.
Thomas Hunt Morgan struck gold when he decided to use the fruit fly as a model. He and his students pushed this prolific little animal to great success. They furthered Mendel’s work to discover that genes are located on chromosomes, where they are arranged, in Morgan’s words, like “beads on a string” – a breakthrough that was recognized with the Nobel prize in 1933. With the success of Morgan’s “flyroom,” the humble fruit fly was set on its way to becoming one of the leading models in modern biology, contributing vast amounts of knowledge to many areas – including genetics, embryology, cell biology, neuroscience. Additional fly Nobel prizes were awarded in 1946, 1995, 2006 and 2011.
A tiny fly stands in for us in basic research
If you ask a geneticist, humans are brothers to mice and just first cousins to flies, sharing 99% and 60% of protein-coding genes, respectively. Our anatomy and physiology are also related, so that we can use these laboratory animals to design powerful experiments, hoping what we find will be of significance to animals and humans alike. It’s undeniable that the research on animal models – such as nematodes, flies, fish and mice – has contributed immensely to what we know about our own body and as a result is helping us tackle the diseases that plague us. On this front, the services of the fruit fly will certainly be required for some time to come.
Studying fly brains to understand our own
A recent renaissance in neuroscience is also bringing the fly to the forefront of our efforts to understand the brain. One of the things we least understand is how our own brain produces our emotions and behavior. Scientists are naturally attracted by the unknown, making this one of the most exciting open frontiers in biology. Perhaps, our brain, the ultimate Narcissus, cannot resist the temptation to study itself. Can the humble fly really contribute to our understanding of how our own brain works?
The fruit fly brain is a miracle of miniaturization. It deals with an incredible flow of sensory information: an obstacle approaching, the enticing smell of overripe banana, a hot windowsill to stay away from, a sexy potential mate. And it does this literally on-the-fly, as the little marvel is computing suitable trajectories around the room. Yet the fly brain is composed of only about 100,000 neurons (compared with nearly 100 billion for human beings) and can fit easily through the eye of the finest needle.
The relatively small number of cells is a key advantage for brain mapping, and large efforts are under way to label, trace and catalog every single neuron in the fly brain. Combine this with the unique wealth of information on the genetics of this little animal, and you will see how we are now able to design incredibly powerful experiments in which we alter the “software” (that is, introduce specific changes in the genome) to create animals with unique and predictable changes in the “hardware” (the brain circuits) to ask questions about brain function.
Following this playbook are recent experiments demonstrating, for example:
how the brain processes simple hot and cold stimuli to keep this little animal away from danger (my own area of research)
and many more.
Of course, we can do these kinds of experiments in a number of animal models. But the unique advantage of the fly is that we can pinpoint every single neuron that’s important for a particular response or behavior, precisely map how they connect to each other and silence or activate each one to figure out how the whole thing works.
Don’t forget the flies
Just a few weeks back, Chicago hosted the Genetics Society of America’s annual “fly meeting,” bringing together thousands of fly scientists from around the world. One of the topics discussed was that, in this tough economic climate, funding cuts to public agencies are disproportionately hurting research on fruit flies in favor of more “translational” approaches – that is, research that has more immediate practical applications.
It’s worth remembering that neither Mendel nor Morgan expected that their work could have a direct impact on medicine. Yet when, hopefully soon, we manage to “cure” cancer – a genetic disease par excellence – they should be among the very first people receiving a thank you note from humanity.
Flies still have a lot to contribute to our understanding of all aspects of biology. As with much basic research, the direct benefits from this work may be around the corner, or may take a little longer to find. It would be a big mistake to curb fruit fly research now that the flies are just getting warmed up to tackle some of the most interesting questions in biology.
They are the answer to the classic quiz question “what is the most deadly animal on earth?”
By the time contestants have debated the demerits of tigers, cobras and great white sharks scores of victims of the real worst killer will have died and other people will have been infected by the diseases they spread. The mosquito goes about its deadly business every day of every month, spreading infections that will kill hundreds of thousands of humans every year.
It increasingly seems nowhere is safe – experts have warned mosquitoes could bring malaria and dengue fever to the UK within decades.
There is nothing good to be said for mosquitoes. Scientists willingly concede that their eradication would bring significant benefits for humanity with no obvious downsides. What good mosquitoes might do, mostly through sheer weight of numbers as food for other creatures or as amateurish pollinators, are roles readily filled by alternative species.
As the famous and charming folk song has it: “All God’s creatures got a place in the choir”, some singing higher, some lower and some just clapping their paws. However the lyrics do not suggest that any of the choir are sneaking off for a clandestine blood meal, infecting millions of people with malaria, yellow fever, dengue fever, west Nile virus and a host of other less familiar dreads. Even the most generous explanations of the mosquito’s place in the world is that it is here to remind us of our fall from grace.
Instead of trying to invent a place for the mosquito in a supposed natural balance that is a cosy but flawed version of the natural world, perhaps it is better to see these insects as the Gothic fly in the ointment they so clearly are. The mosquito has replaced many of the old monsters and demons of earlier folklore in our imaginations.
Mosquito natural history is a perfect mixture of monstrous traits. They are associated with swamps and miasmas, those eerie and uncertain places of which humanity is wary. Even before we understood the role of these blood-sucking flies in transmitting disease, humanity had a sense that there was something carried in the filthy swampland air that brought disease and that these places were best avoided.
Swamps and fens are odd places, neither land nor water, but perfect mosquito habitat. In the UK some of the earliest surveys of ponds and wetlands in East Anglia were driven by the desire to find the mosquitoes’ lair, in the very same swamps where once saints and heroic warriors had ventured to confront fiends.
Mosquitoes are also creatures of the night. The fall of darkness has always been a threat to us light-loving primates, not just at a basic biological level as our senses falter but also in religion and custom. Mosquitoes awake with the failing light, able to find their victims when we can only hear their whine.
Above all they suck blood in order to reproduce, or at least the females do, which only fuels the religious constructions of why humankind is plagued by them. We no longer have the Saxon hero Beowulf to confront the monsters in their water lair, but instead Bill Gates has malaria and its mosquito vectors in his well resourced sights: the rational world of science and technology pitted against a blood sucking foe from the twilight. It is the classic struggle.
Meantime mosquitoes have made some advances of their own. In the UK headlines warn us of a “plague”, that a “killer mosquito lurks in Britain” which will “threaten to terrorise the UK” . Malaria had been indigenous to the country since at least Roman times, notably around the coastal marshes of the Thames estuary, the same marshes from which the terrifying convict Magwitch looms at the start of Charles Dickens’ Great Expectations, in classic swamp monster style. However by the early 20th century the disease had been eradicated.
It is those same marshes that now seem to be home for a bridgehead of invasive mosquito species new to the UK, moving north from the continent. They include the Asian Tiger mosquito, a vector for west Nile virus. This mosquito is a miniature cantilevered marvel of black and white, drawn straight from the pages of a Victorian gothic fantasy. The killer swarms rising from their swamp lairs show no signs of retreat.
Chuck Bednar for redOrbit.com – @BednarChuck Perhaps best known as a massive pest and the only creature able to survive a nuclear apocalypse (in popular theory, at least), cockroaches also apparently have individual personalities, according to new research published recently in the journal Proceedings of the Royal Society B. [STORY: Dannon coloring yogurt with dyes made… Continue reading →
Ever heard of a Papilio polyte? Well she is beautiful. But she is also known to be somewhat of a copycat. The Papilio polyte, also known as the female version of the common mormon butterfly, is known for her mimicry. That is to say, she is a master impressionist. In particular, she impersonates the swallowtail, a butterfly that is more colorful and toxic, in order to trick predators into thinking she is distasteful – and deadly. Explicitly, Miss Mormon is known for imitating the unpalatable – and inedible – red-bodied crimson rose swallowtail.
THE THREE FACES OF…
Beneath her big facade, the common mormon is a lady of real substance. According to Harish Gaonkar, an Indian butterfly specialist at the National History Museum in London, its name is an allusion to the polygamy practiced by members of the Mormon sect (papilio being Latin for butterfly and poly being Greek for many). Says Gaonkar,
“… the first to get such a name was the common Mormon (Papilio polytes), because it had three different females… The name obviously reflected the … Mormon sect in America, which as we know, practiced polygamy.”
Thanks to its uncanny ability to simulate the swallowtail, the aptly named commons are indeed quite common – and bold, as they are not a threatened lot. The female’s three disguises are known as the cyrus, marked by vibrant red crescents, the stichius which most closely resembles the crimson rose swallowtail, and the romulus which is the least adept at mimicry and appears duller in vibrancy than the others. Generally, the common is a jet black butterfly with a row of white spots along the middle part of its hindwing, and measures an approximate 90 -100 mm.
WHAT PUTS THE SUPER IN SUPERGENE
If all of this just feels like one confusing look-alike contest to you, have no worries, there’s no quiz. What you do want to note however, is that for decades, scientists have thought that the female common’s three different masks were controlled by a “supergene”: a cluster of genes, each which manage different parts of the butterfly’s wings. New research has found however, that the once-supposed supergene is actually a single gene called doublesex. By demonstrating different variants of the gene at multiple levels, the butterfly can swap their wing patterns in a quite radical manner. Hitting upon this discovery was a double-play for scientists because the doublesex gene already had a well-established role: to navigate the morphing butterflies down either a male or female trail. That such a well-characterized gene is revealed to carry another function is mind-warping.
The supergene idea was founded in the 1960s by British scientists Sir Cyril Clarke and Philip Sheppard. The duo conducted cross-breeding experiments which showed that common mormons inherit their wing patterns as one – not as separate elements. While this was an amazing unveiling, no one had yet identified the actual cluster of genes that composed the supergene…until a group of scientists at the University of Chicago began tinkering with the flutter-bys. By comparing non-mimetic females that resemble males with those that look like the common rose swallowtail and seeking out parts of the butterfly’s genome that were associated with their methods of imitating, they stumbled upon a tiny section that held five genes, four of which were similar in all of the females, no matter what their wing patterns looked like.
LUCKY NUMBER FIVE
The fifth gene proved to be a hotspot of molecular evolution. The doublesex gene, it differed between the mimetic and the non-mimetic females at more than 1,000 nucleotides. Said Kunte, one of the researchers in Chicago,
“If you look at flies or beetles, this gene is very conserved. Only in mimetic and non-mimetic females of this one species do you see such diversity.”
While these mutations alter the way the doublesex gene works, they have no bearing on the parts of the gene that are responsible for determining the sexes, which allows the gene to simultaneously hold on to the task of wing-controller.
Researchers in Chicago also found that when doublesex is transcribed in RNA, the transcript is divided into four distinct fashions: three identified in females, one in males. The gene showed that the doublesex gene is more strongly exhibited in the burlesque-mormon females, as well as in the small slices of the wing responsible for the insect’s white streaking.
Despite doublesex being a single gene, it appears to be inverted relative to the non-mimetic one so that it is positioned askew in the genome. This prevents different alleles (mutated genes responsible for hereditary variations) from mingling with one another, and for the gene to make certain their thousands of mutations are all inherited in concert. Doublesex is not a cluster of tightly-chained genes. On the contrary, it is a cluster of tightly-chained mutations in one gene.
IT MUST BE GOING AROUND
Amid this flurry of discovery, there are lots of other scientists who, while dabbling in the supergene scavenge, have discovered it in a slew of other organisms, including other butterflies. One example of a lepidopderist’s lightbulb moment was experienced by Matthieu Joron of the French National Centre for Scientific Research when he unveiled that the varied patterns of the Heliconius butterfly (a genus of the boldly striped, black and white brush-footed butterfly commonly known as the longwing) are controlled by a cluster of many genes also yoked by a genomic inversion. While Joron noted that the two lineages independently resulted in an extraordinarily similar solution in response to similar pressures for accurate mimicry, he was hungry for more answers – particularly that to the question of what each element of the doublesex gene actually does and why they need to be tethered in order to result in full mimetic patterns.
There is curiosity in the world of these whispery wonders we call butterflies as to whether or not scientists have inaccurately pigeon-holed doublesex as a sex-differentiating gene when in fact it is capable of so much more, as proven by this latest research. Potentially, this gene may be the agent involved in the decision-making process when it comes to other factors in the animal kingdom like the production of deer antlers or even peacock feathers. For now however, the riddles remain riddles, the researchers continue researching, and the butterflies…well, they just stay beautiful.