Tag: Insect Evolution

Which species of animal is the best flyer? Here are a few words on behalf of flies.

For thousands of years human beings looked with envy on those living creatures that could take to the air and fly. The advantages that an animal can gain from flying are so numerous that many different kinds of creature have evolved one way or another to take flight.

Being able to fly is such an advantage to a creature that flight has evolved many times in the history of life! (Credit: R. A. Lawler)

Now the question of who is the best flier depends a lot on what criteria you’re looking at. In terms of long distance fliers there are several species of bird that fly thousands of kilometers without ever touching the surface. (Notice how I said surface there rather than ground. That’s because those extended flights are mostly over water.) But if you want to talk about maneuverability or a quick takeoff you can’t argue against the animals whose very name means aviation, the insect members of the order Diptera, the flies!

The Albatross is the king of long-range flying. There are actually over twenty different species all of whom are capable of flying hundreds of kilometers without touching the surface. (Credit: Britannica Kids)
While there are about 100,000 known species of the order Diptera, the flies, the common housefly Musca domestica is perhaps the best known. (Credit: University of Nebraska)

While many types of insects fly, some, like many species of beetle are rather clumsy, using flight mainly for escape from predators. Others, like bees, use flight as transportation, going from flower to flower or back to the hive in a straight line without any fancy flying.

In the Beetles, order coleoptera, the front wings have evolved into a hard casing that protects the rear wings which are still used for flying short distances. (Credit: The Guardian)
Dragon and Damsel Flies are not true flies because they still possess two pairs of wings. The pairs beat out of synch with the fore wings beating up while the rear wings beat down. (Credit: National Wildlife Federation)

Flies seem to have evolved just to be able to fly. They are capable of performing the most incredible acrobatic feats in mid air while the speed with which they can take off is quicker than the human eye can follow.

The compound eye of a fly is also a miracle of evolution. The thousands of separate light sensors may not give the fly as clear a vision as our eyes do but they give nearly 360 degree vision and are especially sensitive to motion. Another reason it’s so hard to catch a fly. (Credit: Phys.org)

Unlike most flying insects who have four wings, true flies have only two. The name Diptera in fact means two wings. Flies retain their original front pair of wings but the rear wings have evolved into long thin rods with knobs at the end called halteres. Instead of providing lift as a normal wing would it is the halteres that enable the fly to perform their amazing aero-athletics.

In flies the rear wings have evolved into structures called halteres that the fly uses for balance and control in flight. (Credit: Animalogic)

In straight line flight the halteres beat up and down in exactly the opposite motion of the wings. In other words when the wings go up the halteres go down and vice versa, this gives the fly great stability. Then, when the fly wants to change direction it does so by using the moment of inertia of the halteres. Because of their halteres some flies are able to completely reverse course in a single wing beat, less than ten milliseconds.

Flies are more than just a minor nuisance, they are carriers of many diseases and they will often lay their eggs, which develop into maggots, in our food ruining it. (Credit: BBC)

Flies of the family Calyptratae, which includes houseflies and fruitflies, are considered the best of the best. In order to discover how they use their halteres scientists Gwyneth Card and Michael Dickinson of the California Institute of Technology first used high-speed cameras that could record at as much as three thousand frames per second to get baseline measurements of fly performance. They found that by using their halteres members of Calyptratae could take off or change course in as little as a single wing beat, around seven milliseconds.

Fruit Flies destroy billions of dollars of agricultural products every year. (Credit: The Home Depot)

The scientists then removed the halteres from their test subjects and measured the reduction in performance. Without their halteres to provide balance the insects become much clumsier, like a tightrope walker without their pole, sometimes with disastrous result. Not only did takeoff now require an average of four wing beats instead of the previous one, but also one species of fly, known as blow flies became so awkward that their takeoffs usually resulted in a crash. At the same time the fly’s performance while in the air also deteriorated markedly. While it’s true that flies may not be the best long-distance flies, when it comes to maneuverability and a quick take off members of the order Diptera are capable of aerial acrobatics that would make a jet fighter pilot’s head swim. We all know how difficult it is to catch a fly in the air or swat them when they’re on the ground and halteres are one big reason why!   

New study uses the gene editing tool CRISPR to finally discover how the wings of insects evolved.

After intelligence probably the most astounding ability created by evolution during the history of life is the miracle of flight. The ability to fly gives such an advantage to any living creature that wings have evolved at least four separate times in different animal groups. These groups include the insects, the birds, the mammals and even the reptiles.

Flight has evolved in many very different kinds of animals. (Credit: Pinterest)

The insects were the first to take to the air and fly. We have fossil evidence of flying insects from as far back as the Devonian period when our vertebrate ancestors were just climbing out of the water. Evolutionary biologists have for many years theorized that the first insect ‘proto-wing’ developed not as a organ of flight but instead as an organ to help an insect regulate its body temperature.

The largest insect of all time was named Meganeuridae who lived during the Pennsylvania Period and had a 60-70 cm wingspan. (Credit: Geology In)

You see insects are cold-blooded and on a chilly morning many use the light of the Sun to try to warm up their metabolism. A knob on the insect’s back would increase the amount of the Sun’s heat that the insect could absorb, just like a solar panel, and the bigger the knob the better. Natural selection would then act so as to increase the size of the knobs until they became ‘proto-wings’ that an insect could at first use to glide or even catch the wind for a free ride. As the new wings grew even larger, and acquired muscles that allowed them to move, eventually the insect was able to fly.

Before they evolved for flight Insect wings were used as solar collectors to help the insect warm up their metabolism. (Credit: Ohio’s Electric Cooperatives)

Some modern insects still use their wings in that way. If you’ve ever taken a walk in a swampy area early in the morning you can find dragonflies and damselflies climbing up the stalks of tall grasses or reed. Climbing not flying because their metabolism hasn’t warmed up enough to produce the energy needed to fly. Once near the top the dragonfly will spread it’s wings to face the Sun in order to absorb the warmth of the sunlight which will increase its body temperature so that it can fly.

 So the question for biologists to answer was, where did those original knobs come from? For over a century entomologists looked in vain among the closest relatives of insects the myriapods, that is the centipedes and millipedes for some structure that could have evolved into those knobs. The search was in vain however because, as modern DNA analysis has shown, insects are actually more closely related to crustaceans, shrimp, lobsters and crabs than they are to centipedes and millipedes.

For many years biologists thought that insects were most closely related to centipedes and millipedes. Here’s a quick way to tell the difference between them! (Credit: Seed to Feed Me)
Modern DNA analysis has shown that insects are actually more closely related to shrimp and other crustaceans. (Credit: Arizona Aquatic Gardens)

And now a new study from biologists at the Marine Biological Labouratory (MBL) at Woods Hole has discovered the original bump on a shrimp’s leg that developed into the wings of insects. In a paper published in the journal Nature Ecology & Evolution, Research Associate Heather Bruce along with MBL director Nipam Patel have used the gene editing tool CRISPR to demonstrate how a lobe on the seventh, innermost segment of a crustacean’s leg was incorporated into the body of the ancestors of early insects as they moved onto the land. This segment provided extra strength to the exoskeleton of the early insects. In time the lobe then grew to become the long sought after ‘proto-wing’.

The gene editing tool CRISPR is revolutionizing many different fields of biological research. (Credit: Vox)

Doctor Bruce began by comparing the genetic instructions for the segmented legs of a tiny beach hopper shrimp called Parhyale to those in the fruit fly Drosophila and the beetle Tribolium. Now Parhyale, like all crustaceans have seven segments in their legs while both Drosophila and Tribolium, like all insects have only six segments. However all three species have an identical sequence of five genes that code the instructions for leg development.

Morphology of the legs of an ancestral crustacean, a modern shrimp (Parhyale) and an insect. (Credit: Nature Ecology and Evolution, Bruce & Patel)
Comparing the legs of Parhyale and an insect it is now clear that the Coxal plate of the shrimp is the structure that evolved into the insect wing. (Credit: Nature Ecology and Evolution, Bruce & Patel)

Using CRISPR Bruce disabled those five genes in embryos of all three species one at a time and monitored the results. What she found was that eliminating the genes eliminated the six leg segments farthest from the body. She also found that the seventh, nearest segment of the leg of Parhyale corresponds to a section of the back of the exoskeleton of the insects. Most importantly, a lobe on that seventh segment, called the Tergal Plate moved with the segment becoming a perfect candidate for the knob that evolved into the insect wing. The story of the evolution of the insect’s wing clearly demonstrates the power of natural selection in taking a structure in the body of an animal and altering its shape to perform an entirely new function. The story of how DNA analysis and gene editing have enabled scientists to work out the details of that evolution clearly show the power of the newest tools that biologists possess in their study of life here on Earth.