Shawn Vincent
Assistant professor of Anatomy and Biology, IU Kokomo
Studying evolutionary biology takes this IU researcher to a family of long-living, snakes in the islands of Japan. He's also studying a grasshopper with the kick-force of a Tyrannosaurus rex and if that kick is being guided by natural selection.
Every summer, Shawn Vincent travels to Japan to search for the more than 300 snakes he has tagged in the last four years.
Vincent has been conducting research on the evolution of Colubrid snakes (members of the Colubridae family) to determine the forces that drive the evolution of very large Colubrid snakes -- more than a meter in length -- versus very small Colubrid snakes, no more than half a meter long.
Many factors can determine whether the snakes will grow large or small, such as the different sizes of their prey among the islands of Japan. If the prey is small, then the snakes will be small, but Vincent said there are complications because of the ecological competition among species. If one population of snakes lives longer, then they have more time to grow to a substantial size.
Vincent is mainly studying the different ages of the snakes as well as how the prey size affects the demographics. He's observed that the older snakes, which are 30 to 40-years-old, grow much larger than snakes on other islands because there are large bird eggs present; eggs are easy prey because they are large and immobile. As the snakes grow larger, they have to turn to the eggs for food because they are so large that the lizards can hear when the snakes are nearby and have time to escape.
By tagging the snakes, Vincent can follow their growth as well as learn how long they are living. In the summers, Vincent collects the morphological, genetic and dietary data among the different populations to observe how the populations are evolving.
Vincent has two international researchers who help him tag the snakes each year. Unique patterns are cut into the scales on the snakes' bellies. He searches for the snakes with the unique scars on them and records data.
"The island is less than one square kilometer and hunting them down every year is the fun part," Vincent said. "I've been bitten by other snakes hundreds of times, but not by these snakes. They don't bite, which is different from snakes in North America."
Vincent has an interest in Japanese culture and became interested in studying the Colubrid snakes because they are very common, and there is an abundance of the reptiles. In a typical day, he can catch 30 to 40; with other species of snakes he can only catch three or four per day.
"They are just very majestic kinds of creatures," Vincent said. "In every facet of their biology, you can see evolution -- life history traits, head morphology -- and they are just a great test case for studying evolution.
"They are also easy to catch because they don't really move at all," Vincent continued. "It's part of being an insular animal. They are naïve, and they are not worried about predators. You can walk up on them, you can measure them, make them regurgitate their food and then find them the next year."
The snakes are also ideal for a longitudinal study because they have a long life span, and they are the longest living snakes that scientists have found. Nearly 75 percent of the population survives from year to year, and Vincent said the oldest snake he's tagged is 42 years old. Other species of snakes typically live on average 15 years.
Vincent said most of the snakes die of starvation or old age because no other animal preys on them. With the Colubrid snakes, Vincent said he believes it is the presence of the bird eggs that allow the reptiles to live longer.
Although the research won't directly impact people, Vincent said the evolution of body size is a very prominent theme in evolutionary biology. In addition, Vincent said humans can have an impact on the islands' animal population. There are conservation issues on the islands -- which are tourist destinations -- regarding non-native species that have been introduced to the islands that have attacked and killed other species.
"Some rodents were brought to the islands, and we've seen some interesting things," Vincent said. "The snakes eat rodents on the mainland but not on the Izu Islands, and we've seen a rapid change in snake body size after the rodent prey was introduced. It's a very rapid morphological change, just within three or four generations. There are very few cases that rival that as far as a field-based experiment, and this is one of the most rapid we can study."
Although Vincent will continue his research in Japan for years to come, he is mainly going to focus his attention on studying the highly enlarged femur on male Brikistalus magna grasshoppers.
"We hypothesized that males are combative with one another, and if a male wins a fight with another male, they get the female. They have large tarsal pads, so there is also conflict with the females. After he gets access to the female, he has to do something called forced copulation, and the males have these tarsal pads so that they can ride the female until she gives up. They can produce four Newton of force, which is more than most lizards can."
The grasshoppers produce more force relative to its size than Tyrannosaurus rex - the largest meat-eating dinosaur.
"They make T-rex look like a wimp," Vincent said.
The kick force observed is something very few grasshoppers can do. Vincent is studying the functional morphology of the kicking and clinging. We want to know the genetic basis for the kicking and determine if the males are genetically or environmentally induced to kick so strongly.
In the future, Vincent wants to learn if the grasshoppers have a limitation to the power of their kick, or if they can produce kicks that are three to four times more powerful than the current kick. He's applying for a National Science Foundation grant to make the grasshoppers' kick more exaggerated through breeding.
Eventually, he'd like to go into the field to conduct a selection experiment where the grasshoppers are tagged and tracked to learn which are producing the most offspring, and how long they survive.
"We want to know if the kicking is being shaped by natural selection," Vincent said. "We think it has a genetic basis. We think the males can kick harder, win the fights more and have more access to the females; the ones that can cling more can get more offspring."
