Read this story about a recent example of evolution in action, with a new trait developing in a species called the Cane Toad in Australia. Use details in the text to respond to the following questions:
1. What was the mutation that occurred in the Cane Toads in Australia?
2. Why is the trait caused by that mutation considered an adaptive trait?
"Huge poisonous toads have invaded Australia! Humans brought cane toads from Asia to Australia in the 1930s, hoping the toads would eat beetles that were destroying crops. Unfortunately, the toads didn’t eat many beetles. They ate almost anything else that could fit into their mouths, however. They big toads grow up to 22 centimeters (9 inches) long and weigh up to 1.8 kilograms (4 pounds). Cane toads are extremely poisonous, and no Australian predators can survive eating them. Without predators in their new environment, the cane toad population began growing and spreading. Today, cane toads are common in areas more than 1,500 kilometers (932 miles) from the place where they were first introduced to Australia.
Because there are so many cane toads in Australia, they compete with each other for food. The cane toads are eating everything in sight, so food becomes scarce in any area where they live. To survive, cane toads have to keep moving into new areas with more food sources. The first toads to reach new territory get to eat all the food they want. Slower toads are stuck with whatever is left.
Recently, Australian scientists have been finding cane toads with bigger, more muscular legs. These bigger legs can be traced back to mutations that changed the toads’ genes. Scientists compared the big-legged toads to ordinary cane toads. They identified several gene mutations that gave the cells instructions to make protein molecules that were different from the protein molecules that other toads could make. These new protein molecules affected the cane toads’ legs, increasing the leg size and strength. Having bigger legs is an adaptive trait that helps cane toads survive in an environment where there isn’t much food to go around. Bigger, stronger legs help these toads outrun other cane toads and be the first ones to get to the food in new areas. With better chances of getting food, big-legged toads are more likely to survive and reproduce. Because of this, they are also more likely to pass on their mutated genes to their offspring. Along with these mutated genes, they pass on their adaptive traits."