Adaptation and Natural Selection

Adaptation and Natural Selection In a population of organisms there is always some genetic variability. This means that not all the individuals in a population are exactly alike. If individuals have one or more traits that help them survive to have more offspring more effectively, they have a selective advantage. This is an example of natural selection. Natural selection can lead to a trait showing up in more and more of a population – which leads, over time, to adaptation. Adaptation in a population of organisms occurs as a result of an adaptive trait. This is any inheritable trait that increases an organism’s chances of survival, so it can live longer and have more offspring – who may also have that trait. This is called differential reproduction. An adaptive trait can improve an animal’s ability to find food, make a safer home, escape predators, survive cold, or heat, or lack of water. It can be a physical trait, such as a skunk’s toxic spray, an armadillo’s armored skin, or a walking stick’s body shape which mimics a twig. An adaptive trait can also be a behavioral trait, such as a hedgehog rolling into a ball or a kangaroo rat staying perfectly still when a predator is near. Sometimes an adaptive trait is obvious and a common part of an organism’s life, like the breathtaking speed of a cheetah chasing prey or the silent wings of an owl. But an adaptive trait can also appear only when environmental circumstances drive need. An example of this is when the females of some species of snake, shark, or lizard hatch eggs with viable young without a mate or fertilization. This is called parthenogenesis. To summarize - there are three things that make natural selection work: 1) Genetic variability in a population, so that a trait appears that can give an advantage. 2) The trait must be inheritable so it can be passed on to the offspring. 3) The trait must lead to more surviving offspring – differential reproduction. ©Sheri Amsel • www.exploringnature.org Adaptive Traits - Authentic Performance You are an inventor working for the Department of Defense. You are told to learn how animals defend themselves in nature and make those adaptations work for the military to protect soldiers or people in every day life. Look at the adaptations of the armadillo, skunk, hedgehog, kangaroo rat, and walking stick. Describe how the adaptive traits these five animals can be copied and “adapted” for use by people. Which have already been used in every day life? Armadillo: ________________________________________________________________________________ _________________________________________________________________________________________ _________________________________________________________________________________________ _________________________________________________________________________________________ Skunk: ___________________________________________________________________________________ _________________________________________________________________________________________ _________________________________________________________________________________________ _________________________________________________________________________________________ Hedgehog: ________________________________________________________________________________ _________________________________________________________________________________________ _________________________________________________________________________________________ Kangaroo Rat: _____________________________________________________________________________ _________________________________________________________________________________________ _________________________________________________________________________________________ Walkingstick: _____________________________________________________________________________ _________________________________________________________________________________________ _________________________________________________________________________________________ Natural Selection and the Peppered Moth - Historical Anecdote In the 1800s through the early 1900s, burning coal for heat and power was common in England. In urban areas, this led to some pretty significant air pollution. Coal smoke blackened the trees until their bark was dark brown. This affected human health, but also had a profound affect on one local animal. The peppered moth, a light colored, speckled moth was nocturnal and spent the daylight hours resting, camouflaged on the bark of trees. Once the trees darkened with coal soot, the sleeping moths started to stand out against the darker bark and fell prey to hungry birds. Yet there was some genetic variability in the population of peppered moths resulting from a mutation that caused a darker moth phenotype. In 1848, people noticed a dark version of the moth had emerged and was able to blend in better on soot-blackened trees, so escaped detection by birds. The darker version of the moth had a selective advantage. Their darker color was an inheritable trait and these camouflaged moths were able to survive and have more young. This is an example of differential reproduction. This darker phase that protected them from predation was an adaptive trait. Adaptation had occurred. In 1956, England passed clean air legislation and the burning of coal was reduced throughout the country. Smokestacks were made taller to get pollutants further out into the atmosphere. Within a few years the trees, once blackened from coal smoke, began to take on their natural, light-colored bark again. As the trees got lighter, the dark peppered moths stood out against the bark and were easy targets for hungry birds. Now the lighter moths had the selective advantage. Over many generations, the peppered moth population was once again a light colored, speckled moth. Adaptive Traits in Insects - Matching Add the letters next to the insects of the type of adaptive traits they use to increase their chances for survival. (Hint: They may use more than one.) sphinx moth Blending Camouflage (blending colors) walkingstick B Pattern Camouflage (blending patterns) P preying mantis Disguise Camouflage (physically matching plant structures) katydid D twig caterpillar Adaptive Behavior (behaviorally matching plant structures) flower mantid thorn treehopper A LS4.B: Natural Selection: Natural selection leads to the predominance of certain traits in a population, and the suppression of others. Bt Crops - Modern Application of Artificial Selection Battling the effects of the European corn borer caterpillar has been an ongoing challenge for farmers that grow corn. It is estimated that it costs growers more than a billion dollars every year in pesticides and lost crops. When scientists discovered that the proteins in a very common soil bacterium, called Bacillus thuringiensis (Bt), were toxic to the corn borer, they helped develop the first bio-pesticide. This was sprayed on corn and other crops. It was considered safer than other pesticides because it only killed a small number of targeted pests. The Bt insecticide, when ingested by the caterpillar, binds to the wall of the gut and breaks it down, killing the insects. Then in 1995, scientists were able to move some of the genes from Bt into the corn plant itself. This became genetically engineered (GE) Bt corn (and other crops). Bt crops fight off not just the European corn borer, but other costly pests as well (e.g. rootworm, corn earworm, tobacco budworm, and bollworm). Bt was thought to be such a good match for a GE pesticide because testing showed that it only affects insects and not mammals, fish or birds. Because of the concern over the real health affects associated with synthetic pesticides, scientists hoped that the adoption of Bt crops would decrease the overall use of pesticides. This seems to have borne out, as the USDA released statistics that between 1995 2010, the amount of pesticide used on corn decreased 99%. Studies are still ongoing to assess any downside to the use of Bt crops. A 2015 publication by the National Institute of Health (NIH) supports the safety and benefit of using Bt crops. To date 81% of corn grown in the U.S. have Bt genes. European corn borer caterpillar Bt crops may be the oldest and most successful genetically modified (GM) food in U.S. history. MS-LS4-5. Gather and synthesize information about the technologies that have changed the way humans influence the inheritance of desired traits in organisms.