Examples of Selection in Action Antibiotic resistance in bacteria: the widespread use of antibiotics has led to the evolution of strains of bacteria that are resistant to many of our antibiotics.

What is tuberculosis? Tuberculosis (TB) is an infectious disease caused by the bacteria Mycobacterium tuberculosis. The bacterium has a thick waxy coat, allowing it to lie dormant in the body for many years. The TB bacteria attack the respiratory system, causing coughing, fever and fatigue. Photo credit: CAMR / AB Dowsett / Science Photo Library Colored scanning electron micrograph (SEM) of Mycobacterium tuberculosis bacteria, the main cause of human tuberculosis. These are Gram-positive rod-shaped bacteria. If a bacterium enters the lungs in a droplet coughed or sneezed by an infected person, it multiplies to form a localized bacterial colony (primary tubercle). Normally the tubercle is destroyed by the immune system. In a few cases, however, the bacteria then either spread through the lymphatic system to other parts of the body, which can be fatal, or lie dormant, only becoming active again many years later. Treatment is with antibiotics. Magnification unknown. How do you think TB is transmitted?

TB facts and figures: 2004 Incidence (thousands) Prevalence (thousands) Mortality (thousands) Africa Americas Eastern Mediterranean Europe South-East Asia Western Pacific Total Region 2,573 3,741 587 363 466 52 645 1,090 142 445 575 69 Teacher notes Data from the World Health Organization (www.who.int). Incidence = the number of new cases in a given period Prevalence = the total number of cases in the population at any one time Mortality = number of deaths A math-based exercise would be to ask the students to calculate the percentage incidence, prevalence and mortality each region contributes to the total TB burden. 2,967 4,965 535 1,925 3,765 307 8,918 14,602 1,692 TB is one of the world’s most serious diseases.

Healthy people can fight TB Only 10% of healthy people exposed to TB develop the active disease. People most at risk are those who: have a weakened immune system live in squalid or overcrowded conditions. 1,000 people exposed to TB 900 uninfected 100 infected 90 dormant TB 10 active TB 7 survive 3 die

US TB deaths (1990–2004) Infectious diseases usually decline as living conditions and standards of healthcare improve over time. 30,000 25,000 20,000 15,000 TB deaths in the US 10,000 50,000 Teacher notes Data from the World Health Organization (www.who.int). 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 year

Deaths from TB infections What is different about TB death rates in Africa compared with the rest of the world? They are increasing. deaths (100,000s) 14 12 10 8 6 4 2 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 year Africa rest of world Teacher notes Data from the World Health Organization (www.who.int).

How is TB treated? TB is treated with a 6-month course of antibiotics. Three or four different antibiotics are taken daily to fight the many drug-resistant strains. Why does the treatment last for 6 months? To ensure that dormant bacteria are also killed. Photo credit: Global Alliance for TB Drug Development (www.tballiance.org) Teacher notes Political instability and limited access to hospitals and health centers in developing countries make prolonged treatment regimes difficult. The medicines are expensive to supply. Also, once people start feeling better they stop taking the medicines. They can pass the bacterium to other people, and the bacterial populations that survive the initial treatment can develop resistance. The BCG vaccine for TB was developed in 1921. It is 50-80% effective, but is too expensive for use by developing countries to vaccinate whole populations.

Directly Observed Treatments System To lower the costs of treating TB in developing countries, healthcare workers are paid to make sure patients swallow every pill they are prescribed. This is the Directly Observed Treatments System (DOTS). DOTS helps prevent drug-resistant TB from increasing, and limits the number of patients who relapse and need more expensive treatments. Photo credit: Global Alliance for TB Drug Development (www.tballiance.org) Drug resistance can evolve in just three months but new antibiotics can take years to develop.

Warfarin is a rat poison which kills rats by stopping blood clotting Warfarin is a rat poison which kills rats by stopping blood clotting. Many rats are now resistant to warfarin and have developed an enzyme that still allows their blood to clot even in the presence of the drug!

Copper-tolerant plants have evolved in areas where the land has been mined for copper. Copper is a metabolic poison and usually kills plants, but some have evolved a mechanism to transport the copper out of their cells.

Practice Find an example of a variation in a real organism, something that is distinctive. Describe how this variation is beneficial to the success of this organism in it’s particular environment. Hypothetically alter the organism’s environment enough to make this variation no longer beneficial, but detrimental to the organism’s success. Describe this change and its effects.

How do we know natural selection can change a population? we can recreate a similar process

Artificial Selection For thousands of years, humans have practiced selective breeding, by crossing animals or plants with desired characteristics in the hope that the offspring will inherit the best features. Artificial selection and natural selection have the same end in mind: passing on favorable characteristics. However, artificial selection is human’s way of speeding up the process.

Artificial selection provides a model that helps us understand natural selection.

High milk-yielding cows are mated with fast-growing bulls to produce calves that grow quickly and produce a lot of milk.

Pedigree dogs have been bred for certain desirable features.

Adaptation Evolutionary process whereby a population becomes better suited to its habitat Takes place over many generations.

Adaptation Structural adaptations are those that create a morphological (physical) difference (ex. A mountain goat’s feet have developed for mountainous terrains, or the shape of legs in different animals to run faster or jump higher.)

Camouflage Cryptic coloration (blending into environment) Countershading (dark on top, light on belly region) Warning coloration (bright colors) Mimicry (one organism looks like another, more dangerous, one

Adaptation Evolutionary process whereby a population becomes better suited to its habitat Takes place over many generations.

MISCONCEPTIONS Changes in the body What about behavior? Changes in the body to fit a location Do individuals adapt? Are changes happening because they are needed?

Misconception: “Natural selection involves organisms ‘trying’ to adapt

Natural selection leads to adaptation, but the process doesn’t involve “trying.” Natural selection involves genetic variation and selection among variants present in a population. Either an individual has genes that are good enough to survive and reproduce, or it does not—but it can’t get the right genes by “trying.”

Misconception: “Natural selection gives organisms what they ‘need.’ ”

Natural selection has no intentions or senses; it cannot sense what a species “needs.” If a population happens to have the genetic variation that allows some individuals to survive a particular challenge better than others, then those individuals will have more offspring in the next generation, and the population will evolve.

Different types of environment There are three major types of environment. What are they? land freshwater marine Photo credit: © 2009 Jupiterimages Corporation How do organisms survive in such different environments?

What is adaptation? All organisms are adapted to life in general, such as having legs for walking, wings for flying or leaves for photosynthesizing. These are general adaptations. Organisms also have specific adaptations. These are special features or behaviors that have evolved to make an organism particularly suited to its environmental niche.

A shark’s general adaptations What are a shark’s general adaptations to life in an aquatic environment? streamlined shape to reduce friction when moving through water gills have a large surface area so that oxygen can be extracted from the surrounding water Photo credit: © 2009 Jupiterimages Corporation fins provide stability, power and control

A shark’s specific adaptations What are a shark’s specific adaptations to life as an aquatic predator? specialized sense organs can detect the sound, movement and electrical fields of other organisms highly sensitive sense of smell that can detect drops of blood from miles away lots of very sharp teeth that are constantly replaced Photo credit: © 2009 Jupiterimages Corporation Teacher notes A shark’s teeth are not fixed to its jaw but embedded directly into the flesh. Its teeth are constantly replaced as they fall out or are broken, so that a shark may get through thousands of teeth during its lifetime. The lower teeth are mainly used for holding prey, while the upper teeth are used for cutting. The shark’s specialized sense organs include: lateral lines – a row of fluid-filled sensory canals along each side of the shark. These can detect movement and changes in pressure from about 100m away. ampullae of Lorenzini – small pits in the shark’s snout that detect tiny electrical fields, such as those associated with muscle contraction of prey. auditory system – can detect the sound created by injured prey from over 1 mile away. silver coloring underneath acts as camouflage

The importance of adaptation Why is it important that organisms are adapted to their environment? The better adapted an organism is to its habitat, the more successful it will be when competing for resources such as food and mates. This increases the organism’s chance of survival and so increases its chance of reproducing and passing on its genes.

How is a polar bear adapted? How is a polar bear adapted to its extremely cold climate? white greasy fur repels water and acts as camouflage thick fur and body fat insulate from the cold large, wide feet spread the body’s weight and act as good paddles and snow shoes Photo credit: © 2009 Jupiterimages Corporation

More polar bears adaptations Other adaptations that polar bears have evolved to cope with conditions in the harsh polar environment include: small ears and small body surface area to volume ratio reduces heat loss eyes have brown irises to reduce the glare from the Sun’s reflection Photo credit: © 2009 Jupiterimages Corporation black skin is a good absorber of heat

How is a camel adapted? How is a camel adapted to life in a very hot, dry climate? fat is stored in the hump to reduce overheating little water is lost through sweating or urination long, thin legs help to increase body surface area and increase heat loss Photo credit: Roma Rishkin wide feet spread out body weight on shifting sand

More camel adaptations What other adaptations have camels evolved to cope with the harsh desert environment? long eyelashes and furry ears prevent sand and dust from getting in nostrils can be closed for protection during sandstorms Photo credit: Bas Silderhuis very varied diet, ranging from grass and bark to thorns and bones.

Other Adaptations Biochemical adaptations are those that help to regulate a function of the body. Examples: amount of melanin produced in the skin serves as a protection against UV radiation production of a special fat that bears use as food during hibernation

Kangaroo rat: adapted to desert life Kangaroo rat: adapted to desert life. Conserve water in their bodies—don’t sweat, and only hunt at night. Their bodies are so good at conserving water they don’t even need to drink!

Behavioral Adaptations In simple animals, behavior is governed by instinct (pre-programmed by an animal’s genes) In more complex animals, instinctive behavior is often modified by learning. Many forms of behavior help animals to survive .

Behavioral Adaptations Hibernation, which enables animals to survive cold and food shortages in winter Estivation (burrowing in the cool mud) which allows animals to survive drought and heat in summer Group defense is common in herding mammals, which sometimes form a protective ring around their young

Behavioral Adaptations Individual defensive behavior is often based on threatening gestures that make an animal look larger or more dangerous than it actually is. Some animals also “play dead”.

What is species? Species: a group of individuals that look similar and whose members are capable of producing fertile offspring in the natural environment