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

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 TB bacteria attack the respiratory system, causing coughing, fever and fatigue.

How do you think TB is transmitted?

The bacterium has a thick waxy coat, allowing it to lie dormant in the body for many years.

Incidence(thousands)

Prevalence(thousands)

Mortality(thousands)

Africa

Americas

Eastern Mediterranean

Europe

South-East Asia

Western Pacific

Total

Region

TB facts and figures: 2004

TB is one of the world’s most serious diseases.

2,573 3,741 587

363 466 52

645 1,090 142

445 575 69

2,967 4,965 535

1,925 3,765 307

8,918 14,602 1,692

1,000 people exposed to TB

Healthy people can fight TB

900 uninfected 100 infected

90 dormant TB 10 active TB

7 survive 3 die

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.

Infectious diseases usually decline as living conditions and standards of healthcare improve over time.

US TB deaths (1990–2004)T

B d

eath

s in

th

e U

S

30,000

25,000

20,000

15,000

10,000

50,000

0

19901991

19921993

19941995

19961997

19981999

20002001

2002

year

20032004

What is different about TB death rates in Africa compared with the rest of the world? They are increasing.

Deaths from TB infectionsd

eath

s (1

00,0

00s)

14

12

10

8

6

4

2

01995 1996 1997 1998 1999 2000 2001 2002 2003 2004

year

Africa

rest of world

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.

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 SystemTo 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.

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. 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.)

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.

There are three major types of environment. What are they?

land freshwater marine

How do organisms survive in such different environments?

Different types of environment

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.

What are a shark’s general adaptations to life in an aquatic environment?

A shark’s general adaptations

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

fins provide stability, power and control

What are a shark’s specific adaptations to life as an aquatic predator?

A shark’s specific adaptations

highly sensitive sense of smell that can detect drops of blood from miles away

lots of very sharp teeth that are constantly replaced

silver coloring underneath acts as camouflage

specialized sense organs can detect the sound, movement and electrical fields of other organisms

This increases the organism’s chance of survival and so increases its chance of reproducing and passing on its genes.

The importance of adaptationWhy 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.

How is a polar bear adapted to its extremely cold climate?

How is a polar bear adapted?

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

Other adaptations that polar bears have evolved to cope with conditions in the harsh polar environment include:

More polar bears adaptations

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

black skin is a good absorber of heat

How is a camel adapted to life in a very hot, dry climate?

How is a camel adapted?

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

wide feet spread out body weight on shifting sand

What other adaptations have camels evolved to cope with the harsh desert environment?

More camel adaptations

nostrils can be closed for protection during sandstorms

very varied diet, ranging from grass and bark to thorns and bones.

long eyelashes and furry ears prevent sand and dust from getting in

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. 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!

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”.

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

What is species?