Natural Selection

Question 1

Where did Darwin get his idea for evolution?

Answer 1

The galapagos islands

Question 2

What is natural selection?

Answer 2

• living organisms that reproduce sexually show great variety in their appearance
• organisms produce an excess of offspring (many of the offspring of an organism do not survive to reproduce themselves) so there is always a struggle for survival
• organisms that inherit characteristics that give them an advantage in this struggle are more likely to survive and pass on the desired feature to their offspring
• organisms that inherit characteristics that put them at a disadvantage will be more likely to die out before they can reproduce

Question 3

What is evolution?

Answer 3

A change in the genetic composition of a population of organisms over several generations as a result of natural selection acting upon variation, bringing about adaptations and in some cases leading to the development of new species. The variation may be the result of sexual reproduction, random mutation, inbreeding or hybridisation

Question 4

What is the modern statement of the theory of evolution and what does it suggest?

Answer 4

• the evolution of organisms occurs as a result of the differential fertility and survival of organisms with different genotypes (genetic variation) leading to different phenotypes within a specific environment. Those alleles that deliver the adaptations best suited to the environment are most likely to be passed on to the next generation
• this definition suggests that a disadvantageous trait doesn’t mean that the individuals are wiped out, they just may be less succesfull at reproducing. It also recognises that advantages and disadvantages of a particular trait will differ with the environment. The changes in the frequency of a particular allele in a population is almost always driven by a change in the environment or an organism moving to a different environment

Question 5

What is ecology?

Answer 5

The study of the interactions of organisms with each other and with the environment in which they live

Question 6

What is a niche?

Answer 6

The role of an organism within the habitat it lives

Question 7

What will successful species be well adapted to?

Answer 7

It’s niche

Question 8

What are anatomical adaptations and give examples

Answer 8

• Involves the form and structure of an organism
• E.g. the thick layer of blubber in seals and whales and the sticky hairs of the sundew plant which enable it to capture insects ready to digest

Question 9

What are the three types of adaptations?

Answer 9

Anatomical, physiological and behavioural

Question 10

What are physiological adaptations and give examples

Answer 10

• They involve the way the body of the organism works and include differences in biochemical pathways or enzymes.
• diving mammals can stay under-water much longer than non-diving mammals without drowning. Once they are under water their heart rate drops dramatically, so that blood is pumped around their body less often and the oxygen in their blood is not used as rapidly

Question 11

What are behavioural adaptations and give examples

Answer 11

• involve changes to programmed or instinctive behaviour making organisms better adapted for survival.
• for example:
- many insects and reptiles orientate themselves to get the maximum sunlight on their bodies when the air temperature is relatively low. This allows them to warm up and move fast enough to feed and escape predators.
- social behaviour such as hunting as a team or huddling for warmth
- migrations and courtship rituals

Question 12

What adaptations do butterfly’s have?

Answer 12

• the underside of butterflys wings is a dull, broken pattern of greys and browns. This anatomical adaptation gives them excellent camoflauge against the costal heathlands where they live, however their shadows can be seen if it is sunny
• so they also follow the sun, changing their orientation throughout the day so their shadow is always as small as possible. (A behavioural adaptation). This also helps then to control their body temperature

Question 13

What adaptations have the Arthrobotrys anchonia have to capture and feed neamatodes?

Answer 13

• it actively lassoes nematodes.
• it traps them in hyphal loops called constriction rings as they pass involving both structural and phyisological adaptations
• 3 fungal cells form a ring and when a nematode moves into it, a combination of wall changes and the osmotic potential of the cell results in water moving in fast. Within 0.1 seconds the ring inflates and holds the nematode in its grip
• within hours the fungus grows more hyphae that penetrate rhe body of the nematode and digest it, absorbing the nutrients and transporting them within the fungus
• the nematodes provide the missing nitrates

Question 14

What does natural selection lead to?

Answer 14

Adaptations that give individuals an advantage in a particular niche. If conditions change, those adaptations may notnbe successful, and the selection pressure will change. This may lead to changes in the species and ultimately to the formation of new species

Question 15

Why will the characterisitics of individuals that are not well adapted to their environment become less common in the population?

Answer 15

Because they may not survive to reproduce or may produce fewer offspring than those that are better adapted

Question 16

If the niche occupied by an organism changes due to changes in the enviroment different characteristics may make an individual more successful and natural selection may favour them. What is this called?

Answer 16

The selection pressure changing

Question 17

What is the selection pressure?

Answer 17

The pressure exerted by a changed environment or niche on individuals in a population, causing changes in the population as a result of natural selection

Question 18

How did oysters adapt to change?

Answer 18

In 1915 in the Malpeque Bay there was a disease that nearly wiped out all the oysters. However a few of the oysters carried an allele giving them resistance to the disease. Because only individuals that had this allele were able to survive and reproduce the frequency of this gene in the population increased rapidly. By 1940 there was a large population of oysters again but they contained a high frequency of the disease resistant alleles

Question 19

What happened with natural selection with moths?

Answer 19

• the typical form of B. Betularia moth id a creamy speckled moth found in the British woodlands.
• in the 18th century black specimens (melanics) resulting from a random mutation were captured occasionally. But they were easily visible against the pale bark of the trees so this selection pressure meant that the frequency of the dark allele in the population stayed low
• in the mid-nineteenth century soot and smoke from the factory chimneys of the Industrial revolution darkened the bark of the trees and rhe surfaces of buildings. As a result the melanic form of the morh was at a selective advantage and the frequency of the allele within the population began to increase. This process became known as industrial melanism

Question 20

How was it that discovered the process of industrial melanism?

Answer 20

Bernard Kettlewell

Question 21

What reversed the trend of industrial melanism?

Answer 21

Anti-pollution legislation that was passed in the 1960s resulted in cleaner paler buildings and trees again, so the natural selection pressure has moved back in favour of the typical moth and its allele has increased in the population again

Question 22

Apart from survival in a particular habitat what else does natural selection adapt to?

Answer 22

• selecting for reproductive success:

• male African long-tailed widow birds have very long tails that appear to have very little use except in the mating season to attract mates
• thick skulls and enourmous horns
• tail of the peacock
• insect pollinated flowers have adaptations to bring pollinators to the plant

Question 23

What is directional selection?

Answer 23

Natural selection showing a change from oke dominant phenotype to another in response to a change in the environment- one phenotype is selected for over all the others

Question 24

Where does directional selection occur?

Answer 24

Anywhere that environmental pressure is applied to a population

Question 25

What is a gene pool?

Answer 25

All of the alleles of all of the genes in a population

Question 26

Why can the medicines we develop to destroy pathogens quickly become ineffective?

Answer 26

Because adaptation and natural selection are also seen in pathogens (bacteria and virus)

Question 27

Who did the work that resulted in the mass production of penicillin?

Answer 27

Alexander Fleming, Howard Fporey and Ernst Chain

Question 28

Why did Penicillin stop working?

Answer 28

By the 1960s many bacteria had become resistant to penicillin. A small percentage of the original populations must have carried a random mutation giving them resistance to damage by penicillin (often an enzyme called penicillinase that splits the penicillin molecule). This adaptation gave bacteria a great advantage and so, as a result of natural selection resistance to penicillin became more and more prevalent in bacterial populations

Question 29

What was the antibiotic that was produced after bacteria became penicillin resistant and did it work?

Answer 29

• methicillin

* it worked for a while but then methicillin resistance spread rapidly through bacterial populations

Question 30

What are factors that could contribute to the problem of antibiotics not working?

Answer 30

• antibiotics are too widely prescribed and used
• wide-spectrum antibiotics are often used to make sure if they have an effect, rather than to determine if an infection is bacterial and what bacteria are involved
• people do not complete courses of antibiotics, which makes it easier for resistance to develop
• in some countries antibiotics are widely used in the food chain
• a lack of basic hygiene in hospitals and care homes hae encouraged the spread of antibiotic resistant organisms such as MRSA
• there is no big financial incentive for pharmaceutical companies to develop new antibiotics as new antibiotics will be used sparingly to prevent the development of resistance

Question 31

What are some of the ways that we hope to overcome the problems of antibiotic resistance?

Answer 31

• reducing the use of antibiotics
• better education so people understand that they do not always need antibiotics
• reducing the use of antibiotics in farm animals
• the longitude prize 2014 set the challenge to develop a quick test confirming bacterial infections in the doctors surgery, making ot easier to prescribe the best antibiotic for maximum effect
• DNA sequencing will help identify bacteria and find new ways of targeting them with antibiotic drugs, and genetic engineering will enable large amounts of new drugs to be produced
• development of new antibiotics

Question 32

What is a species?

Answer 32

A group of organisms sharing a number of structural and evolutionary features which are capable on interbreeding to produce fertile offspring

Question 33

What is speciation?

Answer 33

The formation of a new species

Question 34

Why does speciation happen?

Answer 34

• the result of the isolation of parts of the population:
- reproductive isolation: the two isolated populations experience different conditions, and this in turn means that natural selection acts in different directions on the two populations. As a result over time both the genotype and the phenotype of the isolated groups will change. This will continue to the point where even if members of the split population are reunited they can no longer successfully interbreed
• hybridisation: particularly common in plants. Sometimes two closely related species can breed and form fertile hybrids that are successful in their own right and may be better adapted to their niche. In some cases these hybrids do not produce fertile offspring if they are crossed back to their parent plants so a new species is formed, which may out-compete the parent plants

Question 35

Whaat are the isolating mechanisms?

Answer 35

• geographical isolation: a physical barrier such as a river of mountain range seperates individuals from an original population
• ecological isolation: two populations inhabit the same region, but develop preferences for different parts of the habitat
• seasonal isolation: the timing of flowering or sexual receptiveness in some parts of a population drifts away from the norm for the group. This can eventually lead to the two groups reproducing several months apart
• behavioural isolation: changes occur in the courtship ritual, display or mating pattern so that some animals do not recognise others as being potential mates. This might be due to a mutation that changes the colour or pattern of markings
• mechanic isolation: a mutation occurs that changes the genitalia of animals making it physically impossible for them to mate successfully with only some members of the group, or it changes the relationship between the stigma and stamens in flowers making pollination between some individuals unsuccessful

Question 36

What is Allopatric speciation?

Answer 36

It takes place when populations are physically or geographically seperated in some way. The result of physical isolation of populations continue to occur as a result of natural changes, for example and islands form and dissapear, as ice floes melt, rivers change course and lakes either dry up or appear. Some of the changes that result in allopatric speciation are the result of human interventions such as dams, roads and cities

Question 37

Which island has many endemic species and name some of these

Answer 37

• Madagascar

* giant baobab tree and ring tailed lemurs

Question 38

What does it mean if a species is endemic?

Answer 38

That it evolves in geographical isolation and is only found in one place

Question 39

Whybare there four seperate species of desert pupfish in the nevada desert?

Answer 39

It used to have many springs, streams and rivers but around 50 000 years ago the climage changed qnd the area became dry and arid. Most of the water dried up but small individual ponds and springs remained. The fish trapped in this area could no longer inter-breed and evolved independently.

Question 40

Allopatric speciation is frequently followed by adaptive radiation. When does this take place?

Answer 40

When one species evolves rapidly to form a number of different species, which all fill different ecological niches

Question 41

How did adaptive radiation take place with Australian marsupials and monotremes?

Answer 41

• they have two groups of mammals: the marsupials which protect their young in pouches amd the monotremes which lay eggs
• most of the world has placental mammals
• until about 5.5 million years ago australia was joined to the rest of the world when the only mammals were monotremes and marsupials
• after Australia seperated the marsupials evolved to fill an enourmous range of niches
• on other continents plavental mammals evolved and mostly replaced the marsupials but did not reach Australia

Question 42

How did adaptive radiation take place with Darwin’s finches?

Answer 42

• on the Galapagos islands there are a number of feeding niches for birds, for example small seeds, large nuts and insects living in rotten bark. The original finches that arrived on the islands were of a single species
• within the birds that arrived on the island there would have been variation in alleles and characterisitics and different niches on the islands would have favoured individuals with different variations. E.g. a bird with a small strong beak would be ideally adapted to eating seeds
• by exploiting different niches the finches avoided competing for the same relatively scarce food resources. As a result at least 14 different species of finch have evolved over several million years
• because food was such an important selection pressure it was important to mate with a finch with a similar shaped beak to pass on the advantageous characterisitic, so there was a selection pressure on choosing the right kind of mate. As a result any phenotypic and behavioural that made choosing the right mate easier were also selected, so the species look different

Question 43

When does sympatric speciation take place?

Answer 43

Between populations of a species living in the same place that become reproductively isolated by mechanical, behavioural and seasonal changes. Gene flow continues to some extent as speciation takes place. Sympatric species are closely related and occupy overlapping ranges.

Question 44

Why are scientists reluctant to classify examples of sympatric speciation?

Answer 44

• they suggest that when speciation occurs there is always an adaptive preseure which drives the formation of two species and produces a barrier between the population
• DNA evidence often shows that species originally thought to be the result of sympatric speciation actually show evidence of cross-breeding or niche seperation at some point

Question 45

There are two species of palm tree endemic to Lord Howe Island in New South Wales which appear to be an example of pure sympatric evolution. Why is this?

Answer 45

• The island is so tiny that geographical isolation is not possible.
• The trees are wind pollinated and produce lots of pollen so they could interbreed if they were not seperate species.
• The type of soil they grow on seema to influence the timing of flowering and could be the driver for speciation
• DNA evidence supports the theory of sympatic speciation for these trees

Question 46

What is the example of sympatric speciation in progress in the US?

Answer 46

• until the mid-1800s the tint fruit fly Rhagolettis pomonella lived only on hawthorn bushes, laying eggs on the fruits. The larvae responded to the smell of hawthorns and return as adults to reproduce
• over 150 many huge apple orchards were planted. Genetically apple trees are quite similar to Hawthorns.
• some female R. pomonella laid their eggs on the apples either by mistake or because they could not find the Hawthorns.
• the larvae did not do particularly well but some survived to adulthood
• these flies responded to the smell of apples and a breeding group of apple-dwelling flies evolved.
• now there are two breeding groups of R. pomonella in the Hudson River Valley.
• the two populations show reproductive isolation because they only mate with flies on the same food source.
• the apple-dwelling flies have adapted to life on apple trees so they mow emerge from their puppae at a different time of the year. Apples provide more food and better protection for the maggots from parasitic wasps
• scientists have analysed the frequency of a number ofnalleles in the flies and have found they are becoming increasingly different. It seems that two entirely different species will evolve which will no longer intertbreed

Question 47

What types of speciation do the chidchild fish of the African Lakes show?

Answer 47

Allopatric speciation, adaptive radiation and sympatric speciation

Question 48

What do the Cichild fish show variety in?

Answer 48

Shape, size, colour, feeding habitats, courtship displays and breeding habitats. They include a number of species that are mouth brooders: they carry their eggs in their mouths until they hatch and then allow the tiny fish to retreat back into their mouth when danger threatens

Question 49

Why does speciation take place within lakes independently?

Answer 49

Because a lake in a largely enclosed environment so within a lake there will be many different habitats and microhabitats but no readily available way of moving to another lake

Question 50

What does Molecular Phylogent suggest about the evolution of the different species of cichild fish?

Answer 50

That the great majority of cichild fish evolved much more recently than the lakes were formed. The fish in each lake are more closely related to the other species of fish endemic in their own lake than they are to the fish in the other lakes. This suggests that the fish have diversified in the individual lake systems after they have become seperated form eachother

Question 51

In Lake Malawi what does DNA evidence suggest?

Answer 51

That all of the species have evolved from a common ancestor within the last 5 million years. They have less than 6% difference in their mitochondrial DNA. The original ancestor is thought to resemble the swamp-dwelling fhish Astatotilapia calliptera which is the only one the the cichild species found in Lake Malawi that is also found in other lakes

Question 52

What have the cichilds that now fill Lake Malawi evolved to fill?

Answer 52

Almost every feeding niche in a living example of adaptive radiation on a grand scale.

Question 53

What happened with speciation in Lake Victoria?

Answer 53

• it is much younger than the two other big lakes and has dried out 3 times during it’s 400 000 year history.
• the last time it refilled was only 15 000 years ago. The few cichild species that survived the dry period have evolved to produce the 500 or more species scientists have so far recorded in the lake today
• by identifying micro-environments and looking at the alleles that have changed, scientists are unravelling the selection pressures that have driven this fast and rapid evolution
• they have discovered the cloudiness of the water can drive the evolution of species with similar feeding habitats.
• research shows that species living in deeper cloudier water have different optical pigments in their eyes than fish with similar feeding habitats living in the clearer shallower water. The females are less affected by colour in their choice in mates ans the males tend to have red and yellow display colours (penetrate into cloudy water)

Question 54

How does lake Barombi Mbo show sympatric speciation in cichild fish?

Answer 54

• ir is a small lake formed in the crater of a volcano
• it contains 11 species of cichilds. Molecular phylogenetic studies based on both nuclear and mitochondrial DNA show that the species are more closely related to eachother than to any other cichilds. The closest relative of these 11 species is the only fish found in the streams surrounding the lake. This suggests the fish entered the lake from the streams perhaps during a flood and then have evolved into 11 species all in the same small volume of water without any geographical barrier between them. They have evolved to fufil different niches

Question 55

How does the small Lake Ejagham show sympatric speciation?

Answer 55

• it has a number of different habitats
• it contains two closely related species of cichils. The smaller species feed on microscopic animals in the deeper end of the lake. The larger species feeds near the edges on invertebrates.
• they breed as well as feed in different habigats, so although they are in the same small lake they are reproductively isolated and have formed seperate species

Question 56

Why is the diversity of Lake Victoria under threat?

Answer 56

Because Nile perch and water hyacinths were introduced. This changed the ecology: the nile perch is a voracious predator and water hyacinths grow and cover the surface. Deforestation leads to soil erosion to the water has beckme silt and cloudy. As a result the cichilds are under threat and their numbers have been substantially reduced