Evolutionary Biology (Gareth Jenkins 1-6)

Question 1

What are the 4 postulates of evolution by natural selection?

Answer 1

1) There is VARIATION- mutations creating new alleles & shuffling of alleles.
2) Traits are HERITABLE- genes are passed on independently of other genes.
3) OVERPRODUCTION of offspring- more produced than survive.
4) Natural selection is NOT RANDOM

Question 2

What was determined by Clausen, Keck & Heisey in 1948?

Answer 2

3 yarrow cuttings from the same plant were grown at different altitudes and showed dramatic differences in height.
This showed that the environment has an effect on development too.

Question 3

What is discrete variation and continuous variation?

Answer 3

Discrete: where single genes affect the expressed trait e.g. cystic fibrosis

Continuous: affected by many loci e.g. height.

Question 4

3 ways by which variation in a population can be generated.

Answer 4

Recombination between existing chromosomes in meiosis.

Migration (gene flow)- provides movement of alleles between populations.

But NEW variations are only produced by mutations.

Question 5

What is the rate of spontaneous mutations in humans?

Answer 5

Spontaneous mutation rate per gene = 0.00001
But 24,000 genes in humans so in a diploid zygote, the rate is 0.48. (in a population of 100 people, 48 new mutations per generation).

Question 6

What are pleiotropic genes?

Answer 6

Genes which influence more than one trait.

In Drosophila, one locus affects circadian rhythms and wing beat patterns in courtship. Mutations here will have greater consequences.

Question 7

What type of mutation is it called when purine or pyrimidine is replaced with a pyrimidine?

Answer 7

Transition (most common in evolutionary change)

Question 8

What is a transversion mutation?

Answer 8

purine substituted with a pyrimidine or vice versa

Question 9

The ratio of non-synonymous to synonymous mutations provides a measure of what?

Answer 9

Rate of evolutionary change

If >1 then = positive selection
If<1 then = stabilising selection
If = 1 then = neutral

Question 10

What is a significant difference between the FoxP2 gene of humans and chimps?

Answer 10

There are 2 non-synonymous changes (no synonymous) so the rate of evolutionary change = 2:0

Question 11

Give an example of a heterozygote advantage

Answer 11

carriers of sickle cell anaemia are more resistant to malaria. blood cells only sickle if O2 in blood decreases; this occurs when infected with Plasmodium falciparum. the sickle cells are destroyed with the parasite.

Question 12

Give an example of frequency-dependent selection

Answer 12

2 forms of scale-eating fish- right mouthed or left mouthed.
Phenotype has a higher fitness when rarer as it is an advantage over the others.
an equal number of forms but numbers fluctuate as prey learn to defend against the most abundant type.

Question 13

What are the 3 types of selection?

Answer 13

Directional- fitness decreases/increases with trait magnitude
Stabilising- intermediate traits have the highest fitness.
Disruptive- extreme traits selected for (important for diversification of species).

Question 14

Give an example of each of the 3 types of selection

Answer 14

Directional: Bill size in medium ground finches.
Stabilising: Birthweight
Disruptive: bill size in black-bellied seed crackers( 2 distinct morphs which feed on two different sizes of seed).

Question 15

Why are the Galapagos islands great for selection?

Answer 15

They form an archipelago so there are lots of chances for isolation. Big seasonal fluctuations over the years have to lead to population crashes and diversification.

Question 16

Give an example where anthropogenic activity has caused directional selection.

Answer 16

Palm seed size decreased in deforested areas due to the decline in bird species, as they relied on birds for dispersal.
(Galetti et al. 2013)

Question 17

What is microevolution and macroevolution?

Answer 17

Microevolution is responsible for the variation within a generation, whereas macroevolution concerns differing of species.

Question 18

What is the Biological Species Concept?

Answer 18

it incorporates reproductive isolation and highlights lack of gene flow.
“If populations of organisms do not hybridize, or if they fail to produce fertile offspring when they do, then they are reproductively isolated and can be considered as a good species.

Question 19

What are 3 problems with the Biological Species Concept?

Answer 19

• many species can’t be tested for reproductive isolation (especially if extinct).
• Irrelevant to asexual taxa.
• Difficult to apply to plants where populations are divergent but there’s still lots of hybridization.

Question 20

What is the Phylogenetic Species Concept?

Answer 20

Species are defined as the smallest diagnosable monophyletic group.

Question 21

What are 2 problems with the Phylogenetic Species Concept/

Answer 21

• Phylogenies are only available for some species and different characters produce different phylogenies.
• Small genetic differences may be irrelevant to whether taxa can interbreed.

Question 22

What is the Morphospecies Concept?

Answer 22

Groups organism based on body shape and other structural features. Good for palaeontology where the other two concepts can’t be applied.

Question 23

What are 3 problems with the Morphospecies Concept?

Answer 23

• Some species are polymorphic (Salmon & Peacocks etc)
• Some species have morphological features too small to measure (bacteria).
• Hard to apply to cryptic species. (reproductively isolated but not due to morphology e.g. calls in pipistrelle bats)

Question 24

Which gene has been used in DNA barcoding for identifying many new cryptic species?

Answer 24

Mitochondrial CO1; it varies a lot between species, but not within species.

Question 25

Why are Skipper butterflies cryptic species?

Answer 25

Adults all look very similar but there are differences between caterpillars. 2 caterpillar species are grass feeders (generalists) and another two species feed on two different genera of palm (specialists).

Question 26

Evaluate the phrase ‘Are red wolves worth the conservation effort?’

Answer 26

• 3 closely related canids in the U.S.; Grey wolf, Red wolf and Coyote.
• Skulls of red wolves before 1930 had distinct cranial characteristics, suggesting a morphospecies.
• However, skulls after 1930 resemble coyotes- possibly due to a hybridization event when they couldn’t find mates.
• But mtDNA analysis and nuclear microsatellites suggest that red wolves are in fact a hybrid between grey wolves and coyotes.
• This means they’re not technically a species under the BSC or the PSC.

Question 27

What evidence supports the existence of two species of Pipistrellus bats?

Answer 27

• two phonic types (45kHz and 55kHz)
• Both found in the same geographic area but are not an example of sympatric speciation.
• Bats which echolocate at 55 kHz were repelled by a 55kHz social call, instead of being attracted to it.
• Allows for individuals to defend food patch.
• Can’t distinguish between skulls, but the acoustics are more important for bats.
• BSC and PSC support 2 separate species.

Question 28

Is cladogenesis involved with sympatric or allopatric speciation?

Answer 28

Allopatric

Question 29

Name 5 prezygotic barriers

Answer 29

• Temporal isolation
• Habitat isolation
• Behavioural isolation
• Mechanical isolation
• gametic incompatability

Question 30

Name 4 postzygotic barriers

Answer 30

• Zygote death
• Hybrid inviability
• Hybrid sterility
• General reduced fertility

Question 31

Briefly explain allopatric speciation in 4 stages

Answer 31

1) 2 populations with gene flow
2) Reproductive barrier appears; variant types appear
3) Genetic drift and selection pressures isolate gene pools.
4) Barrier removed; reproductive isolation. (prezygotic barriers may continue to evolve during secondary contact)

Question 32

What is reproductive displacement?

Answer 32

When mating signals are more pronounced in contact zones- differences intensify to increase mating success.

Question 33

What is reinforcement?

Answer 33

selective reduction of hybrids e.g. by assortative mating

Question 34

Which example supports natural selection, but contradicts genetic drift?

Answer 34

Three-spined sticklebacks

Limnetic (open water) and benthic forms evolved in lakes by a double invasion event. Each time lead to a different species.

Question 35

What 5 things can accelerate speciation?

Answer 35

• reduced gene flow
• low dispersal rates
• strong sexual selection
• lots of niches
• bottleneck events.

Question 36

What is the theory behind the rapid speciation of cichlids?

Answer 36

• Bright colouration provided strong sexual selection
• Elaborate courtship
• Rapid changes in water levels (& temperature) creating isolating pools

Question 37

Give an example of allopatric speciation

Answer 37

Snapping Shrimps in Panama

land bridge appeared and separated populations; one on the Pacific side and one on the Caribbean side.
mtDNA analysis found 7 pairs of morphospecies, each with a Pacific form and a Caribbean form.

Question 38

What are the 2 types of allopatric speciation?

Answer 38

• Vicariant speciation:
  Where 2 widespread populations are divided by an extrinsic barrier (e.g. shrimps)
• Peripatric speciation:
  Also known as the founder effect!
  e.g. Hawaiian Drosophila - many species endemic to a single island, probably evolved from many founding populations.

Question 39

Explain why Periwinkle populations may be an example of sympatric speciation

Answer 39

• lots of different morphs/ ecotypes.
• In the splash zone, shells are thin, with wide apertures. these morphs are found on vertical surfaces and wave resistant.
• In mid-shore habitats, shells are thick and have small apertures. these are crab resistant.
• rare intermediates are found in transition zones ( gene pools can mix) so possible Incipient speciation (ongoing)
• Could also be parapatric speciation (half allopatric and half sympatric).

Question 40

Explain why Lord Howe Island Palms may be an example of sympatric speciation

Answer 40

• 2 types found; one grows in calcium-rich soils and the other in volcanic soils.
• disruptive selection due to soil type, followed by assortative mating (Volcanic palms flower early& others flower later).

Question 41

Why may cichlids found in the volcanic crater lakes of Cameroon and Nicaragua be an example of sympatric speciation and not allopatric?

Answer 41

• The lakes are small
• Shores are uniform so don’t provide barriers
• Change in water level is unlikely to cause isolation as the lakes are conical
• Crater rims restrict gene flow so gene flow remains within the lake.
• hybridisation may have contributed to diversification.

Question 42

Give an example of a species where a single gene mutation has lead to speciation.

Answer 42

Left or right coiling in Euhadra

• instant reproductive isolation as genitals don’t align
• phylogeny suggests right-coiling has arisen more than once.

Question 43

What is the only universally accepted form of sympatric speciation?

Answer 43

Polyploid Speciation:
more than 2 sets of chromosomes- can occur instantaneously by a single mutation event.
2n gametes are formed.
rare in animals (found in some fish and frogs) but common in plants.
e.g. In a grass species, a 2n form is found in wet habitats, but a 6n form is found in very hot and dry sand dunes. Polyploidy may be a character for increased water retention (6n = larger cell).

Question 44

Define Coevolution

Answer 44

The process of reciprocal evolutionary change in interacting species.

Question 45

Name the 5 types of biological interactions with examples.

Answer 45

• Mutualism; e.g. wrasse removing parasites from potato cod.
• Predator/Parasites; e.g. cuckoo
• Competition; e.g. barnacle species on rocky shores.
• Commensalism; e.g. spider living between the horns of a gazelle.
• One suffers, whilst the other is not affected; e.g humans and most animals.

Question 46

Describe the coevolution between some bat species and moths.

Answer 46

-Bats have evolved to hunt using ultrasound.
- Some insects have independently evolved the ability to detect ultrasound (via tympana)
- When loud enough, the calls can trigger behavioural responses (e.g. a power dive/ spiral to avoid predation)
-Tiger moths can actually jam the sonar or produce startle responses.
Barbastelle bats have counter adapted a fainter call to enable stealthier hunting.

Question 47

Describe the coevolution of Cuckoos and some other bird species.

Answer 47

Cuckoo Brood Parasitism

• Cuckoos will lay eggs in the nests of other birds
• Some host species have evolved to discriminate against cuckoo eggs and eject them; a specific counter-adaptation.
• European Cuckoo has evolved egg mimicry
• Australian bronze cuckoos have evolved to resemble host chicks and mimic their calls.

Question 48

Describe the coevolution of a Plant and a herbivore.

Answer 48

• Passion flowers deter herbivores by producing chemicals.
• Heliconius butterflies are resistant to these deterrents and lay bright yellow eggs on their leaves.
• Conspecifics are encouraged to lay eggs elsewhere to avoid competition.
• Many species of passion flowers have independently evolved structures mimicking these eggs to deter the butterflies. (e.g. yellow dots on leaves).