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LEC 141 - Evolutionary Biology > Week 4 > Flashcards

Week 4 Flashcards

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1
Q

What does natural selection cause?

A

Evolution of traits which enhance survival

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2
Q

Some traits seem to reduce survival… why would these evolve?

(for example some features in the male golden pheasant, dragonfly penis end with barbs, Bower birds obsession with blue, etc)

A

Darwin recognised the problem being a result of Sexual selection and not natural selection

The Descent of Man and Selection in Relation to Sex (1871)

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3
Q

Define sexual selection

A

The cause of evolutionary traits which give the owners a mating advantage over others of the same sex.

Such traits are called secondary sexual characteristics.

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4
Q

What are secondary sexual characteristics?

A

Traits which differ between the sexes.
Not connected with gamete production or transfer

For example: weapons (antlers, horns, etc), size dimorphism, elaborate displays and colours.

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5
Q

There is competition for reproductive opportunities
Why is it usually that males compete?

A
  1. Gamete size (difference bewteen egg and sperm)
  2. Potential rate of reproduction
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6
Q

Why is it usually that males compete: Gamete size?

A

Males: sperm, very small, large numbers, cheap

Females: eggs, large, small numbers, expensive
Female investment per gamete is relatively high

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7
Q

Why is it usually that males compete: Potential rate of reproduction?

A

Female: mate (minutes), gestate (9 months), can breed again in 10 months

Male: mate (minutes), replenish sperm (day), find new mate… could breen 300x faster than female
Males have higher potential rate than females, for example humans.

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8
Q

Bateman’s (1948) Drosophilia mating and reproductive success experiment

A

Studied reproductive success opportunities within fruitfly

Found males are limited by access to female resources
Found females access to more males doesn’t increase their reproductive success

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9
Q

Give an example
Starting 100 male : 100 female ratio where pregnancy lasts 5 months - why females can be choosy and males compete?

A

100m:100f, pregnancy lasts 5 months.
Make 10 females pregnant, males ready to re-mate females are not.
Operational sex ratio is now 90 available female : 100 male

Therefore, females are in short supply so males now have to compete for them. There are excess males, so females can afford to be choosy!
This drives sexual selection

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10
Q

Males compete for females,
Females are choosy

Or, more correctly?

A

The sex with the greater potential rate of reproduction competes whilst the other sex is choosy.

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11
Q

What are the advantages of being choosy, when it comes to successful reproduction?

A

Investment in eggs relatively high
Breeding opportunities relatively rare

Need to get:
- Right species
- Best quality male available

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12
Q

What are the 2 key types of sexual selection?

A

Intra-sexual selection (within)
- Competition for mates between individuals of the same sex
- Use of weapons, signals or size

Inter-sexual selection (between)
- Mate choice
- Usually completed with elaborate displays

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13
Q

Intra-sexual selection - weapons.
Evolution of antlers & horns in ungulates (deers, antelopes, etc) …
is it natural selection (used as defence) or sexual selection (used in competition for mates)?

A
  • Often only male have weapons eg red deer
  • Not always used for defence eg Moose defence by kicking, not using antlers
  • May be used for defence, but differ in shape eg female antelopes, thinner but less often broken
  • Many shed (their antlers) in winter when predation risk is highest

So… intra-sexual selection weapons have evolved due to sexual selection not natural selection

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14
Q

List some features of intra-sexual selection?

A

Weapons
Size
Rituals and displays

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15
Q

Intra-sexual selection - impact of size

A

Male competitions often won by the largest male, which selects for large males in size. This can lead to some extremes of size dismorphism

For example the elephant seal, males weigh 10x more than the female.

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16
Q

Intra-sexual selection: impact of rituals and displays?

A

Neither parties benefit from fighting, so they use ‘sizing up’ rituals instead before fighting to reduce risk of injury.

Eg: Red Deer display increases in intensity and the competition can back out at any point before fighting begins:
1. Roaring (deep, long roar suggests a bigger male)
2. Parallel walking (males walk shoulder to shoulder to evaluate the other deer and ‘size each other up’
3. Fighting (usually occur when the deer are evenly sized or if they cannot decide who is bigger during other displays.

17
Q

What can intra-sexual selection rituals and displays lead to?

A

The evolution of some extravagant body parts,

for example: stalk-eed flies and peacock tails

18
Q

Three drivers of inter-sexual selection?

A

(Selection to be choosy…)

  1. Getting the right species (if incorrect could lead to hybridisation)
  2. Direct benefits - males may come with resources (eg location with good resources, food, shelter, etc)
  3. Indirect benefits - males provide genetic benefits (eg traits male has might be beneficial to her offspring)
19
Q

Inter-sexual selection: Getting right species example of potential hybrid zone

A

Australian Litoria frogs. Males sing to attract females. Overlap in area between Litoria verrauxi and Litoria ewingi (potential hybrid zone)

Can be studied using choice chambers
Found females are under selection pressure to get it right.
Females in hybrid zone go to correct male, while female not in hybrid zones don’t and make mistakes.

Shows: female preference is the greatest when cost of error is greatest.

20
Q

Inter-sexual selection: direct benefits include

A
  • Food
    -Nest or laying sites
  • Parental care
    -Protection from harassment
  • Etc
21
Q

Inter-sexual selection: indirect benefits

A

Male genetic quality is passed to offspring such as parasite resistance, longevity, ‘sexiness’,

‘Good genes’ are inherited by the offspring and increase offspring viability rather than directly going to the female

22
Q

What are the two main ideas on evolution of elaborate traits (eg colouration/song)?

A
  • Fisher’s runway theory
  • Good genes or handicap principle (Zahavi)
23
Q

What is Fisher’s runway theory on the evolution of elaborate traits?

A

Female preference for a trait becomes genetically linked with the trait, which could lead to greater reproductive success merely because of the fact more females prefer it.

24
Q

Fisher’s runway theory on the evolution of elaborate traits - How can preferences arise?

A
  • Arbitrary (no cost or benefit eg eye colour, hair colour)
  • Natural selection to start with (eg preference for faster runner, better flier)
  • Sensory bias (Loud calls or obvious signals are perceived first, so give mating advantage eg frog calls)
25
Q

Fisher’s runway theory of elaborate evolutionary traits: the process

A

Preferred males will leave more young than less preferred males.

The preferences will also be inherited and expressed only in relevant sex. This causes evolution of specific traits
(Trait and preference become linked; Linkage Disequilibrium)

Natural selection may put the brakes on sexual selection so issues don’t occur.

26
Q

What is the ‘Handicap’ principle of elaborate evolution traits?

EG: tail length in birds

A

Long tails are expensive handicaps
Females prefer them because they signal a males ability to survive despite the handicap
May be a reliable signal of male viability
Female select for useful trait rather than arbitrary one

Hotly debated topic - but it could work in theory

27
Q

An example to explain linkage disequilibrium (inter-sexual selection)

A

EG tail length

Females with different tail lengths prefer males with matching tail lengths. Therefore, these preferences are passed onto the offspring.

If preferences overlap (male = female preference) the genes carrying preference and tail length will be passed onto the offspring. When selecting male/female to mate with.

Male trait expressed in tail length
Female trait expressed in preference.

28
Q

Female choice and evolution of extravagant traits: Clive Catchpole’s study on song - Sedge Warbler song

A

Song can be recorded, imaged and analysed using a sonagram.
Songs are made up of elements - more elements means a larger repertoire.

Found doing observational research that males with larger repertoires pair early (they’re preferred by females)

Used a choice chamber test to research further - experimentally produced songs induced a greater response by females. It showed that females preferred more complex song. - Does this signal a useful trait within males over those who produce a more simple song?

29
Q

Female choice and evolution of extravagant traits: Malte Andersson’s Long-tailed Widow Bird experiment?

A

Males have extremely long tails but females do not - suggesting a tole in mate choice.

Experiment:
Trapped males,
shortened some tails, lengthened others,
some stayed the same as a control.

Found:
After tail manipulation, females prefer mails with longer tails.

30
Q

True or False

Individuals of some species have different reproductive behaviours?

A

True!

Individuals within species can have alternative reproductive strategies.

Additional:
However, this raises questions!

If selection maximises lifetime reproductive success, how can two ‘strategies evolve?
Why doesn’t one become extinct?

31
Q

Alternative reproductive strategies example: Natterjack Toads

Mate attraction methods

A
  • Large males display by singing to attract females to the mating pool (not all males call)
  • Females follow a sound gradient towards mating pool
  • Non-calling males act as silent satellites to males in the pool
  • Satellites intercept arriving females (some arrive with males already attached)
32
Q

Alternative reproductive strategies example: Natterjack Toads

How can a non-calling toad breed if females breed to calling males?

A
  • Removal experiments show satellites will be callers if there is room in the pool
  • Callers are larger than satellites, as size increases with age. This year’s satellites will be next year’s callers.
  • Therefore not a genetic difference - its age related, so lifetime reproductive success balances out across males.
33
Q

Alternative reproductive strategies example: Coho Salmon

A brief overview

A

North American species

Mature at sea - migrate up freshwater rivers to spawn

After spawning both males and females die

Eggs hatch, stay in stream one year, then migrate to sea to mature

34
Q

Alternative reproductive strategies example: Coho Salmon

Different types, and maturing for females and (2 types of) males

A
  • Females = mature at three years old, migrate, spawn and die
  • Hook-noses = Mature at 3 years, large size and weight, brightly coloured, have a weapon (hook-nose) used to fight for a female
  • Jacks = Mature at 2 years, small, dull coloured, without weapon
35
Q

Alternative reproductive strategies example: Coho Salmon

Spawning process

A
  • Females scrap holes and bury eggs
  • Males add sperm
  • External fertilization

Hooknoses: Males fight for access to spawning females. Closest males get more fertilizations

Jacks: Do not fight (sneaky spawner). Closest males still get most fertilizations

36
Q

Alternative reproductive strategies example: Coho Salmon

Male morph type is genetically determined. So we should expect the strategies to have equal fitness pay-offs. Otherwise one would be selected out.

How can we get information of this?

A

Fitness = Survivorship to breed & breeding lifespan & mating success.

Fish tagging can provide information on survival. DNA analysis can provide information on reproductive success of Jacks and Hooknose

37
Q

Alternative reproductive strategies example: Coho Salmon

Study results?

A

Survival:
- Jacks = 0.13
- Hooknoses = 0.06

Breeding span:
- Jacks = 8.4 days
- Hooknoses = 12.7 days

Breeding success:
- Jacks = 0.66
- Hooknoses = 1.00

Fitness ration = 0.95 (close to 1. So therefore each strategy pays off)

38
Q

Alternative reproductive strategies example: Coho Salmon

Frequency dependent selection?

A
  • Each fish does best when it is rare,
  • Reaching a stable equilibrium.

(More hooknoses = Jacks do better. More Jacks = Hooknoses do better)

39
Q

Alternative reproductive strategies example: Soay Sheep? Leks?

A

Look on Lecture 12, LEC 141 Slide 26 onwards

LEC 141 - Evolutionary Biology (4 decks)

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