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Evolutionary Biology > Sex, Cooperation and conflict > Flashcards

Sex, Cooperation and conflict Flashcards

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1
Q

What is sex?

A

The occurrence of meiosis

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2
Q

Under the meiosis definition of sex, what 3 things are assumed?

A

Sex does not require separate sexes

Sex is not necessary for reproduction

Sex is not the same as reproduction

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3
Q

What is the paradox of sex?

A

Sex must confer some sort of fitness benefit or it wouldn’t be so pervasive

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4
Q

The cost of sex

A

Takes a long time

Risk of reproducing maladapted offspring

Cost of mating (finding a mate, sexually transmitted diseases)

Loss of half of reproductive output (2-fold cost of sex)

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5
Q

What is the two fold cost of sex?

A

When producing sexually a female must combine her offspring with a male and thus loses 50% of her gene copies.

when producing asexually she has a 2-fold advantage of passing of two copies of her genes

all asexually produced offspring are female

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6
Q

Time difference between yeast reproducing asexually and sexually ?

A

Asexually - 90mins

Sexually - several days

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7
Q

The cost of males (2-fold cost of sex)

A

The clonal offspring of an asexual female multiplies at twice the rate of the progeny descended from a sexual female

a sexual female has only 50% of the fitness of an asexual female

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8
Q

Why is asexual selection favoured more in stable environments?

A

Sex is costly

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9
Q

What is background selection?

A

Selection against strongly deleterious mutations

Fixation of weakly deleterious mutations

Accumulation of deleterious mutations

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10
Q

What happens to an asexually producing population under background selection?

A

The population gets weaker in time due to lack of chromosome mixing

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11
Q

Stochastic loss

A

Random loss

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12
Q

Muller’s ratchet

A

Stochastic loss of mutation-free chromosomes within a population

leads to an accumulation of deleterious mutations

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13
Q

Muller’s ratchet in an asexual population

A

Cannot be revered within an asexual populations

Leads to fitness decline over generations

Accumulation of deleterious mutations

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14
Q

Genetic hitchhiking

A

Deleterious mutations accumulate because they are linked to beneficial mutations

Selection for strongly beneficial mutations

Hitchhiking of linked deleterious mutations

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15
Q

Genetic hitchhiking in asexual populations

A

Recombination could de-couple but this cannot happen in asexual reproduction

beneficial and linked deleterious mutations are linked and cannot be separated

Accumulation of deleterious mutations

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16
Q

Ruby in the rubbish

A

Selection against strongly deleterious mutations

Elimination of linked beneficial mutations

Linked beneficial mutations cannot be de-coupled and so are lost

Less adaptation

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17
Q

The Hill-Robertson effect

A

Without recombination, fixation of beneficial mutations is much slower.

Selection is weaker without sex and recombination.

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18
Q

benefits of sex - increased efficiency of selection

A

Benefit of the group not the individual

This does not fit with how we understand evolution

Evolution doesn’t have foresight

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19
Q

Benefits of sex - Generation genetically variable offspring

A

Advantageous in a variable environment

Red queen hypothesis - running to stand still

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20
Q

What are Facultative asexuals?

A

Organisms that can switch between sexual and asexual reproduction

Favours environmental change

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21
Q

Mud snail - parasite example (sexual/asexual reproduction)

A

Parasite causes castration of snail (complete fitness loss)

High levels of parasite numbers correlate with high levels of sexual reproduction

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22
Q

Nematode example (free living and parasitic) - sexual and asexual

A

Parasitic form reproduce sexually to compete with changing host behaviour

Free living are much more stable

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23
Q

what is Isogamy ?

A

Same sized gametes (ancestral sexual state)

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24
Q

What is anisogamy?

A

Different sized gametes

Balanced polymorphism

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25
Q

What are mating types?

A
  • First steps in sex differentiation
  • Ensures gametes of same organism dont fuse
  • Promotes outbreeding
  • Mating types stop gametes fusing with gametes from the same organism (+/- equivalent to male/female)
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26
Q

Mating type examples

A
  • Chlamydomonas reinhardtii has two mating types (+/-)
  • Schizophyllum commune has thousands of mating types
  • Most common mating type is two (examples up to 10)
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27
Q

how did mating types evolve into sexes?

A

trade-off between size and number of gametes (large is more viable - small and many have more chances of fusion)

Medium gamete size = mediocre (selected against)

Disruptive selection leads to evolution of balanced polymorphism for gamete sizes (Anisogamy)

Large = egg = female
Small (and many) = sperm = male

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28
Q

what makes zygote size

A

The sum of the gametes that fuse to form it

viability increases with size

zygote must be a certain size in order to be functional

positive relationship between zygote size and viability

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29
Q

Consequences of anisogamy

A
  • Sets up potential for sexual selection
  • Sexual selection is responsible for phenotypic differences between male and female
  • E.g. courtship behaviour, ornament (antlers etc), colouration etc.
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30
Q

Differential gamete investment

A

Males produce large quantities of gametes (individual gametes ‘cheap’ to produce)

Females produce fewer larger gametes (individual gametes are more costly)

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31
Q

How do males increase their mating success?

A

Mate with many partners

success increases linearly with number of mates

Females don’t benefit from multiple matings (only one chance of fertilisation)

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32
Q

What is Bateman’s Principle?

A

Male mating success is more variable than female mating success

Females in most mating interactions are the limiting factor

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33
Q

Why is male mating success more variable? (Bateman’s principle)

A

Males mating success is variable because they may or may not be allowed to mate

Females will always have the same mating success because they are the limiting factor

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34
Q

What does Bateman’s principle lead to?

A

Variance leads to competition between males and choosiness of females

known as the parental investment theory

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35
Q

Parental investment theory

A

Variance leads to competition between males and choosiness between females

basis of sexual selection

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36
Q

Why are separate sexes not inevitable?

A

94% of flowering plants (angiosperms) are bisexual (have both male and female sex organs)

produce different sized gametes but fertilise themselves

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37
Q

Example of male variance in mating success

A

Rough-skinned newts: Females don’t benefit as much as males from mating with multiple partners

38
Q

Example of choosy males

A
  1. Sea horses
  2. Poison arrow dart frogs

Males show all parental care

females have multiple partners and males are choosy

39
Q

how does female choice incur a direct benefit?

A

Direct fitness increase

Choose a male that will directly provide resources to the female and her offspring

e.g.

Fertile or fecund males
Good parenting ability
Access to resources (food, nesting sites etc.)

40
Q

What does fecundity mean?

A

potential number of offspring that could be produced

41
Q

Direct benefits of female mate choice (mottled sculpin fish example)

A

males defend females eggs

females choose larger males

larger males have a higher proportion of hatchings

Direct benefit = parental care
Signal = larger size

42
Q

Examples of direct benefit of female mate choice

A

Nuptial gifts
- gifting a snack or something (better the gift more likely to mate) many insects and great grey shrike (bird).

Territory defence
e.g. male zebras defend watering holes - females benefit.

43
Q

Indirect benefit

A

Genetic benefit → choose the male that will provide genes to make fitter offspring

44
Q

Examples of indirect benefit

A

Bird of Paradise dance

no direct benefit to the female

Is a signal of good sperm

sign that male will produce fitter offspring

45
Q

Fisherian runaway selection model

A

Pick sexy traits to have sexy sons that get chosen by choosy females etc

Runaway selection

E.g. Swordtail fish - females love the sword

46
Q

Good genes model

A

Traits have evolved as an honest signal for males genetic quality.

Only males with good genes can afford to invest in the trait

47
Q

Example of good genes (stalk-eyed fly)

A
  • Larger stalks = honest signal of their good health
  • Study showing how different food eaten can cause variation in stalk length (poor nutrition - more chance of shorter stalks)
  • Male selection ornaments: Traits are often condition-dependent
48
Q

Sexual Vs. Natural Selection

A

Sexual selection can sometimes be costly and bad for survival

49
Q

Sexual Vs. Natural Selection Example (marine iguanas)

A

Galapagos marine iguana

Males are often much larger than optimum size (costly, often causes death)

Males attract females by defending territories (bigger body = better territory defence)

female choice is driving sexual selection to outweigh the survival cost

50
Q

What is sex determination?

A

Mechanisms that determine what sex a developing embryo ends up being

51
Q

What is the name for X&Y (as a sex-determining system?

A

Male heterogamety

e.g. humans, mammals, drosophila

52
Q

What is female heterogamety?

A

Z & W chromosomes

e.g. birds, butterflies

53
Q

Male heterogamety

A

X & Y chromosomes

XX = female
XY = male

54
Q

Why is Y a sex limited chromosome?

A

It only shows up in one of the sexes

W is a sex-limited chromosomes in a W&Z

ZZ = male
ZW = female

(There can sometimes be more than 2 chromosomes)

55
Q

In some animals, sex is determined by other triggers

A
  1. Sex determined by temperature

American alligator:
higher temp = males
lower temp = females

issue with climate change

  1. Social factors

blue banded gobi:
Sequencial hermaphrodites

remove male, largest female becomes male and takes over role

56
Q

what are sequencial hermaphrodites ?

A

Born one sex but have the ability to change sexes at some stage in their life

57
Q

sex determination in animals is incredibly diverse

A
  • XY sex chromosomes
  • ZW sex chromosomes
  • Haplodiploidy
  • Paternal genome elimination
  • Genetic sex determination
  • Environmental sex determination
  • Hermaphroditism
58
Q

Who discovered sex chromosomes?

A

Nettie Stevens

59
Q

Recombination suppression

A

Area on chromosome (strata) recombination is turned off

Older strata have fewer similar genes

Degeneration of the sex-limited sex chromosome

60
Q

what is recombination suppression?

A
  • Recombination suppression is key in the evolution of sex chromosomes, sex chromosomes are key drivers in sexual dimorphism and reproductive isolation.
  • Recombination has become suppressed between sex chromosmes.*
61
Q

What causes recombination suppression?

A
62
Q

Is recombination suppression a cause or a consequence of sex chromosome evolution?

A

Step in the process leading to the evolution of sex chromosomes

63
Q

Sex chromosome degradation - what is X-degenerate?

A

Relics of shared ancestry with X chromosome

64
Q

Sex chromosome degradation - what is ampliconic

A
  • Areas where there are multiple copies of the same gene
  • Many have testes-specific expression, suggesting they may be involved in spermatogenesis
65
Q

Sex-specific selection: in chickens

A

Chickens → intense female trait selection and relaxed female trait selection

W genes are convergently up or down-regulated

66
Q

Gene conversion on the Y (slowing degredation)

A

Non-reciprocal intra-chromosomal recombination

Palindromic regions
Human genome has 8 palindrome

Gene conversion from one copy to another

Preventing degeneration of important genes by having back ups

Not swap →is a copy

67
Q

Palindromic regions

Velcro

A

DNA sequence composed of two inverted repeats (arms) separated by a short spacer (can bind to one another like velcro)

causes a loop of dna

DNA can be exchanged within loop

68
Q

Gene movement onto the Y

A

Duplication of autosomal genes onto the Y chromosome

refreshing of genetic material to counter degeneration

69
Q

Divergent fitness optima

A

Fitness landscapes

Peaks and valleys of fitness landscapes dont always align between sexes

Different evolutionary interests

Drosophila show negative correlation between adult male and female but not with juveniles

70
Q

Types of sexual conflict

A
  1. Intra-locus conflict
  2. Inter-locus conflict
71
Q

Intra-locus conflict (definition)

A
  • Tug of war over trait with shared genetic basis
  • Conflict arises when a trait has a shared genetic basis (between males and females) and contradictory selective pressures act on the sexes.
72
Q

Inter-locus conflict (definition)

A

interacting traits on different loci

Trait within one sex interacts with trait in the other sex.

Conflict occurs over the outcome of the interaction between the sexes.

73
Q

Intra-locus conflict Drosophila body size example (sexual conflict)

A
  • Males want to be larger
  • females smaller
  • Due to the shared genetic basis of the trait expression overall size of males and females is in the middle
  • Unresolved conflict (tug of war prevents either sex from reaching their optimum size)
  • Compromise that doesn’t suit either sex
74
Q

How does intra-locus conflict effect diversity?

A

Can lead to balancing selection and elevated genetic diversity

Ongoing sexual conflict prevents purging of genetic diversity - instead it maintains it.

75
Q

Inter-locus sexual conflict examples

A

Drosophila mating:
Sex peptide → connects to sex-peptide receptor in female: Makes female less susceptible to future males & increases egg laying - good for males not good for females.

Bean weavils:
traumatic penis - spiny penis - ensures successful mating, injures female so she can’t mate again

Hard to resolved → leads to arms race between males penis structure and female evolve to reduce direct cost (kicking).

76
Q

Sexually concordant selection

A

→ alleles rise in population to fixation

77
Q

Sexually antagonistic selection

A

→ allele never fixed, maintained at

78
Q

What are the two routes for intra-locus conflict resolution?

A
  1. Sex chromosomes
  2. Gene expression on the autosomes
79
Q

Sex-Linkage (conflict resolution)

A

Genes on autosomes are exposed to male-specific selection 50% of the time and female 50%.

Dominant alleles on X should be more often selected for female-specific effects (because there are two x’s)

Recessive alleles on X should be more often selected for male-specific effects.

80
Q

Sex linkage prediction

A

The X chromosomes should be enriched for dominant female-benefit alleles and recessive male-benefit alleles.

81
Q

Mammalian X sex-linkage example

A

Prediction: X chromosomes is demasculinised (fewer dominant male-benefit alleles)

Evidence: Exodus of many testis-specific genes from the X chromosome to the autosomes in humans and mice

82
Q

Sex-linage: Z&W

A
  • Two Z chromosomes in males only one is females.
  • Prediction:
  • The Z chromosome should be enriched for dominant male-benefit alleles and recessive female-benefit alleles.
  • (opposite to mammals X&Y)
83
Q

Avian Z sex-linkage examples

A

Male wing patch on flycatchers - Map disproportionately to the Z chromosome

The Z chromosome is masculinised in chickens

84
Q

New sex chromosomes?

A

Prediction: there is a correlation between colour and the size of the recombination strata (recombination suppression) on the Y chromosome.

Convergent expansion of the non-recombining region in colourful populations - consistent with selection to resolve sexual conflict

85
Q

Resolving conflict: Gene expression.

A

gene expression can decouple male and female phenotypes and act to resolve conflict

86
Q

The difference between intra- and inter-locus conflict

A

Inter-locus conflict leads to an evolutionary arms race whereas intra-locus conflict leads to elevated genetic diversity through balancing selection

87
Q

How can intra-locus conflict be resolved?

A

By several routes

e.g. sex linkage, sex chromosome formation and sex-biased gene expression.

There is debate around the relative roles of these different routes

88
Q

Genomic conflict and sex

A
  • Genomic conflict arises more commonly in sexually reproducing organisms
  • Not all genes from one parent are inherited
  • Sex allows greater scope for genomic conflict
89
Q

Different levels of selection (genomic conflict)

A

Cells

Nucleus

Mitochondria

Cells and organelles show variation, reproduction and heredity so all subject to natural selection

90
Q
A

Evolutionary Biology (3 decks)

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