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Evolutionary Biology > Sex, Cooperation and conflict > Flashcards

Sex, Cooperation and conflict Flashcards

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
What are mating types?
* 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)
26
Mating type examples
* Chlamydomonas reinhardtii has two mating types (+/-) * Schizophyllum commune has thousands of mating types * Most common mating type is two (examples up to 10)
27
how did mating types evolve into sexes?
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
28
what makes zygote size
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
29
Consequences of anisogamy
* 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.
30
Differential gamete investment
Males produce large quantities of gametes (individual gametes 'cheap' to produce) Females produce fewer larger gametes (individual gametes are more costly)
31
How do males increase their mating success?
Mate with many partners success increases linearly with number of mates Females don't benefit from multiple matings (only one chance of fertilisation)
32
What is Bateman's Principle?
Male mating success is more variable than female mating success Females in most mating interactions are the limiting factor
33
Why is male mating success more variable? (Bateman's principle)
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
34
What does Bateman's principle lead to?
Variance leads to competition between males and choosiness of females known as the **parental investment theory**
35
Parental investment theory
Variance leads to competition between males and choosiness between females basis of sexual selection
36
Why are separate sexes not inevitable?
94% of flowering plants (angiosperms) are bisexual (have both male and female sex organs) produce different sized gametes but fertilise themselves
37
Example of male variance in mating success
Rough-skinned newts: Females don't benefit as much as males from mating with multiple partners
38
Example of choosy males
1. Sea horses 2. Poison arrow dart frogs Males show all parental care females have multiple partners and males are choosy
39
how does female choice incur a direct benefit?
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
What does fecundity mean?
potential number of offspring that could be produced
41
Direct benefits of female mate choice (mottled sculpin fish example)
males defend females eggs females choose larger males larger males have a higher proportion of hatchings Direct benefit = parental care Signal = larger size
42
Examples of direct benefit of female mate choice
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
Indirect benefit
Genetic benefit → choose the male that will provide genes to make fitter offspring
44
Examples of indirect benefit
Bird of Paradise dance no direct benefit to the female Is a signal of good sperm sign that male will produce fitter offspring
45
Fisherian runaway selection model
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
Good genes model
Traits have evolved as an honest signal for males genetic quality. Only males with good genes can afford to invest in the trait
47
Example of good genes (stalk-eyed fly)
* 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
Sexual Vs. Natural Selection
Sexual selection can sometimes be costly and bad for survival
49
Sexual Vs. Natural Selection Example (marine iguanas)
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
What is sex determination?
Mechanisms that determine what sex a developing embryo ends up being
51
What is the name for X&Y (as a sex-determining system?
Male heterogamety e.g. humans, mammals, drosophila
52
What is female heterogamety?
Z & W chromosomes e.g. birds, butterflies
53
Male heterogamety
X & Y chromosomes XX = female XY = male
54
Why is Y a sex limited chromosome?
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
In some animals, sex is determined by other triggers
1. Sex determined by temperature American alligator: higher temp = males lower temp = females issue with climate change 2. Social factors blue banded gobi: Sequencial hermaphrodites remove male, largest female becomes male and takes over role
56
what are sequencial hermaphrodites ?
Born one sex but have the ability to change sexes at some stage in their life
57
sex determination in animals is incredibly diverse
- XY sex chromosomes - ZW sex chromosomes - Haplodiploidy - Paternal genome elimination - Genetic sex determination - Environmental sex determination - Hermaphroditism
58
Who discovered sex chromosomes?
Nettie Stevens
59
Recombination suppression
Area on chromosome (strata) recombination is turned off Older strata have fewer similar genes Degeneration of the sex-limited sex chromosome
60
what is recombination suppression?
* 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
What causes recombination suppression?
62
Is recombination suppression a cause or a consequence of sex chromosome evolution?
Step in the process leading to the evolution of sex chromosomes
63
Sex chromosome degradation - what is X-degenerate?
Relics of shared ancestry with X chromosome
64
Sex chromosome degradation - what is ampliconic
* Areas where there are multiple copies of the same gene * Many have testes-specific expression, suggesting they may be involved in spermatogenesis
65
Sex-specific selection: in chickens
Chickens → intense female trait selection and relaxed female trait selection W genes are convergently up or down-regulated
66
Gene conversion on the Y (slowing degredation)
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
Palindromic regions ## Footnote Velcro
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
Gene movement onto the Y
Duplication of autosomal genes onto the Y chromosome refreshing of genetic material to counter degeneration
69
Divergent fitness optima
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
Types of sexual conflict
1. Intra-locus conflict 2. Inter-locus conflict
71
Intra-locus conflict (definition)
* 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
Inter-locus conflict (definition)
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
Intra-locus conflict Drosophila body size example (sexual conflict)
* 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
How does intra-locus conflict effect diversity?
Can lead to balancing selection and elevated genetic diversity Ongoing sexual conflict prevents purging of genetic diversity - instead it maintains it.
75
Inter-locus sexual conflict examples
**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
Sexually concordant selection
→ alleles rise in population to fixation
77
Sexually antagonistic selection
→ allele never fixed, maintained at
78
What are the two routes for intra-locus conflict resolution?
1. Sex chromosomes 2. Gene expression on the autosomes
79
Sex-Linkage (conflict resolution)
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
Sex linkage prediction
The X chromosomes should be enriched for dominant female-benefit alleles and recessive male-benefit alleles.
81
Mammalian X sex-linkage example
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
Sex-linage: Z&W
* 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
Avian Z sex-linkage examples
Male wing patch on flycatchers - Map disproportionately to the Z chromosome The Z chromosome is masculinised in chickens
84
New sex chromosomes?
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
Resolving conflict: Gene expression.
gene expression can decouple male and female phenotypes and act to resolve conflict
86
The difference between intra- and inter-locus conflict
Inter-locus conflict leads to an evolutionary arms race whereas intra-locus conflict leads to elevated genetic diversity through balancing selection
87
How can intra-locus conflict be resolved?
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
Genomic conflict and sex
* 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
Different levels of selection (genomic conflict)
Cells Nucleus Mitochondria Cells and organelles show variation, reproduction and heredity so all subject to natural selection
90

Evolutionary Biology (3 decks)

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