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Fundamentals to Evolutionary Biology > Lecture 19 - Evolution of sex > Flashcards

Lecture 19 - Evolution of sex Flashcards

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1
Q

What is sexual reproduction?

A

The union of two genomes, usually carried out by gametes

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2
Q

Anisogamy

A

Distinct male/female functions

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3
Q

What percentage of eukaryotic organisms are sexually reproducing?

A

99.9%

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4
Q

Sex of dioecious species

A

Seperate males and females

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5
Q

Sex of hermaphroditic species

A

Individuals produce both kinds of gametes

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6
Q

Examples of Dioecious species?

A

Willows and Badgers

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7
Q

Examples of Hermaphroditic species

A

Roses and earthworms

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8
Q

Parthenogenesis

A

Type of asexual reproduction

Development of a new individual from an unfertilised egg (apoxmixis)

Essentially a clone of the mother

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9
Q

Examples of parthenogenesis

A

Komodo dragon, aphids and Daphnia

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10
Q

Gynogenesis

A

Type of asexual reproduction

Sperm-dependent parthenogenesis

Sperm triggers it but without contributing genetically

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11
Q

Adventitious embyrony

A

Type of asexual reproduction

Development of a new individual from a somatic cell

Occurs in plants

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12
Q

Vegetative reproduction

A

Type of asexual reproduction

Development of new individual from a group of somatic cells

In plants

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13
Q

Example of vegetative reproduction

A

rhizomes of ginger

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14
Q

What is the use of sex?

A

Not for reproduction as can reproduce asexually

Sex is therefore for recombination

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15
Q

When did recombination first occur?

A

3 billion years ago as a DNA repair mechanism

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16
Q

When did sex first evolve?

A

1-2 billion years ago

17
Q

What are the two parts to the evolution of sex?

A

Origen of sexual reproduction (cellular evolution) - the evolution of diploidy (that has the advantage of making deleterious mutations) is likely to have been part of the process

Evolution of and maintenance of sexual reproduction and recombination i.e. how does natural selection favour sex

18
Q

What is the cost of males?

A

Producing males is costly as does not directly contribute to population growth

Males cannot produce offspring, therefore need to produce two offspring to produce further offspring

Theoretically asexually reproducing organisms should outcompete sexually reproducing organisms as they grow exponentially as all offspring can produce their own offspring

Also in asexual reproduction all of the genes are your own genes whereas in sexual reproduction they are shared 50/50

19
Q

Costs of sex

A

Cost of finding a mate (locating, competing etc)

Risk of not finding a mate

Rise of disease transmission in mating

Increased predation risk

At the cellular level sexual cycle requires addition time and energy as meiotic cell division takes considerably longer than mitosis

20
Q

Costs of recombination

A

Breaks up favourable combination of alleles

21
Q

Example of recombination breaking up favorable characteristics?

A

Primrose (Primula vulgaris) heterostyly

Individuals with Ga genotype have lower fitness than GA or ga

This is due to the positioning of the style and stamen

22
Q

What is the distribution of parthenogenesis?

A

Widely distributed but generally short-lived

23
Q

What are the two possible long-term advantages to sex?

A

Sex accelerates adaptive evolution

Sex prevents the accumulation of deleterious mutations

24
Q

How does sex accelerate evolution?

A

Example

In a population in which AB is optimal but starts with ab

Sexual:

ab can mutate into aB and Ab and sexual reproduction can combine the two to form AB

Asexual

ab can mutate into aB and aB however they cannot combine so need to wait for another mutation to convert either of them into AB

Also in the meantime one of the alleles will outcompete the other

25
Q

Mullers ratchet

A

Sex prevents the accumulation of deleterious mutations

In a population with deleterious alleles spread across

If there is an event in which individuals with no deleterious mutants become eliminated then there is no way to get less than 1 deleterious mutations

However in sexual you can due to recombination

26
Q

Synergistic selection

A

Sex prevents the accumulation of deleterious mutants

Recombination could potentially reduce mutational load if deleterious mutation act synergistically

Recombination increases the variance in the distribution of mutations (deleterious and beneficial) so selection is more effective

27
Q

What is the probelm with mullers ratchet?

A

Not as effective in larger populations

28
Q

What is the problem with the long term advantages of sex?

A

They all involve group selection

For sex to persist there must be a short-term advantage

29
Q

Short -term advantage of sex?

A

Sex generates a greater number of different genotypes, adapted to a wider range of conditions

30
Q

What organisms can be studied to find out the short term benefits of sex?

A

Organisms that have sex occasionally such as strawberry plants

They reproduce asexually when conditions are good to make as many well adapted offspring as possible

When conditions are bad they have sex so they can adapt to the new environment

31
Q

Frozen niche hypothesis

A

Asexual fish, Poeciliopsis monacha- lucida exist in mexican stream as many different clones

The proportion of fish that are sexual decreases as the number of asexual clones increases

Since asexuals do better when they have more clonal diversity this demonstrates short-term advantage that sexuals usually have due to their diverse genotypes adapted to a wide range of conditions

32
Q

Sib-competition

A

Asexual organisms occupy the same niches so compete with themselves

33
Q

Red queen hypothesis for the evolution of sex

A

Coevolution in response to a biotic environment full of parasites

Incredibly strong selective force

Frequency-dependent selection will favour rare host genotyes

Sex produces more variable progeny so is more likely to produce rare genotypes that can escape infection

34
Q

Evidence of the red queen hypothesis?

A

Snail Potamopyrgus antipodarum

Lives in muds of new zealands lakes, rivers and estuaries

Can be infected with a worm parasite

Both sexual and parthenogenetic snails

HIgh clonal diversity of asexuals

Parthogenetic snails have not been able to outcompete sexual snails

Where there are more parasites in shallow areas there were more sexual snails and more clonal diveristy than in deeper areas with less parasites

Fundamentals to Evolutionary Biology (19 decks)

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