Sperm Competition

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What is Sexual Selection?
Competition that occurs via competition for reproductive success rather than survival purposes.
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What is Bateman's principle? (Anisogamy and effective polgyny)?
Sex that invests more in the young becomes a limiting resource for which members of the opposite sex compete for.
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What was Bateman's study that highlighted this?
Fruit flies. Males increase reproductive success by having more mates, women do not. Less variance in women.
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How does social context influence what we've learnt about females mating behaviour thus far?
No real obvious benefit to female promiscuity - influenced by Darwins social context i.e. chovenistic environment, so female promiscuity was not investigated/observed.
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What are the practical considerations of observing female promiscuity?
Practical limitations - would have to watch female constantly to observe behaviour. Until DNA came out, could not tell who offspring was due to.
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Reasons female may mate with multiple males?
'Good Genes', '**** Sons', genetic diversity, fertility back up, material resources, protection, paternity confusion
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Reasons for female promiscuity: 'good genes'?
Extra-pair copulations - benefit from copulating with male with good genes (increased survival of young) and forming relationship with good male parent/rearer
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Reasons for female promiscuity: '**** sons'?
Benefit from copulating with males who possess good heritable secondary sexual characteristics to increase success of offspring and forming relationship with good parent males
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Reasons for female promiscuity: genetic diversity?
Benefit from fertilised eggs by various males in case of environmental change e.g. diseases
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Reasons for female promiscuity: fertility back up?
Increase chances of mating with a fertile male, so mate with many to ensure fertility.
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Reasons for female promiscuity: materials and resources?
Benefit from gifts, provide nutritional gifts for offspring conception and once born. Increase reproductive success and survival of young.
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Reasons for female promiscuity: protection?
Keep female safe ensuring young survive.
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Reasons for female promiscuity: paternal confusion?
Some species kill offspring if not theirs. Mating with many causes confusion, which makes it more likely offspring will survive.
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Multiple copulations: lack of choice
Some species, e.g. ducks, males are aggressive. Have no choice in who they mate with.
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What causes post-copulatory competition?
Female promiscuity.
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Name some post-copulatory mechanisms?
Prolonged copulations/mate guarding, Mating plugs/repellent, Sperm displacement, Sperm competition (number, size and characteristics), Infanticide
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Explain 'Prolonged Copulations'?
Form of mate guarding, prevent others from copulating/gaining access. E.g. tiger beetles - ride around on back.
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Explain 'Mating Plugs/Repellent'?
Block passage for males to copulate. Ensures their sperm goes into the tract and prevents others gaining access. E.g. rats.
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Explain 'Sperm Displacement'?
Penises designed to remove competitors sperm e.g. shaped like a hook/barbs. E.g. damselfly.
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Explain 'Sperm Competition'?
Competition between the sperm of different males to fertile females gametes.
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Why does 'Sperm Competition' arise?
Heterospermic insemination - internally fertilising environment, where males will compete to fertile female if she mates with many males in a short space of time.
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What characteristics can sperm differ in in order to compete?
Sperm Head Morphology - e.g. sperm head. Differs among species e.g. rats = hooked, drosophila = large sperm cell in relation to body size.
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What is the 'Raffle Principle'?
Like a raffle, the more tickets you buy - more likely to win. Males increase chance of fertilisation by inseminating more sperm.
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What are the costs of ejaculate production?
Cheap but not limitless. Takes energy to produce.
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What does the Sperm Competition Theory state?
Males must make trade-offs between cost of sperm production and risk of sperm competition.
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Predictions of between species sperm competition?
Investment in sperm production greater for species that experience high competition.
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Predictions of within species/between individuals sperm competition?
Chronically high sperm competition environment - invest more in sperm production.
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What is the effect of high population density on sperm production?
Reared in high density environment = males produce more sperm and bigger spermatophores. Generally have larger testes (seen in Indian Meal Moth).
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Preditions of within species/within individuals?
Males will adjust amount of sperm inseminated based on levels of risk/intensity of sperm competition.
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What is Sperm Prudent Allocation?
Males adjust amount of sperm inseminated based on levels of risk/intensity of sperm competition.
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What are the cues of risk?
Presence of rival male(s) prior to or during copulation, Male mating status, Time spent guarding female prior to copulation.
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Example of Presence of rival male CUE?
Flour Beetle - accompanied by rival, ejaculate more as risk is HIGH. Guard female for longer.
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What influence does monogamy and polygamy have on testes size?
Those more polygamous have bigger testes e.g. chimpanzees. Those more monogamous (less risk) have smaller testes e.g. gorilla.
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Name a theory of sperm design in response to Sperm Competition?
Based on the Raffle Principle (based on numbers). Need to make trade offs between sperm size and number. Increase in risk, sperm will be smaller but more abundant. Negative association between sperm size and number.
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Considerations of theories of sperm design?
Externally fertilised eggs - take more into account (not just more copulations = more offspring), e.g. need to be a good swimmer (swimming against current in Salmon).
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Name an alternative theory of sperm design in response to Sperm Competition?
Predicts if size gives sperm an advantage, increase in sperm competition = increase in sperm size AND numbers. No trade offs. Size and number increase = total ejaculate expenditure needs to increase.
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What is the relationship between sperm length and Sperm Competition?
Increase in sperm competition = increase in sperm length. Due to increase in components that make up sperm.
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ADAPTATIONS TO SPERM COMPETITION???
Mate Guarding/Prolonged Copulations. Mating Plugs/Repellants. Sperm Displacement. Increased Investment in Sperm Production. Prudent Sperm Allocation (adjustment of sperm ejaculate). Sperm Characteristics (size, trains).
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Relationship between testes size and Sperm Competition?
Bigger testes size with higher competition. E.g. chimpanzees (polygamous) = bigger testes. Gorillas (monogamous) = smaller testes. Relationship between sperm size and testes size is significant and relative.
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What are 'Sperm Trains'?
Sperm forms trains that hook together, meaning they swim faster (reach egg quicker). Mostly in rodents.
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Other cards in this set

Card 2

Front

What is Bateman's principle? (Anisogamy and effective polgyny)?

Back

Sex that invests more in the young becomes a limiting resource for which members of the opposite sex compete for.

Card 3

Front

What was Bateman's study that highlighted this?

Back

Preview of the front of card 3

Card 4

Front

How does social context influence what we've learnt about females mating behaviour thus far?

Back

Preview of the front of card 4

Card 5

Front

What are the practical considerations of observing female promiscuity?

Back

Preview of the front of card 5
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