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Flashcards in Reproductive Behaviour Deck (12)
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What is sexual selection?

A form of natural selection that favours the evolution of elaborate traits – and preferences for those traits by the opposite sex – which results in an increased chance of mating success
Most often favours evolution of the traits in one sex and not the other – often results in a sex difference in not just the trait itself, but also in reproductive behaviours


Describe Sex difference in reproductive behaviour.

Males produce many, small sperm
Females produce few, large eggs
Eggs are ‘expensive’
Sperm are ‘cheap’
Sets the stage for competition among males to fertilize the rarer eggs
The more mates, the more eggs fertilized


Describe the costs and benefits of Parental investment.

Putting resources into production & helping offspring reach adulthood increases the probability they will live long enough to reproduce
Pass on parental genes to next generation
Resources supplied to one offspring can’t be used to make additional offspring


Describe parental investment.

In most species, females more likely than males to care for offspring.
Offspring a female cares for are extremely likely to carry her genes
In contrast, a male’s paternity is often less certain.
Less incentive to be parental if results in a loss of fertilization opportunities.
Females generally have less to gain from repeat mating + more ‘expensive’ to replace eggs than sperm.
Male biased operational sex ratio


Describe a Role reversal aquarium study.

Aquarium study
Start of breeding season – males opt to spend more time feeding than responding to potential mates (Berglund et al 2006)
Large males with free pouch space actively choose mates – discriminate against plain, smaller females


Describe a Role reversal controlled lab study.

Controlled lab study
Offspring survival partly influenced by female body size
Males prefer females with temporary striping on their sides
Trait which emphasizes size during F-F aggressive interactions


What is Intrasexual Selection?

Winners of male-male competition tend to mate more often
Evolution of larger body size
Tend to be larger than females
When intrasexual selection on male body size is strong – Sexual dimorphism in body size evolves


What are Alternative mating tactics?

Individuals that are unlikely to be successful adopt alternative tactics to allow some level of reproductive success


Describe a study on Alternative mating tactics.

Lab study Thornhill 1981
Caged groups of 10M and 10F
A ) Large males monopolized the two dead crickets in the cage
B)Medium sized crickets produced salivary gifts
C) Small crickets unable to claim crickets or produce salivary gifts
Theory tested by removing the group A
Males switch to a tactic yielding a higher reproductive success if social conditions allow


What is Sperm competition?

Females may mate with >1 male in a short period of time
Rarely are the available eggs split evenly between the males she has mated with
Older males, nesting in the interior
Produce more sperm
Sperm swim faster
Sneaky male
Is close by territory holder
Sperm release at the same time
Sneaky male closer to eggs


Describe sperm competition in mice.

In some species of mice, sperm form aggregations
Sperm aggregate more with conspecifics than heterospecific
Sperm aggregate more with that from a closely related individual vs distantly related


What is Mate guarding?

In some species, the male will remain with female following mating